text: /*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:4;coding:utf-8 -*-│
  │vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
  ╞══════════════════════════════════════════════════════════════════════════════╡
  │ Copyright The Mbed TLS Contributors                                          │
  │                                                                              │
  │ Licensed under the Apache License, Version 2.0 (the "License");              │
  │ you may not use this file except in compliance with the License.             │
  │ You may obtain a copy of the License at                                      │
  │                                                                              │
  │     http://www.apache.org/licenses/LICENSE-2.0                               │
  │                                                                              │
  │ Unless required by applicable law or agreed to in writing, software          │
  │ distributed under the License is distributed on an "AS IS" BASIS,            │
  │ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.     │
  │ See the License for the specific language governing permissions and          │
  │ limitations under the License.                                               │
  ╚─────────────────────────────────────────────────────────────────────────────*/
  #include "libc/log/log.h"
  #include "libc/macros.internal.h"
  #include "libc/str/str.h"
  #include "third_party/mbedtls/common.h"
  #include "third_party/mbedtls/debug.h"
  #include "third_party/mbedtls/ecp.h"
  #include "third_party/mbedtls/error.h"
  #include "third_party/mbedtls/platform.h"
  #include "third_party/mbedtls/profile.h"
  #include "third_party/mbedtls/ssl.h"
  #include "third_party/mbedtls/ssl_internal.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 */
  /*
   *  SSLv3/TLSv1 server-side functions
   *
   *  Copyright The Mbed TLS Contributors
   *  SPDX-License-Identifier: Apache-2.0
   *
   *  Licensed under the Apache License, Version 2.0 (the "License"); you may
   *  not use this file except in compliance with the License.
   *  You may obtain a copy of the License at
   *
   *  http://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing, software
   *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *  See the License for the specific language governing permissions and
   *  limitations under the License.
   */
  
  #if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY)
  /**
   * \brief          Set client's transport-level identification info.
   *                 (Server only. DTLS only.)
   *
   *                 This is usually the IP address (and port), but could be
   *                 anything identify the client depending on the underlying
   *                 network stack. Used for HelloVerifyRequest with DTLS.
   *                 This is *not* used to route the actual packets.
   *
   * \param ssl      SSL context
   * \param info     Transport-level info identifying the client (eg IP + port)
   * \param ilen     Length of info in bytes
   *
   * \note           An internal copy is made, so the info buffer can be reused.
   *
   * \return         0 on success,
   *                 MBEDTLS_ERR_SSL_BAD_INPUT_DATA if used on client,
   *                 MBEDTLS_ERR_SSL_ALLOC_FAILED if out of memory.
   */
  int mbedtls_ssl_set_client_transport_id( mbedtls_ssl_context *ssl,
                                   const unsigned char *info,
                                   size_t ilen )
  {
      if( ssl->conf->endpoint != MBEDTLS_SSL_IS_SERVER )
          return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
  
      mbedtls_free( ssl->cli_id );
  
      if( ( ssl->cli_id = mbedtls_calloc( 1, ilen ) ) == NULL )
          return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
  
      memcpy( ssl->cli_id, info, ilen );
      ssl->cli_id_len = ilen;
  
      return( 0 );
  }
  
  /**
   * \brief           Register callbacks for DTLS cookies
   *                  (Server only. DTLS only.)
   *
   *                  Default: dummy callbacks that fail, in order to force you to
   *                  register working callbacks (and initialize their context).
   *
   *                  To disable HelloVerifyRequest, register NULL callbacks.
   *
   * \warning         Disabling hello verification allows your server to be used
   *                  for amplification in DoS attacks against other hosts.
   *                  Only disable if you known this can't happen in your
   *                  particular environment.
   *
   * \note            See comments on \c mbedtls_ssl_handshake() about handling
   *                  the MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED that is expected
   *                  on the first handshake attempt when this is enabled.
   *
   * \note            This is also necessary to handle client reconnection from
   *                  the same port as described in RFC 6347 section 4.2.8 (only
   *                  the variant with cookies is supported currently). See
   *                  comments on \c mbedtls_ssl_read() for details.
   *
   * \param conf              SSL configuration
   * \param f_cookie_write    Cookie write callback
   * \param f_cookie_check    Cookie check callback
   * \param p_cookie          Context for both callbacks
   */
  void mbedtls_ssl_conf_dtls_cookies( mbedtls_ssl_config *conf,
                             mbedtls_ssl_cookie_write_t *f_cookie_write,
                             mbedtls_ssl_cookie_check_t *f_cookie_check,
                             void *p_cookie )
  {
      conf->f_cookie_write = f_cookie_write;
      conf->f_cookie_check = f_cookie_check;
      conf->p_cookie       = p_cookie;
  }
  #endif /* MBEDTLS_SSL_DTLS_HELLO_VERIFY */
  
  #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
  static int ssl_parse_servername_ext( mbedtls_ssl_context *ssl,
                                       const unsigned char *buf,
                                       size_t len )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      size_t servername_list_size, hostname_len;
      const unsigned char *p;
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "parse ServerName extension" ) );
      if( len < 2 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                         MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
      servername_list_size = ( ( buf[0] << 8 ) | ( buf[1] ) );
      if( servername_list_size + 2 != len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
      p = buf + 2;
      while( servername_list_size > 2 )
      {
          hostname_len = ( ( p[1] << 8 ) | p[2] );
          if( hostname_len + 3 > servername_list_size )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
          }
          if( p[0] == MBEDTLS_TLS_EXT_SERVERNAME_HOSTNAME )
          {
              ret = ssl->conf->f_sni( ssl->conf->p_sni,
                                      ssl, p + 3, hostname_len );
              if( ret != 0 )
              {
                  MBEDTLS_SSL_DEBUG_RET( 1, "ssl_sni_wrapper", ret );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                          MBEDTLS_SSL_ALERT_MSG_UNRECOGNIZED_NAME );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
              return( 0 );
          }
          servername_list_size -= hostname_len + 3;
          p += hostname_len + 3;
      }
      if( servername_list_size != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
  static int ssl_conf_has_psk_or_cb( mbedtls_ssl_config const *conf )
  {
      if( conf->f_psk != NULL )
          return( 1 );
      if( conf->psk_identity_len == 0 || conf->psk_identity == NULL )
          return( 0 );
      if( conf->psk != NULL && conf->psk_len != 0 )
          return( 1 );
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
  
  static int ssl_parse_renegotiation_info( mbedtls_ssl_context *ssl,
                                           const unsigned char *buf,
                                           size_t len )
  {
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE )
      {
          /* Check verify-data in constant-time. The length OTOH is no secret */
          if( len    != 1 + ssl->verify_data_len ||
              buf[0] !=     ssl->verify_data_len ||
              timingsafe_bcmp( buf + 1, ssl->peer_verify_data,
                               ssl->verify_data_len ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-matching renegotiation info" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
          }
      }
      else
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
      {
          if( len != 1 || buf[0] != 0x0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-zero length renegotiation info" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
          }
          ssl->secure_renegotiation = MBEDTLS_SSL_SECURE_RENEGOTIATION;
      }
      return( 0 );
  }
  
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
      defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
  
  /* Add a signature-hash-pair to a signature-hash set */
  static inline void mbedtls_ssl_sig_hash_set_add( mbedtls_ssl_sig_hash_set_t *set,
                                                   mbedtls_pk_type_t sig_alg,
                                                   mbedtls_md_type_t md_alg )
  {
      switch( sig_alg )
      {
          case MBEDTLS_PK_RSA:
              if( set->rsa == MBEDTLS_MD_NONE )
                  set->rsa = md_alg;
              break;
          case MBEDTLS_PK_ECDSA:
              if( set->ecdsa == MBEDTLS_MD_NONE )
                  set->ecdsa = md_alg;
              break;
          default:
              break;
      }
  }
  
  /*
   * Status of the implementation of signature-algorithms extension:
   *
   * Currently, we are only considering the signature-algorithm extension
   * to pick a ciphersuite which allows us to send the ServerKeyExchange
   * message with a signature-hash combination that the user allows.
   *
   * We do *not* check whether all certificates in our certificate
   * chain are signed with an allowed signature-hash pair.
   * This needs to be done at a later stage.
   *
   */
  static int ssl_parse_signature_algorithms_ext( mbedtls_ssl_context *ssl,
                                                 const unsigned char *buf,
                                                 size_t len )
  {
      size_t sig_alg_list_size;
  
      const unsigned char *p;
      const unsigned char *end = buf + len;
  
      mbedtls_md_type_t md_cur;
      mbedtls_pk_type_t sig_cur;
  
      if ( len < 2 ) {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                         MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
      sig_alg_list_size = ( ( buf[0] << 8 ) | ( buf[1] ) );
      if( sig_alg_list_size + 2 != len ||
          sig_alg_list_size % 2 != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /* Currently we only guarantee signing the ServerKeyExchange message according
       * to the constraints specified in this extension (see above), so it suffices
       * to remember only one suitable hash for each possible signature algorithm.
       *
       * This will change when we also consider certificate signatures,
       * in which case we will need to remember the whole signature-hash
       * pair list from the extension.
       */
  
      for( p = buf + 2; p < end; p += 2 )
      {
          /* Silently ignore unknown signature or hash algorithms. */
  
          if( ( sig_cur = mbedtls_ssl_pk_alg_from_sig( p[1] ) ) == MBEDTLS_PK_NONE )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext"
                                          " unknown sig alg encoding %d (%s)", p[1],
                                          mbedtls_sig_alg_name(p[1])) );
              continue;
          }
  
          /* Check if we support the hash the user proposes */
          md_cur = mbedtls_ssl_md_alg_from_hash( p[0] );
          if( md_cur == MBEDTLS_MD_NONE )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext:"
                                          " unknown hash alg encoding %d", p[0] ) );
              continue;
          }
  
          if( mbedtls_ssl_check_sig_hash( ssl, md_cur ) == 0 )
          {
              mbedtls_ssl_sig_hash_set_add( &ssl->handshake->hash_algs, sig_cur, md_cur );
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext:"
                                          " match sig %u (%s) and hash %u (%s)",
                                          sig_cur, mbedtls_pk_type_name(sig_cur),
                                          md_cur, mbedtls_md_type_name(md_cur) ) );
          }
          else
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext: "
                                          "hash alg %u not supported", (unsigned) md_cur ) );
          }
      }
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
            MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
  
