/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:4;coding:utf-8 -*-â
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â Copyright The Mbed TLS Contributors                                          â
â                                                                              â
â Licensed under the Apache License, Version 2.0 (the "License");              â
â you may not use this file except in compliance with the License.             â
â You may obtain a copy of the License at                                      â
â                                                                              â
â     http://www.apache.org/licenses/LICENSE-2.0                               â
â                                                                              â
â Unless required by applicable law or agreed to in writing, software          â
â distributed under the License is distributed on an "AS IS" BASIS,            â
â WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.     â
â See the License for the specific language governing permissions and          â
â limitations under the License.                                               â
ââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââ*/
#include "libc/log/log.h"
#include "third_party/mbedtls/chk.h"
#include "third_party/mbedtls/common.h"
#include "third_party/mbedtls/config.h"
#include "third_party/mbedtls/debug.h"
#include "third_party/mbedtls/endian.h"
#include "third_party/mbedtls/error.h"
#include "third_party/mbedtls/oid.h"
#include "third_party/mbedtls/platform.h"
#include "third_party/mbedtls/ssl.h"
#include "third_party/mbedtls/ssl_ciphersuites.h"
#include "third_party/mbedtls/ssl_internal.h"
#include "third_party/mbedtls/version.h"

asm(".ident\t\"\\n\\n\
Mbed TLS (Apache 2.0)\\n\
Copyright ARM Limited\\n\
Copyright Mbed TLS Contributors\"");
asm(".include \"libc/disclaimer.inc\"");
/* clang-format off */

/**
 * @fileoverview SSLv3/TLSv1 shared functions
 *
 * The SSL 3.0 specification was drafted by Netscape in 1996,
 * and became an IETF standard in 1999.
 *
 * @see http://wp.netscape.com/eng/ssl3/
 * @see http://www.ietf.org/rfc/rfc2246.txt
 * @see http://www.ietf.org/rfc/rfc4346.txt
 */

#if defined(MBEDTLS_SSL_TLS_C)

#if defined(MBEDTLS_SSL_PROTO_DTLS)

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
/* Top-level Connection ID API */

/**
 * \brief               Specify the length of Connection IDs for incoming
 *                      encrypted DTLS records, as well as the behaviour
 *                      on unexpected CIDs.
 *
 *                      By default, the CID length is set to \c 0,
 *                      and unexpected CIDs are silently ignored.
 *
 * \param conf          The SSL configuration to modify.
 * \param len           The length in Bytes of the CID fields in encrypted
 *                      DTLS records using the CID mechanism. This must
 *                      not be larger than #MBEDTLS_SSL_CID_OUT_LEN_MAX.
 * \param ignore_other_cids This determines the stack's behaviour when
 *                          receiving a record with an unexpected CID.
 *                          Possible values are:
 *                          - #MBEDTLS_SSL_UNEXPECTED_CID_IGNORE
 *                            In this case, the record is silently ignored.
 *                          - #MBEDTLS_SSL_UNEXPECTED_CID_FAIL
 *                            In this case, the stack fails with the specific
 *                            error code #MBEDTLS_ERR_SSL_UNEXPECTED_CID.
 *
 * \note                The CID specification allows implementations to either
 *                      use a common length for all incoming connection IDs or
 *                      allow variable-length incoming IDs. Mbed TLS currently
 *                      requires a common length for all connections sharing the
 *                      same SSL configuration; this allows simpler parsing of
 *                      record headers.
 *
 * \return              \c 0 on success.
 * \return              #MBEDTLS_ERR_SSL_BAD_INPUT_DATA if \p own_cid_len
 *                      is too large.
 */
int mbedtls_ssl_conf_cid( mbedtls_ssl_config *conf,
                          size_t len,
                          int ignore_other_cid )
{
    if( len > MBEDTLS_SSL_CID_IN_LEN_MAX )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    if( ignore_other_cid != MBEDTLS_SSL_UNEXPECTED_CID_FAIL &&
        ignore_other_cid != MBEDTLS_SSL_UNEXPECTED_CID_IGNORE )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    conf->ignore_unexpected_cid = ignore_other_cid;
    conf->cid_len = len;
    return( 0 );
}

/**
 * \brief             Configure the use of the Connection ID (CID)
 *                    extension in the next handshake.
 *
 *                    Reference: draft-ietf-tls-dtls-connection-id-05
 *                    https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05
 *
 *                    The DTLS CID extension allows the reliable association of
 *                    DTLS records to DTLS connections across changes in the
 *                    underlying transport (changed IP and Port metadata) by
 *                    adding explicit connection identifiers (CIDs) to the
 *                    headers of encrypted DTLS records. The desired CIDs are
 *                    configured by the application layer and are exchanged in
 *                    new `ClientHello` / `ServerHello` extensions during the
 *                    handshake, where each side indicates the CID it wants the
 *                    peer to use when writing encrypted messages. The CIDs are
 *                    put to use once records get encrypted: the stack discards
 *                    any incoming records that don't include the configured CID
 *                    in their header, and adds the peer's requested CID to the
 *                    headers of outgoing messages.
 *
 *                    This API enables or disables the use of the CID extension
 *                    in the next handshake and sets the value of the CID to
 *                    be used for incoming messages.
 *
 * \param ssl         The SSL context to configure. This must be initialized.
 * \param enable      This value determines whether the CID extension should
 *                    be used or not. Possible values are:
 *                    - MBEDTLS_SSL_CID_ENABLED to enable the use of the CID.
 *                    - MBEDTLS_SSL_CID_DISABLED (default) to disable the use
 *                      of the CID.
 * \param own_cid     The address of the readable buffer holding the CID we want
 *                    the peer to use when sending encrypted messages to us.
 *                    This may be \c NULL if \p own_cid_len is \c 0.
 *                    This parameter is unused if \p enabled is set to
 *                    MBEDTLS_SSL_CID_DISABLED.
 * \param own_cid_len The length of \p own_cid.
 *                    This parameter is unused if \p enabled is set to
 *                    MBEDTLS_SSL_CID_DISABLED.
 *
 * \note              The value of \p own_cid_len must match the value of the
 *                    \c len parameter passed to mbedtls_ssl_conf_cid()
 *                    when configuring the ::mbedtls_ssl_config that \p ssl
 *                    is bound to.
 *
 * \note              This CID configuration applies to subsequent handshakes
 *                    performed on the SSL context \p ssl, but does not trigger
 *                    one. You still have to call `mbedtls_ssl_handshake()`
 *                    (for the initial handshake) or `mbedtls_ssl_renegotiate()`
 *                    (for a renegotiation handshake) explicitly after a
 *                    successful call to this function to run the handshake.
 *
 * \note              This call cannot guarantee that the use of the CID
 *                    will be successfully negotiated in the next handshake,
 *                    because the peer might not support it. Specifically:
 *                    - On the Client, enabling the use of the CID through
 *                      this call implies that the `ClientHello` in the next
 *                      handshake will include the CID extension, thereby
 *                      offering the use of the CID to the server. Only if
 *                      the `ServerHello` contains the CID extension, too,
 *                      the CID extension will actually be put to use.
 *                    - On the Server, enabling the use of the CID through
 *                      this call implies that that the server will look for
 *                      the CID extension in a `ClientHello` from the client,
 *                      and, if present, reply with a CID extension in its
 *                      `ServerHello`.
 *
 * \note              To check whether the use of the CID was negotiated
 *                    after the subsequent handshake has completed, please
 *                    use the API mbedtls_ssl_get_peer_cid().
 *
 * \warning           If the use of the CID extension is enabled in this call
 *                    and the subsequent handshake negotiates its use, Mbed TLS
 *                    will silently drop every packet whose CID does not match
 *                    the CID configured in \p own_cid. It is the responsibility
 *                    of the user to adapt the underlying transport to take care
 *                    of CID-based demultiplexing before handing datagrams to
 *                    Mbed TLS.
 *
 * \return            \c 0 on success. In this case, the CID configuration
 *                    applies to the next handshake.
 * \return            A negative error code on failure.
 */
int mbedtls_ssl_set_cid( mbedtls_ssl_context *ssl,
                         int enable,
                         unsigned char const *own_cid,
                         size_t own_cid_len )
{
    if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    ssl->negotiate_cid = enable;
    if( enable == MBEDTLS_SSL_CID_DISABLED )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Disable use of CID extension." ) );
        return( 0 );
    }
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "Enable use of CID extension." ) );
    MBEDTLS_SSL_DEBUG_BUF( 3, "Own CID", own_cid, own_cid_len );
    if( own_cid_len != ssl->conf->cid_len )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "CID length %u does not match CID length %u in config",
                                    (unsigned) own_cid_len,
                                    (unsigned) ssl->conf->cid_len ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    memcpy( ssl->own_cid, own_cid, own_cid_len );
    /* Truncation is not an issue here because
     * MBEDTLS_SSL_CID_IN_LEN_MAX at most 255. */
    ssl->own_cid_len = (uint8_t) own_cid_len;
    return( 0 );
}

/**
 * \brief              Get information about the use of the CID extension
 *                     in the current connection.
 *
 * \param ssl          The SSL context to query.
 * \param enabled      The address at which to store whether the CID extension
 *                     is currently in use or not. If the CID is in use,
 *                     `*enabled` is set to MBEDTLS_SSL_CID_ENABLED;
 *                     otherwise, it is set to MBEDTLS_SSL_CID_DISABLED.
 * \param peer_cid     The address of the buffer in which to store the CID
 *                     chosen by the peer (if the CID extension is used).
 *                     This may be \c NULL in case the value of peer CID
 *                     isn't needed. If it is not \c NULL, \p peer_cid_len
 *                     must not be \c NULL.
 * \param peer_cid_len The address at which to store the size of the CID
 *                     chosen by the peer (if the CID extension is used).
 *                     This is also the number of Bytes in \p peer_cid that
 *                     have been written.
 *                     This may be \c NULL in case the length of the peer CID
 *                     isn't needed. If it is \c NULL, \p peer_cid must be
 *                     \c NULL, too.
 *
 * \note               This applies to the state of the CID negotiated in
 *                     the last complete handshake. If a handshake is in
 *                     progress, this function will attempt to complete
 *                     the handshake first.
 *
 * \note               If CID extensions have been exchanged but both client
 *                     and server chose to use an empty CID, this function
 *                     sets `*enabled` to #MBEDTLS_SSL_CID_DISABLED
 *                     (the rationale for this is that the resulting
 *                     communication is the same as if the CID extensions
 *                     hadn't been used).
 *
 * \return            \c 0 on success.
 * \return            A negative error code on failure.
 */
int mbedtls_ssl_get_peer_cid( mbedtls_ssl_context *ssl,
                     int *enabled,
                     unsigned char peer_cid[ MBEDTLS_SSL_CID_OUT_LEN_MAX ],
                     size_t *peer_cid_len )
{
    *enabled = MBEDTLS_SSL_CID_DISABLED;
    if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM ||
        ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    /* We report MBEDTLS_SSL_CID_DISABLED in case the CID extensions
     * were used, but client and server requested the empty CID.
     * This is indistinguishable from not using the CID extension
     * in the first place. */
    if( ssl->transform_in->in_cid_len  == 0 &&
        ssl->transform_in->out_cid_len == 0 )
    {
        return( 0 );
    }
    if( peer_cid_len != NULL )
    {
        *peer_cid_len = ssl->transform_in->out_cid_len;
        if( peer_cid != NULL )
        {
            memcpy( peer_cid, ssl->transform_in->out_cid,
                    ssl->transform_in->out_cid_len );
        }
    }
    *enabled = MBEDTLS_SSL_CID_ENABLED;
    return( 0 );
}
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

#endif /* MBEDTLS_SSL_PROTO_DTLS */

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
/*
 * Convert max_fragment_length codes to length.
 * RFC 6066 says:
 *    enum{
 *        2^9(1), 2^10(2), 2^11(3), 2^12(4), (255)
 *    } MaxFragmentLength;
 * and we add 0 -> extension unused
 */
static unsigned int ssl_mfl_code_to_length( int mfl )
{
    switch( mfl )
    {
    case MBEDTLS_SSL_MAX_FRAG_LEN_NONE:
        return ( MBEDTLS_TLS_EXT_ADV_CONTENT_LEN );
    case MBEDTLS_SSL_MAX_FRAG_LEN_512:
        return 512;
    case MBEDTLS_SSL_MAX_FRAG_LEN_1024:
        return 1024;
    case MBEDTLS_SSL_MAX_FRAG_LEN_2048:
        return 2048;
    case MBEDTLS_SSL_MAX_FRAG_LEN_4096:
        return 4096;
    default:
        return ( MBEDTLS_TLS_EXT_ADV_CONTENT_LEN );
    }
}
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */

int mbedtls_ssl_session_copy( mbedtls_ssl_session *dst,
                              const mbedtls_ssl_session *src )
{
    mbedtls_ssl_session_free( dst );
    memcpy( dst, src, sizeof( mbedtls_ssl_session ) );
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    if( src->peer_cert != NULL )
    {
        int ret = MBEDTLS_ERR_THIS_CORRUPTION;
        dst->peer_cert = mbedtls_calloc( 1, sizeof(mbedtls_x509_crt) );
        if( dst->peer_cert == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
        mbedtls_x509_crt_init( dst->peer_cert );
        if( ( ret = mbedtls_x509_crt_parse_der( dst->peer_cert, src->peer_cert->raw.p,
                                        src->peer_cert->raw.len ) ) != 0 )
        {
            mbedtls_free( dst->peer_cert );
            dst->peer_cert = NULL;
            return( ret );
        }
    }
#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    if( src->peer_cert_digest != NULL )
    {
        dst->peer_cert_digest =
            mbedtls_calloc( 1, src->peer_cert_digest_len );
        if( dst->peer_cert_digest == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
        memcpy( dst->peer_cert_digest, src->peer_cert_digest,
                src->peer_cert_digest_len );
        dst->peer_cert_digest_type = src->peer_cert_digest_type;
        dst->peer_cert_digest_len = src->peer_cert_digest_len;
    }
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */
#if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
    if( src->ticket != NULL )
    {
        dst->ticket = mbedtls_calloc( 1, src->ticket_len );
        if( dst->ticket == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
        memcpy( dst->ticket, src->ticket, src->ticket_len );
    }
#endif /* MBEDTLS_SSL_SESSION_TICKETS && MBEDTLS_SSL_CLI_C */
    return( 0 );
}

#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
static int resize_buffer( unsigned char **buffer, size_t len_new, size_t *len_old )
{
    unsigned char* resized_buffer = mbedtls_calloc( 1, len_new );
    if( resized_buffer == NULL )
        return -1;
    /* We want to copy len_new bytes when downsizing the buffer, and
     * len_old bytes when upsizing, so we choose the smaller of two sizes,
     * to fit one buffer into another. Size checks, ensuring that no data is
     * lost, are done outside of this function. */
    memcpy( resized_buffer, *buffer,
            ( len_new < *len_old ) ? len_new : *len_old );
    mbedtls_platform_zeroize( *buffer, *len_old );
    mbedtls_free( *buffer );
    *buffer = resized_buffer;
    *len_old = len_new;
    return 0;
}

static void handle_buffer_resizing( mbedtls_ssl_context *ssl, int downsizing,
                                    size_t in_buf_new_len,
                                    size_t out_buf_new_len )
{
    int modified = 0;
    size_t written_in = 0, iv_offset_in = 0, len_offset_in = 0;
    size_t written_out = 0, iv_offset_out = 0, len_offset_out = 0;
    if( ssl->in_buf != NULL )
    {
        written_in = ssl->in_msg - ssl->in_buf;
        iv_offset_in = ssl->in_iv - ssl->in_buf;
        len_offset_in = ssl->in_len - ssl->in_buf;
        if( downsizing ?
            ssl->in_buf_len > in_buf_new_len && ssl->in_left < in_buf_new_len :
            ssl->in_buf_len < in_buf_new_len )
        {
            if( resize_buffer( &ssl->in_buf, in_buf_new_len, &ssl->in_buf_len ) != 0 )
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "input buffer resizing failed - out of memory" ) );
            }
            else
            {
                MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reallocating in_buf to %" MBEDTLS_PRINTF_SIZET,
                                            in_buf_new_len ) );
                modified = 1;
            }
        }
    }
    if( ssl->out_buf != NULL )
    {
        written_out = ssl->out_msg - ssl->out_buf;
        iv_offset_out = ssl->out_iv - ssl->out_buf;
        len_offset_out = ssl->out_len - ssl->out_buf;
        if( downsizing ?
            ssl->out_buf_len > out_buf_new_len && ssl->out_left < out_buf_new_len :
            ssl->out_buf_len < out_buf_new_len )
        {
            if( resize_buffer( &ssl->out_buf, out_buf_new_len, &ssl->out_buf_len ) != 0 )
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "output buffer resizing failed - out of memory" ) );
            }
            else
            {
                MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reallocating out_buf to %" MBEDTLS_PRINTF_SIZET,
                                            out_buf_new_len ) );
                modified = 1;
            }
        }
    }
    if( modified )
    {
        /* Update pointers here to avoid doing it twice. */
        mbedtls_ssl_reset_in_out_pointers( ssl );
        /* Fields below might not be properly updated with record
         * splitting or with CID, so they are manually updated here. */
        ssl->out_msg = ssl->out_buf + written_out;
        ssl->out_len = ssl->out_buf + len_offset_out;
        ssl->out_iv = ssl->out_buf + iv_offset_out;
        ssl->in_msg = ssl->in_buf + written_in;
        ssl->in_len = ssl->in_buf + len_offset_in;
        ssl->in_iv = ssl->in_buf + iv_offset_in;
    }
}
#endif /* MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH */

/*
 * Key material generation
 */
#if defined(MBEDTLS_SSL_PROTO_SSL3)
static int ssl3_prf( const unsigned char *secret, size_t slen,
                     const char *label,
                     const unsigned char *random, size_t rlen,
                     unsigned char *dstbuf, size_t dlen )
{
    int ret = 0;
    size_t i;
    mbedtls_md5_context md5;
    mbedtls_sha1_context sha1;
    unsigned char padding[16];
    unsigned char sha1sum[20];
    mbedtls_md5_init(  &md5  );
    mbedtls_sha1_init( &sha1 );
    /*
     *  SSLv3:
     *    block =
     *      MD5( secret + SHA1( 'A'    + secret + random ) ) +
     *      MD5( secret + SHA1( 'BB'   + secret + random ) ) +
     *      MD5( secret + SHA1( 'CCC'  + secret + random ) ) +
     *      ...
     */
    for( i = 0; i < dlen / 16; i++ )
    {
        memset( padding, (unsigned char) ('A' + i), 1 + i );
        MBEDTLS_CHK( mbedtls_sha1_starts_ret( &sha1 ) );
        MBEDTLS_CHK( mbedtls_sha1_update_ret( &sha1, padding, 1 + i ) );
        MBEDTLS_CHK( mbedtls_sha1_update_ret( &sha1, secret, slen ) );
        MBEDTLS_CHK( mbedtls_sha1_update_ret( &sha1, random, rlen ) );
        MBEDTLS_CHK( mbedtls_sha1_finish_ret( &sha1, sha1sum ) );
        MBEDTLS_CHK( mbedtls_md5_starts_ret( &md5 ) );
        MBEDTLS_CHK( mbedtls_md5_update_ret( &md5, secret, slen ) );
        MBEDTLS_CHK( mbedtls_md5_update_ret( &md5, sha1sum, 20 ) );
        MBEDTLS_CHK( mbedtls_md5_finish_ret( &md5, dstbuf + i * 16 ) );
    }
cleanup:
    mbedtls_md5_free(  &md5  );
    mbedtls_sha1_free( &sha1 );
    mbedtls_platform_zeroize( padding, sizeof( padding ) );
    mbedtls_platform_zeroize( sha1sum, sizeof( sha1sum ) );
    return( ret );
}
#endif /* MBEDTLS_SSL_PROTO_SSL3 */

#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
static int tls1_prf( const unsigned char *secret, size_t slen,
                     const char *label,
                     const unsigned char *random, size_t rlen,
                     unsigned char *dstbuf, size_t dlen )
{
    size_t nb, hs;
    size_t i, j, k;
    const unsigned char *S1, *S2;
    unsigned char *tmp;
    size_t tmp_len = 0;
    unsigned char h_i[20];
    const mbedtls_md_info_t *md_info;
    mbedtls_md_context_t md_ctx;
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
    mbedtls_md_init( &md_ctx );
    tmp_len = 20 + strlen( label ) + rlen;
    if( !( tmp = mbedtls_calloc( 1, tmp_len ) ) )
    {
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto exit;
    }
    hs = ( slen + 1 ) / 2;
    S1 = secret;
    S2 = secret + slen - hs;
    nb = strlen( label );
    memcpy( tmp + 20, label, nb );
    memcpy( tmp + 20 + nb, random, rlen );
    nb += rlen;
    /*
     * First compute P_md5(secret,label+random)[0..dlen]
     */
    if( !( md_info = mbedtls_md_info_from_type( MBEDTLS_MD_MD5 ) ) )
    {
        ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        goto exit;
    }
    if( ( ret = mbedtls_md_setup( &md_ctx, md_info, 1 ) ) != 0 )
    {
        goto exit;
    }
    mbedtls_md_hmac_starts( &md_ctx, S1, hs );
    mbedtls_md_hmac_update( &md_ctx, tmp + 20, nb );
    mbedtls_md_hmac_finish( &md_ctx, 4 + tmp );
    for( i = 0; i < dlen; i += 16 )
    {
        mbedtls_md_hmac_reset ( &md_ctx );
        mbedtls_md_hmac_update( &md_ctx, 4 + tmp, 16 + nb );
        mbedtls_md_hmac_finish( &md_ctx, h_i );
        mbedtls_md_hmac_reset ( &md_ctx );
        mbedtls_md_hmac_update( &md_ctx, 4 + tmp, 16 );
        mbedtls_md_hmac_finish( &md_ctx, 4 + tmp );
        k = ( i + 16 > dlen ) ? dlen % 16 : 16;
        for( j = 0; j < k; j++ )
            dstbuf[i + j]  = h_i[j];
    }
    mbedtls_md_free( &md_ctx );
    /*
     * XOR out with P_sha1(secret,label+random)[0..dlen]
     */
    if( !( md_info = mbedtls_md_info_from_type( MBEDTLS_MD_SHA1 ) ) )
    {
        ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        goto exit;
    }
    if( ( ret = mbedtls_md_setup( &md_ctx, md_info, 1 ) ) != 0 )
    {
        goto exit;
    }
    mbedtls_md_hmac_starts( &md_ctx, S2, hs );
    mbedtls_md_hmac_update( &md_ctx, tmp + 20, nb );
    mbedtls_md_hmac_finish( &md_ctx, tmp );
    for( i = 0; i < dlen; i += 20 )
    {
        mbedtls_md_hmac_reset ( &md_ctx );
        mbedtls_md_hmac_update( &md_ctx, tmp, 20 + nb );
        mbedtls_md_hmac_finish( &md_ctx, h_i );
        mbedtls_md_hmac_reset ( &md_ctx );
        mbedtls_md_hmac_update( &md_ctx, tmp, 20 );
        mbedtls_md_hmac_finish( &md_ctx, tmp );
        k = ( i + 20 > dlen ) ? dlen % 20 : 20;
        for( j = 0; j < k; j++ )
            dstbuf[i + j] = (unsigned char)( dstbuf[i + j] ^ h_i[j] );
    }
exit:
    mbedtls_md_free( &md_ctx );
    mbedtls_platform_zeroize( tmp, tmp_len );
    mbedtls_platform_zeroize( h_i, sizeof( h_i ) );
    mbedtls_free( tmp );
    return( ret );
}
#endif /* MBEDTLS_SSL_PROTO_TLS1) || MBEDTLS_SSL_PROTO_TLS1_1 */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)

static int tls_prf_generic( mbedtls_md_type_t md_type,
                            const unsigned char *secret, size_t slen,
                            const char *label,
                            const unsigned char *random, size_t rlen,
                            unsigned char *dstbuf, size_t dlen )
{
    size_t nb;
    size_t i, j, k, md_len;
    unsigned char *tmp;
    size_t tmp_len = 0;
    unsigned char h_i[MBEDTLS_MD_MAX_SIZE];
    const mbedtls_md_info_t *md_info;
    mbedtls_md_context_t md_ctx;
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;

    mbedtls_md_init( &md_ctx );

    if( ( md_info = mbedtls_md_info_from_type( md_type ) ) == NULL )
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );

    md_len = mbedtls_md_get_size( md_info );

    tmp_len = md_len + strlen( label ) + rlen;
    tmp = mbedtls_calloc( 1, tmp_len );
    if( tmp == NULL )
    {
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto exit;
    }

    nb = strlen( label );
    memcpy( tmp + md_len, label, nb );
    memcpy( tmp + md_len + nb, random, rlen );
    nb += rlen;

    /*
     * Compute P_<hash>(secret, label + random)[0..dlen]
     */
    if ( ( ret = mbedtls_md_setup( &md_ctx, md_info, 1 ) ) != 0 )
        goto exit;

    mbedtls_md_hmac_starts( &md_ctx, secret, slen );
    mbedtls_md_hmac_update( &md_ctx, tmp + md_len, nb );
    mbedtls_md_hmac_finish( &md_ctx, tmp );

    for( i = 0; i < dlen; i += md_len )
    {
        mbedtls_md_hmac_reset ( &md_ctx );
        mbedtls_md_hmac_update( &md_ctx, tmp, md_len + nb );
        mbedtls_md_hmac_finish( &md_ctx, h_i );

        mbedtls_md_hmac_reset ( &md_ctx );
        mbedtls_md_hmac_update( &md_ctx, tmp, md_len );
        mbedtls_md_hmac_finish( &md_ctx, tmp );

        k = ( i + md_len > dlen ) ? dlen % md_len : md_len;

        for( j = 0; j < k; j++ )
            dstbuf[i + j]  = h_i[j];
    }

exit:
    mbedtls_md_free( &md_ctx );

    mbedtls_platform_zeroize( tmp, tmp_len );
    mbedtls_platform_zeroize( h_i, sizeof( h_i ) );

    mbedtls_free( tmp );

    return( ret );
}

#if defined(MBEDTLS_SHA256_C)
static int tls_prf_sha256( const unsigned char *secret, size_t slen,
                           const char *label,
                           const unsigned char *random, size_t rlen,
                           unsigned char *dstbuf, size_t dlen )
{
    return( tls_prf_generic( MBEDTLS_MD_SHA256, secret, slen,
                             label, random, rlen, dstbuf, dlen ) );
}
#endif /* MBEDTLS_SHA256_C */

#if defined(MBEDTLS_SHA512_C)
static int tls_prf_sha384( const unsigned char *secret, size_t slen,
                           const char *label,
                           const unsigned char *random, size_t rlen,
                           unsigned char *dstbuf, size_t dlen )
{
    return( tls_prf_generic( MBEDTLS_MD_SHA384, secret, slen,
                             label, random, rlen, dstbuf, dlen ) );
}
#endif /* MBEDTLS_SHA512_C */
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

static void ssl_update_checksum_start( mbedtls_ssl_context *, const unsigned char *, size_t );

#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_1)
static void ssl_update_checksum_md5sha1( mbedtls_ssl_context *, const unsigned char *, size_t );
#endif

#if defined(MBEDTLS_SSL_PROTO_SSL3)
static void ssl_calc_verify_ssl( const mbedtls_ssl_context *, unsigned char *, size_t * );
static void ssl_calc_finished_ssl( mbedtls_ssl_context *, unsigned char *, int );
#endif

#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
static void ssl_calc_verify_tls( const mbedtls_ssl_context *, unsigned char*, size_t * );
static void ssl_calc_finished_tls( mbedtls_ssl_context *, unsigned char *, int );
#endif

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
static void ssl_update_checksum_sha256( mbedtls_ssl_context *, const unsigned char *, size_t );
static void ssl_calc_verify_tls_sha256( const mbedtls_ssl_context *,unsigned char*, size_t * );
static void ssl_calc_finished_tls_sha256( mbedtls_ssl_context *,unsigned char *, int );
#endif

#if defined(MBEDTLS_SHA512_C)
static void ssl_update_checksum_sha384( mbedtls_ssl_context *, const unsigned char *, size_t );
static void ssl_calc_verify_tls_sha384( const mbedtls_ssl_context *, unsigned char*, size_t * );
static void ssl_calc_finished_tls_sha384( mbedtls_ssl_context *, unsigned char *, int );
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

#if defined(MBEDTLS_SSL_EXPORT_KEYS)
static mbedtls_tls_prf_types tls_prf_get_type( mbedtls_ssl_tls_prf_cb *tls_prf )
{
#if defined(MBEDTLS_SSL_PROTO_SSL3)
    if( tls_prf == ssl3_prf )
    {
        return( MBEDTLS_SSL_TLS_PRF_SSL3 );
    }
    else
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
    if( tls_prf == tls1_prf )
    {
        return( MBEDTLS_SSL_TLS_PRF_TLS1 );
    }
    else
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA512_C)
    if( tls_prf == tls_prf_sha384 )
    {
        return( MBEDTLS_SSL_TLS_PRF_SHA384 );
    }
    else
#endif
#if defined(MBEDTLS_SHA256_C)
    if( tls_prf == tls_prf_sha256 )
    {
        return( MBEDTLS_SSL_TLS_PRF_SHA256 );
    }
    else
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    return( MBEDTLS_SSL_TLS_PRF_NONE );
}
#endif /* MBEDTLS_SSL_EXPORT_KEYS */

/**
 * \brief          TLS-PRF function for key derivation.
 *
 * \param prf      The tls_prf type funtion type to be used.
 * \param secret   Secret for the key derivation function.
 * \param slen     Length of the secret.
 * \param label    String label for the key derivation function,
 *                 terminated with null character.
 * \param random   Random bytes.
 * \param rlen     Length of the random bytes buffer.
 * \param dstbuf   The buffer holding the derived key.
 * \param dlen     Length of the output buffer.
 *
 * \return         0 on sucess. An SSL specific error on failure.
 */
int  mbedtls_ssl_tls_prf( const mbedtls_tls_prf_types prf,
                          const unsigned char *secret, size_t slen,
                          const char *label,
                          const unsigned char *random, size_t rlen,
                          unsigned char *dstbuf, size_t dlen )
{
    mbedtls_ssl_tls_prf_cb *tls_prf = NULL;

    switch( prf )
    {
#if defined(MBEDTLS_SSL_PROTO_SSL3)
        case MBEDTLS_SSL_TLS_PRF_SSL3:
            tls_prf = ssl3_prf;
        break;
#endif /* MBEDTLS_SSL_PROTO_SSL3 */
#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
        case MBEDTLS_SSL_TLS_PRF_TLS1:
            tls_prf = tls1_prf;
        break;
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA512_C)
        case MBEDTLS_SSL_TLS_PRF_SHA384:
            tls_prf = tls_prf_sha384;
        break;
#endif /* MBEDTLS_SHA512_C */
#if defined(MBEDTLS_SHA256_C)
        case MBEDTLS_SSL_TLS_PRF_SHA256:
            tls_prf = tls_prf_sha256;
        break;
#endif /* MBEDTLS_SHA256_C */
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    default:
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
    }

    return( tls_prf( secret, slen, label, random, rlen, dstbuf, dlen ) );
}

/* Type for the TLS PRF */
typedef int ssl_tls_prf_t(const unsigned char *, size_t, const char *,
                          const unsigned char *, size_t,
                          unsigned char *, size_t);

/*
 * Populate a transform structure with session keys and all the other
 * necessary information.
 *
 * Parameters:
 * - [in/out]: transform: structure to populate
 *      [in] must be just initialised with mbedtls_ssl_transform_init()
 *      [out] fully populated, ready for use by mbedtls_ssl_{en,de}crypt_buf()
 * - [in] ciphersuite
 * - [in] master
 * - [in] encrypt_then_mac
 * - [in] trunc_hmac
 * - [in] compression
 * - [in] tls_prf: pointer to PRF to use for key derivation
 * - [in] randbytes: buffer holding ServerHello.random + ClientHello.random
 * - [in] minor_ver: SSL/TLS minor version
 * - [in] endpoint: client or server
 * - [in] ssl: optionally used for:
 *        - MBEDTLS_SSL_HW_RECORD_ACCEL: whole context (non-const)
 *        - MBEDTLS_SSL_EXPORT_KEYS: ssl->conf->{f,p}_export_keys
 *        - MBEDTLS_DEBUG_C: ssl->conf->{f,p}_dbg
 */
static int ssl_populate_transform( mbedtls_ssl_transform *transform,
                                   int ciphersuite,
                                   const unsigned char master[48],
#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                                   int encrypt_then_mac,
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
#if defined(MBEDTLS_ZLIB_SUPPORT)
                                   int compression,
#endif
                                   ssl_tls_prf_t tls_prf,
                                   const unsigned char randbytes[64],
                                   int minor_ver,
                                   unsigned endpoint,
#if !defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
                                   const
#endif
                                   mbedtls_ssl_context *ssl )
{
    int ret = 0;
    unsigned char keyblk[256];
    unsigned char *key1;
    unsigned char *key2;
    unsigned char *mac_enc;
    unsigned char *mac_dec;
    size_t mac_key_len = 0;
    size_t iv_copy_len;
    unsigned keylen;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
    const mbedtls_cipher_info_t *cipher_info;
    const mbedtls_md_info_t *md_info;

#if !defined(MBEDTLS_SSL_HW_RECORD_ACCEL) && \
    !defined(MBEDTLS_SSL_EXPORT_KEYS) && \
    !defined(MBEDTLS_DEBUG_C)
    ssl = NULL; /* make sure we don't use it except for those cases */
    (void) ssl;
#endif

    /*
     * Some data just needs copying into the structure
     */
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC) && \
    defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
    transform->encrypt_then_mac = encrypt_then_mac;
#endif
    transform->minor_ver = minor_ver;

#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)
    memcpy( transform->randbytes, randbytes, sizeof( transform->randbytes ) );
#endif

    /*
     * Get various info structures
     */
    ciphersuite_info = mbedtls_ssl_ciphersuite_from_id( ciphersuite );
    if( ciphersuite_info == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "ciphersuite info for %d not found",
                                    ciphersuite ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    cipher_info = mbedtls_cipher_info_from_type( ciphersuite_info->cipher );
    if( cipher_info == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "cipher info for %u not found",
                                    ciphersuite_info->cipher ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    md_info = mbedtls_md_info_from_type( ciphersuite_info->mac );
    if( md_info == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "mbedtls_md info for %u not found",
                            (unsigned) ciphersuite_info->mac ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
    /* Copy own and peer's CID if the use of the CID
     * extension has been negotiated. */
    if( ssl->handshake->cid_in_use == MBEDTLS_SSL_CID_ENABLED )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Copy CIDs into SSL transform" ) );

        transform->in_cid_len = ssl->own_cid_len;
        memcpy( transform->in_cid, ssl->own_cid, ssl->own_cid_len );
        MBEDTLS_SSL_DEBUG_BUF( 3, "Incoming CID", transform->in_cid,
                               transform->in_cid_len );

        transform->out_cid_len = ssl->handshake->peer_cid_len;
        memcpy( transform->out_cid, ssl->handshake->peer_cid,
                ssl->handshake->peer_cid_len );
        MBEDTLS_SSL_DEBUG_BUF( 3, "Outgoing CID", transform->out_cid,
                               transform->out_cid_len );
    }
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

    /*
     * Compute key block using the PRF
     */
    ret = tls_prf( master, 48, "key expansion", randbytes, 64, keyblk, 256 );
    if( ret != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "prf", ret );
        return( ret );
    }