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
  static int ssl_parse_supported_elliptic_curves( mbedtls_ssl_context *ssl,
                                                  const unsigned char *buf,
                                                  size_t len )
  {
      size_t list_size, our_size;
      const unsigned char *p;
      const mbedtls_ecp_curve_info *curve_info, **curves;
  
      if ( len < 2 ) {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                         MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
      list_size = ( ( buf[0] << 8 ) | ( buf[1] ) );
      if( list_size + 2 != len ||
          list_size % 2 != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /* Should never happen unless client duplicates the extension */
      if( ssl->handshake->curves != NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /* Don't allow our peer to make us allocate too much memory,
       * and leave room for a final 0 */
      our_size = list_size / 2 + 1;
      if( our_size > MBEDTLS_ECP_DP_MAX )
          our_size = MBEDTLS_ECP_DP_MAX;
  
      if( ( curves = mbedtls_calloc( our_size, sizeof( *curves ) ) ) == NULL )
      {
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
          return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
      }
  
      ssl->handshake->curves = curves;
  
      p = buf + 2;
      while( list_size > 0 && our_size > 1 )
      {
          curve_info = mbedtls_ecp_curve_info_from_tls_id( ( p[0] << 8 ) | p[1] );
  
          if( curve_info != NULL )
          {
              *curves++ = curve_info;
              our_size--;
          }
  
          list_size -= 2;
          p += 2;
      }
  
      return( 0 );
  }
  
  static int ssl_parse_supported_point_formats( mbedtls_ssl_context *ssl,
                                                const unsigned char *buf,
                                                size_t len )
  {
      size_t list_size;
      const unsigned char *p;
  
      if( len == 0 || (size_t)( buf[0] + 1 ) != len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
      list_size = buf[0];
  
      p = buf + 1;
      while( list_size > 0 )
      {
          if( p[0] == MBEDTLS_ECP_PF_UNCOMPRESSED ||
              p[0] == MBEDTLS_ECP_PF_COMPRESSED )
          {
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C)
              ssl->handshake->ecdh_ctx.point_format = p[0];
  #endif
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
              ssl->handshake->ecjpake_ctx.point_format = p[0];
  #endif
              MBEDTLS_SSL_DEBUG_MSG( 4, ( "point format selected: %d", p[0] ) );
              return( 0 );
          }
  
          list_size--;
          p++;
      }
  
      return( 0 );
  }
  #endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C ||
            MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
  static int ssl_parse_ecjpake_kkpp( mbedtls_ssl_context *ssl,
                                     const unsigned char *buf,
                                     size_t len )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
  
      if( mbedtls_ecjpake_check( &ssl->handshake->ecjpake_ctx ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "skip ecjpake kkpp extension" ) );
          return( 0 );
      }
  
      if( ( ret = mbedtls_ecjpake_read_round_one( &ssl->handshake->ecjpake_ctx,
                                                  buf, len ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecjpake_read_round_one", ret );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
          return( ret );
      }
  
      /* Only mark the extension as OK when we're sure it is */
      ssl->handshake->cli_exts |= MBEDTLS_TLS_EXT_ECJPAKE_KKPP_OK;
  
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
  
  #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
  static int ssl_parse_max_fragment_length_ext( mbedtls_ssl_context *ssl,
                                                const unsigned char *buf,
                                                size_t len )
  {
      if( len != 1 || buf[0] >= MBEDTLS_SSL_MAX_FRAG_LEN_INVALID )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      ssl->session_negotiate->mfl_code = buf[0];
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
  
  #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
  static int ssl_parse_cid_ext( mbedtls_ssl_context *ssl,
                                const unsigned char *buf,
                                size_t len )
  {
      size_t peer_cid_len;
  
      /* CID extension only makes sense in DTLS */
      if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /*
       * Quoting draft-ietf-tls-dtls-connection-id-05
       * https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05
       *
       *   struct {
       *      opaque cid<0..2^8-1>;
       *   } ConnectionId;
      */
  
      if( len < 1 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      peer_cid_len = *buf++;
      len--;
  
      if( len != peer_cid_len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /* Ignore CID if the user has disabled its use. */
      if( ssl->negotiate_cid == MBEDTLS_SSL_CID_DISABLED )
      {
          /* Leave ssl->handshake->cid_in_use in its default
           * value of MBEDTLS_SSL_CID_DISABLED. */
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "Client sent CID extension, but CID disabled" ) );
          return( 0 );
      }
  
      if( peer_cid_len > MBEDTLS_SSL_CID_OUT_LEN_MAX )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      ssl->handshake->cid_in_use = MBEDTLS_SSL_CID_ENABLED;
      ssl->handshake->peer_cid_len = (uint8_t) peer_cid_len;
      memcpy( ssl->handshake->peer_cid, buf, peer_cid_len );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "Use of CID extension negotiated" ) );
      MBEDTLS_SSL_DEBUG_BUF( 3, "Client CID", buf, peer_cid_len );
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
  
  #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
  static int ssl_parse_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf,
                                        size_t len )
  {
      if( len != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
      ((void) buf);
      if( ssl->conf->encrypt_then_mac == MBEDTLS_SSL_ETM_ENABLED &&
          ssl->minor_ver != MBEDTLS_SSL_MINOR_VERSION_0 )
      {
          ssl->session_negotiate->encrypt_then_mac = MBEDTLS_SSL_ETM_ENABLED;
      }
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
  
  #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
  static int ssl_parse_extended_ms_ext( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf,
                                        size_t len )
  {
      if( len != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      ((void) buf);
  
      if( ssl->conf->extended_ms == MBEDTLS_SSL_EXTENDED_MS_ENABLED &&
          ssl->minor_ver != MBEDTLS_SSL_MINOR_VERSION_0 )
      {
          ssl->handshake->extended_ms = MBEDTLS_SSL_EXTENDED_MS_ENABLED;
      }
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
  static int ssl_parse_session_ticket_ext( mbedtls_ssl_context *ssl,
                                           unsigned char *buf,
                                           size_t len )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      mbedtls_ssl_session session;
  
      mbedtls_ssl_session_init( &session );
  
      if( ssl->conf->f_ticket_parse == NULL ||
          ssl->conf->f_ticket_write == NULL )
      {
          return( 0 );
      }
  
      /* Remember the client asked us to send a new ticket */
      ssl->handshake->new_session_ticket = 1;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "ticket length: %" MBEDTLS_PRINTF_SIZET, len ) );
  
      if( len == 0 )
          return( 0 );
  
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "ticket rejected: renegotiating" ) );
          return( 0 );
      }
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
  
      /*
       * Failures are ok: just ignore the ticket and proceed.
       */
      if( ( ret = ssl->conf->f_ticket_parse( ssl->conf->p_ticket, &session,
                                             buf, len ) ) != 0 )
      {
          mbedtls_ssl_session_free( &session );
  
          if( ret == MBEDTLS_ERR_SSL_INVALID_MAC )
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "ticket is not authentic" ) );
          else if( ret == MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED )
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "ticket is expired" ) );
          else
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_ticket_parse", ret );
  
          return( 0 );
      }
  
      /*
       * Keep the session ID sent by the client, since we MUST send it back to
       * inform them we're accepting the ticket  (RFC 5077 section 3.4)
       */
      session.id_len = ssl->session_negotiate->id_len;
      memcpy( &session.id, ssl->session_negotiate->id, session.id_len );
  
      mbedtls_ssl_session_free( ssl->session_negotiate );
      memcpy( ssl->session_negotiate, &session, sizeof( mbedtls_ssl_session ) );
  
      /* Zeroize instead of free as we copied the content */
      mbedtls_platform_zeroize( &session, sizeof( mbedtls_ssl_session ) );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "session successfully restored from ticket" ) );
  
      ssl->handshake->resume = 1;
  
      /* Don't send a new ticket after all, this one is OK */
      ssl->handshake->new_session_ticket = 0;
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  #if defined(MBEDTLS_SSL_ALPN)
  static int ssl_parse_alpn_ext( mbedtls_ssl_context *ssl,
                                 const unsigned char *buf, size_t len )
  {
      size_t list_len, cur_len, ours_len;
      const unsigned char *theirs, *start, *end;
      const char **ours;
  
      /* If ALPN not configured, just ignore the extension */
      if( ssl->conf->alpn_list == NULL )
          return( 0 );
  
      /*
       * opaque ProtocolName<1..2^8-1>;
       *
       * struct {
       *     ProtocolName protocol_name_list<2..2^16-1>
       * } ProtocolNameList;
       */
  
      /* Min length is 2 (list_len) + 1 (name_len) + 1 (name) */
      if( len < 4 )
      {
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      list_len = ( buf[0] << 8 ) | buf[1];
      if( list_len != len - 2 )
      {
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /*
       * Validate peer's list (lengths)
       */
      start = buf + 2;
      end = buf + len;
      for( theirs = start; theirs != end; theirs += cur_len )
      {
          cur_len = *theirs++;
  
          /* Current identifier must fit in list */
          if( cur_len > (size_t)( end - theirs ) )
          {
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
          }
  
          /* Empty strings MUST NOT be included */
          if( cur_len == 0 )
          {
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
          }
      }
  
      /*
       * Use our order of preference
       */
      for( ours = ssl->conf->alpn_list; *ours != NULL; ours++ )
      {
          ours_len = strlen( *ours );
          for( theirs = start; theirs != end; theirs += cur_len )
          {
              cur_len = *theirs++;
  
              if( cur_len == ours_len &&
                  timingsafe_bcmp( theirs, *ours, cur_len ) == 0 )
              {
                  ssl->alpn_chosen = *ours;
                  return( 0 );
              }
          }
      }
  
      /* If we get there, no match was found */
      mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                              MBEDTLS_SSL_ALERT_MSG_NO_APPLICATION_PROTOCOL );
      return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
  }
  #endif /* MBEDTLS_SSL_ALPN */
  
  #if defined(MBEDTLS_SSL_DTLS_SRTP)
  static int ssl_parse_use_srtp_ext( mbedtls_ssl_context *ssl,
                                     const unsigned char *buf,
                                     size_t len )
  {
      mbedtls_ssl_srtp_profile client_protection = MBEDTLS_TLS_SRTP_UNSET;
      size_t i,j;
      size_t profile_length;
      uint16_t mki_length;
      /*! 2 bytes for profile length and 1 byte for mki len */
      const size_t size_of_lengths = 3;
  
      /* If use_srtp is not configured, just ignore the extension */
      if( ( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM ) ||
          ( ssl->conf->dtls_srtp_profile_list == NULL ) ||
          ( ssl->conf->dtls_srtp_profile_list_len == 0 ) )
      {
          return( 0 );
      }
  
      /* RFC5764 section 4.1.1
       * uint8 SRTPProtectionProfile[2];
       *
       * struct {
       *   SRTPProtectionProfiles SRTPProtectionProfiles;
       *   opaque srtp_mki<0..255>;
       * } UseSRTPData;
  