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite = %s",
                           mbedtls_ssl_get_ciphersuite_name( ciphersuite ) ) );
    MBEDTLS_SSL_DEBUG_BUF( 3, "master secret", master, 48 );
    MBEDTLS_SSL_DEBUG_BUF( 4, "random bytes", randbytes, 64 );
    MBEDTLS_SSL_DEBUG_BUF( 4, "key block", keyblk, 256 );

    /*
     * Determine the appropriate key, IV and MAC length.
     */

    keylen = cipher_info->key_bitlen / 8;

#if defined(MBEDTLS_GCM_C) ||                           \
    defined(MBEDTLS_CCM_C) ||                           \
    defined(MBEDTLS_CHACHAPOLY_C)
    if( cipher_info->mode == MBEDTLS_MODE_GCM ||
        cipher_info->mode == MBEDTLS_MODE_CCM ||
        cipher_info->mode == MBEDTLS_MODE_CHACHAPOLY )
    {
        size_t explicit_ivlen;

        transform->maclen = 0;
        mac_key_len = 0;
        transform->taglen =
            ciphersuite_info->flags & MBEDTLS_CIPHERSUITE_SHORT_TAG ? 8 : 16;

        /* All modes haves 96-bit IVs, but the length of the static parts vary
         * with mode and version:
         * - For GCM and CCM in TLS 1.2, there's a static IV of 4 Bytes
         *   (to be concatenated with a dynamically chosen IV of 8 Bytes)
         * - For ChaChaPoly in TLS 1.2, and all modes in TLS 1.3, there's
         *   a static IV of 12 Bytes (to be XOR'ed with the 8 Byte record
         *   sequence number).
         */
        transform->ivlen = 12;
#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
        if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_4 )
        {
            transform->fixed_ivlen = 12;
        }
        else
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
        {
            if( cipher_info->mode == MBEDTLS_MODE_CHACHAPOLY )
                transform->fixed_ivlen = 12;
            else
                transform->fixed_ivlen = 4;
        }

        /* Minimum length of encrypted record */
        explicit_ivlen = transform->ivlen - transform->fixed_ivlen;
        transform->minlen = explicit_ivlen + transform->taglen;
    }
    else
#endif /* MBEDTLS_GCM_C || MBEDTLS_CCM_C || MBEDTLS_CHACHAPOLY_C */
#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
    if( cipher_info->mode == MBEDTLS_MODE_STREAM ||
        cipher_info->mode == MBEDTLS_MODE_CBC )
    {
        /* Initialize HMAC contexts */
        if( ( ret = mbedtls_md_setup( &transform->md_ctx_enc, md_info, 1 ) ) != 0 ||
            ( ret = mbedtls_md_setup( &transform->md_ctx_dec, md_info, 1 ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_setup", ret );
            goto end;
        }

        /* Get MAC length */
        mac_key_len = mbedtls_md_get_size( md_info );
        transform->maclen = mac_key_len;

        /* IV length */
        transform->ivlen = cipher_info->iv_size;

        /* Minimum length */
        if( cipher_info->mode == MBEDTLS_MODE_STREAM )
            transform->minlen = transform->maclen;
        else
        {
            /*
             * GenericBlockCipher:
             * 1. if EtM is in use: one block plus MAC
             *    otherwise: * first multiple of blocklen greater than maclen
             * 2. IV except for SSL3 and TLS 1.0
             */
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
            if( encrypt_then_mac == MBEDTLS_SSL_ETM_ENABLED )
            {
                transform->minlen = transform->maclen
                                  + cipher_info->block_size;
            }
            else
#endif
            {
                transform->minlen = transform->maclen
                                  + cipher_info->block_size
                                  - transform->maclen % cipher_info->block_size;
            }

#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1)
            if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 ||
                minor_ver == MBEDTLS_SSL_MINOR_VERSION_1 )
                ; /* No need to adjust minlen */
            else
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2)
            if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_2 ||
                minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
            {
                transform->minlen += transform->ivlen;
            }
            else
#endif
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
                ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
                goto end;
            }
        }
    }
    else
#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "keylen: %u, minlen: %u, ivlen: %u, maclen: %u",
                                (unsigned) keylen,
                                (unsigned) transform->minlen,
                                (unsigned) transform->ivlen,
                                (unsigned) transform->maclen ) );

    /*
     * Finally setup the cipher contexts, IVs and MAC secrets.
     */
#if defined(MBEDTLS_SSL_CLI_C)
    if( endpoint == MBEDTLS_SSL_IS_CLIENT )
    {
        key1 = keyblk + mac_key_len * 2;
        key2 = keyblk + mac_key_len * 2 + keylen;

        mac_enc = keyblk;
        mac_dec = keyblk + mac_key_len;

        /*
         * This is not used in TLS v1.1.
         */
        iv_copy_len = ( transform->fixed_ivlen ) ?
                            transform->fixed_ivlen : transform->ivlen;
        memcpy( transform->iv_enc, key2 + keylen,  iv_copy_len );
        memcpy( transform->iv_dec, key2 + keylen + iv_copy_len,
                iv_copy_len );
    }
    else
#endif /* MBEDTLS_SSL_CLI_C */
#if defined(MBEDTLS_SSL_SRV_C)
    if( endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        key1 = keyblk + mac_key_len * 2 + keylen;
        key2 = keyblk + mac_key_len * 2;

        mac_enc = keyblk + mac_key_len;
        mac_dec = keyblk;

        /*
         * This is not used in TLS v1.1.
         */
        iv_copy_len = ( transform->fixed_ivlen ) ?
                            transform->fixed_ivlen : transform->ivlen;
        memcpy( transform->iv_dec, key1 + keylen,  iv_copy_len );
        memcpy( transform->iv_enc, key1 + keylen + iv_copy_len,
                iv_copy_len );
    }
    else
#endif /* MBEDTLS_SSL_SRV_C */
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        goto end;
    }

#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
#if defined(MBEDTLS_SSL_PROTO_SSL3)
    if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
    {
        if( mac_key_len > sizeof( transform->mac_enc ) )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
            ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
            goto end;
        }

        memcpy( transform->mac_enc, mac_enc, mac_key_len );
        memcpy( transform->mac_dec, mac_dec, mac_key_len );
    }
    else
#endif /* MBEDTLS_SSL_PROTO_SSL3 */
#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_2)
    if( minor_ver >= MBEDTLS_SSL_MINOR_VERSION_1 )
    {
        /* For HMAC-based ciphersuites, initialize the HMAC transforms.
           For AEAD-based ciphersuites, there is nothing to do here. */
        if( mac_key_len != 0 )
        {
            mbedtls_md_hmac_starts( &transform->md_ctx_enc, mac_enc, mac_key_len );
            mbedtls_md_hmac_starts( &transform->md_ctx_dec, mac_dec, mac_key_len );
        }
    }
    else
#endif
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        goto end;
    }
#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */

#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
    if( mbedtls_ssl_hw_record_init != NULL )
    {
        ret = 0;

        MBEDTLS_SSL_DEBUG_MSG( 2, ( "going for mbedtls_ssl_hw_record_init()" ) );

        if( ( ret = mbedtls_ssl_hw_record_init( ssl, key1, key2, keylen,
                                        transform->iv_enc, transform->iv_dec,
                                        iv_copy_len,
                                        mac_enc, mac_dec,
                                        mac_key_len ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_hw_record_init", ret );
            ret = MBEDTLS_ERR_SSL_HW_ACCEL_FAILED;
            goto end;
        }
    }
#else
    ((void) mac_dec);
    ((void) mac_enc);
#endif /* MBEDTLS_SSL_HW_RECORD_ACCEL */

#if defined(MBEDTLS_SSL_EXPORT_KEYS)
    if( ssl->conf->f_export_keys != NULL )
    {
        ssl->conf->f_export_keys( ssl->conf->p_export_keys,
                                  master, keyblk,
                                  mac_key_len, keylen,
                                  iv_copy_len );
    }

    if( ssl->conf->f_export_keys_ext != NULL )
    {
        ssl->conf->f_export_keys_ext( ssl->conf->p_export_keys,
                                      master, keyblk,
                                      mac_key_len, keylen,
                                      iv_copy_len,
                                      randbytes + 32,
                                      randbytes,
                                      tls_prf_get_type( tls_prf ) );
    }
#endif

    if( ( ret = mbedtls_cipher_setup( &transform->cipher_ctx_enc,
                                      cipher_info ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_setup", ret );
        goto end;
    }

    if( ( ret = mbedtls_cipher_setup( &transform->cipher_ctx_dec,
                                      cipher_info ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_setup", ret );
        goto end;
    }

    if( ( ret = mbedtls_cipher_setkey( &transform->cipher_ctx_enc, key1,
                                       cipher_info->key_bitlen,
                                       MBEDTLS_ENCRYPT ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_setkey", ret );
        goto end;
    }

    if( ( ret = mbedtls_cipher_setkey( &transform->cipher_ctx_dec, key2,
                                       cipher_info->key_bitlen,
                                       MBEDTLS_DECRYPT ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_setkey", ret );
        goto end;
    }

#if defined(MBEDTLS_CIPHER_MODE_CBC)
    if( cipher_info->mode == MBEDTLS_MODE_CBC )
    {
        if( ( ret = mbedtls_cipher_set_padding_mode( &transform->cipher_ctx_enc,
                                                     MBEDTLS_PADDING_NONE ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_set_padding_mode", ret );
            goto end;
        }

        if( ( ret = mbedtls_cipher_set_padding_mode( &transform->cipher_ctx_dec,
                                                     MBEDTLS_PADDING_NONE ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_set_padding_mode", ret );
            goto end;
        }
    }
#endif /* MBEDTLS_CIPHER_MODE_CBC */


    /* Initialize Zlib contexts */
#if defined(MBEDTLS_ZLIB_SUPPORT)
    if( compression == MBEDTLS_SSL_COMPRESS_DEFLATE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Initializing zlib states" ) );

        mbedtls_platform_zeroize( &transform->ctx_deflate, sizeof( transform->ctx_deflate ) );
        mbedtls_platform_zeroize( &transform->ctx_inflate, sizeof( transform->ctx_inflate ) );

        if( deflateInit( &transform->ctx_deflate,
                         Z_DEFAULT_COMPRESSION )   != Z_OK ||
            inflateInit( &transform->ctx_inflate ) != Z_OK )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "Failed to initialize compression" ) );
            ret = MBEDTLS_ERR_SSL_COMPRESSION_FAILED;
            goto end;
        }
    }
#endif /* MBEDTLS_ZLIB_SUPPORT */

end:
    mbedtls_platform_zeroize( keyblk, sizeof( keyblk ) );
    return( ret );
}

/*
 * Set appropriate PRF function and other SSL / TLS 1.0/1.1 / TLS1.2 functions
 *
 * Inputs:
 * - SSL/TLS minor version
 * - hash associated with the ciphersuite (only used by TLS 1.2)
 *
 * Outputs:
 * - the tls_prf, calc_verify and calc_finished members of handshake structure
 */
static int ssl_set_handshake_prfs( mbedtls_ssl_handshake_params *handshake,
                                   int minor_ver,
                                   mbedtls_md_type_t hash )
{
#if !defined(MBEDTLS_SSL_PROTO_TLS1_2) || !defined(MBEDTLS_SHA512_C)
    (void) hash;
#endif

#if defined(MBEDTLS_SSL_PROTO_SSL3)
    if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
    {
        handshake->tls_prf = ssl3_prf;
        handshake->calc_verify = ssl_calc_verify_ssl;
        handshake->calc_finished = ssl_calc_finished_ssl;
    }
    else
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
    if( minor_ver < MBEDTLS_SSL_MINOR_VERSION_3 )
    {
        handshake->tls_prf = tls1_prf;
        handshake->calc_verify = ssl_calc_verify_tls;
        handshake->calc_finished = ssl_calc_finished_tls;
    }
    else
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA512_C)
    if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 &&
        hash == MBEDTLS_MD_SHA384 )
    {
        handshake->tls_prf = tls_prf_sha384;
        handshake->calc_verify = ssl_calc_verify_tls_sha384;
        handshake->calc_finished = ssl_calc_finished_tls_sha384;
    }
    else
#endif
#if defined(MBEDTLS_SHA256_C)
    if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
    {
        handshake->tls_prf = tls_prf_sha256;
        handshake->calc_verify = ssl_calc_verify_tls_sha256;
        handshake->calc_finished = ssl_calc_finished_tls_sha256;
    }
    else
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    {
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

    return( 0 );
}

/*
 * Compute master secret if needed
 *
 * Parameters:
 * [in/out] handshake
 *          [in] resume, premaster, extended_ms, calc_verify, tls_prf
 *               (PSA-PSK) ciphersuite_info, psk_opaque
 *          [out] premaster (cleared)
 * [out] master
 * [in] ssl: optionally used for debugging, EMS and PSA-PSK
 *      debug: conf->f_dbg, conf->p_dbg
 *      EMS: passed to calc_verify (debug + (SSL3) session_negotiate)
 *      PSA-PSA: minor_ver, conf
 */
static int ssl_compute_master( mbedtls_ssl_handshake_params *handshake,
                               unsigned char *master,
                               const mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;

    /* cf. RFC 5246, Section 8.1:
     * "The master secret is always exactly 48 bytes in length." */
    size_t const master_secret_len = 48;

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
    unsigned char session_hash[48];
#endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */

    /* The label for the KDF used for key expansion.
     * This is either "master secret" or "extended master secret"
     * depending on whether the Extended Master Secret extension
     * is used. */
    char const *lbl = "master secret";

    /* The salt for the KDF used for key expansion.
     * - If the Extended Master Secret extension is not used,
     *   this is ClientHello.Random + ServerHello.Random
     *   (see Sect. 8.1 in RFC 5246).
     * - If the Extended Master Secret extension is used,
     *   this is the transcript of the handshake so far.
     *   (see Sect. 4 in RFC 7627). */
    unsigned char const *salt = handshake->randbytes;
    size_t salt_len = 64;

#if !defined(MBEDTLS_DEBUG_C) &&                    \
    !defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET) && \
    !(defined(MBEDTLS_USE_PSA_CRYPTO) &&            \
      defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED))
    ssl = NULL; /* make sure we don't use it except for those cases */
    (void) ssl;
#endif

    if( handshake->resume != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "no premaster (session resumed)" ) );
        return( 0 );
    }

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
    if( handshake->extended_ms == MBEDTLS_SSL_EXTENDED_MS_ENABLED )
    {
        lbl  = "extended master secret";
        salt = session_hash;
        handshake->calc_verify( ssl, session_hash, &salt_len );

        MBEDTLS_SSL_DEBUG_BUF( 3, "session hash for extended master secret",
                                  session_hash, salt_len );
    }
#endif /* MBEDTLS_SSL_EXTENDED_MS_ENABLED */

    ret = handshake->tls_prf( handshake->premaster, handshake->pmslen,
                              lbl, salt, salt_len,
                              master,
                              master_secret_len );
    if( ret != 0 )
    {
      MBEDTLS_SSL_DEBUG_RET( 1, "prf", ret );
      return( ret );
    }

    MBEDTLS_SSL_DEBUG_BUF( 3, "premaster secret",
                           handshake->premaster,
                           handshake->pmslen );

    mbedtls_platform_zeroize( handshake->premaster,
                              sizeof(handshake->premaster) );

    return( 0 );
}

int mbedtls_ssl_derive_keys( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
    const mbedtls_ssl_ciphersuite_t * const ciphersuite_info =
        ssl->handshake->ciphersuite_info;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> derive keys" ) );

    /* Set PRF, calc_verify and calc_finished function pointers */
    ret = ssl_set_handshake_prfs( ssl->handshake,
                                  ssl->minor_ver,
                                  ciphersuite_info->mac );
    if( ret != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "ssl_set_handshake_prfs", ret );
        return( ret );
    }

    /* Compute master secret if needed */
    ret = ssl_compute_master( ssl->handshake,
                              ssl->session_negotiate->master,
                              ssl );
    if( ret != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "ssl_compute_master", ret );
        return( ret );
    }

    /* Swap the client and server random values:
     * - MS derivation wanted client+server (RFC 5246 8.1)
     * - key derivation wants server+client (RFC 5246 6.3) */
    {
        unsigned char tmp[64];
        memcpy( tmp, ssl->handshake->randbytes, 64 );
        memcpy( ssl->handshake->randbytes, tmp + 32, 32 );
        memcpy( ssl->handshake->randbytes + 32, tmp, 32 );
        mbedtls_platform_zeroize( tmp, sizeof( tmp ) );
    }

    /* Populate transform structure */
    ret = ssl_populate_transform( ssl->transform_negotiate,
                                  ssl->session_negotiate->ciphersuite,
                                  ssl->session_negotiate->master,
#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                                  ssl->session_negotiate->encrypt_then_mac,
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
#if defined(MBEDTLS_ZLIB_SUPPORT)
                                  ssl->session_negotiate->compression,
#endif
                                  ssl->handshake->tls_prf,
                                  ssl->handshake->randbytes,
                                  ssl->minor_ver,
                                  ssl->conf->endpoint,
                                  ssl );
    if( ret != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "ssl_populate_transform", ret );
        return( ret );
    }

    /* We no longer need Server/ClientHello.random values */
    mbedtls_platform_zeroize( ssl->handshake->randbytes,
                      sizeof( ssl->handshake->randbytes ) );

    /* Allocate compression buffer */
#if defined(MBEDTLS_ZLIB_SUPPORT)
    if( ssl->session_negotiate->compression == MBEDTLS_SSL_COMPRESS_DEFLATE &&
        ssl->compress_buf == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Allocating compression buffer" ) );
        ssl->compress_buf = mbedtls_calloc( 1, MBEDTLS_SSL_COMPRESS_BUFFER_LEN );
        if( ssl->compress_buf == NULL )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%d bytes) failed",
                                        MBEDTLS_SSL_COMPRESS_BUFFER_LEN ) );
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
        }
    }
#endif

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= derive keys" ) );

    return( 0 );
}

#if defined(MBEDTLS_SSL_PROTO_SSL3)
void ssl_calc_verify_ssl( const mbedtls_ssl_context *ssl,
                          unsigned char *hash,
                          size_t *hlen )
{
    mbedtls_md5_context md5;
    mbedtls_sha1_context sha1;
    unsigned char pad_1[48];
    unsigned char pad_2[48];

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc verify ssl" ) );

    mbedtls_md5_init( &md5 );
    mbedtls_sha1_init( &sha1 );

    mbedtls_md5_clone( &md5, &ssl->handshake->fin_md5 );
    mbedtls_sha1_clone( &sha1, &ssl->handshake->fin_sha1 );

    memset( pad_1, 0x36, 48 );
    memset( pad_2, 0x5C, 48 );

    mbedtls_md5_update_ret( &md5, ssl->session_negotiate->master, 48 );
    mbedtls_md5_update_ret( &md5, pad_1, 48 );
    mbedtls_md5_finish_ret( &md5, hash );

    mbedtls_md5_starts_ret( &md5 );
    mbedtls_md5_update_ret( &md5, ssl->session_negotiate->master, 48 );
    mbedtls_md5_update_ret( &md5, pad_2, 48 );
    mbedtls_md5_update_ret( &md5, hash,  16 );
    mbedtls_md5_finish_ret( &md5, hash );

    mbedtls_sha1_update_ret( &sha1, ssl->session_negotiate->master, 48 );
    mbedtls_sha1_update_ret( &sha1, pad_1, 40 );
    mbedtls_sha1_finish_ret( &sha1, hash + 16 );

    mbedtls_sha1_starts_ret( &sha1 );
    mbedtls_sha1_update_ret( &sha1, ssl->session_negotiate->master, 48 );
    mbedtls_sha1_update_ret( &sha1, pad_2, 40 );
    mbedtls_sha1_update_ret( &sha1, hash + 16, 20 );
    mbedtls_sha1_finish_ret( &sha1, hash + 16 );

    *hlen = 36;

    MBEDTLS_SSL_DEBUG_BUF( 3, "calculated verify result", hash, *hlen );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc verify" ) );

    mbedtls_md5_free(  &md5  );
    mbedtls_sha1_free( &sha1 );

    return;
}
#endif /* MBEDTLS_SSL_PROTO_SSL3 */

#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
void ssl_calc_verify_tls( const mbedtls_ssl_context *ssl,
                          unsigned char *hash,
                          size_t *hlen )
{
    mbedtls_md5_context md5;
    mbedtls_sha1_context sha1;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc verify tls" ) );

    mbedtls_md5_init( &md5 );
    mbedtls_sha1_init( &sha1 );

    mbedtls_md5_clone( &md5, &ssl->handshake->fin_md5 );
    mbedtls_sha1_clone( &sha1, &ssl->handshake->fin_sha1 );

    mbedtls_md5_finish_ret( &md5,  hash );
    mbedtls_sha1_finish_ret( &sha1, hash + 16 );

    *hlen = 36;

    MBEDTLS_SSL_DEBUG_BUF( 3, "calculated verify result", hash, *hlen );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc verify" ) );

    mbedtls_md5_free(  &md5  );
    mbedtls_sha1_free( &sha1 );

    return;
}
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
void ssl_calc_verify_tls_sha256( const mbedtls_ssl_context *ssl,
                                 unsigned char *hash,
                                 size_t *hlen )
{
    mbedtls_sha256_context sha256;
    mbedtls_sha256_init( &sha256 );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc verify sha256" ) );
    mbedtls_sha256_clone( &sha256, &ssl->handshake->fin_sha256 );
    mbedtls_sha256_finish_ret( &sha256, hash );
    *hlen = 32;
    MBEDTLS_SSL_DEBUG_BUF( 3, "calculated verify result", hash, *hlen );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc verify" ) );
    mbedtls_sha256_free( &sha256 );
    return;
}
#endif /* MBEDTLS_SHA256_C */

#if defined(MBEDTLS_SHA512_C)
void ssl_calc_verify_tls_sha384( const mbedtls_ssl_context *ssl,
                                 unsigned char *hash,
                                 size_t *hlen )
{
    mbedtls_sha512_context sha512;
    mbedtls_sha512_init( &sha512 );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc verify sha384" ) );
    mbedtls_sha512_clone( &sha512, &ssl->handshake->fin_sha512 );
    mbedtls_sha512_finish_ret( &sha512, hash );
    *hlen = 48;
    MBEDTLS_SSL_DEBUG_BUF( 3, "calculated verify result", hash, *hlen );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc verify" ) );
    mbedtls_sha512_free( &sha512 );
    return;
}
#endif /* MBEDTLS_SHA512_C */
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
int mbedtls_ssl_psk_derive_premaster( mbedtls_ssl_context *ssl, mbedtls_key_exchange_type_t key_ex )
{
    unsigned char *p = ssl->handshake->premaster;
    unsigned char *end = p + sizeof( ssl->handshake->premaster );
    const unsigned char *psk = NULL;
    size_t psk_len = 0;

    if( mbedtls_ssl_get_psk( ssl, &psk, &psk_len )
            == MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED )
    {
        /*
         * This should never happen because the existence of a PSK is always
         * checked before calling this function
         */
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

    /*
     * PMS = struct {
     *     opaque other_secret<0..2^16-1>;
     *     opaque psk<0..2^16-1>;
     * };
     * with "other_secret" depending on the particular key exchange
     */
#if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
    if( key_ex == MBEDTLS_KEY_EXCHANGE_PSK )
    {
        if( end - p < 2 )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        *(p++) = (unsigned char)( psk_len >> 8 );
        *(p++) = (unsigned char)( psk_len      );

        if( end < p || (size_t)( end - p ) < psk_len )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        mbedtls_platform_zeroize( p, psk_len );
        p += psk_len;
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
    if( key_ex == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
    {
        /*
         * other_secret already set by the ClientKeyExchange message,
         * and is 48 bytes long
         */
        if( end - p < 2 )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        *p++ = 0;
        *p++ = 48;
        p += 48;
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
    if( key_ex == MBEDTLS_KEY_EXCHANGE_DHE_PSK )
    {
        int ret = MBEDTLS_ERR_THIS_CORRUPTION;
        size_t len;

        /* Write length only when we know the actual value */
        if( ( ret = mbedtls_dhm_calc_secret( &ssl->handshake->dhm_ctx,
                                      p + 2, end - ( p + 2 ), &len,
                                      ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_dhm_calc_secret", ret );
            return( ret );
        }
        *(p++) = (unsigned char)( len >> 8 );
        *(p++) = (unsigned char)( len );
        p += len;

        MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: K ", &ssl->handshake->dhm_ctx.K  );
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
    if( key_ex == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK )
    {
        int ret = MBEDTLS_ERR_THIS_CORRUPTION;
        size_t zlen;

        if( ( ret = mbedtls_ecdh_calc_secret( &ssl->handshake->ecdh_ctx, &zlen,
                                       p + 2, end - ( p + 2 ),
                                       ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_calc_secret", ret );
            return( ret );
        }

        *(p++) = (unsigned char)( zlen >> 8 );
        *(p++) = (unsigned char)( zlen      );
        p += zlen;

        MBEDTLS_SSL_DEBUG_ECDH( 3, &ssl->handshake->ecdh_ctx,
                                MBEDTLS_DEBUG_ECDH_Z );
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

    /* opaque psk<0..2^16-1>; */
    if( end - p < 2 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    *(p++) = (unsigned char)( psk_len >> 8 );
    *(p++) = (unsigned char)( psk_len      );

    if( end < p || (size_t)( end - p ) < psk_len )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    memcpy( p, psk, psk_len );
    p += psk_len;

    ssl->handshake->pmslen = p - ssl->handshake->premaster;

    return( 0 );
}
#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */

#if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_RENEGOTIATION)
static int ssl_write_hello_request( mbedtls_ssl_context *ssl );

#if defined(MBEDTLS_SSL_PROTO_DTLS)
int mbedtls_ssl_resend_hello_request( mbedtls_ssl_context *ssl )
{
    /* If renegotiation is not enforced, retransmit until we would reach max
     * timeout if we were using the usual handshake doubling scheme */
    if( ssl->conf->renego_max_records < 0 )
    {
        uint32_t ratio = ssl->conf->hs_timeout_max / ssl->conf->hs_timeout_min + 1;
        unsigned char doublings = 1;

        while( ratio != 0 )
        {
            ++doublings;
            ratio >>= 1;
        }

        if( ++ssl->renego_records_seen > doublings )
        {
            MBEDTLS_SSL_DEBUG_MSG( 2, ( "no longer retransmitting hello request" ) );
            return( 0 );
        }
    }

    return( ssl_write_hello_request( ssl ) );
}
#endif
#endif /* MBEDTLS_SSL_SRV_C && MBEDTLS_SSL_RENEGOTIATION */

#if defined(MBEDTLS_X509_CRT_PARSE_C)
static void ssl_clear_peer_cert( mbedtls_ssl_session *session )
{
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    if( session->peer_cert != NULL )
    {
        mbedtls_x509_crt_free( session->peer_cert );
        mbedtls_free( session->peer_cert );
        session->peer_cert = NULL;
    }
#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    if( session->peer_cert_digest != NULL )
    {
        /* Zeroization is not necessary. */
        mbedtls_free( session->peer_cert_digest );
        session->peer_cert_digest      = NULL;
        session->peer_cert_digest_type = MBEDTLS_MD_NONE;
        session->peer_cert_digest_len  = 0;
    }
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

/*
 * Handshake functions
 */
#if !defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/* No certificate support -> dummy functions */
int mbedtls_ssl_write_certificate( mbedtls_ssl_context *ssl )
{
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate" ) );
    if( !mbedtls_ssl_ciphersuite_uses_srv_cert( ciphersuite_info ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate" ) );
        ssl->state++;
        return( 0 );
    }
    MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
    return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}

int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
{
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate" ) );
    if( !mbedtls_ssl_ciphersuite_uses_srv_cert( ciphersuite_info ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
        ssl->state++;
        return( 0 );
    }
    MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
    return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}

#else /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
/* Some certificate support -> implement write and parse */

int mbedtls_ssl_write_certificate( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
    size_t i, n;
    const mbedtls_x509_crt *crt;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate" ) );
    if( !mbedtls_ssl_ciphersuite_uses_srv_cert( ciphersuite_info ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate" ) );
        ssl->state++;
        return( 0 );
    }
#if defined(MBEDTLS_SSL_CLI_C)
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
    {
        if( ssl->client_auth == 0 )
        {
            MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate" ) );
            ssl->state++;
            return( 0 );
        }
#if defined(MBEDTLS_SSL_PROTO_SSL3)
        /*
         * If using SSLv3 and got no cert, send an Alert message
         * (otherwise an empty Certificate message will be sent).
         */
        if( mbedtls_ssl_own_cert( ssl )  == NULL &&
            ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
        {
            ssl->out_msglen  = 2;
            ssl->out_msgtype = MBEDTLS_SSL_MSG_ALERT;
            ssl->out_msg[0]  = MBEDTLS_SSL_ALERT_LEVEL_WARNING;
            ssl->out_msg[1]  = MBEDTLS_SSL_ALERT_MSG_NO_CERT;
            MBEDTLS_SSL_DEBUG_MSG( 2, ( "got no certificate to send" ) );
            goto write_msg;
        }
#endif /* MBEDTLS_SSL_PROTO_SSL3 */
    }
#endif /* MBEDTLS_SSL_CLI_C */
#if defined(MBEDTLS_SSL_SRV_C)
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        if( mbedtls_ssl_own_cert( ssl ) == NULL )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no certificate to send" ) );
            return( MBEDTLS_ERR_SSL_CERTIFICATE_REQUIRED );
        }
    }
#endif
    MBEDTLS_SSL_DEBUG_CRT( 3, "own certificate", mbedtls_ssl_own_cert( ssl ) );
    /*
     *     0  .  0    handshake type
     *     1  .  3    handshake length
     *     4  .  6    length of all certs
     *     7  .  9    length of cert. 1
     *    10  . n-1   peer certificate
     *     n  . n+2   length of cert. 2
     *    n+3 . ...   upper level cert, etc.
     */
    i = 7;
    crt = mbedtls_ssl_own_cert( ssl );
    while( crt != NULL )
    {
        n = crt->raw.len;
        if( n > MBEDTLS_SSL_OUT_CONTENT_LEN - 3 - i )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "certificate too large, %" MBEDTLS_PRINTF_SIZET
                                        " > %" MBEDTLS_PRINTF_SIZET,
                           i + 3 + n, (size_t) MBEDTLS_SSL_OUT_CONTENT_LEN ) );
            return( MBEDTLS_ERR_SSL_CERTIFICATE_TOO_LARGE );
        }
        ssl->out_msg[i    ] = (unsigned char)( n >> 16 );
        ssl->out_msg[i + 1] = (unsigned char)( n >>  8 );
        ssl->out_msg[i + 2] = (unsigned char)( n       );
        i += 3; memcpy( ssl->out_msg + i, crt->raw.p, n );
        i += n; crt = crt->next;
    }
    ssl->out_msg[4]  = (unsigned char)( ( i - 7 ) >> 16 );
    ssl->out_msg[5]  = (unsigned char)( ( i - 7 ) >>  8 );
    ssl->out_msg[6]  = (unsigned char)( ( i - 7 )       );
    ssl->out_msglen  = i;
    ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
    ssl->out_msg[0]  = MBEDTLS_SSL_HS_CERTIFICATE;
#if defined(MBEDTLS_SSL_PROTO_SSL3) && defined(MBEDTLS_SSL_CLI_C)
write_msg:
#endif
    ssl->state++;
    if( ( ret = mbedtls_ssl_write_handshake_msg( ssl ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_handshake_msg", ret );
        return( ret );
    }
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write certificate" ) );
    return( ret );
}

#if defined(MBEDTLS_SSL_RENEGOTIATION) && defined(MBEDTLS_SSL_CLI_C)

#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)

static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
                                         unsigned char *crt_buf,
                                         size_t crt_buf_len )
{
    mbedtls_x509_crt const * const peer_crt = ssl->session->peer_cert;
    if( peer_crt == NULL )
        return( -1 );
    if( peer_crt->raw.len != crt_buf_len )
        return( -1 );
    return( timingsafe_bcmp( peer_crt->raw.p, crt_buf, peer_crt->raw.len ) );
}

#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
                                         unsigned char *crt_buf,
                                         size_t crt_buf_len )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
    unsigned char const * const peer_cert_digest =
        ssl->session->peer_cert_digest;
    mbedtls_md_type_t const peer_cert_digest_type =
        ssl->session->peer_cert_digest_type;
    mbedtls_md_info_t const * const digest_info =
        mbedtls_md_info_from_type( peer_cert_digest_type );
    unsigned char tmp_digest[MBEDTLS_SSL_PEER_CERT_DIGEST_MAX_LEN];
    size_t digest_len;
    if( peer_cert_digest == NULL || digest_info == NULL )
        return( -1 );
    digest_len = mbedtls_md_get_size( digest_info );
    if( digest_len > MBEDTLS_SSL_PEER_CERT_DIGEST_MAX_LEN )
        return( -1 );
    ret = mbedtls_md( digest_info, crt_buf, crt_buf_len, tmp_digest );
    if( ret != 0 )
        return( -1 );
    return( timingsafe_bcmp( tmp_digest, peer_cert_digest, digest_len ) );
}

#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_SSL_RENEGOTIATION && MBEDTLS_SSL_CLI_C */

/*
 * Once the certificate message is read, parse it into a cert chain and
 * perform basic checks, but leave actual verification to the caller
 */
static int ssl_parse_certificate_chain( mbedtls_ssl_context *ssl,
                                        mbedtls_x509_crt *chain )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
#if defined(MBEDTLS_SSL_RENEGOTIATION) && defined(MBEDTLS_SSL_CLI_C)
    int crt_cnt=0;
#endif
    size_t i, n;
    uint8_t alert;
    if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
        return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
    }
    if( ssl->in_msg[0] != MBEDTLS_SSL_HS_CERTIFICATE ||
        ssl->in_hslen < mbedtls_ssl_hs_hdr_len( ssl ) + 3 + 3 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
        return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE );
    }
    i = mbedtls_ssl_hs_hdr_len( ssl );
    /*
     * Same message structure as in mbedtls_ssl_write_certificate()
     */
    n = ( ssl->in_msg[i+1] << 8 ) | ssl->in_msg[i+2];
    if( ssl->in_msg[i] != 0 ||
        ssl->in_hslen != n + 3 + mbedtls_ssl_hs_hdr_len( ssl ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
        return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE );
    }
    /* Make &ssl->in_msg[i] point to the beginning of the CRT chain. */
    i += 3;
    /* Iterate through and parse the CRTs in the provided chain. */
    while( i < ssl->in_hslen )
    {
        /* Check that there's room for the next CRT's length fields. */
        if ( i + 3 > ssl->in_hslen ) {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
            mbedtls_ssl_send_alert_message( ssl,
                              MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                              MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
            return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE );
        }
        /* In theory, the CRT can be up to 2**24 Bytes, but we don't support
         * anything beyond 2**16 ~ 64K. */
        if( ssl->in_msg[i] != 0 )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
            mbedtls_ssl_send_alert_message( ssl,
                            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                            MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
            return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE );
        }
        /* Read length of the next CRT in the chain. */
        n = ( (unsigned int) ssl->in_msg[i + 1] << 8 )
            | (unsigned int) ssl->in_msg[i + 2];
        i += 3;
        if( n < 128 || i + n > ssl->in_hslen )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
            mbedtls_ssl_send_alert_message( ssl,
                                 MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                 MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
            return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE );
        }
        /* Check if we're handling the first CRT in the chain. */
#if defined(MBEDTLS_SSL_RENEGOTIATION) && defined(MBEDTLS_SSL_CLI_C)
        if( crt_cnt++ == 0 &&
            ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT &&
            ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
        {
            /* During client-side renegotiation, check that the server's
             * end-CRTs hasn't changed compared to the initial handshake,
             * mitigating the triple handshake attack. On success, reuse
             * the original end-CRT instead of parsing it again. */
            MBEDTLS_SSL_DEBUG_MSG( 3, ( "Check that peer CRT hasn't changed during renegotiation" ) );
            if( ssl_check_peer_crt_unchanged( ssl,
                                              &ssl->in_msg[i],
                                              n ) != 0 )
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "new server cert during renegotiation" ) );
                mbedtls_ssl_send_alert_message( ssl,
                                                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                MBEDTLS_SSL_ALERT_MSG_ACCESS_DENIED );
                return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE );
            }
            /* Now we can safely free the original chain. */
            ssl_clear_peer_cert( ssl->session );
        }
#endif /* MBEDTLS_SSL_RENEGOTIATION && MBEDTLS_SSL_CLI_C */
        /* Parse the next certificate in the chain. */
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
        ret = mbedtls_x509_crt_parse_der( chain, ssl->in_msg + i, n );
#else
        /* If we don't need to store the CRT chain permanently, parse
         * it in-place from the input buffer instead of making a copy. */
        ret = mbedtls_x509_crt_parse_der_nocopy( chain, ssl->in_msg + i, n );
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
        switch( ret )
        {
            case 0: /*ok*/
            case MBEDTLS_ERR_X509_UNKNOWN_SIG_ALG + MBEDTLS_ERR_OID_NOT_FOUND:
                /* Ignore certificate with an unknown algorithm: maybe a
                   prior certificate was already trusted. */
                break;
            case MBEDTLS_ERR_X509_ALLOC_FAILED:
                alert = MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR;
                goto crt_parse_der_failed;
            case MBEDTLS_ERR_X509_UNKNOWN_VERSION:
                alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
                goto crt_parse_der_failed;
            default:
                alert = MBEDTLS_SSL_ALERT_MSG_BAD_CERT;
            crt_parse_der_failed:
                mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL, alert );
                MBEDTLS_SSL_DEBUG_RET( 1, " mbedtls_x509_crt_parse_der", ret );
                return( ret );
        }
        i += n;
    }
    MBEDTLS_SSL_DEBUG_CRT( 3, "peer certificate", chain );
    return( 0 );
}

#if defined(MBEDTLS_SSL_SRV_C)
static int ssl_srv_check_client_no_crt_notification( mbedtls_ssl_context *ssl )
{
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
        return( -1 );

#if defined(MBEDTLS_SSL_PROTO_SSL3)
    /*
     * Check if the client sent an empty certificate
     */
    if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
    {
        if( ssl->in_msglen  == 2                        &&
            ssl->in_msgtype == MBEDTLS_SSL_MSG_ALERT            &&
            ssl->in_msg[0]  == MBEDTLS_SSL_ALERT_LEVEL_WARNING  &&
            ssl->in_msg[1]  == MBEDTLS_SSL_ALERT_MSG_NO_CERT )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "SSLv3 client has no certificate" ) );
            return( 0 );
        }

        return( -1 );
    }
#endif /* MBEDTLS_SSL_PROTO_SSL3 */

#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_2)
    if( ssl->in_hslen   == 3 + mbedtls_ssl_hs_hdr_len( ssl ) &&
        ssl->in_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE    &&
        ssl->in_msg[0]  == MBEDTLS_SSL_HS_CERTIFICATE   &&
        timingsafe_bcmp( ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl ), "\0\0\0", 3 ) == 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "TLSv1 client has no certificate" ) );
        return( 0 );
    }

    return( -1 );
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
          MBEDTLS_SSL_PROTO_TLS1_2 */
}
#endif /* MBEDTLS_SSL_SRV_C */

/* Check if a certificate message is expected.
 * Return either
 * - SSL_CERTIFICATE_EXPECTED, or
 * - SSL_CERTIFICATE_SKIP
 * indicating whether a Certificate message is expected or not.
 */
#define SSL_CERTIFICATE_EXPECTED 0
#define SSL_CERTIFICATE_SKIP     1
static int ssl_parse_certificate_coordinate( mbedtls_ssl_context *ssl,
                                             int authmode )
{
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;

    if( !mbedtls_ssl_ciphersuite_uses_srv_cert( ciphersuite_info ) )
        return( SSL_CERTIFICATE_SKIP );

#if defined(MBEDTLS_SSL_SRV_C)
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
            return( SSL_CERTIFICATE_SKIP );

        if( authmode == MBEDTLS_SSL_VERIFY_NONE )
        {
            ssl->session_negotiate->verify_result =
                MBEDTLS_X509_BADCERT_SKIP_VERIFY;
            return( SSL_CERTIFICATE_SKIP );
        }
    }
#else
    ((void) authmode);
#endif /* MBEDTLS_SSL_SRV_C */

    return( SSL_CERTIFICATE_EXPECTED );
}

static int ssl_parse_certificate_verify( mbedtls_ssl_context *ssl,
                                         int authmode,
                                         mbedtls_x509_crt *chain,
                                         void *rs_ctx )
{
    int ret = 0;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    int have_ca_chain = 0;
    int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *);
    void *p_vrfy;
    if( authmode == MBEDTLS_SSL_VERIFY_NONE )
        return( 0 );
    if( ssl->f_vrfy != NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Use context-specific verification callback" ) );
        f_vrfy = ssl->f_vrfy;
        p_vrfy = ssl->p_vrfy;
    }
    else
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Use configuration-specific verification callback" ) );
        f_vrfy = ssl->conf->f_vrfy;
        p_vrfy = ssl->conf->p_vrfy;
    }
    /*
     * Main check: verify certificate
     */
#if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
    if( ssl->conf->f_ca_cb != NULL )
    {
        ((void) rs_ctx);
        have_ca_chain = 1;
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "use CA callback for X.509 CRT verification" ) );
        ret = mbedtls_x509_crt_verify_with_ca_cb(
            chain,
            ssl->conf->f_ca_cb,
            ssl->conf->p_ca_cb,
            ssl->conf->cert_profile,
            ssl->hostname,
            &ssl->session_negotiate->verify_result,
            f_vrfy, p_vrfy );
    }
    else
#endif /* MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK */
    {
        mbedtls_x509_crt *ca_chain;
        mbedtls_x509_crl *ca_crl;
#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
        if( ssl->handshake->sni_ca_chain != NULL )
        {
            ca_chain = ssl->handshake->sni_ca_chain;
            ca_crl   = ssl->handshake->sni_ca_crl;
        }
        else
#endif
        {
            ca_chain = ssl->conf->ca_chain;
            ca_crl   = ssl->conf->ca_crl;
        }
        if( ca_chain != NULL )
            have_ca_chain = 1;
        ret = mbedtls_x509_crt_verify_restartable(
            chain,
            ca_chain, ca_crl,
            ssl->conf->cert_profile,
            ssl->hostname,
            &ssl->session_negotiate->verify_result,
            f_vrfy, p_vrfy, rs_ctx );
    }
    if( ret != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "x509_verify_cert", ret );
    }
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if( ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
        return( MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS );
#endif
    /*
     * Secondary checks: always done, but change 'ret' only if it was 0
     */
#if defined(MBEDTLS_ECP_C)
    {
        const mbedtls_pk_context *pk = &chain->pk;
        /* If certificate uses an EC key, make sure the curve is OK */
        if( mbedtls_pk_can_do( pk, MBEDTLS_PK_ECKEY ) &&
            mbedtls_ssl_check_curve( ssl, mbedtls_pk_ec( *pk )->grp.id ) != 0 )
        {
            ssl->session_negotiate->verify_result |= MBEDTLS_X509_BADCERT_BAD_KEY;
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate (EC key curve)" ) );
            if( ret == 0 )
                ret = MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE;
        }
    }
#endif /* MBEDTLS_ECP_C */
    if( mbedtls_ssl_check_cert_usage( chain,
                                      ciphersuite_info,
                                      ! ssl->conf->endpoint,
                                      &ssl->session_negotiate->verify_result ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate (usage extensions)" ) );
        if( ret == 0 )
            ret = MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE;
    }
    /* mbedtls_x509_crt_verify_with_profile is supposed to report a
     * verification failure through MBEDTLS_ERR_X509_CERT_VERIFY_FAILED,
     * with details encoded in the verification flags. All other kinds
     * of error codes, including those from the user provided f_vrfy
     * functions, are treated as fatal and lead to a failure of
     * ssl_parse_certificate even if verification was optional. */
    if( authmode == MBEDTLS_SSL_VERIFY_OPTIONAL &&
        ( ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED ||
          ret == MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE ) )
    {
        ret = 0;
    }
    if( have_ca_chain == 0 && authmode == MBEDTLS_SSL_VERIFY_REQUIRED )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no CA chain" ) );
        ret = MBEDTLS_ERR_SSL_CA_CHAIN_REQUIRED;
    }
    if( ret != 0 )
    {
        uint8_t alert;
        /* The certificate may have been rejected for several reasons.
           Pick one and send the corresponding alert. Which alert to send
           may be a subject of debate in some cases. */
        if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_OTHER )
            alert = MBEDTLS_SSL_ALERT_MSG_ACCESS_DENIED;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_CN_MISMATCH )
            alert = MBEDTLS_SSL_ALERT_MSG_BAD_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_KEY_USAGE )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_EXT_KEY_USAGE )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_NS_CERT_TYPE )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_BAD_PK )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_BAD_KEY )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_EXPIRED )
            alert = MBEDTLS_SSL_ALERT_MSG_CERT_EXPIRED;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_REVOKED )
            alert = MBEDTLS_SSL_ALERT_MSG_CERT_REVOKED;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_NOT_TRUSTED )
            alert = MBEDTLS_SSL_ALERT_MSG_UNKNOWN_CA;
        else
            alert = MBEDTLS_SSL_ALERT_MSG_CERT_UNKNOWN;
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        alert );
    }
#if defined(MBEDTLS_DEBUG_C)
    if( ssl->session_negotiate->verify_result != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "! Certificate verification flags %08x",
                                    (unsigned int) ssl->session_negotiate->verify_result ) );
    }
    else
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Certificate verification flags clear" ) );
    }
#endif /* MBEDTLS_DEBUG_C */
    return( ret );
}

#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
static int ssl_remember_peer_crt_digest( mbedtls_ssl_context *ssl,
                                         unsigned char *start, size_t len )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
    /* Remember digest of the peer's end-CRT. */
    ssl->session_negotiate->peer_cert_digest =
        mbedtls_calloc( 1, MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_LEN );
    if( ssl->session_negotiate->peer_cert_digest == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%d bytes) failed",
                                    MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_LEN ) );
        mbedtls_ssl_send_alert_message( ssl,
                                        MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
    }
    ret = mbedtls_md( mbedtls_md_info_from_type(
                          MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_TYPE ),
                      start, len,
                      ssl->session_negotiate->peer_cert_digest );
    ssl->session_negotiate->peer_cert_digest_type =
        MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_TYPE;
    ssl->session_negotiate->peer_cert_digest_len =
        MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_LEN;
    return( ret );
}

static int ssl_remember_peer_pubkey( mbedtls_ssl_context *ssl,
                                     unsigned char *start, size_t len )
{
    unsigned char *end = start + len;
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
    /* Make a copy of the peer's raw public key. */
    mbedtls_pk_init( &ssl->handshake->peer_pubkey );
    ret = mbedtls_pk_parse_subpubkey( &start, end,
                                      &ssl->handshake->peer_pubkey );
    if( ret != 0 )
    {
        /* We should have parsed the public key before. */
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }
    return( 0 );
}
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
{
    int ret = 0;
    int crt_expected;
#if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
    const int authmode = ssl->handshake->sni_authmode != MBEDTLS_SSL_VERIFY_UNSET
                       ? ssl->handshake->sni_authmode
                       : ssl->conf->authmode;
#else
    const int authmode = ssl->conf->authmode;
#endif
    void *rs_ctx = NULL;
    mbedtls_x509_crt *chain = NULL;
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate" ) );
    crt_expected = ssl_parse_certificate_coordinate( ssl, authmode );
    if( crt_expected == SSL_CERTIFICATE_SKIP )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
        goto exit;
    }
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if( ssl->handshake->ecrs_enabled &&
        ssl->handshake->ecrs_state == ssl_ecrs_crt_verify )
    {
        chain = ssl->handshake->ecrs_peer_cert;
        ssl->handshake->ecrs_peer_cert = NULL;
        goto crt_verify;
    }
#endif
    if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
    {
        /* mbedtls_ssl_read_record may have sent an alert already. We
           let it decide whether to alert. */
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
        goto exit;
    }
#if defined(MBEDTLS_SSL_SRV_C)
    if( ssl_srv_check_client_no_crt_notification( ssl ) == 0 )
    {
        ssl->session_negotiate->verify_result = MBEDTLS_X509_BADCERT_MISSING;
        if( authmode != MBEDTLS_SSL_VERIFY_OPTIONAL )
            ret = MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE;
        goto exit;
    }
#endif /* MBEDTLS_SSL_SRV_C */
    /* Clear existing peer CRT structure in case we tried to
     * reuse a session but it failed, and allocate a new one. */
    ssl_clear_peer_cert( ssl->session_negotiate );
    chain = mbedtls_calloc( 1, sizeof( mbedtls_x509_crt ) );
    if( chain == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%" MBEDTLS_PRINTF_SIZET " bytes) failed",
                                    sizeof( mbedtls_x509_crt ) ) );
        mbedtls_ssl_send_alert_message( ssl,
                                        MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto exit;
    }
    mbedtls_x509_crt_init( chain );
    ret = ssl_parse_certificate_chain( ssl, chain );
    if( ret != 0 )
        goto exit;
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if( ssl->handshake->ecrs_enabled)
        ssl->handshake->ecrs_state = ssl_ecrs_crt_verify;
crt_verify:
    if( ssl->handshake->ecrs_enabled)
        rs_ctx = &ssl->handshake->ecrs_ctx;
#endif
    ret = ssl_parse_certificate_verify( ssl, authmode,
                                        chain, rs_ctx );
    if( ret != 0 )
        goto exit;
#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    {
        unsigned char *crt_start, *pk_start;
        size_t crt_len, pk_len;
        /* We parse the CRT chain without copying, so
         * these pointers point into the input buffer,
         * and are hence still valid after freeing the
         * CRT chain. */
        crt_start = chain->raw.p;
        crt_len   = chain->raw.len;
        pk_start = chain->pk_raw.p;
        pk_len   = chain->pk_raw.len;
        /* Free the CRT structures before computing
         * digest and copying the peer's public key. */
        mbedtls_x509_crt_free( chain );
        mbedtls_free( chain );
        chain = NULL;
        ret = ssl_remember_peer_crt_digest( ssl, crt_start, crt_len );
        if( ret != 0 )
            goto exit;
        ret = ssl_remember_peer_pubkey( ssl, pk_start, pk_len );
        if( ret != 0 )
            goto exit;
    }
#else /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    /* Pass ownership to session structure. */
    ssl->session_negotiate->peer_cert = chain;
    chain = NULL;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse certificate" ) );
exit:
    if( ret == 0 )
        ssl->state++;
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if( ret == MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS )
    {
        ssl->handshake->ecrs_peer_cert = chain;
        chain = NULL;
    }
#endif
    if( chain != NULL )
    {
        mbedtls_x509_crt_free( chain );
        mbedtls_free( chain );
    }
    return( ret );
}
#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */

void mbedtls_ssl_optimize_checksum( mbedtls_ssl_context *ssl,
                                    const mbedtls_ssl_ciphersuite_t *ciphersuite_info )
{
    ((void) ciphersuite_info);

#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_1)
    if( ssl->minor_ver < MBEDTLS_SSL_MINOR_VERSION_3 )
        ssl->handshake->update_checksum = ssl_update_checksum_md5sha1;
    else
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA512_C)
    if( ciphersuite_info->mac == MBEDTLS_MD_SHA384 )
        ssl->handshake->update_checksum = ssl_update_checksum_sha384;
    else
#endif
#if defined(MBEDTLS_SHA256_C)
    if( ciphersuite_info->mac != MBEDTLS_MD_SHA384 )
        ssl->handshake->update_checksum = ssl_update_checksum_sha256;
    else
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        return;
    }
}

void mbedtls_ssl_reset_checksum( mbedtls_ssl_context *ssl )
{
#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_1)
     mbedtls_md5_starts_ret( &ssl->handshake->fin_md5  );
    mbedtls_sha1_starts_ret( &ssl->handshake->fin_sha1 );
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
    mbedtls_sha256_starts_ret( &ssl->handshake->fin_sha256, 0 );
#endif
#if defined(MBEDTLS_SHA512_C)
    mbedtls_sha512_starts_ret( &ssl->handshake->fin_sha512, 1 );
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
}

static void ssl_update_checksum_start( mbedtls_ssl_context *ssl,
                                       const unsigned char *buf, size_t len )
{
#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_1)
     mbedtls_md5_update_ret( &ssl->handshake->fin_md5 , buf, len );
    mbedtls_sha1_update_ret( &ssl->handshake->fin_sha1, buf, len );
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
    mbedtls_sha256_update_ret( &ssl->handshake->fin_sha256, buf, len );
#endif
#if defined(MBEDTLS_SHA512_C)
    mbedtls_sha512_update_ret( &ssl->handshake->fin_sha512, buf, len );
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
}

#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_1)
static void ssl_update_checksum_md5sha1( mbedtls_ssl_context *ssl,
                                         const unsigned char *buf, size_t len )
{
     mbedtls_md5_update_ret( &ssl->handshake->fin_md5 , buf, len );
    mbedtls_sha1_update_ret( &ssl->handshake->fin_sha1, buf, len );
}
#endif

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
static void ssl_update_checksum_sha256( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf, size_t len )
{
    mbedtls_sha256_update_ret( &ssl->handshake->fin_sha256, buf, len );
}
#endif

#if defined(MBEDTLS_SHA512_C)
static void ssl_update_checksum_sha384( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf, size_t len )
{
    mbedtls_sha512_update_ret( &ssl->handshake->fin_sha512, buf, len );
}
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

#if defined(MBEDTLS_SSL_PROTO_SSL3)
static void ssl_calc_finished_ssl(
                mbedtls_ssl_context *ssl, unsigned char *buf, int from )
{
    const char *sender;
    mbedtls_md5_context  md5;
    mbedtls_sha1_context sha1;
    unsigned char padbuf[48];
    unsigned char md5sum[16];
    unsigned char sha1sum[20];
    mbedtls_ssl_session *session = ssl->session_negotiate;
    if( !session )
        session = ssl->session;
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc  finished ssl" ) );
    mbedtls_md5_init( &md5 );
    mbedtls_sha1_init( &sha1 );
    mbedtls_md5_clone( &md5, &ssl->handshake->fin_md5 );
    mbedtls_sha1_clone( &sha1, &ssl->handshake->fin_sha1 );
    /*
     * SSLv3:
     *   hash =
     *      MD5( master + pad2 +
     *          MD5( handshake + sender + master + pad1 ) )
     *   + SHA1( master + pad2 +
     *         SHA1( handshake + sender + master + pad1 ) )
     */
#if !defined(MBEDTLS_MD5_ALT)
    MBEDTLS_SSL_DEBUG_BUF( 4, "finished  md5 state", (unsigned char *)
                    md5.state, sizeof(  md5.state ) );
#endif
#if !defined(MBEDTLS_SHA1_ALT)
    MBEDTLS_SSL_DEBUG_BUF( 4, "finished sha1 state", (unsigned char *)
                   sha1.state, sizeof( sha1.state ) );
#endif
    sender = ( from == MBEDTLS_SSL_IS_CLIENT ) ? "CLNT"
                                       : "SRVR";
    memset( padbuf, 0x36, 48 );
    mbedtls_md5_update_ret( &md5, (const unsigned char *) sender, 4 );
    mbedtls_md5_update_ret( &md5, session->master, 48 );
    mbedtls_md5_update_ret( &md5, padbuf, 48 );
    mbedtls_md5_finish_ret( &md5, md5sum );
    mbedtls_sha1_update_ret( &sha1, (const unsigned char *) sender, 4 );
    mbedtls_sha1_update_ret( &sha1, session->master, 48 );
    mbedtls_sha1_update_ret( &sha1, padbuf, 40 );
    mbedtls_sha1_finish_ret( &sha1, sha1sum );
    memset( padbuf, 0x5C, 48 );
    mbedtls_md5_starts_ret( &md5 );
    mbedtls_md5_update_ret( &md5, session->master, 48 );
    mbedtls_md5_update_ret( &md5, padbuf, 48 );
    mbedtls_md5_update_ret( &md5, md5sum, 16 );
    mbedtls_md5_finish_ret( &md5, buf );
    mbedtls_sha1_starts_ret( &sha1 );
    mbedtls_sha1_update_ret( &sha1, session->master, 48 );
    mbedtls_sha1_update_ret( &sha1, padbuf , 40 );
    mbedtls_sha1_update_ret( &sha1, sha1sum, 20 );
    mbedtls_sha1_finish_ret( &sha1, buf + 16 );
    MBEDTLS_SSL_DEBUG_BUF( 3, "calc finished result", buf, 36 );
    mbedtls_md5_free(  &md5  );
    mbedtls_sha1_free( &sha1 );
    mbedtls_platform_zeroize(  padbuf, sizeof(  padbuf ) );
    mbedtls_platform_zeroize(  md5sum, sizeof(  md5sum ) );
    mbedtls_platform_zeroize( sha1sum, sizeof( sha1sum ) );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc  finished" ) );
}
#endif /* MBEDTLS_SSL_PROTO_SSL3 */

#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
static void ssl_calc_finished_tls(
                mbedtls_ssl_context *ssl, unsigned char *buf, int from )
{
    int len = 12;
    const char *sender;
    mbedtls_md5_context  md5;
    mbedtls_sha1_context sha1;
    unsigned char padbuf[36];
    mbedtls_ssl_session *session = ssl->session_negotiate;
    if( !session )
        session = ssl->session;
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc  finished tls" ) );
    mbedtls_md5_init( &md5 );
    mbedtls_sha1_init( &sha1 );
    mbedtls_md5_clone( &md5, &ssl->handshake->fin_md5 );
    mbedtls_sha1_clone( &sha1, &ssl->handshake->fin_sha1 );
    /*
     * TLSv1:
     *   hash = PRF( master, finished_label,
     *               MD5( handshake ) + SHA1( handshake ) )[0..11]
     */
#if !defined(MBEDTLS_MD5_ALT)
    MBEDTLS_SSL_DEBUG_BUF( 4, "finished  md5 state", (unsigned char *)
                           md5.state, sizeof(  md5.state ) );
#endif
#if !defined(MBEDTLS_SHA1_ALT)
    MBEDTLS_SSL_DEBUG_BUF( 4, "finished sha1 state", (unsigned char *)
                           sha1.state, sizeof( sha1.state ) );
#endif
    sender = ( from == MBEDTLS_SSL_IS_CLIENT )
             ? "client finished"
             : "server finished";
    mbedtls_md5_finish_ret(  &md5, padbuf );
    mbedtls_sha1_finish_ret( &sha1, padbuf + 16 );
    ssl->handshake->tls_prf( session->master, 48, sender,
                             padbuf, 36, buf, len );
    MBEDTLS_SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
    mbedtls_md5_free(  &md5  );
    mbedtls_sha1_free( &sha1 );
    mbedtls_platform_zeroize(  padbuf, sizeof(  padbuf ) );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc  finished" ) );
}
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
static void ssl_calc_finished_tls_sha256(
                mbedtls_ssl_context *ssl, unsigned char *buf, int from )
{
    int len = 12;
    const char *sender;
    unsigned char padbuf[32];
    mbedtls_sha256_context sha256;
    mbedtls_ssl_session *session = ssl->session_negotiate;
    if( !session )
        session = ssl->session;
    sender = ( from == MBEDTLS_SSL_IS_CLIENT )
             ? "client finished"
             : "server finished";

    mbedtls_sha256_init( &sha256 );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc  finished tls sha256" ) );
    mbedtls_sha256_clone( &sha256, &ssl->handshake->fin_sha256 );
    /*
     * TLSv1.2:
     *   hash = PRF( master, finished_label,
     *               Hash( handshake ) )[0.11]
     */
#if !defined(MBEDTLS_SHA256_ALT)
    MBEDTLS_SSL_DEBUG_BUF( 4, "finished sha2 state", (unsigned char *)
                   sha256.state, sizeof( sha256.state ) );
#endif
    mbedtls_sha256_finish_ret( &sha256, padbuf );
    mbedtls_sha256_free( &sha256 );
    ssl->handshake->tls_prf( session->master, 48, sender,
                             padbuf, 32, buf, len );
    MBEDTLS_SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
    mbedtls_platform_zeroize(  padbuf, sizeof(  padbuf ) );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc  finished" ) );
}
#endif /* MBEDTLS_SHA256_C */

#if defined(MBEDTLS_SHA512_C)

typedef int (*finish_sha384_t)(mbedtls_sha512_context*, unsigned char*);

static void ssl_calc_finished_tls_sha384(
                mbedtls_ssl_context *ssl, unsigned char *buf, int from )
{
    int len = 12;
    const char *sender;
    unsigned char padbuf[48];
    mbedtls_sha512_context sha512;
    mbedtls_ssl_session *session = ssl->session_negotiate;
    if( !session )
        session = ssl->session;
    sender = ( from == MBEDTLS_SSL_IS_CLIENT )
                ? "client finished"
                : "server finished";
    mbedtls_sha512_init( &sha512 );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc  finished tls sha384" ) );
    mbedtls_sha512_clone( &sha512, &ssl->handshake->fin_sha512 );
    /*
     * TLSv1.2:
     *   hash = PRF( master, finished_label,
     *               Hash( handshake ) )[0.11]
     */
#if !defined(MBEDTLS_SHA512_ALT)
    MBEDTLS_SSL_DEBUG_BUF( 4, "finished sha512 state", (unsigned char *)
                   sha512.state, sizeof( sha512.state ) );
    /*
     * For SHA-384, we can save 16 bytes by keeping padbuf 48 bytes long.
     * However, to avoid stringop-overflow warning in gcc, we have to cast
     * mbedtls_sha512_finish_ret().
     */
    finish_sha384_t finish = (finish_sha384_t)mbedtls_sha512_finish_ret;
    finish( &sha512, padbuf );
    mbedtls_sha512_free( &sha512 );
#endif
    ssl->handshake->tls_prf( session->master, 48, sender,
                             padbuf, 48, buf, len );
    MBEDTLS_SSL_DEBUG_BUF( 3, "calc finished result", buf, len );
    mbedtls_platform_zeroize(  padbuf, sizeof( padbuf ) );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc  finished" ) );
}
#endif /* MBEDTLS_SHA512_C */
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

void mbedtls_ssl_handshake_wrapup_free_hs_transform( mbedtls_ssl_context *ssl )
{
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "=> handshake wrapup: final free" ) );
    /*
     * Free our handshake params
     */
    mbedtls_ssl_handshake_free( ssl );
    mbedtls_free( ssl->handshake );
    ssl->handshake = NULL;
    /*
     * Free the previous transform and swith in the current one
     */
    if( ssl->transform )
    {
        mbedtls_ssl_transform_free( ssl->transform );
        mbedtls_free( ssl->transform );
    }
    ssl->transform = ssl->transform_negotiate;
    ssl->transform_negotiate = NULL;
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "<= handshake wrapup: final free" ) );
}

void mbedtls_ssl_handshake_wrapup( mbedtls_ssl_context *ssl )
{
    int resume = ssl->handshake->resume;
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "=> handshake wrapup" ) );
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
    {
        ssl->renego_status =  MBEDTLS_SSL_RENEGOTIATION_DONE;
        ssl->renego_records_seen = 0;
    }
#endif
    /*
     * Free the previous session and switch in the current one
     */
    if( ssl->session )
    {
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
        /* RFC 7366 3.1: keep the EtM state */
        ssl->session_negotiate->encrypt_then_mac =
                  ssl->session->encrypt_then_mac;
#endif
        mbedtls_ssl_session_free( ssl->session );
        mbedtls_free( ssl->session );
    }
    ssl->session = ssl->session_negotiate;
    ssl->session_negotiate = NULL;
    /*
     * Add cache entry
     */
    if( ssl->conf->f_set_cache != NULL &&
        ssl->session->id_len != 0 &&
        resume == 0 )
    {
        if( ssl->conf->f_set_cache( ssl->conf->p_cache, ssl->session ) != 0 )
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "cache did not store session" ) );
    }
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
        ssl->handshake->flight != NULL )
    {
        /* Cancel handshake timer */
        mbedtls_ssl_set_timer( ssl, 0 );
        /* Keep last flight around in case we need to resend it:
         * we need the handshake and transform structures for that */
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "skip freeing handshake and transform" ) );
    }
    else
#endif
        mbedtls_ssl_handshake_wrapup_free_hs_transform( ssl );
    ssl->state++;
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "<= handshake wrapup" ) );
}

int mbedtls_ssl_write_finished( mbedtls_ssl_context *ssl )
{
    int ret, hash_len;
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write finished" ) );
    mbedtls_ssl_update_out_pointers( ssl, ssl->transform_negotiate );
    ssl->handshake->calc_finished( ssl, ssl->out_msg + 4, ssl->conf->endpoint );
    /*
     * RFC 5246 7.4.9 (Page 63) says 12 is the default length and ciphersuites
     * may define some other value. Currently (early 2016), no defined
     * ciphersuite does this (and this is unlikely to change as activity has
     * moved to TLS 1.3 now) so we can keep the hardcoded 12 here.
     */
    hash_len = ( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 ) ? 36 : 12;
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    ssl->verify_data_len = hash_len;
    memcpy( ssl->own_verify_data, ssl->out_msg + 4, hash_len );
#endif
    ssl->out_msglen  = 4 + hash_len;
    ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
    ssl->out_msg[0]  = MBEDTLS_SSL_HS_FINISHED;
    /*
     * In case of session resuming, invert the client and server
     * ChangeCipherSpec messages order.
     */
    if( ssl->handshake->resume != 0 )
    {
#if defined(MBEDTLS_SSL_CLI_C)
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
            ssl->state = MBEDTLS_SSL_HANDSHAKE_WRAPUP;
#endif
#if defined(MBEDTLS_SSL_SRV_C)
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
            ssl->state = MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC;
#endif
    }
    else
        ssl->state++;
    /*
     * Switch to our negotiated transform and session parameters for outbound
     * data.
     */
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "switching to new transform spec for outbound data" ) );
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
    {
        unsigned char i;
        /* Remember current epoch settings for resending */
        ssl->handshake->alt_transform_out = ssl->transform_out;
        memcpy( ssl->handshake->alt_out_ctr, ssl->cur_out_ctr, 8 );
        /* Set sequence_number to zero */
        mbedtls_platform_zeroize( ssl->cur_out_ctr + 2, 6 );
        /* Increment epoch */
        for( i = 2; i > 0; i-- )
            if( ++ssl->cur_out_ctr[i - 1] != 0 )
                break;
        /* The loop goes to its end iff the counter is wrapping */
        if( i == 0 )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "DTLS epoch would wrap" ) );
            return( MBEDTLS_ERR_SSL_COUNTER_WRAPPING );
        }
    }
    else
#endif /* MBEDTLS_SSL_PROTO_DTLS */
    mbedtls_platform_zeroize( ssl->cur_out_ctr, 8 );
    ssl->transform_out = ssl->transform_negotiate;
    ssl->session_out = ssl->session_negotiate;
#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
    if( mbedtls_ssl_hw_record_activate != NULL )
    {
        if( ( ret = mbedtls_ssl_hw_record_activate( ssl, MBEDTLS_SSL_CHANNEL_OUTBOUND ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_hw_record_activate", ret );
            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
        }
    }
#endif
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
        mbedtls_ssl_send_flight_completed( ssl );
#endif
    if( ( ret = mbedtls_ssl_write_handshake_msg( ssl ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_handshake_msg", ret );
        return( ret );
    }
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
        ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
        return( ret );
    }
#endif
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write finished" ) );
    return( 0 );
}

#if defined(MBEDTLS_SSL_PROTO_SSL3)
#define SSL_MAX_HASH_LEN 36
#else
#define SSL_MAX_HASH_LEN 12
#endif

int mbedtls_ssl_parse_finished( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
    unsigned int hash_len;
    unsigned char buf[SSL_MAX_HASH_LEN];
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse finished" ) );
    ssl->handshake->calc_finished( ssl, buf, ssl->conf->endpoint ^ 1 );
    if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
        return( ret );
    }
    if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad finished message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
        return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
    }
    /* There is currently no ciphersuite using another length with TLS 1.2 */
#if defined(MBEDTLS_SSL_PROTO_SSL3)
    if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
        hash_len = 36;
    else
#endif
        hash_len = 12;
    if( ssl->in_msg[0] != MBEDTLS_SSL_HS_FINISHED ||
        ssl->in_hslen  != mbedtls_ssl_hs_hdr_len( ssl ) + hash_len )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad finished message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
        return( MBEDTLS_ERR_SSL_BAD_HS_FINISHED );
    }
    if( timingsafe_bcmp( ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl ),
                         buf, hash_len ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad finished message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
        return( MBEDTLS_ERR_SSL_BAD_HS_FINISHED );
    }
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    ssl->verify_data_len = hash_len;
    memcpy( ssl->peer_verify_data, buf, hash_len );
#endif
    if( ssl->handshake->resume != 0 )
    {
#if defined(MBEDTLS_SSL_CLI_C)
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
            ssl->state = MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC;
#endif
#if defined(MBEDTLS_SSL_SRV_C)
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
            ssl->state = MBEDTLS_SSL_HANDSHAKE_WRAPUP;
#endif
    }
    else
        ssl->state++;
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
        mbedtls_ssl_recv_flight_completed( ssl );
#endif
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse finished" ) );
    return( 0 );
}

static void ssl_handshake_params_init( mbedtls_ssl_handshake_params *handshake )
{
    mbedtls_platform_zeroize( handshake, sizeof( mbedtls_ssl_handshake_params ) );
#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_1)
     mbedtls_md5_init(   &handshake->fin_md5  );
    mbedtls_sha1_init(   &handshake->fin_sha1 );
     mbedtls_md5_starts_ret( &handshake->fin_md5  );
    mbedtls_sha1_starts_ret( &handshake->fin_sha1 );
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
    mbedtls_sha256_init(   &handshake->fin_sha256    );
    mbedtls_sha256_starts_ret( &handshake->fin_sha256, 0 );
#endif
#if defined(MBEDTLS_SHA512_C)
    mbedtls_sha512_init(   &handshake->fin_sha512    );
    mbedtls_sha512_starts_ret( &handshake->fin_sha512, 1 );
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    handshake->update_checksum = ssl_update_checksum_start;
#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
    defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
    mbedtls_ssl_sig_hash_set_init( &handshake->hash_algs );
#endif
#if defined(MBEDTLS_DHM_C)
    mbedtls_dhm_init( &handshake->dhm_ctx );
#endif
#if defined(MBEDTLS_ECDH_C)
    mbedtls_ecdh_init( &handshake->ecdh_ctx );
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    mbedtls_ecjpake_init( &handshake->ecjpake_ctx );
#if defined(MBEDTLS_SSL_CLI_C)
    handshake->ecjpake_cache = NULL;
    handshake->ecjpake_cache_len = 0;
#endif
#endif
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    mbedtls_x509_crt_restart_init( &handshake->ecrs_ctx );
#endif
#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
    handshake->sni_authmode = MBEDTLS_SSL_VERIFY_UNSET;
#endif
#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
    !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    mbedtls_pk_init( &handshake->peer_pubkey );
#endif
}

void mbedtls_ssl_transform_init( mbedtls_ssl_transform *transform )
{
    mbedtls_platform_zeroize( transform, sizeof(mbedtls_ssl_transform) );
    mbedtls_cipher_init( &transform->cipher_ctx_enc );
    mbedtls_cipher_init( &transform->cipher_ctx_dec );
#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
    mbedtls_md_init( &transform->md_ctx_enc );
    mbedtls_md_init( &transform->md_ctx_dec );
#endif
}