       * SRTPProtectionProfile SRTPProtectionProfiles<2..2^16-1>;
       */
  
      /*
       * Min length is 5: at least one protection profile(2 bytes)
       *                  and length(2 bytes) + srtp_mki length(1 byte)
       * Check here that we have at least 2 bytes of protection profiles length
       * and one of srtp_mki length
       */
      if( len < size_of_lengths )
      {
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
     ssl->dtls_srtp_info.chosen_dtls_srtp_profile = MBEDTLS_TLS_SRTP_UNSET;
  
      /* first 2 bytes are protection profile length(in bytes) */
      profile_length = ( buf[0] << 8 ) | buf[1];
      buf += 2;
  
      /* The profile length cannot be bigger than input buffer size - lengths fields */
      if( profile_length > len - size_of_lengths ||
          profile_length % 2 != 0 ) /* profiles are 2 bytes long, so the length must be even */
      {
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
      /*
       * parse the extension list values are defined in
       * http://www.iana.org/assignments/srtp-protection/srtp-protection.xhtml
       */
      for( j = 0; j < profile_length; j += 2 )
      {
          uint16_t protection_profile_value = buf[j] << 8 | buf[j + 1];
          client_protection = mbedtls_ssl_check_srtp_profile_value( protection_profile_value );
  
          if( client_protection != MBEDTLS_TLS_SRTP_UNSET )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "found srtp profile: %s",
                                      mbedtls_ssl_get_srtp_profile_as_string(
                                              client_protection ) ) );
          }
          else
          {
              continue;
          }
          /* check if suggested profile is in our list */
          for( i = 0; i < ssl->conf->dtls_srtp_profile_list_len; i++)
          {
              if( client_protection == ssl->conf->dtls_srtp_profile_list[i] )
              {
                  ssl->dtls_srtp_info.chosen_dtls_srtp_profile = ssl->conf->dtls_srtp_profile_list[i];
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "selected srtp profile: %s",
                                              mbedtls_ssl_get_srtp_profile_as_string(
                                                      client_protection ) ) );
                  break;
              }
          }
          if( ssl->dtls_srtp_info.chosen_dtls_srtp_profile != MBEDTLS_TLS_SRTP_UNSET )
              break;
      }
      buf += profile_length; /* buf points to the mki length */
      mki_length = *buf;
      buf++;
  
      if( mki_length > MBEDTLS_TLS_SRTP_MAX_MKI_LENGTH ||
          mki_length + profile_length + size_of_lengths != len )
      {
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /* Parse the mki only if present and mki is supported locally */
      if( ssl->conf->dtls_srtp_mki_support == MBEDTLS_SSL_DTLS_SRTP_MKI_SUPPORTED &&
            mki_length > 0 )
      {
          ssl->dtls_srtp_info.mki_len = mki_length;
  
          memcpy( ssl->dtls_srtp_info.mki_value, buf, mki_length );
  
          MBEDTLS_SSL_DEBUG_BUF( 3, "using mki",  ssl->dtls_srtp_info.mki_value,
                                                  ssl->dtls_srtp_info.mki_len );
      }
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_DTLS_SRTP */
  
  /*
   * Auxiliary functions for ServerHello parsing and related actions
   */
  
  #if defined(MBEDTLS_X509_CRT_PARSE_C)
  /*
   * Return 0 if the given key uses one of the acceptable curves, -1 otherwise
   */
  #if defined(MBEDTLS_ECDSA_C)
  static int ssl_check_key_curve( mbedtls_pk_context *pk,
                                  const mbedtls_ecp_curve_info **curves )
  {
      const mbedtls_ecp_curve_info **crv = curves;
      mbedtls_ecp_group_id grp_id = mbedtls_pk_ec( *pk )->grp.id;
  
      while( *crv != NULL )
      {
          if( (*crv)->grp_id == grp_id )
              return( 0 );
          crv++;
      }
  
      return( -1 );
  }
  #endif /* MBEDTLS_ECDSA_C */
  
  /*
   * Try picking a certificate for this ciphersuite,
   * return 0 on success and -1 on failure.
   */
  static int ssl_pick_cert( mbedtls_ssl_context *ssl,
                            const mbedtls_ssl_ciphersuite_t * ciphersuite_info )
  {
      mbedtls_ssl_key_cert *cur, *list, *fallback = NULL;
      mbedtls_pk_type_t pk_alg =
          mbedtls_ssl_get_ciphersuite_sig_pk_alg( ciphersuite_info );
      uint32_t flags;
  
  #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
      if( ssl->handshake->sni_key_cert != NULL )
          list = ssl->handshake->sni_key_cert;
      else
  #endif
          list = ssl->conf->key_cert;
  
      if( pk_alg == MBEDTLS_PK_NONE )
          return( 0 );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite requires certificate" ) );
  
      if( list == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "server has no certificate" ) );
          return( -1 );
      }
  
      for( cur = list; cur != NULL; cur = cur->next )
      {
          flags = 0;
          MBEDTLS_SSL_DEBUG_CRT( 3, "candidate certificate chain, certificate",
                            cur->cert );
  
          if( ! mbedtls_pk_can_do( &cur->cert->pk, pk_alg ) )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "certificate mismatch: key type" ) );
              continue;
          }
  
          /*
           * This avoids sending the client a cert it'll reject based on
           * keyUsage or other extensions.
           *
           * It also allows the user to provision different certificates for
           * different uses based on keyUsage, eg if they want to avoid signing
           * and decrypting with the same RSA key.
           */
          if( mbedtls_ssl_check_cert_usage( cur->cert, ciphersuite_info,
                                    MBEDTLS_SSL_IS_SERVER, &flags ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "certificate mismatch: "
                                  "(extended) key usage extension" ) );
              continue;
          }
  
  #if defined(MBEDTLS_ECDSA_C)
          if( pk_alg == MBEDTLS_PK_ECDSA &&
              ssl_check_key_curve( &cur->cert->pk, ssl->handshake->curves ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "certificate mismatch: elliptic curve" ) );
              continue;
          }
  #endif
  
          /*
           * Try to select a SHA-1 certificate for pre-1.2 clients, but still
           * present them a SHA-higher cert rather than failing if it's the only
           * one we got that satisfies the other conditions.
           */
          if( ssl->minor_ver < MBEDTLS_SSL_MINOR_VERSION_3 &&
              cur->cert->sig_md != MBEDTLS_MD_SHA1 )
          {
              if( fallback == NULL )
                  fallback = cur;
              {
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "certificate not preferred: "
                                      "sha-2 with pre-TLS 1.2 client" ) );
              continue;
              }
          }
  
          /* If we get there, we got a winner */
          break;
      }
  
      if( cur == NULL )
          cur = fallback;
  
      /* Do not update ssl->handshake->key_cert unless there is a match */
      if( cur != NULL )
      {
          ssl->handshake->key_cert = cur;
          MBEDTLS_SSL_DEBUG_CRT( 3, "selected certificate chain, certificate",
                            ssl->handshake->key_cert->cert );
          return( 0 );
      }
  
      return( -1 );
  }
  #endif /* MBEDTLS_X509_CRT_PARSE_C */
  
  /*
   * Check if a given ciphersuite is suitable for use with our config/keys/etc
   * Sets ciphersuite_info only if the suite matches.
   */
  static int ssl_ciphersuite_match( mbedtls_ssl_context *ssl, int suite_id,
                                    const mbedtls_ssl_ciphersuite_t **ciphersuite_info )
  {
      const mbedtls_ssl_ciphersuite_t *suite_info;
  
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
      defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
      mbedtls_pk_type_t sig_type;
  #endif
  
      suite_info = mbedtls_ssl_ciphersuite_from_id( suite_id );
      if( suite_info == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "trying ciphersuite: %#04x (%s)",
                                  (unsigned int) suite_id, suite_info->name ) );
  
      if( suite_info->min_minor_ver > ssl->minor_ver ||
          suite_info->max_minor_ver < ssl->minor_ver )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite mismatch: version" ) );
          return( 0 );
      }
  
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
          ( suite_info->flags & MBEDTLS_CIPHERSUITE_NODTLS ) )
          return( 0 );
  #endif
  
  #if defined(MBEDTLS_ARC4_C)
      if( ssl->conf->arc4_disabled == MBEDTLS_SSL_ARC4_DISABLED &&
              suite_info->cipher == MBEDTLS_CIPHER_ARC4_128 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite mismatch: rc4" ) );
          return( 0 );
      }
  #endif
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
      if( suite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE &&
          ( ssl->handshake->cli_exts & MBEDTLS_TLS_EXT_ECJPAKE_KKPP_OK ) == 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite mismatch: ecjpake "
                                      "not configured or ext missing" ) );
          return( 0 );
      }
  #endif
  
  
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C)
      if( mbedtls_ssl_ciphersuite_uses_ec( suite_info ) &&
          ( ssl->handshake->curves == NULL ||
            ssl->handshake->curves[0] == NULL ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite mismatch: "
                              "no common elliptic curve" ) );
          return( 0 );
      }
  #endif
  
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
      /* If the ciphersuite requires a pre-shared key and we don't
       * have one, skip it now rather than failing later */
      if( mbedtls_ssl_ciphersuite_uses_psk( suite_info ) &&
          ssl_conf_has_psk_or_cb( ssl->conf ) == 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite mismatch: no pre-shared key" ) );
          return( 0 );
      }
  #endif
  
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
      defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
      /* If the ciphersuite requires signing, check whether
       * a suitable hash algorithm is present. */
      if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
      {
          sig_type = mbedtls_ssl_get_ciphersuite_sig_alg( suite_info );
          if( sig_type != MBEDTLS_PK_NONE &&
              mbedtls_ssl_sig_hash_set_find( &ssl->handshake->hash_algs, sig_type ) == MBEDTLS_MD_NONE )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite mismatch: no suitable hash algorithm "
                                          "for signature algorithm %u", (unsigned) sig_type ) );
              return( 0 );
          }
      }
  
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
            MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
  
  #if defined(MBEDTLS_X509_CRT_PARSE_C)
      /*
       * Final check: if ciphersuite requires us to have a
       * certificate/key of a particular type:
       * - select the appropriate certificate if we have one, or
       * - try the next ciphersuite if we don't
       * This must be done last since we modify the key_cert list.
       */
      if( ssl_pick_cert( ssl, suite_info ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciphersuite mismatch: "
                              "no suitable certificate" ) );
          return( 0 );
      }
  #endif
  