/**
 * \brief          Initialize SSL session structure
 *
 * \param session  SSL session
 */
void mbedtls_ssl_session_init( mbedtls_ssl_session *session )
{
    mbedtls_platform_zeroize( session, sizeof(mbedtls_ssl_session) );
}

static int ssl_handshake_init( mbedtls_ssl_context *ssl )
{
    /* Clear old handshake information if present */
    ssl->curve = 0;
    if( ssl->transform_negotiate )
        mbedtls_ssl_transform_free( ssl->transform_negotiate );
    if( ssl->session_negotiate )
        mbedtls_ssl_session_free( ssl->session_negotiate );
    if( ssl->handshake )
        mbedtls_ssl_handshake_free( ssl );
    /*
     * Either the pointers are now NULL or cleared properly and can be freed.
     * Now allocate missing structures.
     */
    if( ssl->transform_negotiate == NULL )
    {
        ssl->transform_negotiate = mbedtls_calloc( 1, sizeof(mbedtls_ssl_transform) );
    }
    if( ssl->session_negotiate == NULL )
    {
        ssl->session_negotiate = mbedtls_calloc( 1, sizeof(mbedtls_ssl_session) );
    }
    if( ssl->handshake == NULL )
    {
        ssl->handshake = mbedtls_calloc( 1, sizeof(mbedtls_ssl_handshake_params) );
    }
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    /* If the buffers are too small - reallocate */
    handle_buffer_resizing( ssl, 0, MBEDTLS_SSL_IN_BUFFER_LEN,
                                    MBEDTLS_SSL_OUT_BUFFER_LEN );
#endif
    /* All pointers should exist and can be directly freed without issue */
    if( ssl->handshake == NULL ||
        ssl->transform_negotiate == NULL ||
        ssl->session_negotiate == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc() of ssl sub-contexts failed" ) );
        mbedtls_free( ssl->handshake );
        mbedtls_free( ssl->transform_negotiate );
        mbedtls_free( ssl->session_negotiate );
        ssl->handshake = NULL;
        ssl->transform_negotiate = NULL;
        ssl->session_negotiate = NULL;
        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
    }
    /* Initialize structures */
    mbedtls_ssl_session_init( ssl->session_negotiate );
    mbedtls_ssl_transform_init( ssl->transform_negotiate );
    ssl_handshake_params_init( ssl->handshake );
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
    {
        ssl->handshake->alt_transform_out = ssl->transform_out;
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
            ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_PREPARING;
        else
            ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_WAITING;
        mbedtls_ssl_set_timer( ssl, 0 );
    }
#endif
    return( 0 );
}

#if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY) && defined(MBEDTLS_SSL_SRV_C)
/* Dummy cookie callbacks for defaults */
static int ssl_cookie_write_dummy( void *ctx,
                      unsigned char **p, unsigned char *end,
                      const unsigned char *cli_id, size_t cli_id_len )
{
    ((void) ctx);
    ((void) p);
    ((void) end);
    ((void) cli_id);
    ((void) cli_id_len);
    return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
}

static int ssl_cookie_check_dummy( void *ctx,
                      const unsigned char *cookie, size_t cookie_len,
                      const unsigned char *cli_id, size_t cli_id_len )
{
    ((void) ctx);
    ((void) cookie);
    ((void) cookie_len);
    ((void) cli_id);
    ((void) cli_id_len);
    return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
}
#endif /* MBEDTLS_SSL_DTLS_HELLO_VERIFY && MBEDTLS_SSL_SRV_C */

/**
 * \brief          Initialize an SSL context
 *                 Just makes the context ready for mbedtls_ssl_setup() or
 *                 mbedtls_ssl_free()
 *
 * \param ssl      SSL context
 */
void mbedtls_ssl_init( mbedtls_ssl_context *ssl )
{
    mbedtls_platform_zeroize( ssl, sizeof( mbedtls_ssl_context ) );
}

/**
 * \brief          Set up an SSL context for use
 *
 * \note           No copy of the configuration context is made, it can be
 *                 shared by many mbedtls_ssl_context structures.
 *
 * \warning        The conf structure will be accessed during the session.
 *                 It must not be modified or freed as long as the session
 *                 is active.
 *
 * \warning        This function must be called exactly once per context.
 *                 Calling mbedtls_ssl_setup again is not supported, even
 *                 if no session is active.
 *
 * \param ssl      SSL context
 * \param conf     SSL configuration to use
 *
 * \return         0 if successful, or MBEDTLS_ERR_SSL_ALLOC_FAILED if
 *                 memory allocation failed
 */
int mbedtls_ssl_setup( mbedtls_ssl_context *ssl,
                       const mbedtls_ssl_config *conf )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
    ssl->conf = conf;
    /*
     * Prepare base structures
     */
    /* Set to NULL in case of an error condition */
    ssl->out_buf = NULL;
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    ssl->in_buf_len = in_buf_len;
#endif
    ssl->in_buf = mbedtls_calloc( 1, in_buf_len );
    if( ssl->in_buf == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%" MBEDTLS_PRINTF_SIZET " bytes) failed", in_buf_len ) );
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto error;
    }
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    ssl->out_buf_len = out_buf_len;
#endif
    ssl->out_buf = mbedtls_calloc( 1, out_buf_len );
    if( ssl->out_buf == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%" MBEDTLS_PRINTF_SIZET " bytes) failed", out_buf_len ) );
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto error;
    }
    mbedtls_ssl_reset_in_out_pointers( ssl );
#if defined(MBEDTLS_SSL_DTLS_SRTP)
    mbedtls_platform_zeroize( &ssl->dtls_srtp_info, sizeof(ssl->dtls_srtp_info) );
#endif
    if( ( ret = ssl_handshake_init( ssl ) ) != 0 )
        goto error;
    return( 0 );
error:
    mbedtls_free( ssl->in_buf );
    mbedtls_free( ssl->out_buf );
    ssl->conf = NULL;
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    ssl->in_buf_len = 0;
    ssl->out_buf_len = 0;
#endif
    ssl->in_buf = NULL;
    ssl->out_buf = NULL;
    ssl->in_hdr = NULL;
    ssl->in_ctr = NULL;
    ssl->in_len = NULL;
    ssl->in_iv = NULL;
    ssl->in_msg = NULL;
    ssl->out_hdr = NULL;
    ssl->out_ctr = NULL;
    ssl->out_len = NULL;
    ssl->out_iv = NULL;
    ssl->out_msg = NULL;
    return( ret );
}

/*
 * Reset an initialized and used SSL context for re-use while retaining
 * all application-set variables, function pointers and data.
 *
 * If partial is non-zero, keep data in the input buffer and client ID.
 * (Use when a DTLS client reconnects from the same port.)
 */
int mbedtls_ssl_session_reset_int( mbedtls_ssl_context *ssl, int partial )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    size_t in_buf_len = ssl->in_buf_len;
    size_t out_buf_len = ssl->out_buf_len;
#else
    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
#endif

#if !defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) ||     \
    !defined(MBEDTLS_SSL_SRV_C)
    ((void) partial);
#endif

    ssl->state = MBEDTLS_SSL_HELLO_REQUEST;

    /* Cancel any possibly running timer */
    mbedtls_ssl_set_timer( ssl, 0 );

#if defined(MBEDTLS_SSL_RENEGOTIATION)
    ssl->renego_status = MBEDTLS_SSL_INITIAL_HANDSHAKE;
    ssl->renego_records_seen = 0;

    ssl->verify_data_len = 0;
    mbedtls_platform_zeroize( ssl->own_verify_data, MBEDTLS_SSL_VERIFY_DATA_MAX_LEN );
    mbedtls_platform_zeroize( ssl->peer_verify_data, MBEDTLS_SSL_VERIFY_DATA_MAX_LEN );
#endif
    ssl->secure_renegotiation = MBEDTLS_SSL_LEGACY_RENEGOTIATION;

    ssl->in_offt = NULL;
    mbedtls_ssl_reset_in_out_pointers( ssl );

    ssl->in_msgtype = 0;
    ssl->in_msglen = 0;
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    ssl->next_record_offset = 0;
    ssl->in_epoch = 0;
#endif
#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
    mbedtls_ssl_dtls_replay_reset( ssl );
#endif

    ssl->in_hslen = 0;
    ssl->nb_zero = 0;

    ssl->keep_current_message = 0;

    ssl->out_msgtype = 0;
    ssl->out_msglen = 0;
    ssl->out_left = 0;
#if defined(MBEDTLS_SSL_CBC_RECORD_SPLITTING)
    if( ssl->split_done != MBEDTLS_SSL_CBC_RECORD_SPLITTING_DISABLED )
        ssl->split_done = 0;
#endif

    mbedtls_platform_zeroize( ssl->cur_out_ctr, sizeof( ssl->cur_out_ctr ) );

    ssl->transform_in = NULL;
    ssl->transform_out = NULL;

    ssl->session_in = NULL;
    ssl->session_out = NULL;

    mbedtls_platform_zeroize( ssl->out_buf, out_buf_len );

#if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
    if( partial == 0 )
#endif /* MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE && MBEDTLS_SSL_SRV_C */
    {
        ssl->in_left = 0;
        mbedtls_platform_zeroize( ssl->in_buf, in_buf_len );
    }

#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
    if( mbedtls_ssl_hw_record_reset != NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "going for mbedtls_ssl_hw_record_reset()" ) );
        if( ( ret = mbedtls_ssl_hw_record_reset( ssl ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_hw_record_reset", ret );
            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
        }
    }
#endif

    if( ssl->transform )
    {
        mbedtls_ssl_transform_free( ssl->transform );
        mbedtls_free( ssl->transform );
        ssl->transform = NULL;
    }

    if( ssl->session )
    {
        mbedtls_ssl_session_free( ssl->session );
        mbedtls_free( ssl->session );
        ssl->session = NULL;
    }

#if defined(MBEDTLS_SSL_ALPN)
    ssl->alpn_chosen = NULL;
#endif

#if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY) && defined(MBEDTLS_SSL_SRV_C)
#if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE)
    if( partial == 0 )
#endif
    {
        mbedtls_free( ssl->cli_id );
        ssl->cli_id = NULL;
        ssl->cli_id_len = 0;
    }
#endif

    if( ( ret = ssl_handshake_init( ssl ) ) != 0 )
        return( ret );

    return( 0 );
}

/**
 * \brief          Reset an already initialized SSL context for re-use
 *                 while retaining application-set variables, function
 *                 pointers and data.
 *
 * \param ssl      SSL context
 * \return         0 if successful, or MBEDTLS_ERR_SSL_ALLOC_FAILED,
 MBEDTLS_ERR_SSL_HW_ACCEL_FAILED or
 *                 MBEDTLS_ERR_SSL_COMPRESSION_FAILED
 */
int mbedtls_ssl_session_reset( mbedtls_ssl_context *ssl )
{
    return( mbedtls_ssl_session_reset_int( ssl, 0 ) );
}

/**
 * \brief          Set the current endpoint type
 *
 * \param conf     SSL configuration
 * \param endpoint must be MBEDTLS_SSL_IS_CLIENT or MBEDTLS_SSL_IS_SERVER
 */
void mbedtls_ssl_conf_endpoint( mbedtls_ssl_config *conf, int endpoint )
{
    conf->endpoint   = endpoint;
}

/**
 * \brief           Set the transport type (TLS or DTLS).
 *                  Default: TLS
 *
 * \note            For DTLS, you must either provide a recv callback that
 *                  doesn't block, or one that handles timeouts, see
 *                  \c mbedtls_ssl_set_bio(). You also need to provide timer
 *                  callbacks with \c mbedtls_ssl_set_timer_cb().
 *
 * \param conf      SSL configuration
 * \param transport transport type:
 *                  MBEDTLS_SSL_TRANSPORT_STREAM for TLS,
 *                  MBEDTLS_SSL_TRANSPORT_DATAGRAM for DTLS.
 */
void mbedtls_ssl_conf_transport( mbedtls_ssl_config *conf, int transport )
{
    conf->transport = transport;
}

#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
/**
 * \brief          Enable or disable anti-replay protection for DTLS.
 *                 (DTLS only, no effect on TLS.)
 *                 Default: enabled.
 *
 * \param conf     SSL configuration
 * \param mode     MBEDTLS_SSL_ANTI_REPLAY_ENABLED or MBEDTLS_SSL_ANTI_REPLAY_DISABLED.
 *
 * \warning        Disabling this is a security risk unless the application
 *                 protocol handles duplicated packets in a safe way. You
 *                 should not disable this without careful consideration.
 *                 However, if your application already detects duplicated
 *                 packets and needs information about them to adjust its
 *                 transmission strategy, then you'll want to disable this.
 */
void mbedtls_ssl_conf_dtls_anti_replay( mbedtls_ssl_config *conf, char mode )
{
    conf->anti_replay = mode;
}
#endif

#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
/**
 * \brief          Set a limit on the number of records with a bad MAC
 *                 before terminating the connection.
 *                 (DTLS only, no effect on TLS.)
 *                 Default: 0 (disabled).
 *
 * \param conf     SSL configuration
 * \param limit    Limit, or 0 to disable.
 *
 * \note           If the limit is N, then the connection is terminated when
 *                 the Nth non-authentic record is seen.
 *
 * \note           Records with an invalid header are not counted, only the
 *                 ones going through the authentication-decryption phase.
 *
 * \note           This is a security trade-off related to the fact that it's
 *                 often relatively easy for an active attacker ot inject UDP
 *                 datagrams. On one hand, setting a low limit here makes it
 *                 easier for such an attacker to forcibly terminated a
 *                 connection. On the other hand, a high limit or no limit
 *                 might make us waste resources checking authentication on
 *                 many bogus packets.
 */
void mbedtls_ssl_conf_dtls_badmac_limit( mbedtls_ssl_config *conf, unsigned limit )
{
    conf->badmac_limit = limit;
}
#endif

#if defined(MBEDTLS_SSL_PROTO_DTLS)

/**
 * \brief          Allow or disallow packing of multiple handshake records
 *                 within a single datagram.
 *
 * \param ssl           The SSL context to configure.
 * \param allow_packing This determines whether datagram packing may
 *                      be used or not. A value of \c 0 means that every
 *                      record will be sent in a separate datagram; a
 *                      value of \c 1 means that, if space permits,
 *                      multiple handshake messages (including CCS) belonging to
 *                      a single flight may be packed within a single datagram.
 *
 * \note           This is enabled by default and should only be disabled
 *                 for test purposes, or if datagram packing causes
 *                 interoperability issues with peers that don't support it.
 *
 * \note           Allowing datagram packing reduces the network load since
 *                 there's less overhead if multiple messages share the same
 *                 datagram. Also, it increases the handshake efficiency
 *                 since messages belonging to a single datagram will not
 *                 be reordered in transit, and so future message buffering
 *                 or flight retransmission (if no buffering is used) as
 *                 means to deal with reordering are needed less frequently.
 *
 * \note           Application records are not affected by this option and
 *                 are currently always sent in separate datagrams.
 *
 */
void mbedtls_ssl_set_datagram_packing( mbedtls_ssl_context *ssl,
                                       unsigned allow_packing )
{
    ssl->disable_datagram_packing = !allow_packing;
}

/**
 * \brief          Set retransmit timeout values for the DTLS handshake.
 *                 (DTLS only, no effect on TLS.)
 *
 * \param conf     SSL configuration
 * \param min      Initial timeout value in milliseconds.
 *                 Default: 1000 (1 second).
 * \param max      Maximum timeout value in milliseconds.
 *                 Default: 60000 (60 seconds).
 *
 * \note           Default values are from RFC 6347 section 4.2.4.1.
 *
 * \note           The 'min' value should typically be slightly above the
 *                 expected round-trip time to your peer, plus whatever time
 *                 it takes for the peer to process the message. For example,
 *                 if your RTT is about 600ms and you peer needs up to 1s to
 *                 do the cryptographic operations in the handshake, then you
 *                 should set 'min' slightly above 1600. Lower values of 'min'
 *                 might cause spurious resends which waste network resources,
 *                 while larger value of 'min' will increase overall latency
 *                 on unreliable network links.
 *
 * \note           The more unreliable your network connection is, the larger
 *                 your max / min ratio needs to be in order to achieve
 *                 reliable handshakes.
 *
 * \note           Messages are retransmitted up to log2(ceil(max/min)) times.
 *                 For example, if min = 1s and max = 5s, the retransmit plan
 *                 goes: send ... 1s -> resend ... 2s -> resend ... 4s ->
 *                 resend ... 5s -> give up and return a timeout error.
 */
void mbedtls_ssl_conf_handshake_timeout( mbedtls_ssl_config *conf,
                                         uint32_t min, uint32_t max )
{
    conf->hs_timeout_min = min;
    conf->hs_timeout_max = max;
}

#endif /* MBEDTLS_SSL_PROTO_DTLS */

/**
 * \brief          Set the certificate verification mode
 *                 Default: NONE on server, REQUIRED on client
 *
 * \param conf     SSL configuration
 * \param authmode can be:
 *
 *  MBEDTLS_SSL_VERIFY_NONE:      peer certificate is not checked
 *                        (default on server)
 *                        (insecure on client)
 *
 *  MBEDTLS_SSL_VERIFY_OPTIONAL:  peer certificate is checked, however the
 *                        handshake continues even if verification failed;
 *                        mbedtls_ssl_get_verify_result() can be called after the
 *                        handshake is complete.
 *
 *  MBEDTLS_SSL_VERIFY_REQUIRED:  peer *must* present a valid certificate,
 *                        handshake is aborted if verification failed.
 *                        (default on client)
 *
 * \note On client, MBEDTLS_SSL_VERIFY_REQUIRED is the recommended mode.
 * With MBEDTLS_SSL_VERIFY_OPTIONAL, the user needs to call mbedtls_ssl_get_verify_result() at
 * the right time(s), which may not be obvious, while REQUIRED always perform
 * the verification as soon as possible. For example, REQUIRED was protecting
 * against the "triple handshake" attack even before it was found.
 */
void mbedtls_ssl_conf_authmode( mbedtls_ssl_config *conf, int authmode )
{
    conf->authmode   = authmode;
}

#if defined(MBEDTLS_X509_CRT_PARSE_C)
/**
 * \brief          Set the verification callback (Optional).
 *
 *                 If set, the provided verify callback is called for each
 *                 certificate in the peer's CRT chain, including the trusted
 *                 root. For more information, please see the documentation of
 *                 \c mbedtls_x509_crt_verify().
 *
 * \note           For per context callbacks and contexts, please use
 *                 mbedtls_ssl_set_verify() instead.
 *
 * \param conf     The SSL configuration to use.
 * \param f_vrfy   The verification callback to use during CRT verification.
 * \param p_vrfy   The opaque context to be passed to the callback.
 */
void mbedtls_ssl_conf_verify( mbedtls_ssl_config *conf,
                     int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
                     void *p_vrfy )
{
    conf->f_vrfy      = f_vrfy;
    conf->p_vrfy      = p_vrfy;
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

/**
 * \brief          Set the random number generator callback
 *
 * \param conf     SSL configuration
 * \param f_rng    RNG function
 * \param p_rng    RNG parameter
 */
void mbedtls_ssl_conf_rng( mbedtls_ssl_config *conf,
                  int (*f_rng)(void *, unsigned char *, size_t),
                  void *p_rng )
{
    conf->f_rng      = f_rng;
    conf->p_rng      = p_rng;
}

/**
 * \brief          Set the debug callback
 *
 *                 The callback has the following argument:
 *                 void *           opaque context for the callback
 *                 int              debug level
 *                 const char *     file name
 *                 int              line number
 *                 const char *     message
 *
 * \param conf     SSL configuration
 * \param f_dbg    debug function
 * \param p_dbg    debug parameter
 */
void mbedtls_ssl_conf_dbg( mbedtls_ssl_config *conf,
                  void (*f_dbg)(void *, int, const char *, int, const char *),
                  void  *p_dbg )
{
    conf->f_dbg      = f_dbg;
    conf->p_dbg      = p_dbg;
}

/**
 * \brief          Set the underlying BIO callbacks for write, read and
 *                 read-with-timeout.
 *
 * \param ssl      SSL context
 * \param p_bio    parameter (context) shared by BIO callbacks
 * \param f_send   write callback
 * \param f_recv   read callback
 * \param f_recv_timeout blocking read callback with timeout.
 *
 * \note           One of f_recv or f_recv_timeout can be NULL, in which case
 *                 the other is used. If both are non-NULL, f_recv_timeout is
 *                 used and f_recv is ignored (as if it were NULL).
 *
 * \note           The two most common use cases are:
 *                 - non-blocking I/O, f_recv != NULL, f_recv_timeout == NULL
 *                 - blocking I/O, f_recv == NULL, f_recv_timout != NULL
 *
 * \note           For DTLS, you need to provide either a non-NULL
 *                 f_recv_timeout callback, or a f_recv that doesn't block.
 *
 * \note           See the documentations of \c mbedtls_ssl_send_t,
 *                 \c mbedtls_ssl_recv_t and \c mbedtls_ssl_recv_timeout_t for
 *                 the conventions those callbacks must follow.
 *
 * \note           On some platforms, net_sockets.c provides
 *                 \c mbedtls_net_send(), \c mbedtls_net_recv() and
 *                 \c mbedtls_net_recv_timeout() that are suitable to be used
 *                 here.
 */
void mbedtls_ssl_set_bio( mbedtls_ssl_context *ssl,
        void *p_bio,
        mbedtls_ssl_send_t *f_send,
        mbedtls_ssl_recv_t *f_recv,
        mbedtls_ssl_recv_timeout_t *f_recv_timeout )
{
    ssl->p_bio          = p_bio;
    ssl->f_send         = f_send;
    ssl->f_recv         = f_recv;
    ssl->f_recv_timeout = f_recv_timeout;
}

#if defined(MBEDTLS_SSL_PROTO_DTLS)
/**
 * \brief          Set the Maximum Tranport Unit (MTU).
 *                 Special value: 0 means unset (no limit).
 *                 This represents the maximum size of a datagram payload
 *                 handled by the transport layer (usually UDP) as determined
 *                 by the network link and stack. In practice, this controls
 *                 the maximum size datagram the DTLS layer will pass to the
 *                 \c f_send() callback set using \c mbedtls_ssl_set_bio().
 *
 * \note           The limit on datagram size is converted to a limit on
 *                 record payload by subtracting the current overhead of
 *                 encapsulation and encryption/authentication if any.
 *
 * \note           This can be called at any point during the connection, for
 *                 example when a Path Maximum Transfer Unit (PMTU)
 *                 estimate becomes available from other sources,
 *                 such as lower (or higher) protocol layers.
 *
 * \note           This setting only controls the size of the packets we send,
 *                 and does not restrict the size of the datagrams we're
 *                 willing to receive. Client-side, you can request the
 *                 server to use smaller records with \c
 *                 mbedtls_ssl_conf_max_frag_len().
 *
 * \note           If both a MTU and a maximum fragment length have been
 *                 configured (or negotiated with the peer), the resulting
 *                 lower limit on record payload (see first note) is used.
 *
 * \note           This can only be used to decrease the maximum size
 *                 of datagrams (hence records, see first note) sent. It
 *                 cannot be used to increase the maximum size of records over
 *                 the limit set by #MBEDTLS_SSL_OUT_CONTENT_LEN.
 *
 * \note           Values lower than the current record layer expansion will
 *                 result in an error when trying to send data.
 *
 * \note           Using record compression together with a non-zero MTU value
 *                 will result in an error when trying to send data.
 *
 * \param ssl      SSL context
 * \param mtu      Value of the path MTU in bytes
 */
void mbedtls_ssl_set_mtu( mbedtls_ssl_context *ssl, uint16_t mtu )
{
    ssl->mtu = mtu;
}
#endif

/**
 * \brief          Set the timeout period for mbedtls_ssl_read()
 *                 (Default: no timeout.)
 *
 * \param conf     SSL configuration context
 * \param timeout  Timeout value in milliseconds.
 *                 Use 0 for no timeout (default).
 *
 * \note           With blocking I/O, this will only work if a non-NULL
 *                 \c f_recv_timeout was set with \c mbedtls_ssl_set_bio().
 *                 With non-blocking I/O, this will only work if timer
 *                 callbacks were set with \c mbedtls_ssl_set_timer_cb().
 *
 * \note           With non-blocking I/O, you may also skip this function
 *                 altogether and handle timeouts at the application layer.
 */
void mbedtls_ssl_conf_read_timeout( mbedtls_ssl_config *conf, uint32_t timeout )
{
    conf->read_timeout   = timeout;
}

/**
 * \brief          Set the timer callbacks (Mandatory for DTLS.)
 *
 * \param ssl      SSL context
 * \param p_timer  parameter (context) shared by timer callbacks
 * \param f_set_timer   set timer callback
 * \param f_get_timer   get timer callback. Must return:
 *
 * \note           See the documentation of \c mbedtls_ssl_set_timer_t and
 *                 \c mbedtls_ssl_get_timer_t for the conventions this pair of
 *                 callbacks must follow.
 *
 * \note           On some platforms, timing.c provides
 *                 \c mbedtls_timing_set_delay() and
 *                 \c mbedtls_timing_get_delay() that are suitable for using
 *                 here, except if using an event-driven style.
 *
 * \note           See also the "DTLS tutorial" article in our knowledge base.
 *                 https://tls.mbed.org/kb/how-to/dtls-tutorial
 */
void mbedtls_ssl_set_timer_cb( mbedtls_ssl_context *ssl,
                               void *p_timer,
                               mbedtls_ssl_set_timer_t *f_set_timer,
                               mbedtls_ssl_get_timer_t *f_get_timer )
{
    ssl->p_timer        = p_timer;
    ssl->f_set_timer    = f_set_timer;
    ssl->f_get_timer    = f_get_timer;

    /* Make sure we start with no timer running */
    mbedtls_ssl_set_timer( ssl, 0 );
}

#if defined(MBEDTLS_SSL_SRV_C)
/**
 * \brief          Set the session cache callbacks (server-side only)
 *                 If not set, no session resuming is done (except if session
 *                 tickets are enabled too).
 *
 *                 The session cache has the responsibility to check for stale
 *                 entries based on timeout. See RFC 5246 for recommendations.
 *
 *                 Warning: session.peer_cert is cleared by the SSL/TLS layer on
 *                 connection shutdown, so do not cache the pointer! Either set
 *                 it to NULL or make a full copy of the certificate.
 *
 *                 The get callback is called once during the initial handshake
 *                 to enable session resuming. The get function has the
 *                 following parameters: (void *parameter, mbedtls_ssl_session *session)
 *                 If a valid entry is found, it should fill the master of
 *                 the session object with the cached values and return 0,
 *                 return 1 otherwise. Optionally peer_cert can be set as well
 *                 if it is properly present in cache entry.
 *
 *                 The set callback is called once during the initial handshake
 *                 to enable session resuming after the entire handshake has
 *                 been finished. The set function has the following parameters:
 *                 (void *parameter, const mbedtls_ssl_session *session). The function
 *                 should create a cache entry for future retrieval based on
 *                 the data in the session structure and should keep in mind
 *                 that the mbedtls_ssl_session object presented (and all its referenced
 *                 data) is cleared by the SSL/TLS layer when the connection is
 *                 terminated. It is recommended to add metadata to determine if
 *                 an entry is still valid in the future. Return 0 if
 *                 successfully cached, return 1 otherwise.
 *
 * \param conf           SSL configuration
 * \param p_cache        parmater (context) for both callbacks
 * \param f_get_cache    session get callback
 * \param f_set_cache    session set callback
 */
void mbedtls_ssl_conf_session_cache( mbedtls_ssl_config *conf,
        void *p_cache,
        int (*f_get_cache)(void *, mbedtls_ssl_session *),
        int (*f_set_cache)(void *, const mbedtls_ssl_session *) )
{
    conf->p_cache = p_cache;
    conf->f_get_cache = f_get_cache;
    conf->f_set_cache = f_set_cache;
}
#endif /* MBEDTLS_SSL_SRV_C */

#if defined(MBEDTLS_SSL_CLI_C)
/**
 * \brief          Request resumption of session (client-side only)
 *                 Session data is copied from presented session structure.
 *
 * \param ssl      SSL context
 * \param session  session context
 *
 * \return         0 if successful,
 *                 MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed,
 *                 MBEDTLS_ERR_SSL_BAD_INPUT_DATA if used server-side or
 *                 arguments are otherwise invalid
 *
 * \sa             mbedtls_ssl_get_session()
 */
int mbedtls_ssl_set_session( mbedtls_ssl_context *ssl, const mbedtls_ssl_session *session )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;

    if( ssl == NULL ||
        session == NULL ||
        ssl->session_negotiate == NULL ||
        ssl->conf->endpoint != MBEDTLS_SSL_IS_CLIENT )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    if( ( ret = mbedtls_ssl_session_copy( ssl->session_negotiate,
                                          session ) ) != 0 )
        return( ret );

    ssl->handshake->resume = 1;

    return( 0 );
}
#endif /* MBEDTLS_SSL_CLI_C */

/**
 * \brief               Set the list of allowed ciphersuites and the preference
 *                      order. First in the list has the highest preference.
 *                      (Overrides all version-specific lists)
 *
 *                      The ciphersuites array is not copied, and must remain
 *                      valid for the lifetime of the ssl_config.
 *
 *                      Note: The server uses its own preferences
 *                      over the preference of the client unless
 *                      MBEDTLS_SSL_SRV_RESPECT_CLIENT_PREFERENCE is defined!
 *
 * \param conf          SSL configuration
 * \param ciphersuites  0-terminated list of allowed ciphersuites
 */
void mbedtls_ssl_conf_ciphersuites( mbedtls_ssl_config *conf,
                                    const uint16_t *ciphersuites )
{
    conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_0] = ciphersuites;
    conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_1] = ciphersuites;
    conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_2] = ciphersuites;
    conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_3] = ciphersuites;
}

/**
 * \brief               Set the list of allowed ciphersuites and the
 *                      preference order for a specific version of the protocol.
 *                      (Only useful on the server side)
 *
 *                      The ciphersuites array is not copied, and must remain
 *                      valid for the lifetime of the ssl_config.
 *
 * \param conf          SSL configuration
 * \param ciphersuites  0-terminated list of allowed ciphersuites
 * \param major         Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3
 *                      supported)
 * \param minor         Minor version number (MBEDTLS_SSL_MINOR_VERSION_0,
 *                      MBEDTLS_SSL_MINOR_VERSION_1 and MBEDTLS_SSL_MINOR_VERSION_2,
 *                      MBEDTLS_SSL_MINOR_VERSION_3 supported)
 *
 * \note                With DTLS, use MBEDTLS_SSL_MINOR_VERSION_2 for DTLS 1.0
 *                      and MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2
 */
void mbedtls_ssl_conf_ciphersuites_for_version( mbedtls_ssl_config *conf,
                                                const uint16_t *ciphersuites,
                                                int major, int minor )
{
    if( major != MBEDTLS_SSL_MAJOR_VERSION_3 )
        return;

    if( minor < MBEDTLS_SSL_MINOR_VERSION_0 || minor > MBEDTLS_SSL_MINOR_VERSION_3 )
        return;

    conf->ciphersuite_list[minor] = ciphersuites;
}

#if defined(MBEDTLS_X509_CRT_PARSE_C)
/**
 * \brief          Set the X.509 security profile used for verification
 *
 * \note           The restrictions are enforced for all certificates in the
 *                 chain. However, signatures in the handshake are not covered
 *                 by this setting but by \b mbedtls_ssl_conf_sig_hashes().
 *
 * \param conf     SSL configuration
 * \param profile  Profile to use
 */
void mbedtls_ssl_conf_cert_profile( mbedtls_ssl_config *conf,
                                    const mbedtls_x509_crt_profile *profile )
{
    conf->cert_profile = profile;
}

/* Append a new keycert entry to a (possibly empty) list */
static int ssl_append_key_cert( mbedtls_ssl_key_cert **head,
                                mbedtls_x509_crt *cert,
                                mbedtls_pk_context *key )
{
    mbedtls_ssl_key_cert *new_cert;

    new_cert = mbedtls_calloc( 1, sizeof( mbedtls_ssl_key_cert ) );
    if( new_cert == NULL )
        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

    new_cert->cert = cert;
    new_cert->key  = key;
    new_cert->next = NULL;

    /* Update head is the list was null, else add to the end */
    if( *head == NULL )
    {
        *head = new_cert;
    }
    else
    {
        mbedtls_ssl_key_cert *cur = *head;
        while( cur->next != NULL )
            cur = cur->next;
        cur->next = new_cert;
    }

    return( 0 );
}

/**
 * \brief          Set own certificate chain and private key
 *
 * \note           own_cert should contain in order from the bottom up your
 *                 certificate chain. The top certificate (self-signed)
 *                 can be omitted.
 *
 * \note           On server, this function can be called multiple times to
 *                 provision more than one cert/key pair (eg one ECDSA, one
 *                 RSA with SHA-256, one RSA with SHA-1). An adequate
 *                 certificate will be selected according to the client's
 *                 advertised capabilities. In case multiple certificates are
 *                 adequate, preference is given to the one set by the first
 *                 call to this function, then second, etc.
 *
 * \note           On client, only the first call has any effect. That is,
 *                 only one client certificate can be provisioned. The
 *                 server's preferences in its CertficateRequest message will
 *                 be ignored and our only cert will be sent regardless of
 *                 whether it matches those preferences - the server can then
 *                 decide what it wants to do with it.
 *
 * \note           The provided \p pk_key needs to match the public key in the
 *                 first certificate in \p own_cert, or all handshakes using
 *                 that certificate will fail. It is your responsibility
 *                 to ensure that; this function will not perform any check.
 *                 You may use mbedtls_pk_check_pair() in order to perform
 *                 this check yourself, but be aware that this function can
 *                 be computationally expensive on some key types.
 *
 * \param conf     SSL configuration
 * \param own_cert own public certificate chain
 * \param pk_key   own private key
 *
 * \return         0 on success or MBEDTLS_ERR_SSL_ALLOC_FAILED
 */
int mbedtls_ssl_conf_own_cert( mbedtls_ssl_config *conf,
                               mbedtls_x509_crt *own_cert,
                               mbedtls_pk_context *pk_key )
{
    return( ssl_append_key_cert( &conf->key_cert, own_cert, pk_key ) );
}

/**
 * \brief          Set the data required to verify peer certificate
 *
 * \note           See \c mbedtls_x509_crt_verify() for notes regarding the
 *                 parameters ca_chain (maps to trust_ca for that function)
 *                 and ca_crl.
 *
 * \param conf     SSL configuration
 * \param ca_chain trusted CA chain (meaning all fully trusted top-level CAs)
 * \param ca_crl   trusted CA CRLs
 */
void mbedtls_ssl_conf_ca_chain( mbedtls_ssl_config *conf,
                                mbedtls_x509_crt *ca_chain,
                                mbedtls_x509_crl *ca_crl )
{
    conf->ca_chain   = ca_chain;
    conf->ca_crl     = ca_crl;
#if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
    /* mbedtls_ssl_conf_ca_chain() and mbedtls_ssl_conf_ca_cb()
     * cannot be used together. */
    conf->f_ca_cb = NULL;
    conf->p_ca_cb = NULL;
#endif /* MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK */
}

#if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
/**
 * \brief          Set the trusted certificate callback.
 *
 *                 This API allows to register the set of trusted certificates
 *                 through a callback, instead of a linked list as configured
 *                 by mbedtls_ssl_conf_ca_chain().
 *
 *                 This is useful for example in contexts where a large number
 *                 of CAs are used, and the inefficiency of maintaining them
 *                 in a linked list cannot be tolerated. It is also useful when
 *                 the set of trusted CAs needs to be modified frequently.
 *
 *                 See the documentation of `mbedtls_x509_crt_ca_cb_t` for
 *                 more information.
 *
 * \param conf     The SSL configuration to register the callback with.
 * \param f_ca_cb  The trusted certificate callback to use when verifying
 *                 certificate chains.
 * \param p_ca_cb  The context to be passed to \p f_ca_cb (for example,
 *                 a reference to a trusted CA database).
 *
 * \note           This API is incompatible with mbedtls_ssl_conf_ca_chain():
 *                 Any call to this function overwrites the values set through
 *                 earlier calls to mbedtls_ssl_conf_ca_chain() or
 *                 mbedtls_ssl_conf_ca_cb().
 *
 * \note           This API is incompatible with CA indication in
 *                 CertificateRequest messages: A server-side SSL context which
 *                 is bound to an SSL configuration that uses a CA callback
 *                 configured via mbedtls_ssl_conf_ca_cb(), and which requires
 *                 client authentication, will send an empty CA list in the
 *                 corresponding CertificateRequest message.
 *
 * \note           This API is incompatible with mbedtls_ssl_set_hs_ca_chain():
 *                 If an SSL context is bound to an SSL configuration which uses
 *                 CA callbacks configured via mbedtls_ssl_conf_ca_cb(), then
 *                 calls to mbedtls_ssl_set_hs_ca_chain() have no effect.
 *
 * \note           The use of this API disables the use of restartable ECC
 *                 during X.509 CRT signature verification (but doesn't affect
 *                 other uses).
 *
 * \warning        This API is incompatible with the use of CRLs. Any call to
 *                 mbedtls_ssl_conf_ca_cb() unsets CRLs configured through
 *                 earlier calls to mbedtls_ssl_conf_ca_chain().
 *
 * \warning        In multi-threaded environments, the callback \p f_ca_cb
 *                 must be thread-safe, and it is the user's responsibility
 *                 to guarantee this (for example through a mutex
 *                 contained in the callback context pointed to by \p p_ca_cb).
 */
void mbedtls_ssl_conf_ca_cb( mbedtls_ssl_config *conf,
                             mbedtls_x509_crt_ca_cb_t f_ca_cb,
                             void *p_ca_cb )
{
    conf->f_ca_cb = f_ca_cb;
    conf->p_ca_cb = p_ca_cb;

    /* mbedtls_ssl_conf_ca_chain() and mbedtls_ssl_conf_ca_cb()
     * cannot be used together. */
    conf->ca_chain   = NULL;
    conf->ca_crl     = NULL;
}
#endif /* MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK */
#endif /* MBEDTLS_X509_CRT_PARSE_C */

#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
/**
 * \brief          Set own certificate and key for the current handshake
 *
 * \note           Same as \c mbedtls_ssl_conf_own_cert() but for use within
 *                 the SNI callback.
 *
 * \param ssl      SSL context
 * \param own_cert own public certificate chain
 * \param pk_key   own private key
 *
 * \return         0 on success or MBEDTLS_ERR_SSL_ALLOC_FAILED
 */
int mbedtls_ssl_set_hs_own_cert( mbedtls_ssl_context *ssl,
                                 mbedtls_x509_crt *own_cert,
                                 mbedtls_pk_context *pk_key )
{
    return( ssl_append_key_cert( &ssl->handshake->sni_key_cert,
                                 own_cert, pk_key ) );
}

/**
 * \brief          Set the data required to verify peer certificate for the
 *                 current handshake
 *
 * \note           Same as \c mbedtls_ssl_conf_ca_chain() but for use within
 *                 the SNI callback.
 *
 * \param ssl      SSL context
 * \param ca_chain trusted CA chain (meaning all fully trusted top-level CAs)
 * \param ca_crl   trusted CA CRLs
 */
void mbedtls_ssl_set_hs_ca_chain( mbedtls_ssl_context *ssl,
                                  mbedtls_x509_crt *ca_chain,
                                  mbedtls_x509_crl *ca_crl )
{
    ssl->handshake->sni_ca_chain   = ca_chain;
    ssl->handshake->sni_ca_crl     = ca_crl;
}

/**
 * \brief          Set authmode for the current handshake.
 *
 * \note           Same as \c mbedtls_ssl_conf_authmode() but for use within
 *                 the SNI callback.
 *
 * \param ssl      SSL context
 * \param authmode MBEDTLS_SSL_VERIFY_NONE, MBEDTLS_SSL_VERIFY_OPTIONAL or
 *                 MBEDTLS_SSL_VERIFY_REQUIRED
 */
void mbedtls_ssl_set_hs_authmode( mbedtls_ssl_context *ssl,
                                  int authmode )
{
    ssl->handshake->sni_authmode = authmode;
}
#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */

#if defined(MBEDTLS_X509_CRT_PARSE_C)
/**
 * \brief          Set a connection-specific verification callback (optional).
 *
 *                 If set, the provided verify callback is called for each
 *                 certificate in the peer's CRT chain, including the trusted
 *                 root. For more information, please see the documentation of
 *                 \c mbedtls_x509_crt_verify().
 *
 * \note           This call is analogous to mbedtls_ssl_conf_verify() but
 *                 binds the verification callback and context to an SSL context
 *                 as opposed to an SSL configuration.
 *                 If mbedtls_ssl_conf_verify() and mbedtls_ssl_set_verify()
 *                 are both used, mbedtls_ssl_set_verify() takes precedence.
 *
 * \param ssl      The SSL context to use.
 * \param f_vrfy   The verification callback to use during CRT verification.
 * \param p_vrfy   The opaque context to be passed to the callback.
 */
void mbedtls_ssl_set_verify( mbedtls_ssl_context *ssl,
                             int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
                             void *p_vrfy )
{
    ssl->f_vrfy = f_vrfy;
    ssl->p_vrfy = p_vrfy;
}
#endif

#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
/**
 * \brief          Set the EC J-PAKE password for current handshake.
 *
 * \note           An internal copy is made, and destroyed as soon as the
 *                 handshake is completed, or when the SSL context is reset or
 *                 freed.
 *
 * \note           The SSL context needs to be already set up. The right place
 *                 to call this function is between \c mbedtls_ssl_setup() or
 *                 \c mbedtls_ssl_reset() and \c mbedtls_ssl_handshake().
 *
 * \param ssl      SSL context
 * \param pw       EC J-PAKE password (pre-shared secret)
 * \param pw_len   length of pw in bytes
 *
 * \return         0 on success, or a negative error code.
 */
int mbedtls_ssl_set_hs_ecjpake_password( mbedtls_ssl_context *ssl,
                                         const unsigned char *pw,
                                         size_t pw_len )
{
    mbedtls_ecjpake_role role;

    if( ssl->handshake == NULL || ssl->conf == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
        role = MBEDTLS_ECJPAKE_SERVER;
    else
        role = MBEDTLS_ECJPAKE_CLIENT;

    return( mbedtls_ecjpake_setup( &ssl->handshake->ecjpake_ctx,
                                   role,
                                   MBEDTLS_MD_SHA256,
                                   MBEDTLS_ECP_DP_SECP256R1,
                                   pw, pw_len ) );
}
#endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */

#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)

static void ssl_conf_remove_psk( mbedtls_ssl_config *conf )
{
    /* Remove reference to existing PSK, if any. */
    if( conf->psk != NULL )
    {
        mbedtls_platform_zeroize( conf->psk, conf->psk_len );
        mbedtls_free( conf->psk );
        conf->psk = NULL;
        conf->psk_len = 0;
    }
    /* Remove reference to PSK identity, if any. */
    if( conf->psk_identity != NULL )
    {
        mbedtls_free( conf->psk_identity );
        conf->psk_identity = NULL;
        conf->psk_identity_len = 0;
    }
}

/* This function assumes that PSK identity in the SSL config is unset.
 * It checks that the provided identity is well-formed and attempts
 * to make a copy of it in the SSL config.
 * On failure, the PSK identity in the config remains unset. */
static int ssl_conf_set_psk_identity( mbedtls_ssl_config *conf,
                                      unsigned char const *psk_identity,
                                      size_t psk_identity_len )
{
    /* Identity len will be encoded on two bytes */
    if( psk_identity               == NULL ||
        ( psk_identity_len >> 16 ) != 0    ||
        psk_identity_len > MBEDTLS_SSL_OUT_CONTENT_LEN )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    conf->psk_identity = mbedtls_calloc( 1, psk_identity_len );
    if( conf->psk_identity == NULL )
        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

    conf->psk_identity_len = psk_identity_len;
    memcpy( conf->psk_identity, psk_identity, conf->psk_identity_len );

    return( 0 );
}

/**
 * \brief          Configure a pre-shared key (PSK) and identity
 *                 to be used in PSK-based ciphersuites.
 *
 * \note           This is mainly useful for clients. Servers will usually
 *                 want to use \c mbedtls_ssl_conf_psk_cb() instead.
 *
 * \note           A PSK set by \c mbedtls_ssl_set_hs_psk() in the PSK callback
 *                 takes precedence over a PSK configured by this function.
 *
 * \warning        Currently, clients can only register a single pre-shared key.
 *                 Calling this function or mbedtls_ssl_conf_psk_opaque() more
 *                 than once will overwrite values configured in previous calls.
 *                 Support for setting multiple PSKs on clients and selecting
 *                 one based on the identity hint is not a planned feature,
 *                 but feedback is welcomed.
 *
 * \param conf     The SSL configuration to register the PSK with.
 * \param psk      The pointer to the pre-shared key to use.
 * \param psk_len  The length of the pre-shared key in bytes.
 * \param psk_identity      The pointer to the pre-shared key identity.
 * \param psk_identity_len  The length of the pre-shared key identity
 *                          in bytes.
 *
 * \note           The PSK and its identity are copied internally and
 *                 hence need not be preserved by the caller for the lifetime
 *                 of the SSL configuration.
 *
 * \return         \c 0 if successful.
 * \return         An \c MBEDTLS_ERR_SSL_XXX error code on failure.
 */
int mbedtls_ssl_conf_psk( mbedtls_ssl_config *conf,
                          const void *psk, size_t psk_len,
                          const void *psk_identity,
                          size_t psk_identity_len )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
    /* Remove opaque/raw PSK + PSK Identity */
    ssl_conf_remove_psk( conf );
    /* Check and set raw PSK */
    if( psk == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    if( psk_len == 0 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    if( psk_len > MBEDTLS_PSK_MAX_LEN )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    if( ( conf->psk = mbedtls_calloc( 1, psk_len ) ) == NULL )
        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
    conf->psk_len = psk_len;
    memcpy( conf->psk, psk, conf->psk_len );
    /* Check and set PSK Identity */
    ret = ssl_conf_set_psk_identity( conf, psk_identity, psk_identity_len );
    if( ret != 0 )
        ssl_conf_remove_psk( conf );
    return( ret );
}

static void ssl_remove_psk( mbedtls_ssl_context *ssl )
{
    if( ssl->handshake->psk != NULL )
    {
        mbedtls_platform_zeroize( ssl->handshake->psk,
                                  ssl->handshake->psk_len );
        mbedtls_free( ssl->handshake->psk );
        ssl->handshake->psk_len = 0;
    }
}

/**
 * \brief          Set the pre-shared Key (PSK) for the current handshake.
 *
 * \note           This should only be called inside the PSK callback,
 *                 i.e. the function passed to \c mbedtls_ssl_conf_psk_cb().
 *
 * \note           A PSK set by this function takes precedence over a PSK
 *                 configured by \c mbedtls_ssl_conf_psk().
 *
 * \param ssl      The SSL context to configure a PSK for.
 * \param psk      The pointer to the pre-shared key.
 * \param psk_len  The length of the pre-shared key in bytes.
 *
 * \return         \c 0 if successful.
 * \return         An \c MBEDTLS_ERR_SSL_XXX error code on failure.
 */
int mbedtls_ssl_set_hs_psk( mbedtls_ssl_context *ssl,
                            const void *psk, size_t psk_len )
{
    if( psk == NULL || ssl->handshake == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    if( psk_len > MBEDTLS_PSK_MAX_LEN )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl_remove_psk( ssl );

    if( ( ssl->handshake->psk = mbedtls_calloc( 1, psk_len ) ) == NULL )
        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

    ssl->handshake->psk_len = psk_len;
    memcpy( ssl->handshake->psk, psk, ssl->handshake->psk_len );

    return( 0 );
}

/**
 * \brief          Set the PSK callback (server-side only).
 *
 *                 If set, the PSK callback is called for each
 *                 handshake where a PSK-based ciphersuite was negotiated.
 *                 The caller provides the identity received and wants to
 *                 receive the actual PSK data and length.
 *
 *                 The callback has the following parameters:
 *                 - \c void*: The opaque pointer \p p_psk.
 *                 - \c mbedtls_ssl_context*: The SSL context to which
 *                                            the operation applies.
 *                 - \c const unsigned char*: The PSK identity
 *                                            selected by the client.
 *                 - \c size_t: The length of the PSK identity
 *                              selected by the client.
 *
 *                 If a valid PSK identity is found, the callback should use
 *                 \c mbedtls_ssl_set_hs_psk() or
 *                 \c mbedtls_ssl_set_hs_psk_opaque()
 *                 on the SSL context to set the correct PSK and return \c 0.
 *                 Any other return value will result in a denied PSK identity.
 *
 * \note           A dynamic PSK (i.e. set by the PSK callback) takes
 *                 precedence over a static PSK (i.e. set by
 *                 \c mbedtls_ssl_conf_psk() or
 *                 \c mbedtls_ssl_conf_psk_opaque()).
 *                 This means that if you set a PSK callback using this
 *                 function, you don't need to set a PSK using
 *                 \c mbedtls_ssl_conf_psk() or
 *                 \c mbedtls_ssl_conf_psk_opaque()).
 *
 * \param conf     The SSL configuration to register the callback with.
 * \param f_psk    The callback for selecting and setting the PSK based
 *                 in the PSK identity chosen by the client.
 * \param p_psk    A pointer to an opaque structure to be passed to
 *                 the callback, for example a PSK store.
 */
void mbedtls_ssl_conf_psk_cb( mbedtls_ssl_config *conf,
                     int (*f_psk)(void *, mbedtls_ssl_context *, const unsigned char *,
                     size_t),
                     void *p_psk )
{
    conf->f_psk = f_psk;
    conf->p_psk = p_psk;
}
#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */

#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C)

/**
 * \brief          Set the Diffie-Hellman public P and G values
 *                 from big-endian binary presentations.
 *                 (Default values: MBEDTLS_DHM_RFC3526_MODP_2048_[PG]_BIN)
 *
 * \param conf     SSL configuration
 * \param dhm_P    Diffie-Hellman-Merkle modulus in big-endian binary form
 * \param P_len    Length of DHM modulus
 * \param dhm_G    Diffie-Hellman-Merkle generator in big-endian binary form
 * \param G_len    Length of DHM generator
 *
 * \return         0 if successful
 */
int mbedtls_ssl_conf_dh_param_bin( mbedtls_ssl_config *conf,
                                   const unsigned char *dhm_P, size_t P_len,
                                   const unsigned char *dhm_G, size_t G_len )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;

    if( ( ret = mbedtls_mpi_read_binary( &conf->dhm_P, dhm_P, P_len ) ) != 0 ||
        ( ret = mbedtls_mpi_read_binary( &conf->dhm_G, dhm_G, G_len ) ) != 0 )
    {
        mbedtls_mpi_free( &conf->dhm_P );
        mbedtls_mpi_free( &conf->dhm_G );
        return( ret );
    }

    return( 0 );
}

/**
 * \brief          Set the Diffie-Hellman public P and G values,
 *                 read from existing context (server-side only)
 *
 * \param conf     SSL configuration
 * \param dhm_ctx  Diffie-Hellman-Merkle context
 *
 * \return         0 if successful
 */
int mbedtls_ssl_conf_dh_param_ctx( mbedtls_ssl_config *conf, mbedtls_dhm_context *dhm_ctx )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;

    if( ( ret = mbedtls_mpi_copy( &conf->dhm_P, &dhm_ctx->P ) ) != 0 ||
        ( ret = mbedtls_mpi_copy( &conf->dhm_G, &dhm_ctx->G ) ) != 0 )
    {
        mbedtls_mpi_free( &conf->dhm_P );
        mbedtls_mpi_free( &conf->dhm_G );
        return( ret );
    }

    return( 0 );
}
#endif /* MBEDTLS_DHM_C && MBEDTLS_SSL_SRV_C */

#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_CLI_C)
/**
 * \brief          Set the minimum length for Diffie-Hellman parameters.
 *                 (Client-side only.)
 *                 (Default: 1024 bits.)
 *
 * \param conf     SSL configuration
 * \param bitlen   Minimum bit length of the DHM prime
 */
void mbedtls_ssl_conf_dhm_min_bitlen( mbedtls_ssl_config *conf,
                                      unsigned int bitlen )
{
    conf->dhm_min_bitlen = bitlen;
}
#endif /* MBEDTLS_DHM_C && MBEDTLS_SSL_CLI_C */

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/**
 * \brief          Set the allowed hashes for signatures during the handshake.
 *                 (Default: all available hashes except MD5.)
 *
 * \note           This only affects which hashes are offered and can be used
 *                 for signatures during the handshake. Hashes for message
 *                 authentication and the TLS PRF are controlled by the
 *                 ciphersuite, see \c mbedtls_ssl_conf_ciphersuites(). Hashes
 *                 used for certificate signature are controlled by the
 *                 verification profile, see \c mbedtls_ssl_conf_cert_profile().
 *
 * \note           This list should be ordered by decreasing preference
 *                 (preferred hash first).
 *
 * \param conf     SSL configuration
 * \param hashes   Ordered list of allowed signature hashes,
 *                 terminated by \c MBEDTLS_MD_NONE.
 */
void mbedtls_ssl_conf_sig_hashes( mbedtls_ssl_config *conf,
                                  const uint8_t *hashes )
{
    conf->sig_hashes = hashes;
}
#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */

#if defined(MBEDTLS_ECP_C)
/**
 * \brief          Set the allowed curves in order of preference.
 *                 (Default: all defined curves.)
 *
 *                 On server: this only affects selection of the ECDHE curve;
 *                 the curves used for ECDH and ECDSA are determined by the
 *                 list of available certificates instead.
 *
 *                 On client: this affects the list of curves offered for any
 *                 use. The server can override our preference order.
 *
 *                 Both sides: limits the set of curves accepted for use in
 *                 ECDHE and in the peer's end-entity certificate.
 *
 * \note           This has no influence on which curves are allowed inside the
 *                 certificate chains, see \c mbedtls_ssl_conf_cert_profile()
 *                 for that. For the end-entity certificate however, the key
 *                 will be accepted only if it is allowed both by this list
 *                 and by the cert profile.
 *
 * \note           This list should be ordered by decreasing preference
 *                 (preferred curve first).
 *
 * \param conf     SSL configuration
 * \param curves   Ordered list of allowed curves,
 *                 terminated by MBEDTLS_ECP_DP_NONE.
 */
void mbedtls_ssl_conf_curves( mbedtls_ssl_config *conf,
                             const mbedtls_ecp_group_id *curve_list )
{
    conf->curve_list = curve_list;
}
#endif /* MBEDTLS_ECP_C */

#if defined(MBEDTLS_X509_CRT_PARSE_C)
/**
 * \brief          Set or reset the hostname to check against the received
 *                 server certificate. It sets the ServerName TLS extension,
 *                 too, if that extension is enabled. (client-side only)
 *
 * \param ssl      SSL context
 * \param hostname the server hostname, may be NULL to clear hostname
 *
 * \note           Maximum hostname length MBEDTLS_SSL_MAX_HOST_NAME_LEN.
 *
 * \return         0 if successful, MBEDTLS_ERR_SSL_ALLOC_FAILED on
 *                 allocation failure, MBEDTLS_ERR_SSL_BAD_INPUT_DATA on
 *                 too long input hostname.
 *
 *                 Hostname set to the one provided on success (cleared
 *                 when NULL). On allocation failure hostname is cleared.
 *                 On too long input failure, old hostname is unchanged.
 */
int mbedtls_ssl_set_hostname( mbedtls_ssl_context *ssl, const char *hostname )
{
    /* Initialize to suppress unnecessary compiler warning */
    size_t hostname_len = 0;

    /* Check if new hostname is valid before
     * making any change to current one */
    if( hostname != NULL )
    {
        hostname_len = strlen( hostname );

        if( hostname_len > MBEDTLS_SSL_MAX_HOST_NAME_LEN )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    /* Now it's clear that we will overwrite the old hostname,
     * so we can free it safely */

    if( ssl->hostname != NULL )
    {
        mbedtls_platform_zeroize( ssl->hostname, strlen( ssl->hostname ) );
        mbedtls_free( ssl->hostname );
    }

    /* Passing NULL as hostname shall clear the old one */

    if( hostname == NULL )
    {
        ssl->hostname = NULL;
    }
    else
    {
        ssl->hostname = mbedtls_calloc( 1, hostname_len + 1 );
        if( ssl->hostname == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

        memcpy( ssl->hostname, hostname, hostname_len );

        ssl->hostname[hostname_len] = '\0';
    }

    return( 0 );
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
/**
 * \brief          Set server side ServerName TLS extension callback
 *                 (optional, server-side only).
 *
 *                 If set, the ServerName callback is called whenever the
 *                 server receives a ServerName TLS extension from the client
 *                 during a handshake. The ServerName callback has the
 *                 following parameters: (void *parameter, mbedtls_ssl_context *ssl,
 *                 const unsigned char *hostname, size_t len). If a suitable
 *                 certificate is found, the callback must set the
 *                 certificate(s) and key(s) to use with \c
 *                 mbedtls_ssl_set_hs_own_cert() (can be called repeatedly),
 *                 and may optionally adjust the CA and associated CRL with \c
 *                 mbedtls_ssl_set_hs_ca_chain() as well as the client
 *                 authentication mode with \c mbedtls_ssl_set_hs_authmode(),
 *                 then must return 0. If no matching name is found, the
 *                 callback must either set a default cert, or
 *                 return non-zero to abort the handshake at this point.
 *
 * \param conf     SSL configuration
 * \param f_sni    verification function
 * \param p_sni    verification parameter
 */
void mbedtls_ssl_conf_sni( mbedtls_ssl_config *conf,
                           int (*f_sni)(void *, mbedtls_ssl_context *,
                                        const unsigned char *, size_t),
                           void *p_sni )
{
    conf->f_sni = f_sni;
    conf->p_sni = p_sni;
}
#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */

#if defined(MBEDTLS_SSL_ALPN)
/**
 * \brief          Set the supported Application Layer Protocols.
 *
 * \param conf     SSL configuration
 * \param protos   Pointer to a NULL-terminated list of supported protocols,
 *                 in decreasing preference order. The pointer to the list is
 *                 recorded by the library for later reference as required, so
 *                 the lifetime of the table must be atleast as long as the
 *                 lifetime of the SSL configuration structure.
 *
 * \return         0 on success, or MBEDTLS_ERR_SSL_BAD_INPUT_DATA.
 */
int mbedtls_ssl_conf_alpn_protocols( mbedtls_ssl_config *conf, const char **protos )
{
    size_t cur_len, tot_len;
    const char **p;
    /*
     * RFC 7301 3.1: "Empty strings MUST NOT be included and byte strings
     * MUST NOT be truncated."
     * We check lengths now rather than later.
     */
    tot_len = 0;
    for( p = protos; *p != NULL; p++ )
    {
        cur_len = strlen( *p );
        tot_len += cur_len;
        if( ( cur_len == 0 ) ||
            ( cur_len > MBEDTLS_SSL_MAX_ALPN_NAME_LEN ) ||
            ( tot_len > MBEDTLS_SSL_MAX_ALPN_LIST_LEN ) )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    conf->alpn_list = protos;
    return( 0 );
}

/**
 * \brief          Get the name of the negotiated Application Layer Protocol.
 *                 This function should be called after the handshake is
 *                 completed.
 *
 * \param ssl      SSL context
 *
 * \return         Protcol name, or NULL if no protocol was negotiated.
 */
const char *mbedtls_ssl_get_alpn_protocol( const mbedtls_ssl_context *ssl )
{
    return( ssl->alpn_chosen );
}

#endif /* MBEDTLS_SSL_ALPN */

#if defined(MBEDTLS_SSL_DTLS_SRTP)
/**
 * \brief                   Manage support for mki(master key id) value
 *                          in use_srtp extension.
 *                          MKI is an optional part of SRTP used for key management
 *                          and re-keying. See RFC3711 section 3.1 for details.
 *                          The default value is
 *                          #MBEDTLS_SSL_DTLS_SRTP_MKI_UNSUPPORTED.
 *
 * \param conf              The SSL configuration to manage mki support.
 * \param support_mki_value Enable or disable mki usage. Values are
 *                          #MBEDTLS_SSL_DTLS_SRTP_MKI_UNSUPPORTED
 *                          or #MBEDTLS_SSL_DTLS_SRTP_MKI_SUPPORTED.
 */
void mbedtls_ssl_conf_srtp_mki_value_supported( mbedtls_ssl_config *conf,
                                                int support_mki_value )
{
    conf->dtls_srtp_mki_support = support_mki_value;
}

int mbedtls_ssl_dtls_srtp_set_mki_value( mbedtls_ssl_context *ssl,
                                         unsigned char *mki_value,
                                         uint16_t mki_len )
{
    if( mki_len > MBEDTLS_TLS_SRTP_MAX_MKI_LENGTH )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    if( ssl->conf->dtls_srtp_mki_support == MBEDTLS_SSL_DTLS_SRTP_MKI_UNSUPPORTED )
    {
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
    }
    memcpy( ssl->dtls_srtp_info.mki_value, mki_value, mki_len );
    ssl->dtls_srtp_info.mki_len = mki_len;
    return( 0 );
}

/**
 * \brief                   Set the supported DTLS-SRTP protection profiles.
 *
 * \param conf              SSL configuration
 * \param profiles          Pointer to a List of MBEDTLS_TLS_SRTP_UNSET terminated
 *                          supported protection profiles
 *                          in decreasing preference order.
 *                          The pointer to the list is recorded by the library
 *                          for later reference as required, so the lifetime
 *                          of the table must be at least as long as the lifetime
 *                          of the SSL configuration structure.
 *                          The list must not hold more than
 *                          MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH elements
 *                          (excluding the terminating MBEDTLS_TLS_SRTP_UNSET).
 *
 * \return                  0 on success
 * \return                  #MBEDTLS_ERR_SSL_BAD_INPUT_DATA when the list of
 *                          protection profiles is incorrect.
 */
int mbedtls_ssl_conf_dtls_srtp_protection_profiles( mbedtls_ssl_config *conf,
                                                    const mbedtls_ssl_srtp_profile *profiles )
{
    const mbedtls_ssl_srtp_profile *p;
    size_t list_size = 0;
    /* check the profiles list: all entry must be valid,
     * its size cannot be more than the total number of supported profiles, currently 4 */
    for( p = profiles; *p != MBEDTLS_TLS_SRTP_UNSET &&
                       list_size <= MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH;
         p++ )
    {
        if( mbedtls_ssl_check_srtp_profile_value( *p ) != MBEDTLS_TLS_SRTP_UNSET )
        {
            list_size++;
        }
        else
        {
            /* unsupported value, stop parsing and set the size to an error value */
            list_size = MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH + 1;
        }
    }
    if( list_size > MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH )
    {
                conf->dtls_srtp_profile_list = NULL;
                conf->dtls_srtp_profile_list_len = 0;
                return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    conf->dtls_srtp_profile_list = profiles;
    conf->dtls_srtp_profile_list_len = list_size;
    return( 0 );
}

/**
 * \brief                  Set the mki_value for the current DTLS-SRTP session.
 *
 * \param ssl              SSL context to use.
 * \param mki_value        The MKI value to set.
 * \param mki_len          The length of the MKI value.
 *
 * \note                   This function is relevant on client side only.
 *                         The server discovers the mki value during handshake.
 *                         A mki value set on server side using this function
 *                         is ignored.
 *
 * \return                 0 on success
 * \return                 #MBEDTLS_ERR_SSL_BAD_INPUT_DATA
 * \return                 #MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE
 */
int mbedtls_ssl_dtls_srtp_set_mki_value( mbedtls_ssl_context *ssl,
                                         unsigned char *mki_value,
                                         uint16_t mki_len );
/**
 * \brief                  Get the negotiated DTLS-SRTP informations:
 *                         Protection profile and MKI value.
 *
 * \warning                This function must be called after the handshake is
 *                         completed. The value returned by this function must
 *                         not be trusted or acted upon before the handshake completes.
 *
 * \param ssl              The SSL context to query.
 * \param dtls_srtp_info   The negotiated DTLS-SRTP informations:
 *                         - Protection profile in use.
 *                         A direct mapping of the iana defined value for protection
 *                         profile on an uint16_t.
 http://www.iana.org/assignments/srtp-protection/srtp-protection.xhtml
 *                         #MBEDTLS_TLS_SRTP_UNSET if the use of SRTP was not negotiated
 *                         or peer's Hello packet was not parsed yet.
 *                         - mki size and value( if size is > 0 ).
 */
void mbedtls_ssl_get_dtls_srtp_negotiation_result( const mbedtls_ssl_context *ssl,
                                                   mbedtls_dtls_srtp_info *dtls_srtp_info )
{
    dtls_srtp_info->chosen_dtls_srtp_profile = ssl->dtls_srtp_info.chosen_dtls_srtp_profile;
    /* do not copy the mki value if there is no chosen profile */
    if( dtls_srtp_info->chosen_dtls_srtp_profile == MBEDTLS_TLS_SRTP_UNSET )
    {
        dtls_srtp_info->mki_len = 0;
    }
    else
    {
        dtls_srtp_info->mki_len = ssl->dtls_srtp_info.mki_len;
        memcpy( dtls_srtp_info->mki_value, ssl->dtls_srtp_info.mki_value,
                ssl->dtls_srtp_info.mki_len );
    }
}
#endif /* MBEDTLS_SSL_DTLS_SRTP */

/**
 * \brief          Set the maximum supported version sent from the client side
 *                 and/or accepted at the server side
 *                 (Default: MBEDTLS_SSL_MAX_MAJOR_VERSION, MBEDTLS_SSL_MAX_MINOR_VERSION)
 *
 * \note           This ignores ciphersuites from higher versions.
 *
 * \note           With DTLS, use MBEDTLS_SSL_MINOR_VERSION_2 for DTLS 1.0 and
 *                 MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2
 *
 * \param conf     SSL configuration
 * \param major    Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3 supported)
 * \param minor    Minor version number (MBEDTLS_SSL_MINOR_VERSION_0,
 *                 MBEDTLS_SSL_MINOR_VERSION_1 and MBEDTLS_SSL_MINOR_VERSION_2,
 *                 MBEDTLS_SSL_MINOR_VERSION_3 supported)
 */
void mbedtls_ssl_conf_max_version( mbedtls_ssl_config *conf, int major, int minor )
{
    conf->max_major_ver = major;
    conf->max_minor_ver = minor;
}

/**
 * \brief          Set the minimum accepted SSL/TLS protocol version
 *                 (Default: TLS 1.0)
 *
 * \note           Input outside of the SSL_MAX_XXXXX_VERSION and
 *                 SSL_MIN_XXXXX_VERSION range is ignored.
 *
 * \note           MBEDTLS_SSL_MINOR_VERSION_0 (SSL v3) should be avoided.
 *
 * \note           With DTLS, use MBEDTLS_SSL_MINOR_VERSION_2 for DTLS 1.0 and
 *                 MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2
 *
 * \param conf     SSL configuration
 * \param major    Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3 supported)
 * \param minor    Minor version number (MBEDTLS_SSL_MINOR_VERSION_0,
 *                 MBEDTLS_SSL_MINOR_VERSION_1 and MBEDTLS_SSL_MINOR_VERSION_2,
 *                 MBEDTLS_SSL_MINOR_VERSION_3 supported)
 */
void mbedtls_ssl_conf_min_version( mbedtls_ssl_config *conf, int major, int minor )
{
    conf->min_major_ver = major;
    conf->min_minor_ver = minor;
}

#if defined(MBEDTLS_SSL_FALLBACK_SCSV) && defined(MBEDTLS_SSL_CLI_C)
/**
 * \brief          Set the fallback flag (client-side only).
 *                 (Default: MBEDTLS_SSL_IS_NOT_FALLBACK).
 *
 * \note           Set to MBEDTLS_SSL_IS_FALLBACK when preparing a fallback
 *                 connection, that is a connection with max_version set to a
 *                 lower value than the value you're willing to use. Such
 *                 fallback connections are not recommended but are sometimes
 *                 necessary to interoperate with buggy (version-intolerant)
 *                 servers.
 *
 * \warning        You should NOT set this to MBEDTLS_SSL_IS_FALLBACK for
 *                 non-fallback connections! This would appear to work for a
 *                 while, then cause failures when the server is upgraded to
 *                 support a newer TLS version.
 *
 * \param conf     SSL configuration
 * \param fallback MBEDTLS_SSL_IS_NOT_FALLBACK or MBEDTLS_SSL_IS_FALLBACK
 */
void mbedtls_ssl_conf_fallback( mbedtls_ssl_config *conf, char fallback )
{
    conf->fallback = fallback;
}
#endif

#if defined(MBEDTLS_SSL_SRV_C)
/**
 * \brief          Whether to send a list of acceptable CAs in
 *                 CertificateRequest messages.
 *                 (Default: do send)
 *
 * \param conf     SSL configuration
 * \param cert_req_ca_list   MBEDTLS_SSL_CERT_REQ_CA_LIST_ENABLED or
 *                          MBEDTLS_SSL_CERT_REQ_CA_LIST_DISABLED
 */
void mbedtls_ssl_conf_cert_req_ca_list( mbedtls_ssl_config *conf,
                                          char cert_req_ca_list )
{
    conf->cert_req_ca_list = cert_req_ca_list;
}
#endif

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
/**
 * \brief           Enable or disable Encrypt-then-MAC
 *                  (Default: MBEDTLS_SSL_ETM_ENABLED)
 *
 * \note            This should always be enabled, it is a security
 *                  improvement, and should not cause any interoperability
 *                  issue (used only if the peer supports it too).
 *
 * \param conf      SSL configuration
 * \param etm       MBEDTLS_SSL_ETM_ENABLED or MBEDTLS_SSL_ETM_DISABLED
 */
void mbedtls_ssl_conf_encrypt_then_mac( mbedtls_ssl_config *conf, char etm )
{
    conf->encrypt_then_mac = etm;
}
#endif

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
/**
 * \brief           Enable or disable Extended Master Secret negotiation.
 *                  (Default: MBEDTLS_SSL_EXTENDED_MS_ENABLED)
 *
 * \note            This should always be enabled, it is a security fix to the
 *                  protocol, and should not cause any interoperability issue
 *                  (used only if the peer supports it too).
 *
 * \param conf      SSL configuration
 * \param ems       MBEDTLS_SSL_EXTENDED_MS_ENABLED or MBEDTLS_SSL_EXTENDED_MS_DISABLED
 */
void mbedtls_ssl_conf_extended_master_secret( mbedtls_ssl_config *conf, char ems )
{
    conf->extended_ms = ems;
}
#endif