      *ciphersuite_info = suite_info;
      return( 0 );
  }
  
  #if defined(MBEDTLS_SSL_SRV_SUPPORT_SSLV2_CLIENT_HELLO)
  static int ssl_parse_client_hello_v2( mbedtls_ssl_context *ssl )
  {
      size_t n;
      unsigned int i, j;
      int ret, got_common_suite;
      unsigned int ciph_len, sess_len, chal_len;
      unsigned char *buf, *p;
      const uint16_t *ciphersuites;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse client hello v2" ) );
  
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "client hello v2 illegal for renegotiation" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
  
      buf = ssl->in_hdr;
  
      MBEDTLS_SSL_DEBUG_BUF( 4, "record header", buf, 5 );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v2, message type: %d",
                     buf[2] ) );
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v2, message len.: %d",
                     ( ( buf[0] & 0x7F ) << 8 ) | buf[1] ) );
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v2, max. version: [%d:%d]",
                     buf[3], buf[4] ) );
  
      /*
       * SSLv2 Client Hello
       *
       * Record layer:
       *     0  .   1   message length
       *
       * SSL layer:
       *     2  .   2   message type
       *     3  .   4   protocol version
       */
      if( buf[2] != MBEDTLS_SSL_HS_CLIENT_HELLO ||
          buf[3] != MBEDTLS_SSL_MAJOR_VERSION_3 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      n = ( ( buf[0] << 8 ) | buf[1] ) & 0x7FFF;
  
      if( n < 17 || n > 512 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      ssl->major_ver = MBEDTLS_SSL_MAJOR_VERSION_3;
      ssl->minor_ver = ( buf[4] <= ssl->conf->max_minor_ver )
                       ? buf[4]  : ssl->conf->max_minor_ver;
  
      if( ssl->minor_ver < ssl->conf->min_minor_ver )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "client only supports ssl smaller than minimum"
                              " [%d:%d] < [%d:%d]",
                              ssl->major_ver, ssl->minor_ver,
                              ssl->conf->min_major_ver, ssl->conf->min_minor_ver ) );
  
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION );
          return( MBEDTLS_ERR_SSL_BAD_HS_PROTOCOL_VERSION );
      }
  
      ssl->handshake->max_major_ver = buf[3];
      ssl->handshake->max_minor_ver = buf[4];
  
      if( ( ret = mbedtls_ssl_fetch_input( ssl, 2 + n ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_fetch_input", ret );
          return( ret );
      }
  
      ssl->handshake->update_checksum( ssl, buf + 2, n );
  
      buf = ssl->in_msg;
      n = ssl->in_left - 5;
  
      /*
       *    0  .   1   ciphersuitelist length
       *    2  .   3   session id length
       *    4  .   5   challenge length
       *    6  .  ..   ciphersuitelist
       *   ..  .  ..   session id
       *   ..  .  ..   challenge
       */
      MBEDTLS_SSL_DEBUG_BUF( 4, "record contents", buf, n );
  
      ciph_len = ( buf[0] << 8 ) | buf[1];
      sess_len = ( buf[2] << 8 ) | buf[3];
      chal_len = ( buf[4] << 8 ) | buf[5];
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "ciph_len: %u, sess_len: %u, chal_len: %u",
                     ciph_len, sess_len, chal_len ) );
  
      /*
       * Make sure each parameter length is valid
       */
      if( ciph_len < 3 || ( ciph_len % 3 ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      if( sess_len > 32 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      if( chal_len < 8 || chal_len > 32 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      if( n != 6 + ciph_len + sess_len + chal_len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, ciphersuitelist",
                     buf + 6, ciph_len );
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, session id",
                     buf + 6 + ciph_len, sess_len );
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, challenge",
                     buf + 6 + ciph_len + sess_len, chal_len );
  
      p = buf + 6 + ciph_len;
      ssl->session_negotiate->id_len = sess_len;
      memset( ssl->session_negotiate->id, 0,
              sizeof( ssl->session_negotiate->id ) );
      memcpy( ssl->session_negotiate->id, p, ssl->session_negotiate->id_len );
  
      p += sess_len;
      mbedtls_platform_zeroize( ssl->handshake->randbytes, 64 );
      memcpy( ssl->handshake->randbytes + 32 - chal_len, p, chal_len );
  
      /*
       * Check for TLS_EMPTY_RENEGOTIATION_INFO_SCSV
       */
      for( i = 0, p = buf + 6; i < ciph_len; i += 3, p += 3 )
      {
          if( p[0] == 0 && p[1] == 0 && p[2] == MBEDTLS_SSL_EMPTY_RENEGOTIATION_INFO )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "received TLS_EMPTY_RENEGOTIATION_INFO " ) );
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
              if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "received RENEGOTIATION SCSV "
                                      "during renegotiation" ) );
  
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
              ssl->secure_renegotiation = MBEDTLS_SSL_SECURE_RENEGOTIATION;
              break;
          }
      }
  
  #if defined(MBEDTLS_SSL_FALLBACK_SCSV)
      for( i = 0, p = buf + 6; i < ciph_len; i += 3, p += 3 )
      {
          if( p[0] == 0 &&
              p[1] == (unsigned char)( ( MBEDTLS_SSL_FALLBACK_SCSV_VALUE >> 8 ) & 0xff ) &&
              p[2] == (unsigned char)( ( MBEDTLS_SSL_FALLBACK_SCSV_VALUE      ) & 0xff ) )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "received FALLBACK_SCSV" ) );
  
              if( ssl->minor_ver < ssl->conf->max_minor_ver )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "inapropriate fallback" ) );
  
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_INAPROPRIATE_FALLBACK );
  
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
  
              break;
          }
      }
  #endif /* MBEDTLS_SSL_FALLBACK_SCSV */
  
      got_common_suite = 0;
      ciphersuites = ssl->conf->ciphersuite_list[ssl->minor_ver];
      ciphersuite_info = NULL;
  
      /* [jart] grab some client ciphers for error messages */
      bzero(ssl->client_ciphers, sizeof(ssl->client_ciphers));
      for( i = j = 0, p = buf + 6; j < ciph_len; j += 3, p += 3 )
          if( !p[0] && i < ARRAYLEN( ssl->client_ciphers ) )
              ssl->client_ciphers[i++] = p[1] << 8 | p[2];
  
  #if defined(MBEDTLS_SSL_SRV_RESPECT_CLIENT_PREFERENCE)
      for( j = 0, p = buf + 6; j < ciph_len; j += 3, p += 3 )
          for( i = 0; ciphersuites[i] != 0; i++ )
  #else
      for( i = 0; ciphersuites[i] != 0; i++ )
          for( j = 0, p = buf + 6; j < ciph_len; j += 3, p += 3 )
  #endif
          {
              if( p[0] || (p[1] << 8 | p[2]) != ciphersuites[i] )
                  continue;
  
              got_common_suite = 1;
  
              if( ( ret = ssl_ciphersuite_match( ssl, ciphersuites[i],
                                                 &ciphersuite_info ) ) != 0 )
                  return( ret );
  
              if( ciphersuite_info != NULL )
                  goto have_ciphersuite_v2;
          }
  
      if( got_common_suite )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "got ciphersuites in common, "
                              "but none of them usable" ) );
          return( MBEDTLS_ERR_SSL_NO_USABLE_CIPHERSUITE );
      }
      else
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no ciphersuites in common" ) );
          return( MBEDTLS_ERR_SSL_NO_CIPHER_CHOSEN );
      }
  
  have_ciphersuite_v2:
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "selected ciphersuite: %s", ciphersuite_info->name ) );
  
      ssl->session_negotiate->ciphersuite = ciphersuites[i];
      ssl->handshake->ciphersuite_info = ciphersuite_info;
  
      /*
       * SSLv2 Client Hello relevant renegotiation security checks
       */
      if( ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
          ssl->conf->allow_legacy_renegotiation == MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "legacy renegotiation, breaking off handshake" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      ssl->in_left = 0;
      ssl->state++;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse client hello v2" ) );
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_SRV_SUPPORT_SSLV2_CLIENT_HELLO */
  
  /* This function doesn't alert on errors that happen early during
     ClientHello parsing because they might indicate that the client is
     not talking SSL/TLS at all and would not understand our alert. */
  static int ssl_parse_client_hello( mbedtls_ssl_context *ssl )
  {
      int ret, got_common_suite;
      size_t i, j;
      size_t ciph_offset, comp_offset, ext_offset;
      size_t msg_len, ciph_len, sess_len, comp_len, ext_len;
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      size_t cookie_offset, cookie_len;
  #endif
      unsigned char *buf, *p, *ext;
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      int renegotiation_info_seen = 0;
  #endif
      int handshake_failure = 0;
      const uint16_t *ciphersuites;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
      int major, minor;
  
      /* If there is no signature-algorithm extension present,
       * we need to fall back to the default values for allowed
       * signature-hash pairs. */
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
      defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
      int sig_hash_alg_ext_present = 0;
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
            MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse client hello" ) );
  
  #if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
  read_record_header:
  #endif
      /*
       * If renegotiating, then the input was read with mbedtls_ssl_read_record(),
       * otherwise read it ourselves manually in order to support SSLv2
       * ClientHello, which doesn't use the same record layer format.
       */
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status == MBEDTLS_SSL_INITIAL_HANDSHAKE )
  #endif
      {
          if( ( ret = mbedtls_ssl_fetch_input( ssl, 5 ) ) != 0 )
          {
              /* No alert on a read error. */
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_fetch_input", ret );
              return( ret );
          }
      }
  
      buf = ssl->in_hdr;
  
  #if defined(MBEDTLS_SSL_SRV_SUPPORT_SSLV2_CLIENT_HELLO)
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_STREAM )
  #endif
          if( ( buf[0] & 0x80 ) != 0 )
              return( ssl_parse_client_hello_v2( ssl ) );
  #endif
  
      MBEDTLS_SSL_DEBUG_BUF( 4, "record header", buf, mbedtls_ssl_in_hdr_len( ssl ) );
  
      /*
       * SSLv3/TLS Client Hello
       *
       * Record layer:
       *     0  .   0   message type
       *     1  .   2   protocol version
       *     3  .   11  DTLS: epoch + record sequence number
       *     3  .   4   message length
       */
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, message type: %d",
                     buf[0] ) );
  
      if( buf[0] != MBEDTLS_SSL_MSG_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, message len.: %d",
                     ( ssl->in_len[0] << 8 ) | ssl->in_len[1] ) );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, protocol version: [%d:%d]",
                     buf[1], buf[2] ) );
  
      mbedtls_ssl_read_version( &major, &minor, ssl->conf->transport, buf + 1 );
  