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
/**
 * \brief          Set the maximum fragment length to emit and/or negotiate.
 *                 (Typical: the smaller of #MBEDTLS_SSL_IN_CONTENT_LEN and
 *                 #MBEDTLS_SSL_OUT_CONTENT_LEN, usually `2^14` bytes)
 *                 (Server: set maximum fragment length to emit,
 *                 usually negotiated by the client during handshake)
 *                 (Client: set maximum fragment length to emit *and*
 *                 negotiate with the server during handshake)
 *                 (Default: #MBEDTLS_SSL_MAX_FRAG_LEN_NONE)
 *
 * \note           On the client side, the maximum fragment length extension
 *                 *will not* be used, unless the maximum fragment length has
 *                 been set via this function to a value different than
 *                 #MBEDTLS_SSL_MAX_FRAG_LEN_NONE.
 *
 * \note           With TLS, this currently only affects ApplicationData (sent
 *                 with \c mbedtls_ssl_read()), not handshake messages.
 *                 With DTLS, this affects both ApplicationData and handshake.
 *
 * \note           This sets the maximum length for a record's payload,
 *                 excluding record overhead that will be added to it, see
 *                 \c mbedtls_ssl_get_record_expansion().
 *
 * \note           For DTLS, it is also possible to set a limit for the total
 *                 size of daragrams passed to the transport layer, including
 *                 record overhead, see \c mbedtls_ssl_set_mtu().
 *
 * \param conf     SSL configuration
 * \param mfl_code Code for maximum fragment length (allowed values:
 *                 MBEDTLS_SSL_MAX_FRAG_LEN_512,  MBEDTLS_SSL_MAX_FRAG_LEN_1024,
 *                 MBEDTLS_SSL_MAX_FRAG_LEN_2048, MBEDTLS_SSL_MAX_FRAG_LEN_4096)
 *
 * \return         0 if successful or MBEDTLS_ERR_SSL_BAD_INPUT_DATA
 */
int mbedtls_ssl_conf_max_frag_len( mbedtls_ssl_config *conf, unsigned char mfl_code )
{
    if( mfl_code >= MBEDTLS_SSL_MAX_FRAG_LEN_INVALID ||
        ssl_mfl_code_to_length( mfl_code ) > MBEDTLS_TLS_EXT_ADV_CONTENT_LEN )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    conf->mfl_code = mfl_code;
    return( 0 );
}
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */

#if defined(MBEDTLS_SSL_CBC_RECORD_SPLITTING)
/**
 * \brief          Enable / Disable 1/n-1 record splitting
 *                 (Default: MBEDTLS_SSL_CBC_RECORD_SPLITTING_ENABLED)
 *
 * \note           Only affects SSLv3 and TLS 1.0, not higher versions.
 *                 Does not affect non-CBC ciphersuites in any version.
 *
 * \param conf     SSL configuration
 * \param split    MBEDTLS_SSL_CBC_RECORD_SPLITTING_ENABLED or
 *                 MBEDTLS_SSL_CBC_RECORD_SPLITTING_DISABLED
 */
void mbedtls_ssl_conf_cbc_record_splitting( mbedtls_ssl_config *conf, char split )
{
    conf->cbc_record_splitting = split;
}
#endif

/**
 * \brief          Prevent or allow legacy renegotiation.
 *                 (Default: MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION)
 *
 *                 MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION allows connections to
 *                 be established even if the peer does not support
 *                 secure renegotiation, but does not allow renegotiation
 *                 to take place if not secure.
 *                 (Interoperable and secure option)
 *
 *                 MBEDTLS_SSL_LEGACY_ALLOW_RENEGOTIATION allows renegotiations
 *                 with non-upgraded peers. Allowing legacy renegotiation
 *                 makes the connection vulnerable to specific man in the
 *                 middle attacks. (See RFC 5746)
 *                 (Most interoperable and least secure option)
 *
 *                 MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE breaks off connections
 *                 if peer does not support secure renegotiation. Results
 *                 in interoperability issues with non-upgraded peers
 *                 that do not support renegotiation altogether.
 *                 (Most secure option, interoperability issues)
 *
 * \param conf     SSL configuration
 * \param allow_legacy  Prevent or allow (SSL_NO_LEGACY_RENEGOTIATION,
 *                                        SSL_ALLOW_LEGACY_RENEGOTIATION or
 *                                        MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE)
 */
void mbedtls_ssl_conf_legacy_renegotiation( mbedtls_ssl_config *conf, int allow_legacy )
{
    conf->allow_legacy_renegotiation = allow_legacy;
}

#if defined(MBEDTLS_SSL_RENEGOTIATION)
/**
 * \brief          Enable / Disable renegotiation support for connection when
 *                 initiated by peer
 *                 (Default: MBEDTLS_SSL_RENEGOTIATION_DISABLED)
 *
 * \warning        It is recommended to always disable renegotation unless you
 *                 know you need it and you know what you're doing. In the
 *                 past, there have been several issues associated with
 *                 renegotiation or a poor understanding of its properties.
 *
 * \note           Server-side, enabling renegotiation also makes the server
 *                 susceptible to a resource DoS by a malicious client.
 *
 * \param conf    SSL configuration
 * \param renegotiation     Enable or disable (MBEDTLS_SSL_RENEGOTIATION_ENABLED or
 *                                             MBEDTLS_SSL_RENEGOTIATION_DISABLED)
 */
void mbedtls_ssl_conf_renegotiation( mbedtls_ssl_config *conf, int renegotiation )
{
    conf->disable_renegotiation = renegotiation;
}

/**
 * \brief          Enforce renegotiation requests.
 *                 (Default: enforced, max_records = 16)
 *
 *                 When we request a renegotiation, the peer can comply or
 *                 ignore the request. This function allows us to decide
 *                 whether to enforce our renegotiation requests by closing
 *                 the connection if the peer doesn't comply.
 *
 *                 However, records could already be in transit from the peer
 *                 when the request is emitted. In order to increase
 *                 reliability, we can accept a number of records before the
 *                 expected handshake records.
 *
 *                 The optimal value is highly dependent on the specific usage
 *                 scenario.
 *
 * \note           With DTLS and server-initiated renegotiation, the
 *                 HelloRequest is retransmited every time mbedtls_ssl_read() times
 *                 out or receives Application Data, until:
 *                 - max_records records have beens seen, if it is >= 0, or
 *                 - the number of retransmits that would happen during an
 *                 actual handshake has been reached.
 *                 Please remember the request might be lost a few times
 *                 if you consider setting max_records to a really low value.
 *
 * \warning        On client, the grace period can only happen during
 *                 mbedtls_ssl_read(), as opposed to mbedtls_ssl_write() and mbedtls_ssl_renegotiate()
 *                 which always behave as if max_record was 0. The reason is,
 *                 if we receive application data from the server, we need a
 *                 place to write it, which only happens during mbedtls_ssl_read().
 *
 * \param conf     SSL configuration
 * \param max_records Use MBEDTLS_SSL_RENEGOTIATION_NOT_ENFORCED if you don't want to
 *                 enforce renegotiation, or a non-negative value to enforce
 *                 it but allow for a grace period of max_records records.
 */
void mbedtls_ssl_conf_renegotiation_enforced( mbedtls_ssl_config *conf, int max_records )
{
    conf->renego_max_records = max_records;
}

/**
 * \brief          Set record counter threshold for periodic renegotiation.
 *                 (Default: 2^48 - 1)
 *
 *                 Renegotiation is automatically triggered when a record
 *                 counter (outgoing or incoming) crosses the defined
 *                 threshold. The default value is meant to prevent the
 *                 connection from being closed when the counter is about to
 *                 reached its maximal value (it is not allowed to wrap).
 *
 *                 Lower values can be used to enforce policies such as "keys
 *                 must be refreshed every N packets with cipher X".
 *
 *                 The renegotiation period can be disabled by setting
 *                 conf->disable_renegotiation to
 *                 MBEDTLS_SSL_RENEGOTIATION_DISABLED.
 *
 * \note           When the configured transport is
 *                 MBEDTLS_SSL_TRANSPORT_DATAGRAM the maximum renegotiation
 *                 period is 2^48 - 1, and for MBEDTLS_SSL_TRANSPORT_STREAM,
 *                 the maximum renegotiation period is 2^64 - 1.
 *
 * \param conf     SSL configuration
 * \param period   The threshold value: a big-endian 64-bit number.
 */
void mbedtls_ssl_conf_renegotiation_period( mbedtls_ssl_config *conf,
                                            const unsigned char period[8] )
{
    memcpy( conf->renego_period, period, 8 );
}
#endif /* MBEDTLS_SSL_RENEGOTIATION */

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
#if defined(MBEDTLS_SSL_CLI_C)
/**
 * \brief          Enable / Disable session tickets (client only).
 *                 (Default: MBEDTLS_SSL_SESSION_TICKETS_ENABLED.)
 *
 * \note           On server, use \c mbedtls_ssl_conf_session_tickets_cb().
 *
 * \param conf     SSL configuration
 * \param use_tickets   Enable or disable (MBEDTLS_SSL_SESSION_TICKETS_ENABLED or
 *                                         MBEDTLS_SSL_SESSION_TICKETS_DISABLED)
 */
void mbedtls_ssl_conf_session_tickets( mbedtls_ssl_config *conf, int use_tickets )
{
    conf->session_tickets = use_tickets;
}
#endif

#if defined(MBEDTLS_SSL_SRV_C)
/**
 * \brief           Configure SSL session ticket callbacks (server only).
 *                  (Default: none.)
 *
 * \note            On server, session tickets are enabled by providing
 *                  non-NULL callbacks.
 *
 * \note            On client, use \c mbedtls_ssl_conf_session_tickets().
 *
 * \param conf      SSL configuration context
 * \param f_ticket_write    Callback for writing a ticket
 * \param f_ticket_parse    Callback for parsing a ticket
 * \param p_ticket          Context shared by the two callbacks
 */
void mbedtls_ssl_conf_session_tickets_cb( mbedtls_ssl_config *conf,
                                          mbedtls_ssl_ticket_write_t *f_ticket_write,
                                          mbedtls_ssl_ticket_parse_t *f_ticket_parse,
                                          void *p_ticket )
{
    conf->f_ticket_write = f_ticket_write;
    conf->f_ticket_parse = f_ticket_parse;
    conf->p_ticket       = p_ticket;
}
#endif
#endif /* MBEDTLS_SSL_SESSION_TICKETS */

#if defined(MBEDTLS_SSL_EXPORT_KEYS)
/**
 * \brief           Configure key export callback.
 *                  (Default: none.)
 *
 * \note            See \c mbedtls_ssl_export_keys_t.
 *
 * \param conf      SSL configuration context
 * \param f_export_keys     Callback for exporting keys
 * \param p_export_keys     Context for the callback
 */
void mbedtls_ssl_conf_export_keys_cb( mbedtls_ssl_config *conf,
                                      mbedtls_ssl_export_keys_t *f_export_keys,
                                      void *p_export_keys )
{
    conf->f_export_keys = f_export_keys;
    conf->p_export_keys = p_export_keys;
}

/**
 * \brief           Configure extended key export callback.
 *                  (Default: none.)
 *
 * \note            See \c mbedtls_ssl_export_keys_ext_t.
 * \warning         Exported key material must not be used for any purpose
 *                  before the (D)TLS handshake is completed
 *
 * \param conf      SSL configuration context
 * \param f_export_keys_ext Callback for exporting keys
 * \param p_export_keys     Context for the callback
 */
void mbedtls_ssl_conf_export_keys_ext_cb( mbedtls_ssl_config *conf,
                                          mbedtls_ssl_export_keys_ext_t *f_export_keys_ext,
                                          void *p_export_keys )
{
    conf->f_export_keys_ext = f_export_keys_ext;
    conf->p_export_keys = p_export_keys;
}
#endif

#if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
/**
 * \brief           Configure asynchronous private key operation callbacks.
 *
 * \param conf              SSL configuration context
 * \param f_async_sign      Callback to start a signature operation. See
 *                          the description of ::mbedtls_ssl_async_sign_t
 *                          for more information. This may be \c NULL if the
 *                          external processor does not support any signature
 *                          operation; in this case the private key object
 *                          associated with the certificate will be used.
 * \param f_async_decrypt   Callback to start a decryption operation. See
 *                          the description of ::mbedtls_ssl_async_decrypt_t
 *                          for more information. This may be \c NULL if the
 *                          external processor does not support any decryption
 *                          operation; in this case the private key object
 *                          associated with the certificate will be used.
 * \param f_async_resume    Callback to resume an asynchronous operation. See
 *                          the description of ::mbedtls_ssl_async_resume_t
 *                          for more information. This may not be \c NULL unless
 *                          \p f_async_sign and \p f_async_decrypt are both
 *                          \c NULL.
 * \param f_async_cancel    Callback to cancel an asynchronous operation. See
 *                          the description of ::mbedtls_ssl_async_cancel_t
 *                          for more information. This may be \c NULL if
 *                          no cleanup is needed.
 * \param config_data       A pointer to configuration data which can be
 *                          retrieved with
 *                          mbedtls_ssl_conf_get_async_config_data(). The
 *                          library stores this value without dereferencing it.
 */
void mbedtls_ssl_conf_async_private_cb(
    mbedtls_ssl_config *conf,
    mbedtls_ssl_async_sign_t *f_async_sign,
    mbedtls_ssl_async_decrypt_t *f_async_decrypt,
    mbedtls_ssl_async_resume_t *f_async_resume,
    mbedtls_ssl_async_cancel_t *f_async_cancel,
    void *async_config_data )
{
    conf->f_async_sign_start = f_async_sign;
    conf->f_async_decrypt_start = f_async_decrypt;
    conf->f_async_resume = f_async_resume;
    conf->f_async_cancel = f_async_cancel;
    conf->p_async_config_data = async_config_data;
}

/**
 * \brief           Retrieve the configuration data set by
 *                  mbedtls_ssl_conf_async_private_cb().
 *
 * \param conf      SSL configuration context
 * \return          The configuration data set by
 *                  mbedtls_ssl_conf_async_private_cb().
 */
void *mbedtls_ssl_conf_get_async_config_data( const mbedtls_ssl_config *conf )
{
    return( conf->p_async_config_data );
}

/**
 * \brief           Retrieve the asynchronous operation user context.
 *
 * \note            This function may only be called while a handshake
 *                  is in progress.
 *
 * \param ssl       The SSL context to access.
 *
 * \return          The asynchronous operation user context that was last
 *                  set during the current handshake. If
 *                  mbedtls_ssl_set_async_operation_data() has not yet been
 *                  called during the current handshake, this function returns
 *                  \c NULL.
 */
void *mbedtls_ssl_get_async_operation_data( const mbedtls_ssl_context *ssl )
{
    if( ssl->handshake == NULL )
        return( NULL );
    else
        return( ssl->handshake->user_async_ctx );
}

/**
 * \brief           Retrieve the asynchronous operation user context.
 *
 * \note            This function may only be called while a handshake
 *                  is in progress.
 *
 * \param ssl       The SSL context to access.
 * \param ctx       The new value of the asynchronous operation user context.
 *                  Call mbedtls_ssl_get_async_operation_data() later during the
 *                  same handshake to retrieve this value.
 */
void mbedtls_ssl_set_async_operation_data( mbedtls_ssl_context *ssl,
                                 void *ctx )
{
    if( ssl->handshake != NULL )
        ssl->handshake->user_async_ctx = ctx;
}
#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */

/**
 * \brief          Return the result of the certificate verification
 *
 * \param ssl      The SSL context to use.
 *
 * \return         \c 0 if the certificate verification was successful.
 * \return         \c -1u if the result is not available. This may happen
 *                 e.g. if the handshake aborts early, or a verification
 *                 callback returned a fatal error.
 * \return         A bitwise combination of \c MBEDTLS_X509_BADCERT_XXX
 *                 and \c MBEDTLS_X509_BADCRL_XXX failure flags; see x509.h.
 */
uint32_t mbedtls_ssl_get_verify_result( const mbedtls_ssl_context *ssl )
{
    if( ssl->session != NULL )
        return( ssl->session->verify_result );
    if( ssl->session_negotiate != NULL )
        return( ssl->session_negotiate->verify_result );
    return( 0xFFFFFFFF );
}

/**
 * \brief          Return the name of the current ciphersuite
 *
 * \param ssl      SSL context
 *
 * \return         a string containing the ciphersuite name
 */
const char *mbedtls_ssl_get_ciphersuite( const mbedtls_ssl_context *ssl )
{
    if( ssl == NULL || ssl->session == NULL )
        return( NULL );
    return mbedtls_ssl_get_ciphersuite_name( ssl->session->ciphersuite );
}

/**
 * \brief          Return the current SSL version (SSLv3/TLSv1/etc)
 *
 * \param ssl      SSL context
 *
 * \return         a string containing the SSL version
 */
const char *mbedtls_ssl_get_version( const mbedtls_ssl_context *ssl )
{
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
    {
        switch( ssl->minor_ver )
        {
            case MBEDTLS_SSL_MINOR_VERSION_2:
                return( "DTLSv1.0" );
            case MBEDTLS_SSL_MINOR_VERSION_3:
                return( "DTLSv1.2" );
            default:
                return( "unknown (DTLS)" );
        }
    }
#endif
    switch( ssl->minor_ver )
    {
        case MBEDTLS_SSL_MINOR_VERSION_0:
            return( "SSLv3.0" );
        case MBEDTLS_SSL_MINOR_VERSION_1:
            return( "TLSv1.0" );
        case MBEDTLS_SSL_MINOR_VERSION_2:
            return( "TLSv1.1" );
        case MBEDTLS_SSL_MINOR_VERSION_3:
            return( "TLSv1.2" );
        default:
            return( "unknown" );
    }
}

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
/**
 * \brief          Return the maximum fragment length (payload, in bytes) for
 *                 the input buffer. This is the negotiated maximum fragment
 *                 length, or, if there is none, MBEDTLS_SSL_MAX_CONTENT_LEN.
 *                 If it is not defined either, the value is 2^14. This function
 *                 works as its predecessor, \c mbedtls_ssl_get_max_frag_len().
 *
 * \sa             mbedtls_ssl_conf_max_frag_len()
 * \sa             mbedtls_ssl_get_max_record_payload()
 *
 * \param ssl      SSL context
 *
 * \return         Current maximum fragment length for the output buffer.
 */
size_t mbedtls_ssl_get_input_max_frag_len( const mbedtls_ssl_context *ssl )
{
    size_t max_len = MBEDTLS_SSL_MAX_CONTENT_LEN;
    size_t read_mfl;
    /* Use the configured MFL for the client if we're past SERVER_HELLO_DONE */
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT &&
        ssl->state >= MBEDTLS_SSL_SERVER_HELLO_DONE )
    {
        return ssl_mfl_code_to_length( ssl->conf->mfl_code );
    }
    /* Check if a smaller max length was negotiated */
    if( ssl->session_out != NULL )
    {
        read_mfl = ssl_mfl_code_to_length( ssl->session_out->mfl_code );
        if( read_mfl < max_len )
        {
            max_len = read_mfl;
        }
    }
    // During a handshake, use the value being negotiated
    if( ssl->session_negotiate != NULL )
    {
        read_mfl = ssl_mfl_code_to_length( ssl->session_negotiate->mfl_code );
        if( read_mfl < max_len )
        {
            max_len = read_mfl;
        }
    }
    return( max_len );
}

/**
 * \brief          Return the maximum fragment length (payload, in bytes) for
 *                 the output buffer. For the client, this is the configured
 *                 value. For the server, it is the minimum of two - the
 *                 configured value and the negotiated one.
 *
 * \sa             mbedtls_ssl_conf_max_frag_len()
 * \sa             mbedtls_ssl_get_max_record_payload()
 *
 * \param ssl      SSL context
 *
 * \return         Current maximum fragment length for the output buffer.
 */
size_t mbedtls_ssl_get_output_max_frag_len( const mbedtls_ssl_context *ssl )
{
    size_t max_len;
    /*
     * Assume mfl_code is correct since it was checked when set
     */
    max_len = ssl_mfl_code_to_length( ssl->conf->mfl_code );
    /* Check if a smaller max length was negotiated */
    if( ssl->session_out != NULL &&
        ssl_mfl_code_to_length( ssl->session_out->mfl_code ) < max_len )
    {
        max_len = ssl_mfl_code_to_length( ssl->session_out->mfl_code );
    }
    /* During a handshake, use the value being negotiated */
    if( ssl->session_negotiate != NULL &&
        ssl_mfl_code_to_length( ssl->session_negotiate->mfl_code ) < max_len )
    {
        max_len = ssl_mfl_code_to_length( ssl->session_negotiate->mfl_code );
    }
    return( max_len );
}
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */

#if defined(MBEDTLS_SSL_PROTO_DTLS)
size_t mbedtls_ssl_get_current_mtu( const mbedtls_ssl_context *ssl )
{
    /* Return unlimited mtu for client hello messages to avoid fragmentation. */
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT &&
        ( ssl->state == MBEDTLS_SSL_CLIENT_HELLO ||
          ssl->state == MBEDTLS_SSL_SERVER_HELLO ) )
        return ( 0 );
    if( ssl->handshake == NULL || ssl->handshake->mtu == 0 )
        return( ssl->mtu );
    if( ssl->mtu == 0 )
        return( ssl->handshake->mtu );
    return( ssl->mtu < ssl->handshake->mtu ?
            ssl->mtu : ssl->handshake->mtu );
}
#endif /* MBEDTLS_SSL_PROTO_DTLS */

/**
 * \brief          Return the current maximum outgoing record payload in bytes.
 *                 This takes into account the config.h setting \c
 *                 MBEDTLS_SSL_OUT_CONTENT_LEN, the configured and negotiated
 *                 max fragment length extension if used, and for DTLS the
 *                 path MTU as configured and current record expansion.
 *
 * \note           With DTLS, \c mbedtls_ssl_write() will return an error if
 *                 called with a larger length value.
 *                 With TLS, \c mbedtls_ssl_write() will fragment the input if
 *                 necessary and return the number of bytes written; it is up
 *                 to the caller to call \c mbedtls_ssl_write() again in
 *                 order to send the remaining bytes if any.
 *
 * \note           This function is not available (always returns an error)
 *                 when record compression is enabled.
 *
 * \sa             mbedtls_ssl_set_mtu()
 * \sa             mbedtls_ssl_get_output_max_frag_len()
 * \sa             mbedtls_ssl_get_input_max_frag_len()
 * \sa             mbedtls_ssl_get_record_expansion()
 *
 * \param ssl      SSL context
 *
 * \return         Current maximum payload for an outgoing record,
 *                 or a negative error code.
 */
int mbedtls_ssl_get_max_out_record_payload( const mbedtls_ssl_context *ssl )
{
    size_t max_len = MBEDTLS_SSL_OUT_CONTENT_LEN;
#if !defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH) && \
    !defined(MBEDTLS_SSL_PROTO_DTLS)
    (void) ssl;
#endif
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
    const size_t mfl = mbedtls_ssl_get_output_max_frag_len( ssl );
    if( max_len > mfl )
        max_len = mfl;
#endif
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( mbedtls_ssl_get_current_mtu( ssl ) != 0 )
    {
        const size_t mtu = mbedtls_ssl_get_current_mtu( ssl );
        const int ret = mbedtls_ssl_get_record_expansion( ssl );
        const size_t overhead = (size_t) ret;
        if( ret < 0 )
            return( ret );
        if( mtu <= overhead )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "MTU too low for record expansion" ) );
            return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
        }
        if( max_len > mtu - overhead )
            max_len = mtu - overhead;
    }
#endif /* MBEDTLS_SSL_PROTO_DTLS */
#if !defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH) &&        \
    !defined(MBEDTLS_SSL_PROTO_DTLS)
    ((void) ssl);
#endif
    return( (int) max_len );
}

#if defined(MBEDTLS_X509_CRT_PARSE_C)
/**
 * \brief          Return the peer certificate from the current connection.
 *
 * \param  ssl     The SSL context to use. This must be initialized and setup.
 *
 * \return         The current peer certificate, if available.
 *                 The returned certificate is owned by the SSL context and
 *                 is valid only until the next call to the SSL API.
 * \return         \c NULL if no peer certificate is available. This might
 *                 be because the chosen ciphersuite doesn't use CRTs
 *                 (PSK-based ciphersuites, for example), or because
 *                 #MBEDTLS_SSL_KEEP_PEER_CERTIFICATE has been disabled,
 *                 allowing the stack to free the peer's CRT to save memory.
 *
 * \note           For one-time inspection of the peer's certificate during
 *                 the handshake, consider registering an X.509 CRT verification
 *                 callback through mbedtls_ssl_conf_verify() instead of calling
 *                 this function. Using mbedtls_ssl_conf_verify() also comes at
 *                 the benefit of allowing you to influence the verification
 *                 process, for example by masking expected and tolerated
 *                 verification failures.
 *
 * \warning        You must not use the pointer returned by this function
 *                 after any further call to the SSL API, including
 *                 mbedtls_ssl_read() and mbedtls_ssl_write(); this is
 *                 because the pointer might change during renegotiation,
 *                 which happens transparently to the user.
 *                 If you want to use the certificate across API calls,
 *                 you must make a copy.
 */
const mbedtls_x509_crt *mbedtls_ssl_get_peer_cert( const mbedtls_ssl_context *ssl )
{
    if( ssl == NULL || ssl->session == NULL )
        return( NULL );
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    return( ssl->session->peer_cert );
#else
    return( NULL );
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

#if defined(MBEDTLS_SSL_CLI_C)
/**
 * \brief          Save session in order to resume it later (client-side only)
 *                 Session data is copied to presented session structure.
 *
 *
 * \param ssl      SSL context
 * \param session  session context
 *
 * \return         0 if successful,
 *                 MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed,
 *                 MBEDTLS_ERR_SSL_BAD_INPUT_DATA if used server-side or
 *                 arguments are otherwise invalid.
 *
 * \note           Only the server certificate is copied, and not the full chain,
 *                 so you should not attempt to validate the certificate again
 *                 by calling \c mbedtls_x509_crt_verify() on it.
 *                 Instead, you should use the results from the verification
 *                 in the original handshake by calling \c mbedtls_ssl_get_verify_result()
 *                 after loading the session again into a new SSL context
 *                 using \c mbedtls_ssl_set_session().
 *
 * \note           Once the session object is not needed anymore, you should
 *                 free it by calling \c mbedtls_ssl_session_free().
 *
 * \sa             mbedtls_ssl_set_session()
 */
int mbedtls_ssl_get_session( const mbedtls_ssl_context *ssl,
                             mbedtls_ssl_session *dst )
{
    if( ssl == NULL ||
        dst == NULL ||
        ssl->session == NULL ||
        ssl->conf->endpoint != MBEDTLS_SSL_IS_CLIENT )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    return( mbedtls_ssl_session_copy( dst, ssl->session ) );
}
#endif /* MBEDTLS_SSL_CLI_C */

/**
 * \brief          Get a pointer to the current session structure, for example
 *                 to serialize it.
 *
 * \warning        Ownership of the session remains with the SSL context, and
 *                 the returned pointer is only guaranteed to be valid until
 *                 the next API call operating on the same \p ssl context.
 *
 * \see            mbedtls_ssl_session_save()
 *
 * \param ssl      The SSL context.
 *
 * \return         A pointer to the current session if successful.
 * \return         \c NULL if no session is active.
 */
const mbedtls_ssl_session *mbedtls_ssl_get_session_pointer( const mbedtls_ssl_context *ssl )
{
    if( ssl == NULL )
        return( NULL );
    return( ssl->session );
}

/*
 * Define ticket header determining Mbed TLS version
 * and structure of the ticket.
 */

/*
 * Define bitflag determining compile-time settings influencing
 * structure of serialized SSL sessions.
 */

#if defined(MBEDTLS_HAVE_TIME)
#define SSL_SERIALIZED_SESSION_CONFIG_TIME 1
#else
#define SSL_SERIALIZED_SESSION_CONFIG_TIME 0
#endif /* MBEDTLS_HAVE_TIME */

#if defined(MBEDTLS_X509_CRT_PARSE_C)
#define SSL_SERIALIZED_SESSION_CONFIG_CRT 1
#else
#define SSL_SERIALIZED_SESSION_CONFIG_CRT 0
#endif /* MBEDTLS_X509_CRT_PARSE_C */

#if defined(MBEDTLS_SSL_CLI_C) && defined(MBEDTLS_SSL_SESSION_TICKETS)
#define SSL_SERIALIZED_SESSION_CONFIG_CLIENT_TICKET 1
#else
#define SSL_SERIALIZED_SESSION_CONFIG_CLIENT_TICKET 0
#endif /* MBEDTLS_SSL_CLI_C && MBEDTLS_SSL_SESSION_TICKETS */

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
#define SSL_SERIALIZED_SESSION_CONFIG_MFL 1
#else
#define SSL_SERIALIZED_SESSION_CONFIG_MFL 0
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */

#define SSL_SERIALIZED_SESSION_CONFIG_TRUNC_HMAC 0

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
#define SSL_SERIALIZED_SESSION_CONFIG_ETM 1
#else
#define SSL_SERIALIZED_SESSION_CONFIG_ETM 0
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
#define SSL_SERIALIZED_SESSION_CONFIG_TICKET 1
#else
#define SSL_SERIALIZED_SESSION_CONFIG_TICKET 0
#endif /* MBEDTLS_SSL_SESSION_TICKETS */

#define SSL_SERIALIZED_SESSION_CONFIG_TIME_BIT          0
#define SSL_SERIALIZED_SESSION_CONFIG_CRT_BIT           1
#define SSL_SERIALIZED_SESSION_CONFIG_CLIENT_TICKET_BIT 2
#define SSL_SERIALIZED_SESSION_CONFIG_MFL_BIT           3
#define SSL_SERIALIZED_SESSION_CONFIG_TRUNC_HMAC_BIT    4
#define SSL_SERIALIZED_SESSION_CONFIG_ETM_BIT           5
#define SSL_SERIALIZED_SESSION_CONFIG_TICKET_BIT        6

#define SSL_SERIALIZED_SESSION_CONFIG_BITFLAG                           \
    ( (uint16_t) (                                                      \
        ( SSL_SERIALIZED_SESSION_CONFIG_TIME          << SSL_SERIALIZED_SESSION_CONFIG_TIME_BIT          ) | \
        ( SSL_SERIALIZED_SESSION_CONFIG_CRT           << SSL_SERIALIZED_SESSION_CONFIG_CRT_BIT           ) | \
        ( SSL_SERIALIZED_SESSION_CONFIG_CLIENT_TICKET << SSL_SERIALIZED_SESSION_CONFIG_CLIENT_TICKET_BIT ) | \
        ( SSL_SERIALIZED_SESSION_CONFIG_MFL           << SSL_SERIALIZED_SESSION_CONFIG_MFL_BIT           ) | \
        ( SSL_SERIALIZED_SESSION_CONFIG_TRUNC_HMAC    << SSL_SERIALIZED_SESSION_CONFIG_TRUNC_HMAC_BIT    ) | \
        ( SSL_SERIALIZED_SESSION_CONFIG_ETM           << SSL_SERIALIZED_SESSION_CONFIG_ETM_BIT           ) | \
        ( SSL_SERIALIZED_SESSION_CONFIG_TICKET        << SSL_SERIALIZED_SESSION_CONFIG_TICKET_BIT        ) ) )

static unsigned char ssl_serialized_session_header[] = {
    MBEDTLS_VERSION_MAJOR,
    MBEDTLS_VERSION_MINOR,
    MBEDTLS_VERSION_PATCH,
    ( SSL_SERIALIZED_SESSION_CONFIG_BITFLAG >> 8 ) & 0xFF,
    ( SSL_SERIALIZED_SESSION_CONFIG_BITFLAG >> 0 ) & 0xFF,
};

/*
 * Serialize a session in the following format:
 * (in the presentation language of TLS, RFC 8446 section 3)
 *
 *  opaque mbedtls_version[3];   // major, minor, patch
 *  opaque session_format[2];    // version-specific 16-bit field determining
 *                               // the format of the remaining
 *                               // serialized data.
 *
 *  Note: When updating the format, remember to keep
 *        these version+format bytes.
 *
 *                               // In this version, `session_format` determines
 *                               // the setting of those compile-time
 *                               // configuration options which influence
 *                               // the structure of mbedtls_ssl_session.
 *  uint64 start_time;
 *  uint8 ciphersuite[2];        // defined by the standard
 *  uint8 compression;           // 0 or 1
 *  uint8 session_id_len;        // at most 32
 *  opaque session_id[32];
 *  opaque master[48];           // fixed length in the standard
 *  uint32 verify_result;
 *  opaque peer_cert<0..2^24-1>; // length 0 means no peer cert
 *  opaque ticket<0..2^24-1>;    // length 0 means no ticket
 *  uint32 ticket_lifetime;
 *  uint8 mfl_code;              // up to 255 according to standard
 *  uint8 trunc_hmac;            // 0 or 1
 *  uint8 encrypt_then_mac;      // 0 or 1
 *
 * The order is the same as in the definition of the structure, except
 * verify_result is put before peer_cert so that all mandatory fields come
 * together in one block.
 */
static int ssl_session_save( const mbedtls_ssl_session *session,
                             unsigned char omit_header,
                             unsigned char *buf,
                             size_t buf_len,
                             size_t *olen )
{
    unsigned char *p = buf;
    size_t used = 0;
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    size_t cert_len;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */
    if( !omit_header )
    {
        /*
         * Add version identifier
         */
        used += sizeof( ssl_serialized_session_header );
        if( used <= buf_len )
        {
            memcpy( p, ssl_serialized_session_header,
                    sizeof( ssl_serialized_session_header ) );
            p += sizeof( ssl_serialized_session_header );
        }
    }
    /*
     * Time
     */
#if defined(MBEDTLS_HAVE_TIME)
    used += 8;
    if( used <= buf_len )
        p = Write64be(p, session->start);
#endif /* MBEDTLS_HAVE_TIME */
    /*
     * Basic mandatory fields
     */
    used += 2   /* ciphersuite */
          + 1   /* compression */
          + 1   /* id_len */
          + sizeof( session->id )
          + sizeof( session->master )
          + 4;  /* verify_result */
    if( used <= buf_len )
    {
        *p++ = (unsigned char)( ( session->ciphersuite >> 8 ) & 0xFF );
        *p++ = (unsigned char)( ( session->ciphersuite      ) & 0xFF );
        *p++ = (unsigned char)( session->compression & 0xFF );
        *p++ = (unsigned char)( session->id_len & 0xFF );
        memcpy( p, session->id, 32 );
        p += 32;
        memcpy( p, session->master, 48 );
        p += 48;
        *p++ = (unsigned char)( ( session->verify_result >> 24 ) & 0xFF );
        *p++ = (unsigned char)( ( session->verify_result >> 16 ) & 0xFF );
        *p++ = (unsigned char)( ( session->verify_result >>  8 ) & 0xFF );
        *p++ = (unsigned char)( ( session->verify_result       ) & 0xFF );
    }
    /*
     * Peer's end-entity certificate
     */
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    if( session->peer_cert == NULL )
        cert_len = 0;
    else
        cert_len = session->peer_cert->raw.len;
    used += 3 + cert_len;
    if( used <= buf_len )
    {
        *p++ = (unsigned char)( ( cert_len >> 16 ) & 0xFF );
        *p++ = (unsigned char)( ( cert_len >>  8 ) & 0xFF );
        *p++ = (unsigned char)( ( cert_len       ) & 0xFF );
        if( session->peer_cert != NULL )
        {
            memcpy( p, session->peer_cert->raw.p, cert_len );
            p += cert_len;
        }
    }
#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    if( session->peer_cert_digest != NULL )
    {
        used += 1 /* type */ + 1 /* length */ + session->peer_cert_digest_len;
        if( used <= buf_len )
        {
            *p++ = (unsigned char) session->peer_cert_digest_type;
            *p++ = (unsigned char) session->peer_cert_digest_len;
            memcpy( p, session->peer_cert_digest,
                    session->peer_cert_digest_len );
            p += session->peer_cert_digest_len;
        }
    }
    else
    {
        used += 2;
        if( used <= buf_len )
        {
            *p++ = (unsigned char) MBEDTLS_MD_NONE;
            *p++ = 0;
        }
    }
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */
    /*
     * Session ticket if any, plus associated data
     */
#if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
    used += 3 + session->ticket_len + 4; /* len + ticket + lifetime */
    if( used <= buf_len )
    {
        *p++ = (unsigned char)( ( session->ticket_len >> 16 ) & 0xFF );
        *p++ = (unsigned char)( ( session->ticket_len >>  8 ) & 0xFF );
        *p++ = (unsigned char)( ( session->ticket_len       ) & 0xFF );
        if( session->ticket != NULL )
        {
            memcpy( p, session->ticket, session->ticket_len );
            p += session->ticket_len;
        }
        *p++ = (unsigned char)( ( session->ticket_lifetime >> 24 ) & 0xFF );
        *p++ = (unsigned char)( ( session->ticket_lifetime >> 16 ) & 0xFF );
        *p++ = (unsigned char)( ( session->ticket_lifetime >>  8 ) & 0xFF );
        *p++ = (unsigned char)( ( session->ticket_lifetime       ) & 0xFF );
    }
#endif /* MBEDTLS_SSL_SESSION_TICKETS && MBEDTLS_SSL_CLI_C */
    /*
     * Misc extension-related info
     */
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
    used += 1;
    if( used <= buf_len )
        *p++ = session->mfl_code;
#endif
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
    used += 1;
    if( used <= buf_len )
        *p++ = (unsigned char)( ( session->encrypt_then_mac ) & 0xFF );
#endif
    /* Done */
    *olen = used;
    if( used > buf_len )
        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
    return( 0 );
}