      /* According to RFC 5246 Appendix E.1, the version here is typically
       * "{03,00}, the lowest version number supported by the client, [or] the
       * value of ClientHello.client_version", so the only meaningful check here
       * is the major version shouldn't be less than 3 */
      if( major < MBEDTLS_SSL_MAJOR_VERSION_3 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /* For DTLS if this is the initial handshake, remember the client sequence
       * number to use it in our next message (RFC 6347 4.2.1) */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
          && ssl->renego_status == MBEDTLS_SSL_INITIAL_HANDSHAKE
  #endif
          )
      {
          /* Epoch should be 0 for initial handshakes */
          if( ssl->in_ctr[0] != 0 || ssl->in_ctr[1] != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
          }
  
          memcpy( ssl->cur_out_ctr + 2, ssl->in_ctr + 2, 6 );
  
  #if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
          if( mbedtls_ssl_dtls_replay_check( ssl ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "replayed record, discarding" ) );
              ssl->next_record_offset = 0;
              ssl->in_left = 0;
              goto read_record_header;
          }
  
          /* No MAC to check yet, so we can update right now */
          mbedtls_ssl_dtls_replay_update( ssl );
  #endif
      }
  #endif /* MBEDTLS_SSL_PROTO_DTLS */
  
      msg_len = ( ssl->in_len[0] << 8 ) | ssl->in_len[1];
  
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE )
      {
          /* Set by mbedtls_ssl_read_record() */
          msg_len = ssl->in_hslen;
      }
      else
  #endif
      {
          if( msg_len > MBEDTLS_SSL_IN_CONTENT_LEN )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
          }
  
          if( ( ret = mbedtls_ssl_fetch_input( ssl,
                         mbedtls_ssl_in_hdr_len( ssl ) + msg_len ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_fetch_input", ret );
              return( ret );
          }
  
      /* Done reading this record, get ready for the next one */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
          if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
              ssl->next_record_offset = msg_len + mbedtls_ssl_in_hdr_len( ssl );
          else
  #endif
              ssl->in_left = 0;
      }
  
      buf = ssl->in_msg;
  
      MBEDTLS_SSL_DEBUG_BUF( 4, "record contents", buf, msg_len );
  
      ssl->handshake->update_checksum( ssl, buf, msg_len );
  
      /*
       * Handshake layer:
       *     0  .   0   handshake type
       *     1  .   3   handshake length
       *     4  .   5   DTLS only: message seqence number
       *     6  .   8   DTLS only: fragment offset
       *     9  .  11   DTLS only: fragment length
       */
      if( msg_len < mbedtls_ssl_hs_hdr_len( ssl ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, handshake type: %d", buf[0] ) );
  
      if( buf[0] != MBEDTLS_SSL_HS_CLIENT_HELLO )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, handshake len.: %d",
                     ( buf[1] << 16 ) | ( buf[2] << 8 ) | buf[3] ) );
  
      /* We don't support fragmentation of ClientHello (yet?) */
      if( buf[1] != 0 ||
          msg_len != mbedtls_ssl_hs_hdr_len( ssl ) + ( ( buf[2] << 8 ) | buf[3] ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
      {
          /*
           * Copy the client's handshake message_seq on initial handshakes,
           * check sequence number on renego.
           */
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
          if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
          {
              /* This couldn't be done in ssl_prepare_handshake_record() */
              unsigned int cli_msg_seq = ( ssl->in_msg[4] << 8 ) |
                                           ssl->in_msg[5];
  
              if( cli_msg_seq != ssl->handshake->in_msg_seq )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message_seq: "
                                      "%u (expected %u)", cli_msg_seq,
                                      ssl->handshake->in_msg_seq ) );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
  
              ssl->handshake->in_msg_seq++;
          }
          else
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
          {
              unsigned int cli_msg_seq = ( ssl->in_msg[4] << 8 ) |
                                           ssl->in_msg[5];
              ssl->handshake->out_msg_seq = cli_msg_seq;
              ssl->handshake->in_msg_seq  = cli_msg_seq + 1;
          }
  
          /*
           * For now we don't support fragmentation, so make sure
           * fragment_offset == 0 and fragment_length == length
           */
          if( ssl->in_msg[6] != 0 || ssl->in_msg[7] != 0 || ssl->in_msg[8] != 0 ||
              timingsafe_bcmp( ssl->in_msg + 1, ssl->in_msg + 9, 3 ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "ClientHello fragmentation not supported" ) );
              return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
          }
      }
  #endif /* MBEDTLS_SSL_PROTO_DTLS */
  
      buf += mbedtls_ssl_hs_hdr_len( ssl );
      msg_len -= mbedtls_ssl_hs_hdr_len( ssl );
  
      /*
       * ClientHello layer:
       *     0  .   1   protocol version
       *     2  .  33   random bytes (starting with 4 bytes of Unix time)
       *    34  .  35   session id length (1 byte)
       *    35  . 34+x  session id
       *   35+x . 35+x  DTLS only: cookie length (1 byte)
       *   36+x .  ..   DTLS only: cookie
       *    ..  .  ..   ciphersuite list length (2 bytes)
       *    ..  .  ..   ciphersuite list
       *    ..  .  ..   compression alg. list length (1 byte)
       *    ..  .  ..   compression alg. list
       *    ..  .  ..   extensions length (2 bytes, optional)
       *    ..  .  ..   extensions (optional)
       */
  
      /*
       * Minimal length (with everything empty and extensions omitted) is
       * 2 + 32 + 1 + 2 + 1 = 38 bytes. Check that first, so that we can
       * read at least up to session id length without worrying.
       */
      if( msg_len < 38 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /*
       * Check and save the protocol version
       */
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, version", buf, 2 );
  
      mbedtls_ssl_read_version( &ssl->major_ver, &ssl->minor_ver,
                        ssl->conf->transport, buf );
  
      ssl->handshake->max_major_ver = ssl->major_ver;
      ssl->handshake->max_minor_ver = ssl->minor_ver;
  
      if( ssl->major_ver < ssl->conf->min_major_ver ||
          ssl->minor_ver < ssl->conf->min_minor_ver )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "client only supports ssl smaller than minimum"
                              " [%d:%d] < [%d:%d]",
                              ssl->major_ver, ssl->minor_ver,
                              ssl->conf->min_major_ver, ssl->conf->min_minor_ver ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION );
          return( MBEDTLS_ERR_SSL_BAD_HS_PROTOCOL_VERSION );
      }
  
      if( ssl->major_ver > ssl->conf->max_major_ver )
      {
          ssl->major_ver = ssl->conf->max_major_ver;
          ssl->minor_ver = ssl->conf->max_minor_ver;
      }
      else if( ssl->minor_ver > ssl->conf->max_minor_ver )
          ssl->minor_ver = ssl->conf->max_minor_ver;
  
      /*
       * Save client random (inc. Unix time)
       */
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, random bytes", buf + 2, 32 );
  
      memcpy( ssl->handshake->randbytes, buf + 2, 32 );
  
      /*
       * Check the session ID length and save session ID
       */
      sess_len = buf[34];
  
      if( sess_len > sizeof( ssl->session_negotiate->id ) ||
          sess_len + 34 + 2 > msg_len ) /* 2 for cipherlist length field */
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, session id", buf + 35, sess_len );
  
      ssl->session_negotiate->id_len = sess_len;
      mbedtls_platform_zeroize( ssl->session_negotiate->id, 
                                sizeof( ssl->session_negotiate->id ) );
      memcpy( ssl->session_negotiate->id, buf + 35,
              ssl->session_negotiate->id_len );
  
      /*
       * Check the cookie length and content
       */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
      {
          cookie_offset = 35 + sess_len;
          cookie_len = buf[cookie_offset];
  
          if( cookie_offset + 1 + cookie_len + 2 > msg_len )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
          }
  
          MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, cookie",
                         buf + cookie_offset + 1, cookie_len );
  
  #if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY)
          if( ssl->conf->f_cookie_check != NULL
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
              && ssl->renego_status == MBEDTLS_SSL_INITIAL_HANDSHAKE
  #endif
              )
          {
              if( ssl->conf->f_cookie_check( ssl->conf->p_cookie,
                                       buf + cookie_offset + 1, cookie_len,
                                       ssl->cli_id, ssl->cli_id_len ) != 0 )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 2, ( "cookie verification failed" ) );
                  ssl->handshake->verify_cookie_len = 1;
              }
              else
              {
                  MBEDTLS_SSL_DEBUG_MSG( 2, ( "cookie verification passed" ) );
                  ssl->handshake->verify_cookie_len = 0;
              }
          }
          else
  #endif /* MBEDTLS_SSL_DTLS_HELLO_VERIFY */
          {
              /* We know we didn't send a cookie, so it should be empty */
              if( cookie_len != 0 )
              {
                  /* This may be an attacker's probe, so don't send an alert */
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
  
              MBEDTLS_SSL_DEBUG_MSG( 2, ( "cookie verification skipped" ) );
          }
  
      /*
       * Check the ciphersuitelist length (will be parsed later)
       */
          ciph_offset = cookie_offset + 1 + cookie_len;
      }
      else
  #endif /* MBEDTLS_SSL_PROTO_DTLS */
          ciph_offset = 35 + sess_len;
  
      ciph_len = ( buf[ciph_offset + 0] << 8 )
               | ( buf[ciph_offset + 1]      );
  
      if( ciph_len < 2 ||
          ciph_len + 2 + ciph_offset + 1 > msg_len || /* 1 for comp. alg. len */
          ( ciph_len % 2 ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, ciphersuitelist",
                     buf + ciph_offset + 2,  ciph_len );
  
      /*
       * Check the compression algorithms length and pick one
       */
      comp_offset = ciph_offset + 2 + ciph_len;
  
      comp_len = buf[comp_offset];
  
      if( comp_len < 1 ||
          comp_len > 16 ||
          comp_len + comp_offset + 1 > msg_len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, compression",
                        buf + comp_offset + 1, comp_len );
  
      ssl->session_negotiate->compression = MBEDTLS_SSL_COMPRESS_NULL;
  #if defined(MBEDTLS_ZLIB_SUPPORT)
      if( !ssl->conf->disable_compression )
      {
          for( i = 0; i < comp_len; ++i )
          {
              if( buf[comp_offset + 1 + i] == MBEDTLS_SSL_COMPRESS_DEFLATE )
              {
                  ssl->session_negotiate->compression = MBEDTLS_SSL_COMPRESS_DEFLATE;
                  break;
              }
          }
      }
  #endif
  
      /* See comments in ssl_write_client_hello() */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
          ssl->session_negotiate->compression = MBEDTLS_SSL_COMPRESS_NULL;
  #endif
  
      /* Do not parse the extensions if the protocol is SSLv3 */
  #if defined(MBEDTLS_SSL_PROTO_SSL3)
      if( ( ssl->major_ver != 3 ) || ( ssl->minor_ver != 0 ) )
      {
  #endif
          /*
           * Check the extension length
           */
          ext_offset = comp_offset + 1 + comp_len;
          if( msg_len > ext_offset )
          {
              if( msg_len < ext_offset + 2 )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
  
              ext_len = ( buf[ext_offset + 0] << 8 )
                      | ( buf[ext_offset + 1]      );
  
              if( ( ext_len > 0 && ext_len < 4 ) ||
                  msg_len != ext_offset + 2 + ext_len )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
          }
          else
              ext_len = 0;
  
          ext = buf + ext_offset + 2;
          MBEDTLS_SSL_DEBUG_BUF( 3, "client hello extensions", ext, ext_len );
  
          while( ext_len != 0 )
          {
              unsigned int ext_id;
              unsigned int ext_size;
              if ( ext_len < 4 ) {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                 MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
              ext_id   = ( ( ext[0] <<  8 ) | ( ext[1] ) );
              ext_size = ( ( ext[2] <<  8 ) | ( ext[3] ) );
  
              if( ext_size + 4 > ext_len )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
              switch( ext_id )
              {
  #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
              case MBEDTLS_TLS_EXT_SERVERNAME:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found ServerName extension" ) );
                  if( ssl->conf->f_sni == NULL )
                      break;
  
                  ret = ssl_parse_servername_ext( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
  
              case MBEDTLS_TLS_EXT_RENEGOTIATION_INFO:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found renegotiation extension" ) );
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
                  renegotiation_info_seen = 1;
  #endif
  
                  ret = ssl_parse_renegotiation_info( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
      defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
              case MBEDTLS_TLS_EXT_SIG_ALG:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found signature_algorithms extension" ) );
  
                  ret = ssl_parse_signature_algorithms_ext( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
  
                  sig_hash_alg_ext_present = 1;
                  break;
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
            MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
  
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
              case MBEDTLS_TLS_EXT_SUPPORTED_ELLIPTIC_CURVES:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found supported elliptic curves extension" ) );
  
                  ret = ssl_parse_supported_elliptic_curves( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  
              case MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found supported point formats extension" ) );
                  ssl->handshake->cli_exts |= MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS_PRESENT;
  
                  ret = ssl_parse_supported_point_formats( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C ||
            MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
              case MBEDTLS_TLS_EXT_ECJPAKE_KKPP:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found ecjpake kkpp extension" ) );
  
                  ret = ssl_parse_ecjpake_kkpp( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
  
  #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
              case MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found max fragment length extension" ) );
  
                  ret = ssl_parse_max_fragment_length_ext( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
  
  #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
              case MBEDTLS_TLS_EXT_CID:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found CID extension" ) );
  #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
  
  #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
              case MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found encrypt then mac extension" ) );
  
                  ret = ssl_parse_encrypt_then_mac_ext( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
  
  #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
              case MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found extended master secret extension" ) );
  
                  ret = ssl_parse_extended_ms_ext( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
              case MBEDTLS_TLS_EXT_SESSION_TICKET:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found session ticket extension" ) );
  
                  ret = ssl_parse_session_ticket_ext( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  #if defined(MBEDTLS_SSL_ALPN)
              case MBEDTLS_TLS_EXT_ALPN:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found alpn extension" ) );
  
                  ret = ssl_parse_alpn_ext( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  #if defined(MBEDTLS_SSL_DTLS_SRTP)
              case MBEDTLS_TLS_EXT_USE_SRTP:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "found use_srtp extension" ) );
  
                  ret = ssl_parse_use_srtp_ext( ssl, ext + 4, ext_size );
                  if( ret != 0 )
                      return( ret );
                  break;
  #endif /* MBEDTLS_SSL_DTLS_SRTP */
  
              default:
                  MBEDTLS_SSL_DEBUG_MSG( 3, ( "unknown extension found: %u (ignoring)",
                                 ext_id ) );
              }
  
              ext_len -= 4 + ext_size;
              ext += 4 + ext_size;
  
              if( ext_len > 0 && ext_len < 4 )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
          }
  #if defined(MBEDTLS_SSL_PROTO_SSL3)
      }
  #endif
  
  #if defined(MBEDTLS_SSL_FALLBACK_SCSV)
      for( i = 0, p = buf + ciph_offset + 2; i < ciph_len; i += 2, p += 2 )
      {
          if( p[0] == (unsigned char)( ( MBEDTLS_SSL_FALLBACK_SCSV_VALUE >> 8 ) & 0xff ) &&
              p[1] == (unsigned char)( ( MBEDTLS_SSL_FALLBACK_SCSV_VALUE      ) & 0xff ) )
          {
              MBEDTLS_SSL_DEBUG_MSG( 2, ( "received FALLBACK_SCSV" ) );
  
              if( ssl->minor_ver < ssl->conf->max_minor_ver )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "inapropriate fallback" ) );
  
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_INAPROPRIATE_FALLBACK );
  
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
  
              break;
          }
      }
  #endif /* MBEDTLS_SSL_FALLBACK_SCSV */
  
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
      defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
  
      /*
       * Try to fall back to default hash SHA1 if the client
       * hasn't provided any preferred signature-hash combinations.
       */
      if( sig_hash_alg_ext_present == 0 )
      {
          mbedtls_md_type_t md_default = MBEDTLS_MD_SHA1;
  
          if( mbedtls_ssl_check_sig_hash( ssl, md_default ) != 0 )
              md_default = MBEDTLS_MD_NONE;
  
          mbedtls_ssl_sig_hash_set_const_hash( &ssl->handshake->hash_algs, md_default );
      }
  
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
            MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
  
      /*
       * Check for TLS_EMPTY_RENEGOTIATION_INFO_SCSV
       */
      for( i = 0, p = buf + ciph_offset + 2; i < ciph_len; i += 2, p += 2 )
      {
          if( p[0] == 0 && p[1] == MBEDTLS_SSL_EMPTY_RENEGOTIATION_INFO )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "received TLS_EMPTY_RENEGOTIATION_INFO " ) );
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
              if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "received RENEGOTIATION SCSV "
                                              "during renegotiation" ) );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
                  return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
              }
  #endif
              ssl->secure_renegotiation = MBEDTLS_SSL_SECURE_RENEGOTIATION;
              break;
          }
      }
  
      /*
       * Renegotiation security checks
       */
      if( ssl->secure_renegotiation != MBEDTLS_SSL_SECURE_RENEGOTIATION &&
          ssl->conf->allow_legacy_renegotiation == MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "legacy renegotiation, breaking off handshake" ) );
          handshake_failure = 1;
      }
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      else if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
               ssl->secure_renegotiation == MBEDTLS_SSL_SECURE_RENEGOTIATION &&
               renegotiation_info_seen == 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "renegotiation_info extension missing (secure)" ) );
          handshake_failure = 1;
      }
      else if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
               ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
               ssl->conf->allow_legacy_renegotiation == MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "legacy renegotiation not allowed" ) );
          handshake_failure = 1;
      }
      else if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
               ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
               renegotiation_info_seen == 1 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "renegotiation_info extension present (legacy)" ) );
          handshake_failure = 1;
      }
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
  
      if( handshake_failure == 1 )
      {
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
      }
  
      /* [jart] grab some client ciphers for error messages */
      bzero(ssl->client_ciphers, sizeof(ssl->client_ciphers));
      for( i = j = 0, p = buf + ciph_offset + 2; j < ciph_len; j += 2, p += 2 )
          if( i < ARRAYLEN( ssl->client_ciphers ) )
              ssl->client_ciphers[i++] = p[0] << 8 | p[1];
  
      /*
       * Search for a matching ciphersuite
       * (At the end because we need information from the EC-based extensions
       * and certificate from the SNI callback triggered by the SNI extension.)
       */
      got_common_suite = 0;
      ciphersuites = ssl->conf->ciphersuite_list[ssl->minor_ver];
      ciphersuite_info = NULL;
  #if defined(MBEDTLS_SSL_SRV_RESPECT_CLIENT_PREFERENCE)
      for( j = 0, p = buf + ciph_offset + 2; j < ciph_len; j += 2, p += 2 )
          for( i = 0; ciphersuites[i] != 0; i++ )
  #else
      for( i = 0; ciphersuites[i] != 0; i++ )
          for( j = 0, p = buf + ciph_offset + 2; j < ciph_len; j += 2, p += 2 )
  #endif
          {
              if( p[0] != ( ( ciphersuites[i] >> 8 ) & 0xFF ) ||
                  p[1] != ( ( ciphersuites[i]      ) & 0xFF ) )
                  continue;
  
              got_common_suite = 1;
  
              if( ( ret = ssl_ciphersuite_match( ssl, ciphersuites[i],
                                                 &ciphersuite_info ) ) != 0 )
                  return( ret );
  
              if( ciphersuite_info != NULL )
                  goto have_ciphersuite;
          }
  
      if( got_common_suite )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "got ciphersuites in common, "
                              "but none of them usable" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_NO_USABLE_CIPHERSUITE );
      }
      else
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no ciphersuites in common" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_NO_CIPHER_CHOSEN );
      }
  
  have_ciphersuite:
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "selected ciphersuite: %s", ciphersuite_info->name ) );
  
      ssl->session_negotiate->ciphersuite = ciphersuites[i];
      ssl->handshake->ciphersuite_info = ciphersuite_info;
  
      ssl->state++;
  
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
          mbedtls_ssl_recv_flight_completed( ssl );
  #endif
  
      /* Debugging-only output for testsuite */
  #if defined(MBEDTLS_DEBUG_C)                         && \
      defined(MBEDTLS_SSL_PROTO_TLS1_2)                && \
      defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
      if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
      {
          mbedtls_pk_type_t sig_alg = mbedtls_ssl_get_ciphersuite_sig_alg( ciphersuite_info );
          if( sig_alg != MBEDTLS_PK_NONE )
          {
              mbedtls_md_type_t md_alg = mbedtls_ssl_sig_hash_set_find( &ssl->handshake->hash_algs,
                                                                    sig_alg );
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, signature_algorithm ext: %d",
                                          mbedtls_ssl_hash_from_md_alg( md_alg ) ) );
          }
          else
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "no hash algorithm for signature algorithm "
                                          "%u - should not happen", (unsigned) sig_alg ) );
          }
      }
  #endif
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse client hello" ) );
  
      return( 0 );
  }
  
  #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
  static void ssl_write_cid_ext( mbedtls_ssl_context *ssl,
                                 unsigned char *buf,
                                 size_t *olen )
  {
      unsigned char *p = buf;
      size_t ext_len;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
  
      *olen = 0;
  