/**
 * \brief          Save session structure as serialized data in a buffer.
 *                 On client, this can be used for saving session data,
 *                 potentially in non-volatile storage, for resuming later.
 *                 On server, this can be used for alternative implementations
 *                 of session cache or session tickets.
 *
 * \see            mbedtls_ssl_session_load()
 * \see            mbedtls_ssl_get_session_pointer()
 *
 * \param session  The session structure to be saved.
 * \param buf      The buffer to write the serialized data to. It must be a
 *                 writeable buffer of at least \p len bytes, or may be \c
 *                 NULL if \p len is \c 0.
 * \param buf_len  The number of bytes available for writing in \p buf.
 * \param olen     The size in bytes of the data that has been or would have
 *                 been written. It must point to a valid \c size_t.
 *
 * \note           \p olen is updated to the correct value regardless of
 *                 whether \p buf_len was large enough. This makes it possible
 *                 to determine the necessary size by calling this function
 *                 with \p buf set to \c NULL and \p buf_len to \c 0.
 *
 * \return         \c 0 if successful.
 * \return         #MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL if \p buf is too small.
 */
int mbedtls_ssl_session_save( const mbedtls_ssl_session *session,
                              unsigned char *buf,
                              size_t buf_len,
                              size_t *olen )
{
    return( ssl_session_save( session, 0, buf, buf_len, olen ) );
}

/*
 * Deserialize session, see mbedtls_ssl_session_save() for format.
 *
 * This internal version is wrapped by a public function that cleans up in
 * case of error, and has an extra option omit_header.
 */
static int ssl_session_load( mbedtls_ssl_session *session,
                             unsigned char omit_header,
                             const unsigned char *buf,
                             size_t len )
{
    const unsigned char *p = buf;
    const unsigned char * const end = buf + len;
#if defined(MBEDTLS_HAVE_TIME)
    uint64_t start;
#endif
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    size_t cert_len;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */

    if( !omit_header )
    {
        /*
         * Check version identifier
         */

        if( (size_t)( end - p ) < sizeof( ssl_serialized_session_header ) )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        if( timingsafe_bcmp( p, ssl_serialized_session_header,
                    sizeof( ssl_serialized_session_header ) ) != 0 )
        {
            return( MBEDTLS_ERR_SSL_VERSION_MISMATCH );
        }
        p += sizeof( ssl_serialized_session_header );
    }

    /*
     * Time
     */
#if defined(MBEDTLS_HAVE_TIME)
    if( 8 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    start = Read64be(p);
    p += 8;

    session->start = (int64_t) start;
#endif /* MBEDTLS_HAVE_TIME */

    /*
     * Basic mandatory fields
     */
    if( 2 + 1 + 1 + 32 + 48 + 4 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    session->ciphersuite = ( p[0] << 8 ) | p[1];
    p += 2;

    session->compression = *p++;

    session->id_len = *p++;
    memcpy( session->id, p, 32 );
    p += 32;

    memcpy( session->master, p, 48 );
    p += 48;

    session->verify_result = Read32be(p);
    p += 4;

    /* Immediately clear invalid pointer values that have been read, in case
     * we exit early before we replaced them with valid ones. */
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    session->peer_cert = NULL;
#else
    session->peer_cert_digest = NULL;
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */
#if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
    session->ticket = NULL;
#endif /* MBEDTLS_SSL_SESSION_TICKETS && MBEDTLS_SSL_CLI_C */

    /*
     * Peer certificate
     */
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    /* Deserialize CRT from the end of the ticket. */
    if( 3 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    cert_len = ( p[0] << 16 ) | ( p[1] << 8 ) | p[2];
    p += 3;

    if( cert_len != 0 )
    {
        int ret = MBEDTLS_ERR_THIS_CORRUPTION;

        if( cert_len > (size_t)( end - p ) )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        session->peer_cert = mbedtls_calloc( 1, sizeof( mbedtls_x509_crt ) );

        if( session->peer_cert == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

        mbedtls_x509_crt_init( session->peer_cert );

        if( ( ret = mbedtls_x509_crt_parse_der( session->peer_cert,
                                                p, cert_len ) ) != 0 )
        {
            mbedtls_x509_crt_free( session->peer_cert );
            mbedtls_free( session->peer_cert );
            session->peer_cert = NULL;
            return( ret );
        }

        p += cert_len;
    }
#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    /* Deserialize CRT digest from the end of the ticket. */
    if( 2 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    session->peer_cert_digest_type = (mbedtls_md_type_t) *p++;
    session->peer_cert_digest_len  = (size_t) *p++;

    if( session->peer_cert_digest_len != 0 )
    {
        const mbedtls_md_info_t *md_info =
            mbedtls_md_info_from_type( session->peer_cert_digest_type );
        if( md_info == NULL )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
        if( session->peer_cert_digest_len != mbedtls_md_get_size( md_info ) )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        if( session->peer_cert_digest_len > (size_t)( end - p ) )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        session->peer_cert_digest =
            mbedtls_calloc( 1, session->peer_cert_digest_len );
        if( session->peer_cert_digest == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

        memcpy( session->peer_cert_digest, p,
                session->peer_cert_digest_len );
        p += session->peer_cert_digest_len;
    }
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */

    /*
     * Session ticket and associated data
     */
#if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
    if( 3 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    session->ticket_len = ( p[0] << 16 ) | ( p[1] << 8 ) | p[2];
    p += 3;

    if( session->ticket_len != 0 )
    {
        if( session->ticket_len > (size_t)( end - p ) )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        session->ticket = mbedtls_calloc( 1, session->ticket_len );
        if( session->ticket == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

        memcpy( session->ticket, p, session->ticket_len );
        p += session->ticket_len;
    }

    if( 4 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    session->ticket_lifetime = Read32be(p);
    p += 4;
#endif /* MBEDTLS_SSL_SESSION_TICKETS && MBEDTLS_SSL_CLI_C */

    /*
     * Misc extension-related info
     */
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
    if( 1 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    session->mfl_code = *p++;
#endif

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
    if( 1 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    session->encrypt_then_mac = *p++;
#endif

    /* Done, should have consumed entire buffer */
    if( p != end )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    return( 0 );
}

/**
 * \brief          Load serialized session data into a session structure.
 *                 On client, this can be used for loading saved sessions
 *                 before resuming them with mbedstls_ssl_set_session().
 *                 On server, this can be used for alternative implementations
 *                 of session cache or session tickets.
 *
 * \warning        If a peer certificate chain is associated with the session,
 *                 the serialized state will only contain the peer's
 *                 end-entity certificate and the result of the chain
 *                 verification (unless verification was disabled), but not
 *                 the rest of the chain.
 *
 * \see            mbedtls_ssl_session_save()
 * \see            mbedtls_ssl_set_session()
 *
 * \param session  The session structure to be populated. It must have been
 *                 initialised with mbedtls_ssl_session_init() but not
 *                 populated yet.
 * \param buf      The buffer holding the serialized session data. It must be a
 *                 readable buffer of at least \p len bytes.
 * \param len      The size of the serialized data in bytes.
 *
 * \return         \c 0 if successful.
 * \return         #MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed.
 * \return         #MBEDTLS_ERR_SSL_BAD_INPUT_DATA if input data is invalid.
 * \return         #MBEDTLS_ERR_SSL_VERSION_MISMATCH if the serialized data
 *                 was generated in a different version or configuration of
 *                 Mbed TLS.
 * \return         Another negative value for other kinds of errors (for
 *                 example, unsupported features in the embedded certificate).
 */
int mbedtls_ssl_session_load( mbedtls_ssl_session *session,
                              const unsigned char *buf,
                              size_t len )
{
    int ret = ssl_session_load( session, 0, buf, len );

    if( ret != 0 )
        mbedtls_ssl_session_free( session );

    return( ret );
}

/**
 * \brief          Perform a single step of the SSL handshake
 *
 * \note           The state of the context (ssl->state) will be at
 *                 the next state after this function returns \c 0. Do not
 *                 call this function if state is MBEDTLS_SSL_HANDSHAKE_OVER.
 *
 * \param ssl      SSL context
 *
 * \return         See mbedtls_ssl_handshake().
 *
 * \warning        If this function returns something other than \c 0,
 *                 #MBEDTLS_ERR_SSL_WANT_READ, #MBEDTLS_ERR_SSL_WANT_WRITE,
 *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or
 *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS, you must stop using
 *                 the SSL context for reading or writing, and either free it
 *                 or call \c mbedtls_ssl_session_reset() on it before
 *                 re-using it for a new connection; the current connection
 *                 must be closed.
 */
int mbedtls_ssl_handshake_step( mbedtls_ssl_context *ssl )
{
    if( ssl == NULL || ssl->conf == NULL || ssl->conf->f_step == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    return ssl->conf->f_step(ssl);
}

/**
 * \brief          Perform the SSL handshake
 *
 * \param ssl      SSL context
 *
 * \return         \c 0 if successful.
 * \return         #MBEDTLS_ERR_SSL_WANT_READ or #MBEDTLS_ERR_SSL_WANT_WRITE
 *                 if the handshake is incomplete and waiting for data to
 *                 be available for reading from or writing to the underlying
 *                 transport - in this case you must call this function again
 *                 when the underlying transport is ready for the operation.
 * \return         #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS if an asynchronous
 *                 operation is in progress (see
 *                 mbedtls_ssl_conf_async_private_cb()) - in this case you
 *                 must call this function again when the operation is ready.
 * \return         #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS if a cryptographic
 *                 operation is in progress (see mbedtls_ecp_set_max_ops()) -
 *                 in this case you must call this function again to complete
 *                 the handshake when you're done attending other tasks.
 * \return         #MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED if DTLS is in use
 *                 and the client did not demonstrate reachability yet - in
 *                 this case you must stop using the context (see below).
 * \return         Another SSL error code - in this case you must stop using
 *                 the context (see below).
 *
 * \warning        If this function returns something other than
 *                 \c 0,
 *                 #MBEDTLS_ERR_SSL_WANT_READ,
 *                 #MBEDTLS_ERR_SSL_WANT_WRITE,
 *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or
 *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS,
 *                 you must stop using the SSL context for reading or writing,
 *                 and either free it or call \c mbedtls_ssl_session_reset()
 *                 on it before re-using it for a new connection; the current
 *                 connection must be closed.
 *
 * \note           If DTLS is in use, then you may choose to handle
 *                 #MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED specially for logging
 *                 purposes, as it is an expected return value rather than an
 *                 actual error, but you still need to reset/free the context.
 *
 * \note           Remarks regarding event-driven DTLS:
 *                 If the function returns #MBEDTLS_ERR_SSL_WANT_READ, no datagram
 *                 from the underlying transport layer is currently being processed,
 *                 and it is safe to idle until the timer or the underlying transport
 *                 signal a new event. This is not true for a successful handshake,
 *                 in which case the datagram of the underlying transport that is
 *                 currently being processed might or might not contain further
 *                 DTLS records.
 */
int mbedtls_ssl_handshake( mbedtls_ssl_context *ssl )
{
    int ret = 0;

    /* Sanity checks */

    if( ssl == NULL || ssl->conf == NULL || ssl->conf->f_step == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
        ( ssl->f_set_timer == NULL || ssl->f_get_timer == NULL ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "You must use "
                                     "mbedtls_ssl_set_timer_cb() for DTLS" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
#endif /* MBEDTLS_SSL_PROTO_DTLS */

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> handshake" ) );

    /* Main handshake loop */
    while( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
    {
        ret = ssl->conf->f_step( ssl );

        if( ret != 0 )
            break;
    }

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= handshake" ) );

    return( ret );
}

#if defined(MBEDTLS_SSL_RENEGOTIATION)
#if defined(MBEDTLS_SSL_SRV_C)
/*
 * Write HelloRequest to request renegotiation on server
 */
static int ssl_write_hello_request( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write hello request" ) );

    ssl->out_msglen  = 4;
    ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
    ssl->out_msg[0]  = MBEDTLS_SSL_HS_HELLO_REQUEST;

    if( ( ret = mbedtls_ssl_write_handshake_msg( ssl ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_handshake_msg", ret );
        return( ret );
    }

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write hello request" ) );

    return( 0 );
}
#endif /* MBEDTLS_SSL_SRV_C */

/*
 * Actually renegotiate current connection, triggered by either:
 * - any side: calling mbedtls_ssl_renegotiate(),
 * - client: receiving a HelloRequest during mbedtls_ssl_read(),
 * - server: receiving any handshake message on server during mbedtls_ssl_read() after
 *   the initial handshake is completed.
 * If the handshake doesn't complete due to waiting for I/O, it will continue
 * during the next calls to mbedtls_ssl_renegotiate() or mbedtls_ssl_read() respectively.
 */
int mbedtls_ssl_start_renegotiation( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> renegotiate" ) );

    if( ( ret = ssl_handshake_init( ssl ) ) != 0 )
        return( ret );

    /* RFC 6347 4.2.2: "[...] the HelloRequest will have message_seq = 0 and
     * the ServerHello will have message_seq = 1" */
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
        ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING )
    {
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
            ssl->handshake->out_msg_seq = 1;
        else
            ssl->handshake->in_msg_seq = 1;
    }
#endif

    ssl->state = MBEDTLS_SSL_HELLO_REQUEST;
    ssl->renego_status = MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS;

    if( ( ret = mbedtls_ssl_handshake( ssl ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_handshake", ret );
        return( ret );
    }

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= renegotiate" ) );

    return( 0 );
}

/**
 * \brief          Initiate an SSL renegotiation on the running connection.
 *                 Client: perform the renegotiation right now.
 *                 Server: request renegotiation, which will be performed
 *                 during the next call to mbedtls_ssl_read() if honored by
 *                 client.
 *
 * \param ssl      SSL context
 *
 * \return         0 if successful, or any mbedtls_ssl_handshake() return
 *                 value except #MBEDTLS_ERR_SSL_CLIENT_RECONNECT that can't
 *                 happen during a renegotiation.
 *
 * \warning        If this function returns something other than \c 0,
 *                 #MBEDTLS_ERR_SSL_WANT_READ, #MBEDTLS_ERR_SSL_WANT_WRITE,
 *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or
 *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS, you must stop using
 *                 the SSL context for reading or writing, and either free it
 *                 or call \c mbedtls_ssl_session_reset() on it before
 *                 re-using it for a new connection; the current connection
 *                 must be closed.
 *
 */
int mbedtls_ssl_renegotiate( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;

    if( ssl == NULL || ssl->conf == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

#if defined(MBEDTLS_SSL_SRV_C)
    /* On server, just send the request */
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        ssl->renego_status = MBEDTLS_SSL_RENEGOTIATION_PENDING;

        /* Did we already try/start sending HelloRequest? */
        if( ssl->out_left != 0 )
            return( mbedtls_ssl_flush_output( ssl ) );

        return( ssl_write_hello_request( ssl ) );
    }
#endif /* MBEDTLS_SSL_SRV_C */

#if defined(MBEDTLS_SSL_CLI_C)
    /*
     * On client, either start the renegotiation process or,
     * if already in progress, continue the handshake
     */
    if( ssl->renego_status != MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
    {
        if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        if( ( ret = mbedtls_ssl_start_renegotiation( ssl ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_start_renegotiation", ret );
            return( ret );
        }
    }
    else
    {
        if( ( ret = mbedtls_ssl_handshake( ssl ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_handshake", ret );
            return( ret );
        }
    }
#endif /* MBEDTLS_SSL_CLI_C */

    return( ret );
}
#endif /* MBEDTLS_SSL_RENEGOTIATION */

#if defined(MBEDTLS_X509_CRT_PARSE_C)
void mbedtls_ssl_key_cert_free( mbedtls_ssl_key_cert *key_cert )
{
    mbedtls_ssl_key_cert *cur = key_cert, *next;
    while( cur != NULL )
    {
        next = cur->next;
        mbedtls_free( cur );
        cur = next;
    }
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

/**
 * \brief           Free referenced items in an SSL handshake context and clear
 *                  memory
 *
 * \param ssl       SSL context
 */
void mbedtls_ssl_handshake_free( mbedtls_ssl_context *ssl )
{
    mbedtls_ssl_handshake_params *handshake = ssl->handshake;
    if( handshake == NULL )
        return;
#if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
    if( ssl->conf->f_async_cancel != NULL && handshake->async_in_progress != 0 )
    {
        ssl->conf->f_async_cancel( ssl );
        handshake->async_in_progress = 0;
    }
#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_1)
    mbedtls_md5_free(    &handshake->fin_md5  );
    mbedtls_sha1_free(   &handshake->fin_sha1 );
#endif
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
    mbedtls_sha256_free(   &handshake->fin_sha256    );
#endif
#if defined(MBEDTLS_SHA512_C)
    mbedtls_sha512_free(   &handshake->fin_sha512    );
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
#if defined(MBEDTLS_DHM_C)
    mbedtls_dhm_free( &handshake->dhm_ctx );
#endif
#if defined(MBEDTLS_ECDH_C)
    mbedtls_ecdh_free( &handshake->ecdh_ctx );
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    mbedtls_ecjpake_free( &handshake->ecjpake_ctx );
#if defined(MBEDTLS_SSL_CLI_C)
    mbedtls_free( handshake->ecjpake_cache );
    handshake->ecjpake_cache = NULL;
    handshake->ecjpake_cache_len = 0;
#endif
#endif
#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    /* explicit void pointer cast for buggy MS compiler */
    mbedtls_free( (void *) handshake->curves );
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
    if( handshake->psk != NULL )
    {
        mbedtls_platform_zeroize( handshake->psk, handshake->psk_len );
        mbedtls_free( handshake->psk );
    }
#endif
#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
    defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
    /*
     * Free only the linked list wrapper, not the keys themselves
     * since the belong to the SNI callback
     */
    if( handshake->sni_key_cert != NULL )
    {
        mbedtls_ssl_key_cert *cur = handshake->sni_key_cert, *next;
        while( cur != NULL )
        {
            next = cur->next;
            mbedtls_free( cur );
            cur = next;
        }
    }
#endif /* MBEDTLS_X509_CRT_PARSE_C && MBEDTLS_SSL_SERVER_NAME_INDICATION */
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    mbedtls_x509_crt_restart_free( &handshake->ecrs_ctx );
    if( handshake->ecrs_peer_cert != NULL )
    {
        mbedtls_x509_crt_free( handshake->ecrs_peer_cert );
        mbedtls_free( handshake->ecrs_peer_cert );
    }
#endif
#if defined(MBEDTLS_X509_CRT_PARSE_C) &&        \
    !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    mbedtls_pk_free( &handshake->peer_pubkey );
#endif /* MBEDTLS_X509_CRT_PARSE_C && !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    mbedtls_free( handshake->verify_cookie );
    mbedtls_ssl_flight_free( handshake->flight );
    mbedtls_ssl_buffering_free( ssl );
#endif
    mbedtls_platform_zeroize( handshake,
                              sizeof( mbedtls_ssl_handshake_params ) );
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    /* If the buffers are too big - reallocate. Because of the way Mbed TLS
     * processes datagrams and the fact that a datagram is allowed to have
     * several records in it, it is possible that the I/O buffers are not
     * empty at this stage */
    handle_buffer_resizing( ssl, 1, mbedtls_ssl_get_input_buflen( ssl ),
                                    mbedtls_ssl_get_output_buflen( ssl ) );
#endif
}

/**
 * \brief          Free referenced items in an SSL session including the
 *                 peer certificate and clear memory
 *
 * \note           A session object can be freed even if the SSL context
 *                 that was used to retrieve the session is still in use.
 *
 * \param session  SSL session
 */
void mbedtls_ssl_session_free( mbedtls_ssl_session *session )
{
    if( session == NULL )
        return;

#if defined(MBEDTLS_X509_CRT_PARSE_C)
    ssl_clear_peer_cert( session );
#endif

#if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
    mbedtls_free( session->ticket );
#endif

    mbedtls_platform_zeroize( session, sizeof( mbedtls_ssl_session ) );
}

#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_CONNECTION_ID 1u
#else
#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_CONNECTION_ID 0u
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_BADMAC_LIMIT 1u
#else
#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_BADMAC_LIMIT 0u
#endif /* MBEDTLS_SSL_DTLS_BADMAC_LIMIT */

#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_ANTI_REPLAY 1u
#else
#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_ANTI_REPLAY 0u
#endif /* MBEDTLS_SSL_DTLS_ANTI_REPLAY */

#if defined(MBEDTLS_SSL_ALPN)
#define SSL_SERIALIZED_CONTEXT_CONFIG_ALPN 1u
#else
#define SSL_SERIALIZED_CONTEXT_CONFIG_ALPN 0u
#endif /* MBEDTLS_SSL_ALPN */

#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_CONNECTION_ID_BIT    0
#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_BADMAC_LIMIT_BIT     1
#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_ANTI_REPLAY_BIT      2
#define SSL_SERIALIZED_CONTEXT_CONFIG_ALPN_BIT                  3

#define SSL_SERIALIZED_CONTEXT_CONFIG_BITFLAG   \
    ( (uint32_t) (                              \
        ( SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_CONNECTION_ID     << SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_CONNECTION_ID_BIT     ) | \
        ( SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_BADMAC_LIMIT      << SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_BADMAC_LIMIT_BIT      ) | \
        ( SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_ANTI_REPLAY       << SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_ANTI_REPLAY_BIT       ) | \
        ( SSL_SERIALIZED_CONTEXT_CONFIG_ALPN                   << SSL_SERIALIZED_CONTEXT_CONFIG_ALPN_BIT                   ) | \
        0u ) )

static unsigned char ssl_serialized_context_header[] = {
    MBEDTLS_VERSION_MAJOR,
    MBEDTLS_VERSION_MINOR,
    MBEDTLS_VERSION_PATCH,
    ( SSL_SERIALIZED_SESSION_CONFIG_BITFLAG >>  8 ) & 0xFF,
    ( SSL_SERIALIZED_SESSION_CONFIG_BITFLAG >>  0 ) & 0xFF,
    ( SSL_SERIALIZED_CONTEXT_CONFIG_BITFLAG >> 16 ) & 0xFF,
    ( SSL_SERIALIZED_CONTEXT_CONFIG_BITFLAG >>  8 ) & 0xFF,
    ( SSL_SERIALIZED_CONTEXT_CONFIG_BITFLAG >>  0 ) & 0xFF,
};

/**
 * Serialize a full SSL context
 *
 * The format of the serialized data is:
 * (in the presentation language of TLS, RFC 8446 section 3)
 *
 *  // header
 *  opaque mbedtls_version[3];   // major, minor, patch
 *  opaque context_format[5];    // version-specific field determining
 *                               // the format of the remaining
 *                               // serialized data.
 *  Note: When updating the format, remember to keep these
 *        version+format bytes. (We may make their size part of the API.)
 *
 *  // session sub-structure
 *  opaque session<1..2^32-1>;  // see mbedtls_ssl_session_save()
 *  // transform sub-structure
 *  uint8 random[64];           // ServerHello.random+ClientHello.random
 *  uint8 in_cid<0..2^8-1>      // Connection ID: expected incoming value
 *  uint8 out_cid<0..2^8-1>     // Connection ID: outgoing value to use
 *  // fields from ssl_context
 *  uint32 badmac_seen;         // DTLS: number of records with failing MAC
 *  uint64 in_window_top;       // DTLS: last validated record seq_num
 *  uint64 in_window;           // DTLS: bitmask for replay protection
 *  uint8 disable_datagram_packing; // DTLS: only one record per datagram
 *  uint64 cur_out_ctr;         // Record layer: outgoing sequence number
 *  uint16 mtu;                 // DTLS: path mtu (max outgoing fragment size)
 *  uint8 alpn_chosen<0..2^8-1> // ALPN: negotiated application protocol
 *
 * Note that many fields of the ssl_context or sub-structures are not
 * serialized, as they fall in one of the following categories:
 *
 *  1. forced value (eg in_left must be 0)
 *  2. pointer to dynamically-allocated memory (eg session, transform)
 *  3. value can be re-derived from other data (eg session keys from MS)
 *  4. value was temporary (eg content of input buffer)
 *  5. value will be provided by the user again (eg I/O callbacks and context)
 *
 * \brief          Save an active connection as serialized data in a buffer.
 *                 This allows the freeing or re-using of the SSL context
 *                 while still picking up the connection later in a way that
 *                 it entirely transparent to the peer.
 *
 * \see            mbedtls_ssl_context_load()
 *
 * \note           This feature is currently only available under certain
 *                 conditions, see the documentation of the return value
 *                 #MBEDTLS_ERR_SSL_BAD_INPUT_DATA for details.
 *
 * \note           When this function succeeds, it calls
 *                 mbedtls_ssl_session_reset() on \p ssl which as a result is
 *                 no longer associated with the connection that has been
 *                 serialized. This avoids creating copies of the connection
 *                 state. You're then free to either re-use the context
 *                 structure for a different connection, or call
 *                 mbedtls_ssl_free() on it. See the documentation of
 *                 mbedtls_ssl_session_reset() for more details.
 *
 * \param ssl      The SSL context to save. On success, it is no longer
 *                 associated with the connection that has been serialized.
 * \param buf      The buffer to write the serialized data to. It must be a
 *                 writeable buffer of at least \p buf_len bytes, or may be \c
 *                 NULL if \p buf_len is \c 0.
 * \param buf_len  The number of bytes available for writing in \p buf.
 * \param olen     The size in bytes of the data that has been or would have
 *                 been written. It must point to a valid \c size_t.
 *
 * \note           \p olen is updated to the correct value regardless of
 *                 whether \p buf_len was large enough. This makes it possible
 *                 to determine the necessary size by calling this function
 *                 with \p buf set to \c NULL and \p buf_len to \c 0. However,
 *                 the value of \p olen is only guaranteed to be correct when
 *                 the function returns #MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL or
 *                 \c 0. If the return value is different, then the value of
 *                 \p olen is undefined.
 *
 * \return         \c 0 if successful.
 * \return         #MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL if \p buf is too small.
 * \return         #MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed
 *                 while reseting the context.
 * \return         #MBEDTLS_ERR_SSL_BAD_INPUT_DATA if a handshake is in
 *                 progress, or there is pending data for reading or sending,
 *                 or the connection does not use DTLS 1.2 with an AEAD
 *                 ciphersuite, or renegotiation is enabled.
 */
int mbedtls_ssl_context_save( mbedtls_ssl_context *ssl,
                              unsigned char *buf,
                              size_t buf_len,
                              size_t *olen )
{
    unsigned char *p = buf;
    size_t used = 0;
    size_t session_len;
    int ret = 0;

    /*
     * Enforce usage restrictions, see "return BAD_INPUT_DATA" in
     * this function's documentation.
     *
     * These are due to assumptions/limitations in the implementation. Some of
     * them are likely to stay (no handshake in progress) some might go away
     * (only DTLS) but are currently used to simplify the implementation.
     */
    /* The initial handshake must be over */
    if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Initial handshake isn't over" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    if( ssl->handshake != NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Handshake isn't completed" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    /* Double-check that sub-structures are indeed ready */
    if( ssl->transform == NULL || ssl->session == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Serialised structures aren't ready" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    /* There must be no pending incoming or outgoing data */
    if( mbedtls_ssl_check_pending( ssl ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "There is pending incoming data" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    if( ssl->out_left != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "There is pending outgoing data" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    /* Protocol must be DLTS, not TLS */
    if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Only DTLS is supported" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    /* Version must be 1.2 */
    if( ssl->major_ver != MBEDTLS_SSL_MAJOR_VERSION_3 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Only version 1.2 supported" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    if( ssl->minor_ver != MBEDTLS_SSL_MINOR_VERSION_3 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Only version 1.2 supported" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    /* We must be using an AEAD ciphersuite */
    if( mbedtls_ssl_transform_uses_aead( ssl->transform ) != 1 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Only AEAD ciphersuites supported" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
    /* Renegotiation must not be enabled */
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    if( ssl->conf->disable_renegotiation != MBEDTLS_SSL_RENEGOTIATION_DISABLED )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Renegotiation must not be enabled" ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
#endif

    /*
     * Version and format identifier
     */
    used += sizeof( ssl_serialized_context_header );

    if( used <= buf_len )
    {
        p = mempcpy( p, ssl_serialized_context_header,
                     sizeof( ssl_serialized_context_header ) );
    }

    /*
     * Session (length + data)
     */
    ret = ssl_session_save( ssl->session, 1, NULL, 0, &session_len );
    if( ret != MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL )
        return( ret );

    used += 4 + session_len;
    if( used <= buf_len )
    {
        p = Write32be(p, session_len);
        ret = ssl_session_save( ssl->session, 1,
                                p, session_len, &session_len );
        if( ret != 0 )
            return( ret );
        p += session_len;
    }

    /*
     * Transform
     */
    used += sizeof( ssl->transform->randbytes );
    if( used <= buf_len )
    {
        memcpy( p, ssl->transform->randbytes,
           sizeof( ssl->transform->randbytes ) );
        p += sizeof( ssl->transform->randbytes );
    }

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
    used += 2 + ssl->transform->in_cid_len + ssl->transform->out_cid_len;
    if( used <= buf_len )
    {
        *p++ = ssl->transform->in_cid_len;
        memcpy( p, ssl->transform->in_cid, ssl->transform->in_cid_len );
        p += ssl->transform->in_cid_len;

        *p++ = ssl->transform->out_cid_len;
        memcpy( p, ssl->transform->out_cid, ssl->transform->out_cid_len );
        p += ssl->transform->out_cid_len;
    }
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

    /*
     * Saved fields from top-level ssl_context structure
     */
#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
    used += 4;
    if( used <= buf_len )
    {
        p = Write32be(p, ssl->badmac_seen);
    }
#endif /* MBEDTLS_SSL_DTLS_BADMAC_LIMIT */

#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
    used += 16;
    if( used <= buf_len )
    {
        p = Write64be(p, ssl->in_window_top);
        p = Write64be(p, ssl->in_window);
    }
#endif /* MBEDTLS_SSL_DTLS_ANTI_REPLAY */

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    used += 1;
    if( used <= buf_len )
    {
        *p++ = ssl->disable_datagram_packing;
    }
#endif /* MBEDTLS_SSL_PROTO_DTLS */

    used += 8;
    if( used <= buf_len )
    {
        memcpy( p, ssl->cur_out_ctr, 8 );
        p += 8;
    }

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    used += 2;
    if( used <= buf_len )
    {
        *p++ = (unsigned char)( ( ssl->mtu >>  8 ) & 0xFF );
        *p++ = (unsigned char)( ( ssl->mtu       ) & 0xFF );
    }
#endif /* MBEDTLS_SSL_PROTO_DTLS */

#if defined(MBEDTLS_SSL_ALPN)
    {
        const uint8_t alpn_len = ssl->alpn_chosen
                               ? (uint8_t) strlen( ssl->alpn_chosen )
                               : 0;

        used += 1 + alpn_len;
        if( used <= buf_len )
        {
            *p++ = alpn_len;

            if( ssl->alpn_chosen != NULL )
            {
                memcpy( p, ssl->alpn_chosen, alpn_len );
                p += alpn_len;
            }
        }
    }
#endif /* MBEDTLS_SSL_ALPN */

    /*
     * Done
     */
    *olen = used;

    if( used > buf_len )
        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );

    MBEDTLS_SSL_DEBUG_BUF( 4, "saved context", buf, used );

    return( mbedtls_ssl_session_reset_int( ssl, 0 ) );
}

/*
 * Helper to get TLS 1.2 PRF from ciphersuite
 * (Duplicates bits of logic from ssl_set_handshake_prfs().)
 */
typedef int (*tls_prf_fn)( const unsigned char *secret, size_t slen,
                           const char *label,
                           const unsigned char *random, size_t rlen,
                           unsigned char *dstbuf, size_t dlen );
static tls_prf_fn ssl_tls12prf_from_cs( int ciphersuite_id )
{
#if defined(MBEDTLS_SHA512_C)
    const mbedtls_ssl_ciphersuite_t * const ciphersuite_info =
         mbedtls_ssl_ciphersuite_from_id( ciphersuite_id );

    if( ciphersuite_info->mac == MBEDTLS_MD_SHA384 )
        return( tls_prf_sha384 );
#else
    (void) ciphersuite_id;
#endif
    return( tls_prf_sha256 );
}

/*
 * Deserialize context, see mbedtls_ssl_context_save() for format.
 *
 * This internal version is wrapped by a public function that cleans up in
 * case of error.
 */
static int ssl_context_load( mbedtls_ssl_context *ssl,
                             const unsigned char *buf,
                             size_t len )
{
    const unsigned char *p = buf;
    const unsigned char * const end = buf + len;
    size_t session_len;
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;