      /* Skip writing the extension if we don't want to use it or if
       * the client hasn't offered it. */
      if( ssl->handshake->cid_in_use == MBEDTLS_SSL_CID_DISABLED )
          return;
  
      /* ssl->own_cid_len is at most MBEDTLS_SSL_CID_IN_LEN_MAX
       * which is at most 255, so the increment cannot overflow. */
      if( end < p || (size_t)( end - p ) < (unsigned)( ssl->own_cid_len + 5 ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, adding CID extension" ) );
  
      /*
       * Quoting draft-ietf-tls-dtls-connection-id-05
       * https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05
       *
       *   struct {
       *      opaque cid<0..2^8-1>;
       *   } ConnectionId;
      */
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_CID >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_CID      ) & 0xFF );
      ext_len = (size_t) ssl->own_cid_len + 1;
      *p++ = (unsigned char)( ( ext_len >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( ext_len      ) & 0xFF );
  
      *p++ = (uint8_t) ssl->own_cid_len;
      memcpy( p, ssl->own_cid, ssl->own_cid_len );
  
      *olen = ssl->own_cid_len + 5;
  }
  #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
  
  #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
  static void ssl_write_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
                                              unsigned char *buf,
                                              size_t *olen )
  {
      unsigned char *p = buf;
      const mbedtls_ssl_ciphersuite_t *suite = NULL;
      const mbedtls_cipher_info_t *cipher = NULL;
  
      if( ssl->session_negotiate->encrypt_then_mac == MBEDTLS_SSL_ETM_DISABLED ||
          ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
      {
          *olen = 0;
          return;
      }
  
      /*
       * RFC 7366: "If a server receives an encrypt-then-MAC request extension
       * from a client and then selects a stream or Authenticated Encryption
       * with Associated Data (AEAD) ciphersuite, it MUST NOT send an
       * encrypt-then-MAC response extension back to the client."
       */
      if( ( suite = mbedtls_ssl_ciphersuite_from_id(
                      ssl->session_negotiate->ciphersuite ) ) == NULL ||
          ( cipher = mbedtls_cipher_info_from_type( suite->cipher ) ) == NULL ||
          cipher->mode != MBEDTLS_MODE_CBC )
      {
          *olen = 0;
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, adding encrypt then mac extension" ) );
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC      ) & 0xFF );
  
      *p++ = 0x00;
      *p++ = 0x00;
  
      *olen = 4;
  }
  #endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
  
  #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
  static void ssl_write_extended_ms_ext( mbedtls_ssl_context *ssl,
                                         unsigned char *buf,
                                         size_t *olen )
  {
      unsigned char *p = buf;
  
      if( ssl->handshake->extended_ms == MBEDTLS_SSL_EXTENDED_MS_DISABLED ||
          ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
      {
          *olen = 0;
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, adding extended master secret "
                          "extension" ) );
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET      ) & 0xFF );
  
      *p++ = 0x00;
      *p++ = 0x00;
  
      *olen = 4;
  }
  #endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
  static void ssl_write_session_ticket_ext( mbedtls_ssl_context *ssl,
                                            unsigned char *buf,
                                            size_t *olen )
  {
      unsigned char *p = buf;
  
      if( ssl->handshake->new_session_ticket == 0 )
      {
          *olen = 0;
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, adding session ticket extension" ) );
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SESSION_TICKET >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SESSION_TICKET      ) & 0xFF );
  
      *p++ = 0x00;
      *p++ = 0x00;
  
      *olen = 4;
  }
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  static void ssl_write_renegotiation_ext( mbedtls_ssl_context *ssl,
                                           unsigned char *buf,
                                           size_t *olen )
  {
      unsigned char *p = buf;
  
      if( ssl->secure_renegotiation != MBEDTLS_SSL_SECURE_RENEGOTIATION )
      {
          *olen = 0;
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, secure renegotiation extension" ) );
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_RENEGOTIATION_INFO >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_RENEGOTIATION_INFO      ) & 0xFF );
  
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE )
      {
          *p++ = 0x00;
          *p++ = ( ssl->verify_data_len * 2 + 1 ) & 0xFF;
          *p++ = ssl->verify_data_len * 2 & 0xFF;
  
          memcpy( p, ssl->peer_verify_data, ssl->verify_data_len );
          p += ssl->verify_data_len;
          memcpy( p, ssl->own_verify_data, ssl->verify_data_len );
          p += ssl->verify_data_len;
      }
      else
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
      {
          *p++ = 0x00;
          *p++ = 0x01;
          *p++ = 0x00;
      }
  
      *olen = p - buf;
  }
  
  #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
  static void ssl_write_max_fragment_length_ext( mbedtls_ssl_context *ssl,
                                                 unsigned char *buf,
                                                 size_t *olen )
  {
      unsigned char *p = buf;
  
      if( ssl->session_negotiate->mfl_code == MBEDTLS_SSL_MAX_FRAG_LEN_NONE )
      {
          *olen = 0;
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, max_fragment_length extension" ) );
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH      ) & 0xFF );
  
      *p++ = 0x00;
      *p++ = 1;
  
      *p++ = ssl->session_negotiate->mfl_code;
  
      *olen = 5;
  }
  #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
  
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
  static void ssl_write_supported_point_formats_ext( mbedtls_ssl_context *ssl,
                                                     unsigned char *buf,
                                                     size_t *olen )
  {
      unsigned char *p = buf;
      ((void) ssl);
  
      if( ( ssl->handshake->cli_exts &
            MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS_PRESENT ) == 0 )
      {
          *olen = 0;
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, supported_point_formats extension" ) );
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS      ) & 0xFF );
  
      *p++ = 0x00;
      *p++ = 2;
  
      *p++ = 1;
      *p++ = MBEDTLS_ECP_PF_UNCOMPRESSED;
  
      *olen = 6;
  }
  #endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C || MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
  static void ssl_write_ecjpake_kkpp_ext( mbedtls_ssl_context *ssl,
                                          unsigned char *buf,
                                          size_t *olen )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
      size_t kkpp_len;
  
      *olen = 0;
  
      /* Skip costly computation if not needed */
      if( ssl->handshake->ciphersuite_info->key_exchange !=
          MBEDTLS_KEY_EXCHANGE_ECJPAKE )
          return;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, ecjpake kkpp extension" ) );
  
      if( end - p < 4 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ECJPAKE_KKPP >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ECJPAKE_KKPP      ) & 0xFF );
  
      ret = mbedtls_ecjpake_write_round_one( &ssl->handshake->ecjpake_ctx,
                                          p + 2, end - p - 2, &kkpp_len,
                                          ssl->conf->f_rng, ssl->conf->p_rng );
      if( ret != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1 , "mbedtls_ecjpake_write_round_one", ret );
          return;
      }
  
      *p++ = (unsigned char)( ( kkpp_len >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( kkpp_len      ) & 0xFF );
  
      *olen = kkpp_len + 4;
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
  
  #if defined(MBEDTLS_SSL_ALPN )
  static void ssl_write_alpn_ext( mbedtls_ssl_context *ssl,
                                  unsigned char *buf, size_t *olen )
  {
      if( ssl->alpn_chosen == NULL )
      {
          *olen = 0;
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, adding alpn extension" ) );
  
      /*
       * 0 . 1    ext identifier
       * 2 . 3    ext length
       * 4 . 5    protocol list length
       * 6 . 6    protocol name length
       * 7 . 7+n  protocol name
       */
      buf[0] = (unsigned char)( ( MBEDTLS_TLS_EXT_ALPN >> 8 ) & 0xFF );
      buf[1] = (unsigned char)( ( MBEDTLS_TLS_EXT_ALPN      ) & 0xFF );
  
      *olen = 7 + strlen( ssl->alpn_chosen );
  
      buf[2] = (unsigned char)( ( ( *olen - 4 ) >> 8 ) & 0xFF );
      buf[3] = (unsigned char)( ( ( *olen - 4 )      ) & 0xFF );
  
      buf[4] = (unsigned char)( ( ( *olen - 6 ) >> 8 ) & 0xFF );
      buf[5] = (unsigned char)( ( ( *olen - 6 )      ) & 0xFF );
  
      buf[6] = (unsigned char)( ( ( *olen - 7 )      ) & 0xFF );
  
      memcpy( buf + 7, ssl->alpn_chosen, *olen - 7 );
  }
  #endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C */
  
  #if defined(MBEDTLS_SSL_DTLS_SRTP ) && defined(MBEDTLS_SSL_PROTO_DTLS)
  static void ssl_write_use_srtp_ext( mbedtls_ssl_context *ssl,
                                      unsigned char *buf,
                                      size_t *olen )
  {
      size_t mki_len = 0, ext_len = 0;
      uint16_t profile_value = 0;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
  
      *olen = 0;
  
      if( ( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM ) ||
          ( ssl->dtls_srtp_info.chosen_dtls_srtp_profile == MBEDTLS_TLS_SRTP_UNSET ) )
      {
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, adding use_srtp extension" ) );
  
      if( ssl->conf->dtls_srtp_mki_support == MBEDTLS_SSL_DTLS_SRTP_MKI_SUPPORTED )
      {
          mki_len = ssl->dtls_srtp_info.mki_len;
      }
  
      /* The extension total size is 9 bytes :
       * - 2 bytes for the extension tag
       * - 2 bytes for the total size
       * - 2 bytes for the protection profile length
       * - 2 bytes for the protection profile
       * - 1 byte for the mki length
       * +  the actual mki length
       * Check we have enough room in the output buffer */
      if( (size_t)( end - buf ) < mki_len + 9 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      /* extension */
      buf[0] = (unsigned char)( ( MBEDTLS_TLS_EXT_USE_SRTP >> 8 ) & 0xFF );
      buf[1] = (unsigned char)( ( MBEDTLS_TLS_EXT_USE_SRTP      ) & 0xFF );
      /*
       * total length 5 and mki value: only one profile(2 bytes)
       *              and length(2 bytes) and srtp_mki  )
       */
      ext_len = 5 + mki_len;
      buf[2] = (unsigned char)( ( ext_len >> 8 ) & 0xFF );
      buf[3] = (unsigned char)( ext_len & 0xFF );
  
      /* protection profile length: 2 */
      buf[4] = 0x00;
      buf[5] = 0x02;
      profile_value = mbedtls_ssl_check_srtp_profile_value(
                                  ssl->dtls_srtp_info.chosen_dtls_srtp_profile );
      if( profile_value != MBEDTLS_TLS_SRTP_UNSET )
      {
          buf[6] = (unsigned char)( ( profile_value >> 8 ) & 0xFF );
          buf[7] = (unsigned char)( profile_value & 0xFF );
      }
      else
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "use_srtp extension invalid profile" ) );
          return;
      }
  
      buf[8] = mki_len & 0xFF;
      memcpy( &buf[9], ssl->dtls_srtp_info.mki_value, mki_len );
  