    /*
     * The context should have been freshly setup or reset.
     * Give the user an error in case of obvious misuse.
     * (Checking session is useful because it won't be NULL if we're
     * renegotiating, or if the user mistakenly loaded a session first.)
     */
    if( ssl->state != MBEDTLS_SSL_HELLO_REQUEST ||
        ssl->session != NULL )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    /*
     * We can't check that the config matches the initial one, but we can at
     * least check it matches the requirements for serializing.
     */
    if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM ||
        ssl->conf->max_major_ver < MBEDTLS_SSL_MAJOR_VERSION_3 ||
        ssl->conf->min_major_ver > MBEDTLS_SSL_MAJOR_VERSION_3 ||
        ssl->conf->max_minor_ver < MBEDTLS_SSL_MINOR_VERSION_3 ||
        ssl->conf->min_minor_ver > MBEDTLS_SSL_MINOR_VERSION_3 ||
#if defined(MBEDTLS_SSL_RENEGOTIATION)
        ssl->conf->disable_renegotiation != MBEDTLS_SSL_RENEGOTIATION_DISABLED ||
#endif
        0 )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    MBEDTLS_SSL_DEBUG_BUF( 4, "context to load", buf, len );

    /*
     * Check version identifier
     */
    if( (size_t)( end - p ) < sizeof( ssl_serialized_context_header ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    if( timingsafe_bcmp( p, ssl_serialized_context_header,
                         sizeof( ssl_serialized_context_header ) ) != 0 )
    {
        return( MBEDTLS_ERR_SSL_VERSION_MISMATCH );
    }
    p += sizeof( ssl_serialized_context_header );

    /*
     * Session
     */
    if( (size_t)( end - p ) < 4 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    session_len = ( (size_t) p[0] << 24 ) |
                  ( (size_t) p[1] << 16 ) |
                  ( (size_t) p[2] <<  8 ) |
                  ( (size_t) p[3]       );
    p += 4;

    /* This has been allocated by ssl_handshake_init(), called by
     * by either mbedtls_ssl_session_reset_int() or mbedtls_ssl_setup(). */
    ssl->session = ssl->session_negotiate;
    ssl->session_in = ssl->session;
    ssl->session_out = ssl->session;
    ssl->session_negotiate = NULL;

    if( (size_t)( end - p ) < session_len )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ret = ssl_session_load( ssl->session, 1, p, session_len );
    if( ret != 0 )
    {
        mbedtls_ssl_session_free( ssl->session );
        return( ret );
    }

    p += session_len;

    /*
     * Transform
     */

    /* This has been allocated by ssl_handshake_init(), called by
     * by either mbedtls_ssl_session_reset_int() or mbedtls_ssl_setup(). */
    ssl->transform = ssl->transform_negotiate;
    ssl->transform_in = ssl->transform;
    ssl->transform_out = ssl->transform;
    ssl->transform_negotiate = NULL;

    /* Read random bytes and populate structure */
    if( (size_t)( end - p ) < sizeof( ssl->transform->randbytes ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ret = ssl_populate_transform( ssl->transform,
                  ssl->session->ciphersuite,
                  ssl->session->master,
#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                  ssl->session->encrypt_then_mac,
#endif
#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
                  ssl->session->trunc_hmac,
#endif
#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
#if defined(MBEDTLS_ZLIB_SUPPORT)
                  ssl->session->compression,
#endif
                  ssl_tls12prf_from_cs( ssl->session->ciphersuite ),
                  p, /* currently pointing to randbytes */
                  MBEDTLS_SSL_MINOR_VERSION_3, /* (D)TLS 1.2 is forced */
                  ssl->conf->endpoint,
                  ssl );
    if( ret != 0 )
        return( ret );

    p += sizeof( ssl->transform->randbytes );

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
    /* Read connection IDs and store them */
    if( (size_t)( end - p ) < 1 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl->transform->in_cid_len = *p++;

    if( (size_t)( end - p ) < ssl->transform->in_cid_len + 1u )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    memcpy( ssl->transform->in_cid, p, ssl->transform->in_cid_len );
    p += ssl->transform->in_cid_len;

    ssl->transform->out_cid_len = *p++;

    if( (size_t)( end - p ) < ssl->transform->out_cid_len )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    memcpy( ssl->transform->out_cid, p, ssl->transform->out_cid_len );
    p += ssl->transform->out_cid_len;
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

    /*
     * Saved fields from top-level ssl_context structure
     */
#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
    if( (size_t)( end - p ) < 4 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl->badmac_seen = ( (uint32_t) p[0] << 24 ) |
                       ( (uint32_t) p[1] << 16 ) |
                       ( (uint32_t) p[2] <<  8 ) |
                       ( (uint32_t) p[3]       );
    p += 4;
#endif /* MBEDTLS_SSL_DTLS_BADMAC_LIMIT */

#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
    if( (size_t)( end - p ) < 16 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl->in_window_top = ( (uint64_t) p[0] << 56 ) |
                         ( (uint64_t) p[1] << 48 ) |
                         ( (uint64_t) p[2] << 40 ) |
                         ( (uint64_t) p[3] << 32 ) |
                         ( (uint64_t) p[4] << 24 ) |
                         ( (uint64_t) p[5] << 16 ) |
                         ( (uint64_t) p[6] <<  8 ) |
                         ( (uint64_t) p[7]       );
    p += 8;

    ssl->in_window = ( (uint64_t) p[0] << 56 ) |
                     ( (uint64_t) p[1] << 48 ) |
                     ( (uint64_t) p[2] << 40 ) |
                     ( (uint64_t) p[3] << 32 ) |
                     ( (uint64_t) p[4] << 24 ) |
                     ( (uint64_t) p[5] << 16 ) |
                     ( (uint64_t) p[6] <<  8 ) |
                     ( (uint64_t) p[7]       );
    p += 8;
#endif /* MBEDTLS_SSL_DTLS_ANTI_REPLAY */

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( (size_t)( end - p ) < 1 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl->disable_datagram_packing = *p++;
#endif /* MBEDTLS_SSL_PROTO_DTLS */

    if( (size_t)( end - p ) < 8 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    memcpy( ssl->cur_out_ctr, p, 8 );
    p += 8;

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( (size_t)( end - p ) < 2 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl->mtu = ( p[0] << 8 ) | p[1];
    p += 2;
#endif /* MBEDTLS_SSL_PROTO_DTLS */

#if defined(MBEDTLS_SSL_ALPN)
    {
        uint8_t alpn_len;
        const char **cur;

        if( (size_t)( end - p ) < 1 )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        alpn_len = *p++;

        if( alpn_len != 0 && ssl->conf->alpn_list != NULL )
        {
            /* alpn_chosen should point to an item in the configured list */
            for( cur = ssl->conf->alpn_list; *cur != NULL; cur++ )
            {
                if( strlen( *cur ) == alpn_len &&
                    timingsafe_bcmp( p, cur, alpn_len ) == 0 )
                {
                    ssl->alpn_chosen = *cur;
                    break;
                }
            }
        }

        /* can only happen on conf mismatch */
        if( alpn_len != 0 && ssl->alpn_chosen == NULL )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

        p += alpn_len;
    }
#endif /* MBEDTLS_SSL_ALPN */

    /*
     * Forced fields from top-level ssl_context structure
     *
     * Most of them already set to the correct value by mbedtls_ssl_init() and
     * mbedtls_ssl_reset(), so we only need to set the remaining ones.
     */
    ssl->state = MBEDTLS_SSL_HANDSHAKE_OVER;

    ssl->major_ver = MBEDTLS_SSL_MAJOR_VERSION_3;
    ssl->minor_ver = MBEDTLS_SSL_MINOR_VERSION_3;

    /* Adjust pointers for header fields of outgoing records to
     * the given transform, accounting for explicit IV and CID. */
    mbedtls_ssl_update_out_pointers( ssl, ssl->transform );

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    ssl->in_epoch = 1;
#endif

    /* mbedtls_ssl_reset() leaves the handshake sub-structure allocated,
     * which we don't want - otherwise we'd end up freeing the wrong transform
     * by calling mbedtls_ssl_handshake_wrapup_free_hs_transform()
     * inappropriately. */
    if( ssl->handshake != NULL )
    {
        mbedtls_ssl_handshake_free( ssl );
        mbedtls_free( ssl->handshake );
        ssl->handshake = NULL;
    }

    /*
     * Done - should have consumed entire buffer
     */
    if( p != end )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    return( 0 );
}

/**
 * \brief          Load serialized connection data to an SSL context.
 *
 * \see            mbedtls_ssl_context_save()
 *
 * \warning        The same serialized data must never be loaded into more
 *                 that one context. In order to ensure that, after
 *                 successfully loading serialized data to an SSL context, you
 *                 should immediately destroy or invalidate all copies of the
 *                 serialized data that was loaded. Loading the same data in
 *                 more than one context would cause severe security failures
 *                 including but not limited to loss of confidentiality.
 *
 * \note           Before calling this function, the SSL context must be
 *                 prepared in one of the two following ways. The first way is
 *                 to take a context freshly initialised with
 *                 mbedtls_ssl_init() and call mbedtls_ssl_setup() on it with
 *                 the same ::mbedtls_ssl_config structure that was used in
 *                 the original connection. The second way is to
 *                 call mbedtls_ssl_session_reset() on a context that was
 *                 previously prepared as above but used in the meantime.
 *                 Either way, you must not use the context to perform a
 *                 handshake between calling mbedtls_ssl_setup() or
 *                 mbedtls_ssl_session_reset() and calling this function. You
 *                 may however call other setter functions in that time frame
 *                 as indicated in the note below.
 *
 * \note           Before or after calling this function successfully, you
 *                 also need to configure some connection-specific callbacks
 *                 and settings before you can use the connection again
 *                 (unless they were already set before calling
 *                 mbedtls_ssl_session_reset() and the values are suitable for
 *                 the present connection). Specifically, you want to call
 *                 at least mbedtls_ssl_set_bio() and
 *                 mbedtls_ssl_set_timer_cb(). All other SSL setter functions
 *                 are not necessary to call, either because they're only used
 *                 in handshakes, or because the setting is already saved. You
 *                 might choose to call them anyway, for example in order to
 *                 share code between the cases of establishing a new
 *                 connection and the case of loading an already-established
 *                 connection.
 *
 * \note           If you have new information about the path MTU, you want to
 *                 call mbedtls_ssl_set_mtu() after calling this function, as
 *                 otherwise this function would overwrite your
 *                 newly-configured value with the value that was active when
 *                 the context was saved.
 *
 * \note           When this function returns an error code, it calls
 *                 mbedtls_ssl_free() on \p ssl. In this case, you need to
 *                 prepare the context with the usual sequence starting with a
 *                 call to mbedtls_ssl_init() if you want to use it again.
 *
 * \param ssl      The SSL context structure to be populated. It must have
 *                 been prepared as described in the note above.
 * \param buf      The buffer holding the serialized connection data. It must
 *                 be a readable buffer of at least \p len bytes.
 * \param len      The size of the serialized data in bytes.
 *
 * \return         \c 0 if successful.
 * \return         #MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed.
 * \return         #MBEDTLS_ERR_SSL_VERSION_MISMATCH if the serialized data
 *                 comes from a different Mbed TLS version or build.
 * \return         #MBEDTLS_ERR_SSL_BAD_INPUT_DATA if input data is invalid.
 */
int mbedtls_ssl_context_load( mbedtls_ssl_context *context,
                              const unsigned char *buf,
                              size_t len )
{
    int ret = ssl_context_load( context, buf, len );

    if( ret != 0 )
        mbedtls_ssl_free( context );

    return( ret );
}
#endif /* MBEDTLS_SSL_CONTEXT_SERIALIZATION */

/**
 * \brief          Free referenced items in an SSL context and clear memory
 *
 * \param ssl      SSL context
 */
void mbedtls_ssl_free( mbedtls_ssl_context *ssl )
{
    if( ssl == NULL )
        return;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> free" ) );

    if( ssl->out_buf != NULL )
    {
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
        size_t out_buf_len = ssl->out_buf_len;
#else
        size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
#endif

        mbedtls_platform_zeroize( ssl->out_buf, out_buf_len );
        mbedtls_free( ssl->out_buf );
        ssl->out_buf = NULL;
    }

    if( ssl->in_buf != NULL )
    {
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
        size_t in_buf_len = ssl->in_buf_len;
#else
        size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
#endif

        mbedtls_platform_zeroize( ssl->in_buf, in_buf_len );
        mbedtls_free( ssl->in_buf );
        ssl->in_buf = NULL;
    }

#if defined(MBEDTLS_ZLIB_SUPPORT)
    if( ssl->compress_buf != NULL )
    {
        mbedtls_platform_zeroize( ssl->compress_buf, MBEDTLS_SSL_COMPRESS_BUFFER_LEN );
        mbedtls_free( ssl->compress_buf );
    }
#endif

    if( ssl->transform )
    {
        mbedtls_ssl_transform_free( ssl->transform );
        mbedtls_free( ssl->transform );
    }

    if( ssl->handshake )
    {
        mbedtls_ssl_handshake_free( ssl );
        mbedtls_ssl_transform_free( ssl->transform_negotiate );
        mbedtls_ssl_session_free( ssl->session_negotiate );

        mbedtls_free( ssl->handshake );
        mbedtls_free( ssl->transform_negotiate );
        mbedtls_free( ssl->session_negotiate );
    }

    if( ssl->session )
    {
        mbedtls_ssl_session_free( ssl->session );
        mbedtls_free( ssl->session );
    }

#if defined(MBEDTLS_X509_CRT_PARSE_C)
    if( ssl->hostname != NULL )
    {
        mbedtls_platform_zeroize( ssl->hostname, strlen( ssl->hostname ) );
        mbedtls_free( ssl->hostname );
    }
#endif

#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
    if( mbedtls_ssl_hw_record_finish != NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "going for mbedtls_ssl_hw_record_finish()" ) );
        mbedtls_ssl_hw_record_finish( ssl );
    }
#endif

#if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY) && defined(MBEDTLS_SSL_SRV_C)
    mbedtls_free( ssl->cli_id );
#endif

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= free" ) );

    /* Actually clear after last debug message */
    mbedtls_platform_zeroize( ssl, sizeof( mbedtls_ssl_context ) );
}

/**
 * \brief          Initialize an SSL configuration context
 *                 Just makes the context ready for
 *                 mbedtls_ssl_config_defaults() or mbedtls_ssl_config_free().
 *
 * \note           You need to call mbedtls_ssl_config_defaults() unless you
 *                 manually set all of the relevant fields yourself.
 *
 * \param conf     SSL configuration context
 */
void mbedtls_ssl_config_init( mbedtls_ssl_config *conf )
{
    mbedtls_platform_zeroize( conf, sizeof( mbedtls_ssl_config ) );
}

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
static uint8_t ssl_preset_default_hashes[] = {
#if defined(MBEDTLS_SHA512_C)
    MBEDTLS_MD_SHA512,
    MBEDTLS_MD_SHA384,
#endif
#if defined(MBEDTLS_SHA256_C)
    MBEDTLS_MD_SHA256,
    MBEDTLS_MD_SHA224,
#endif
#if defined(MBEDTLS_SHA1_C) && defined(MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE)
    MBEDTLS_MD_SHA1,
#endif
    MBEDTLS_MD_NONE
};
#endif

static uint16_t ssl_preset_suiteb_ciphersuites[] = {
    MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
    MBEDTLS_TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
    MBEDTLS_TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384,
    MBEDTLS_TLS_ECDHE_PSK_WITH_AES_256_GCM_SHA384,
    0
};

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
static uint8_t ssl_preset_suiteb_hashes[] = {
    MBEDTLS_MD_SHA384,
    MBEDTLS_MD_NONE
};
#endif

#if defined(MBEDTLS_ECP_C)
static mbedtls_ecp_group_id ssl_preset_suiteb_curves[] = {
#if defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
    MBEDTLS_ECP_DP_SECP384R1,
#endif
#if defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
    MBEDTLS_ECP_DP_SECP256R1,
#endif
    MBEDTLS_ECP_DP_NONE
};
#endif

/*
 * Load default in mbedtls_ssl_config
 */
int mbedtls_ssl_config_defaults_impl( mbedtls_ssl_config *conf,
                                      int endpoint, int transport, int preset,
                                      int ssl_handshake_step(mbedtls_ssl_context *) )
{
#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C)
    int ret = MBEDTLS_ERR_THIS_CORRUPTION;
#endif
    conf->f_step = ssl_handshake_step;
    /* Use the functions here so that they are covered in tests,
     * but otherwise access member directly for efficiency */
    mbedtls_ssl_conf_endpoint( conf, endpoint );
    mbedtls_ssl_conf_transport( conf, transport );
    /*
     * Things that are common to all presets
     */
#if defined(MBEDTLS_SSL_CLI_C)
    if( endpoint == MBEDTLS_SSL_IS_CLIENT )
    {
        conf->authmode = MBEDTLS_SSL_VERIFY_REQUIRED;
#if defined(MBEDTLS_SSL_SESSION_TICKETS)
        conf->session_tickets = MBEDTLS_SSL_SESSION_TICKETS_ENABLED;
#endif
    }
#endif
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
    conf->encrypt_then_mac = MBEDTLS_SSL_ETM_ENABLED;
#endif
#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
    conf->extended_ms = MBEDTLS_SSL_EXTENDED_MS_ENABLED;
#endif
#if defined(MBEDTLS_SSL_CBC_RECORD_SPLITTING)
    conf->cbc_record_splitting = MBEDTLS_SSL_CBC_RECORD_SPLITTING_ENABLED;
#endif
#if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY) && defined(MBEDTLS_SSL_SRV_C)
    conf->f_cookie_write = ssl_cookie_write_dummy;
    conf->f_cookie_check = ssl_cookie_check_dummy;
#endif
#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
    conf->anti_replay = MBEDTLS_SSL_ANTI_REPLAY_ENABLED;
#endif
#if defined(MBEDTLS_SSL_SRV_C)
    conf->cert_req_ca_list = MBEDTLS_SSL_CERT_REQ_CA_LIST_ENABLED;
#endif
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    conf->hs_timeout_min = MBEDTLS_SSL_DTLS_TIMEOUT_DFL_MIN;
    conf->hs_timeout_max = MBEDTLS_SSL_DTLS_TIMEOUT_DFL_MAX;
#endif
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    conf->renego_max_records = MBEDTLS_SSL_RENEGO_MAX_RECORDS_DEFAULT;
    memset( conf->renego_period,     0x00, 2 );
    memset( conf->renego_period + 2, 0xFF, 6 );
#endif
#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C)
            if( endpoint == MBEDTLS_SSL_IS_SERVER )
            {
                const unsigned char dhm_p[] =
                    MBEDTLS_DHM_RFC3526_MODP_2048_P_BIN;
                const unsigned char dhm_g[] =
                    MBEDTLS_DHM_RFC3526_MODP_2048_G_BIN;
                if ( ( ret = mbedtls_ssl_conf_dh_param_bin( conf,
                                               dhm_p, sizeof( dhm_p ),
                                               dhm_g, sizeof( dhm_g ) ) ) != 0 )
                {
                    return( ret );
                }
            }
#endif
    /*
     * Preset-specific defaults
     */
    switch( preset )
    {
        /*
         * NSA Suite B
         */
        case MBEDTLS_SSL_PRESET_SUITEB:
            conf->min_major_ver = MBEDTLS_SSL_MAJOR_VERSION_3;
            conf->min_minor_ver = MBEDTLS_SSL_MINOR_VERSION_3; /* TLS 1.2 */
            conf->max_major_ver = MBEDTLS_SSL_MAX_MAJOR_VERSION;
            conf->max_minor_ver = MBEDTLS_SSL_MAX_MINOR_VERSION;
            conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_0] =
            conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_1] =
            conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_2] =
            conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_3] =
                                   ssl_preset_suiteb_ciphersuites;
#if defined(MBEDTLS_X509_CRT_PARSE_C)
            conf->cert_profile = &mbedtls_x509_crt_profile_suiteb;
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
            conf->sig_hashes = ssl_preset_suiteb_hashes;
#endif
#if defined(MBEDTLS_ECP_C)
            conf->curve_list = ssl_preset_suiteb_curves;
#endif
            break;
        /*
         * Default
         */
        default:
            conf->min_major_ver = ( MBEDTLS_SSL_MIN_MAJOR_VERSION >
                                    MBEDTLS_SSL_MIN_VALID_MAJOR_VERSION ) ?
                                    MBEDTLS_SSL_MIN_MAJOR_VERSION :
                                    MBEDTLS_SSL_MIN_VALID_MAJOR_VERSION;
            conf->min_minor_ver = ( MBEDTLS_SSL_MIN_MINOR_VERSION >
                                    MBEDTLS_SSL_MIN_VALID_MINOR_VERSION ) ?
                                    MBEDTLS_SSL_MIN_MINOR_VERSION :
                                    MBEDTLS_SSL_MIN_VALID_MINOR_VERSION;
            conf->max_major_ver = MBEDTLS_SSL_MAX_MAJOR_VERSION;
            conf->max_minor_ver = MBEDTLS_SSL_MAX_MINOR_VERSION;
#if defined(MBEDTLS_SSL_PROTO_DTLS)
            if( transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
                conf->min_minor_ver = MBEDTLS_SSL_MINOR_VERSION_2;
#endif
            conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_0] =
            conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_1] =
            conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_2] =
            conf->ciphersuite_list[MBEDTLS_SSL_MINOR_VERSION_3] =
                                   mbedtls_ssl_list_ciphersuites();
#if defined(MBEDTLS_X509_CRT_PARSE_C)
            conf->cert_profile = &mbedtls_x509_crt_profile_default;
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
            conf->sig_hashes = ssl_preset_default_hashes;
#endif
#if defined(MBEDTLS_ECP_C)
            conf->curve_list = mbedtls_ecp_grp_id_list();
#endif
#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_CLI_C)
            conf->dhm_min_bitlen = 1024;
#endif
    }
    return( 0 );
}

/**
 * \brief          Free an SSL configuration context
 *
 * \param conf     SSL configuration context
 */
void mbedtls_ssl_config_free( mbedtls_ssl_config *conf )
{
#if defined(MBEDTLS_DHM_C)
    mbedtls_mpi_free( &conf->dhm_P );
    mbedtls_mpi_free( &conf->dhm_G );
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
    if( conf->psk != NULL )
    {
        mbedtls_platform_zeroize( conf->psk, conf->psk_len );
        mbedtls_free( conf->psk );
        conf->psk = NULL;
        conf->psk_len = 0;
    }
    if( conf->psk_identity != NULL )
    {
        mbedtls_platform_zeroize( conf->psk_identity, conf->psk_identity_len );
        mbedtls_free( conf->psk_identity );
        conf->psk_identity = NULL;
        conf->psk_identity_len = 0;
    }
#endif
#if defined(MBEDTLS_X509_CRT_PARSE_C)
    mbedtls_ssl_key_cert_free( conf->key_cert );
#endif
    mbedtls_platform_zeroize( conf, sizeof( mbedtls_ssl_config ) );
}

int mbedtls_ssl_get_key_exchange_md_tls1_2( mbedtls_ssl_context *ssl,
                                            unsigned char *hash, size_t *hashlen,
                                            unsigned char *data, size_t data_len,
                                            mbedtls_md_type_t md_alg )
{
    int ret = 0;
    mbedtls_md_context_t ctx;
    const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type( md_alg );
    *hashlen = mbedtls_md_get_size( md_info );
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "Perform mbedtls-based computation of digest of ServerKeyExchange" ) );
    mbedtls_md_init( &ctx );
    /*
     * digitally-signed struct {
     *     opaque client_random[32];
     *     opaque server_random[32];
     *     ServerDHParams params;
     * };
     */
    if( ( ret = mbedtls_md_setup( &ctx, md_info, 0 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_setup", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md_starts( &ctx ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_starts", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md_update( &ctx, ssl->handshake->randbytes, 64 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_update", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md_update( &ctx, data, data_len ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_update", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md_finish( &ctx, hash ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_finish", ret );
        goto exit;
    }
exit:
    mbedtls_md_free( &ctx );
    if( ret != 0 )
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
    return( ret );
}

#if defined(MBEDTLS_PK_C) && \
    ( defined(MBEDTLS_RSA_C) || defined(MBEDTLS_ECDSA_C) )

/*
 * Convert between MBEDTLS_PK_XXX and SSL_SIG_XXX
 */
unsigned char mbedtls_ssl_sig_from_pk( mbedtls_pk_context *pk )
{
#if defined(MBEDTLS_RSA_C)
    if( mbedtls_pk_can_do( pk, MBEDTLS_PK_RSA ) )
        return( MBEDTLS_SSL_SIG_RSA );
#endif
#if defined(MBEDTLS_ECDSA_C)
    if( mbedtls_pk_can_do( pk, MBEDTLS_PK_ECDSA ) )
        return( MBEDTLS_SSL_SIG_ECDSA );
#endif
    return( MBEDTLS_SSL_SIG_ANON );
}

unsigned char mbedtls_ssl_sig_from_pk_alg( mbedtls_pk_type_t type )
{
    switch( type ) {
        case MBEDTLS_PK_RSA:
            return( MBEDTLS_SSL_SIG_RSA );
        case MBEDTLS_PK_ECDSA:
        case MBEDTLS_PK_ECKEY:
            return( MBEDTLS_SSL_SIG_ECDSA );
        default:
            return( MBEDTLS_SSL_SIG_ANON );
    }
}

#endif /* MBEDTLS_PK_C && ( MBEDTLS_RSA_C || MBEDTLS_ECDSA_C ) */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
    defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)

/* Find an entry in a signature-hash set matching a given hash algorithm. */
mbedtls_md_type_t mbedtls_ssl_sig_hash_set_find( mbedtls_ssl_sig_hash_set_t *set,
                                                 mbedtls_pk_type_t sig_alg )
{
    switch( sig_alg )
    {
        case MBEDTLS_PK_RSA:
            return( set->rsa );
        case MBEDTLS_PK_ECDSA:
            return( set->ecdsa );
        default:
            return( MBEDTLS_MD_NONE );
    }
}

/* Allow exactly one hash algorithm for each signature. */
void mbedtls_ssl_sig_hash_set_const_hash( mbedtls_ssl_sig_hash_set_t *set,
                                          mbedtls_md_type_t md_alg )
{
    set->rsa   = md_alg;
    set->ecdsa = md_alg;
}

#endif /* MBEDTLS_SSL_PROTO_TLS1_2) &&
          MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */

/*
 * Convert from MBEDTLS_MD_XXX to MBEDTLS_SSL_HASH_XXX
 */
unsigned char mbedtls_ssl_hash_from_md_alg( int md )
{
    switch( md )
    {
#if defined(MBEDTLS_MD5_C)
        case MBEDTLS_MD_MD5:
            return( MBEDTLS_SSL_HASH_MD5 );
#endif
#if defined(MBEDTLS_SHA1_C)
        case MBEDTLS_MD_SHA1:
            return( MBEDTLS_SSL_HASH_SHA1 );
#endif
#if defined(MBEDTLS_SHA256_C)
        case MBEDTLS_MD_SHA224:
            return( MBEDTLS_SSL_HASH_SHA224 );
        case MBEDTLS_MD_SHA256:
            return( MBEDTLS_SSL_HASH_SHA256 );
#endif
#if defined(MBEDTLS_SHA512_C)
        case MBEDTLS_MD_SHA384:
            return( MBEDTLS_SSL_HASH_SHA384 );
        case MBEDTLS_MD_SHA512:
            return( MBEDTLS_SSL_HASH_SHA512 );
#endif
        default:
            return( MBEDTLS_SSL_HASH_NONE );
    }
}

#if defined(MBEDTLS_ECP_C)
/*
 * Check if a curve proposed by the peer is in our list.
 * Return 0 if we're willing to use it, -1 otherwise.
 */
int mbedtls_ssl_check_curve( const mbedtls_ssl_context *ssl, mbedtls_ecp_group_id grp_id )
{
    const mbedtls_ecp_group_id *gid;
    if( ssl->conf->curve_list == NULL )
        return( -1 );
    for( gid = ssl->conf->curve_list; *gid != MBEDTLS_ECP_DP_NONE; gid++ )
        if( *gid == grp_id )
            return( 0 );
    return( -1 );
}
#endif /* MBEDTLS_ECP_C */

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/*
 * Check if a hash proposed by the peer is in our list.
 * Return 0 if we're willing to use it, -1 otherwise.
 */
int mbedtls_ssl_check_sig_hash( const mbedtls_ssl_context *ssl,
                                mbedtls_md_type_t md )
{
    const uint8_t *cur;
    if( ssl->conf->sig_hashes == NULL )
        return( -1 );
    for( cur = ssl->conf->sig_hashes; *cur != MBEDTLS_MD_NONE; cur++ )
        if( *cur == (int) md )
            return( 0 );
    return( -1 );
}
#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */

#if defined(MBEDTLS_X509_CRT_PARSE_C)
int mbedtls_ssl_check_cert_usage( const mbedtls_x509_crt *cert,
                                  const mbedtls_ssl_ciphersuite_t *ciphersuite,
                                  int cert_endpoint,
                                  uint32_t *flags )
{
    int ret = 0;
#if defined(MBEDTLS_X509_CHECK_KEY_USAGE)
    int usage = 0;
#endif
#if defined(MBEDTLS_X509_CHECK_EXTENDED_KEY_USAGE)
    const char *ext_oid;
    size_t ext_len;
#endif
#if !defined(MBEDTLS_X509_CHECK_KEY_USAGE) &&          \
    !defined(MBEDTLS_X509_CHECK_EXTENDED_KEY_USAGE)
    ((void) cert);
    ((void) cert_endpoint);
    ((void) flags);
#endif
#if defined(MBEDTLS_X509_CHECK_KEY_USAGE)
    if( cert_endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        /* Server part of the key exchange */
        switch( ciphersuite->key_exchange )
        {
            case MBEDTLS_KEY_EXCHANGE_RSA:
            case MBEDTLS_KEY_EXCHANGE_RSA_PSK:
                usage = MBEDTLS_X509_KU_KEY_ENCIPHERMENT;
                break;
            case MBEDTLS_KEY_EXCHANGE_DHE_RSA:
            case MBEDTLS_KEY_EXCHANGE_ECDHE_RSA:
            case MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA:
                usage = MBEDTLS_X509_KU_DIGITAL_SIGNATURE;
                break;
            case MBEDTLS_KEY_EXCHANGE_ECDH_RSA:
            case MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA:
                usage = MBEDTLS_X509_KU_KEY_AGREEMENT;
                break;
            /* Don't use default: we want warnings when adding new values */
            case MBEDTLS_KEY_EXCHANGE_NONE:
            case MBEDTLS_KEY_EXCHANGE_PSK:
            case MBEDTLS_KEY_EXCHANGE_DHE_PSK:
            case MBEDTLS_KEY_EXCHANGE_ECDHE_PSK:
            case MBEDTLS_KEY_EXCHANGE_ECJPAKE:
                usage = 0;
        }
    }
    else
    {
        /* Client auth: we only implement rsa_sign and mbedtls_ecdsa_sign for now */
        usage = MBEDTLS_X509_KU_DIGITAL_SIGNATURE;
    }
    if( mbedtls_x509_crt_check_key_usage( cert, usage ) != 0 )
    {
        *flags |= MBEDTLS_X509_BADCERT_KEY_USAGE;
        ret = -1;
    }
#else
    ((void) ciphersuite);
#endif /* MBEDTLS_X509_CHECK_KEY_USAGE */
#if defined(MBEDTLS_X509_CHECK_EXTENDED_KEY_USAGE)
    if( cert_endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        ext_oid = MBEDTLS_OID_SERVER_AUTH;
        ext_len = MBEDTLS_OID_SIZE( MBEDTLS_OID_SERVER_AUTH );
    }
    else
    {
        ext_oid = MBEDTLS_OID_CLIENT_AUTH;
        ext_len = MBEDTLS_OID_SIZE( MBEDTLS_OID_CLIENT_AUTH );
    }
    if( mbedtls_x509_crt_check_extended_key_usage( cert, ext_oid, ext_len ) != 0 )
    {
        *flags |= MBEDTLS_X509_BADCERT_EXT_KEY_USAGE;
        ret = -1;
    }
#endif /* MBEDTLS_X509_CHECK_EXTENDED_KEY_USAGE */
    return( ret );
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

int mbedtls_ssl_set_calc_verify_md( mbedtls_ssl_context *ssl, int md )
{
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
    if( ssl->minor_ver != MBEDTLS_SSL_MINOR_VERSION_3 )
        return MBEDTLS_ERR_SSL_INVALID_VERIFY_HASH;
    switch( md )
    {
#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
#if defined(MBEDTLS_MD5_C)
        case MBEDTLS_SSL_HASH_MD5:
            return MBEDTLS_ERR_SSL_INVALID_VERIFY_HASH;
#endif
#if defined(MBEDTLS_SHA1_C)
        case MBEDTLS_SSL_HASH_SHA1:
            ssl->handshake->calc_verify = ssl_calc_verify_tls;
            break;
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 */
#if defined(MBEDTLS_SHA512_C)
        case MBEDTLS_SSL_HASH_SHA384:
            ssl->handshake->calc_verify = ssl_calc_verify_tls_sha384;
            break;
#endif
#if defined(MBEDTLS_SHA256_C)
        case MBEDTLS_SSL_HASH_SHA256:
            ssl->handshake->calc_verify = ssl_calc_verify_tls_sha256;
            break;
#endif
        default:
            return MBEDTLS_ERR_SSL_INVALID_VERIFY_HASH;
    }
    return 0;
#else /* !MBEDTLS_SSL_PROTO_TLS1_2 */
    (void) ssl;
    (void) md;
    return MBEDTLS_ERR_SSL_INVALID_VERIFY_HASH;
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
}

#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
    defined(MBEDTLS_SSL_PROTO_TLS1_1)
int mbedtls_ssl_get_key_exchange_md_ssl_tls( mbedtls_ssl_context *ssl,
                                             unsigned char *output,
                                             unsigned char *data, size_t data_len )
{
    int ret = 0;
    mbedtls_md5_context mbedtls_md5;
    mbedtls_sha1_context mbedtls_sha1;
    mbedtls_md5_init( &mbedtls_md5 );
    mbedtls_sha1_init( &mbedtls_sha1 );
    /*
     * digitally-signed struct {
     *     opaque md5_hash[16];
     *     opaque sha_hash[20];
     * };
     *
     * md5_hash
     *     MD5(ClientHello.random + ServerHello.random
     *                            + ServerParams);
     * sha_hash
     *     SHA(ClientHello.random + ServerHello.random
     *                            + ServerParams);
     */
    if( ( ret = mbedtls_md5_starts_ret( &mbedtls_md5 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md5_starts_ret", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md5_update_ret( &mbedtls_md5,
                                        ssl->handshake->randbytes, 64 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md5_update_ret", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md5_update_ret( &mbedtls_md5, data, data_len ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md5_update_ret", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md5_finish_ret( &mbedtls_md5, output ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md5_finish_ret", ret );
        goto exit;
    }
    if( ( ret = mbedtls_sha1_starts_ret( &mbedtls_sha1 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_sha1_starts_ret", ret );
        goto exit;
    }
    if( ( ret = mbedtls_sha1_update_ret( &mbedtls_sha1,
                                         ssl->handshake->randbytes, 64 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_sha1_update_ret", ret );
        goto exit;
    }
    if( ( ret = mbedtls_sha1_update_ret( &mbedtls_sha1, data,
                                         data_len ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_sha1_update_ret", ret );
        goto exit;
    }
    if( ( ret = mbedtls_sha1_finish_ret( &mbedtls_sha1,
                                         output + 16 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_sha1_finish_ret", ret );
        goto exit;
    }
exit:
    mbedtls_md5_free( &mbedtls_md5 );
    mbedtls_sha1_free( &mbedtls_sha1 );
    if( ret != 0 )
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
    return( ret );
}
#endif /* MBEDTLS_SSL_PROTO_SSL3 || MBEDTLS_SSL_PROTO_TLS1 || \
          MBEDTLS_SSL_PROTO_TLS1_1 */

#endif /* MBEDTLS_SSL_TLS_C */