      *olen = 9 + mki_len;
  }
  #endif /* MBEDTLS_SSL_DTLS_SRTP */
  
  #if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY)
  static int ssl_write_hello_verify_request( mbedtls_ssl_context *ssl )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      unsigned char *p = ssl->out_msg + 4;
      unsigned char *cookie_len_byte;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write hello verify request" ) );
  
      /*
       * struct {
       *   ProtocolVersion server_version;
       *   opaque cookie<0..2^8-1>;
       * } HelloVerifyRequest;
       */
  
      /* The RFC is not clear on this point, but sending the actual negotiated
       * version looks like the most interoperable thing to do. */
      mbedtls_ssl_write_version( ssl->major_ver, ssl->minor_ver,
                         ssl->conf->transport, p );
      MBEDTLS_SSL_DEBUG_BUF( 3, "server version", p, 2 );
      p += 2;
  
      /* If we get here, f_cookie_check is not null */
      if( ssl->conf->f_cookie_write == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "inconsistent cookie callbacks" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
  
      /* Skip length byte until we know the length */
      cookie_len_byte = p++;
  
      if( ( ret = ssl->conf->f_cookie_write( ssl->conf->p_cookie,
                                       &p, ssl->out_buf + MBEDTLS_SSL_OUT_BUFFER_LEN,
                                       ssl->cli_id, ssl->cli_id_len ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "f_cookie_write", ret );
          return( ret );
      }
  
      *cookie_len_byte = (unsigned char)( p - ( cookie_len_byte + 1 ) );
  
      MBEDTLS_SSL_DEBUG_BUF( 3, "cookie sent", cookie_len_byte + 1, *cookie_len_byte );
  
      ssl->out_msglen  = p - ssl->out_msg;
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_HELLO_VERIFY_REQUEST;
  
      ssl->state = MBEDTLS_SSL_SERVER_HELLO_VERIFY_REQUEST_SENT;
  
      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_PROTO_DTLS */
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write hello verify request" ) );
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_DTLS_HELLO_VERIFY */
  
  static int ssl_write_server_hello( mbedtls_ssl_context *ssl )
  {
  #if defined(MBEDTLS_HAVE_TIME)
      mbedtls_time_t t;
  #endif
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      size_t olen, ext_len = 0, n;
      unsigned char *buf, *p;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write server hello" ) );
  
  #if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
          ssl->handshake->verify_cookie_len != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "client hello was not authenticated" ) );
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write server hello" ) );
  
          return( ssl_write_hello_verify_request( ssl ) );
      }
  #endif /* MBEDTLS_SSL_DTLS_HELLO_VERIFY */
  
      if( ssl->conf->f_rng == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided") );
          return( MBEDTLS_ERR_SSL_NO_RNG );
      }
  
      /*
       *     0  .   0   handshake type
       *     1  .   3   handshake length
       *     4  .   5   protocol version
       *     6  .   9   UNIX time()
       *    10  .  37   random bytes
       */
      buf = ssl->out_msg;
      p = buf + 4;
  
      mbedtls_ssl_write_version( ssl->major_ver, ssl->minor_ver,
                         ssl->conf->transport, p );
      p += 2;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, chosen version: [%d:%d]",
                          buf[4], buf[5] ) );
  
  #if defined(MBEDTLS_HAVE_TIME)
      t = mbedtls_time( NULL );
      *p++ = (unsigned char)( t >> 24 );
      *p++ = (unsigned char)( t >> 16 );
      *p++ = (unsigned char)( t >>  8 );
      *p++ = (unsigned char)( t       );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, current time: %" MBEDTLS_PRINTF_LONGLONG,
                                  (long long) t ) );
  #else
      if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng, p, 4 ) ) != 0 )
          return( ret );
  
      p += 4;
  #endif /* MBEDTLS_HAVE_TIME */
  
      if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng, p, 28 ) ) != 0 )
          return( ret );
  
      p += 28;
  
      memcpy( ssl->handshake->randbytes + 32, buf + 6, 32 );
  
      MBEDTLS_SSL_DEBUG_BUF( 3, "server hello, random bytes", buf + 6, 32 );
  
      /*
       * Resume is 0  by default, see ssl_handshake_init().
       * It may be already set to 1 by ssl_parse_session_ticket_ext().
       * If not, try looking up session ID in our cache.
       */
      if( ssl->handshake->resume == 0 &&
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
          ssl->renego_status == MBEDTLS_SSL_INITIAL_HANDSHAKE &&
  #endif
          ssl->session_negotiate->id_len != 0 &&
          ssl->conf->f_get_cache != NULL &&
          ssl->conf->f_get_cache( ssl->conf->p_cache, ssl->session_negotiate ) == 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "session successfully restored from cache" ) );
          ssl->handshake->resume = 1;
      }
  
      if( ssl->handshake->resume == 0 )
      {
          /*
           * New session, create a new session id,
           * unless we're about to issue a session ticket
           */
          ssl->state++;
  
  #if defined(MBEDTLS_HAVE_TIME)
          ssl->session_negotiate->start = mbedtls_time( NULL );
  #endif
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
          if( ssl->handshake->new_session_ticket != 0 )
          {
              ssl->session_negotiate->id_len = n = 0;
              mbedtls_platform_zeroize( ssl->session_negotiate->id, 32 );
          }
          else
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
          {
              ssl->session_negotiate->id_len = n = 32;
              if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng, ssl->session_negotiate->id,
                                      n ) ) != 0 )
                  return( ret );
          }
      }
      else
      {
          /*
           * Resuming a session
           */
          n = ssl->session_negotiate->id_len;
          ssl->state = MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC;
  
          if( ( ret = mbedtls_ssl_derive_keys( ssl ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_derive_keys", ret );
              return( ret );
          }
      }
  
      /*
       *    38  .  38     session id length
       *    39  . 38+n    session id
       *   39+n . 40+n    chosen ciphersuite
       *   41+n . 41+n    chosen compression alg.
       *   42+n . 43+n    extensions length
       *   44+n . 43+n+m  extensions
       */
      *p++ = (unsigned char) ssl->session_negotiate->id_len;
      memcpy( p, ssl->session_negotiate->id, ssl->session_negotiate->id_len );
      p += ssl->session_negotiate->id_len;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, session id len.: %" MBEDTLS_PRINTF_SIZET, n ) );
      MBEDTLS_SSL_DEBUG_BUF( 3,   "server hello, session id", buf + 39, n );
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "%s session has been resumed",
                     ssl->handshake->resume ? "a" : "no" ) );
  
      *p++ = (unsigned char)( ssl->session_negotiate->ciphersuite >> 8 );
      *p++ = (unsigned char)( ssl->session_negotiate->ciphersuite      );
      *p++ = (unsigned char)( ssl->session_negotiate->compression      );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, chosen ciphersuite: %s",
             mbedtls_ssl_get_ciphersuite_name( ssl->session_negotiate->ciphersuite ) ) );
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, compress alg.: 0x%02X",
                     (unsigned int) ssl->session_negotiate->compression ) );
  
      /* Do not write the extensions if the protocol is SSLv3 */
  #if defined(MBEDTLS_SSL_PROTO_SSL3)
      if( ( ssl->major_ver != 3 ) || ( ssl->minor_ver != 0 ) )
      {
  #endif
  
      /*
       *  First write extensions, then the total length
       */
      ssl_write_renegotiation_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  
  #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
      ssl_write_max_fragment_length_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
      ssl_write_cid_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
      ssl_write_encrypt_then_mac_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
      ssl_write_extended_ms_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
      ssl_write_session_ticket_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
      if ( mbedtls_ssl_ciphersuite_uses_ec(
           mbedtls_ssl_ciphersuite_from_id( ssl->session_negotiate->ciphersuite ) ) )
      {
          ssl_write_supported_point_formats_ext( ssl, p + 2 + ext_len, &olen );
          ext_len += olen;
      }
  #endif
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
      ssl_write_ecjpake_kkpp_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_SSL_ALPN)
      ssl_write_alpn_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_SSL_DTLS_SRTP)
      ssl_write_use_srtp_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, total extension length: %" MBEDTLS_PRINTF_SIZET,
                                  ext_len ) );
  
      if( ext_len > 0 )
      {
          *p++ = (unsigned char)( ( ext_len >> 8 ) & 0xFF );
          *p++ = (unsigned char)( ( ext_len      ) & 0xFF );
          p += ext_len;
      }
  
  #if defined(MBEDTLS_SSL_PROTO_SSL3)
      }
  #endif
  
      ssl->out_msglen  = p - buf;
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_SERVER_HELLO;
  
      ret = mbedtls_ssl_write_handshake_msg( ssl );
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write server hello" ) );
  
      return( ret );
  }
  
  #if !defined(MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED)
  static int ssl_write_certificate_request( mbedtls_ssl_context *ssl )
  {
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate request" ) );
  
      if( !mbedtls_ssl_ciphersuite_cert_req_allowed( ciphersuite_info ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate request" ) );
          ssl->state++;
          return( 0 );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
      return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
  }
  #else /* !MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
  static int ssl_write_certificate_request( mbedtls_ssl_context *ssl )
  {
      int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
      uint16_t dn_size, total_dn_size; /* excluding length bytes */
      size_t ct_len, sa_len; /* including length bytes */
      unsigned char *buf, *p;
      const unsigned char * const end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
      const mbedtls_x509_crt *crt;
      int authmode;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate request" ) );
  
      ssl->state++;
  
  #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
      if( ssl->handshake->sni_authmode != MBEDTLS_SSL_VERIFY_UNSET )
          authmode = ssl->handshake->sni_authmode;
      else
  #endif
          authmode = ssl->conf->authmode;
  
      if( !mbedtls_ssl_ciphersuite_cert_req_allowed( ciphersuite_info ) ||
          authmode == MBEDTLS_SSL_VERIFY_NONE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate request" ) );
          return( 0 );
      }
  
      /*
       *     0  .   0   handshake type
       *     1  .   3   handshake length
       *     4  .   4   cert type count
       *     5  .. m-1  cert types
       *     m  .. m+1  sig alg length (TLS 1.2 only)
       *    m+1 .. n-1  SignatureAndHashAlgorithms (TLS 1.2 only)
       *     n  .. n+1  length of all DNs
       *    n+2 .. n+3  length of DN 1
       *    n+4 .. ...  Distinguished Name #1
       *    ... .. ...  length of DN 2, etc.
       */
      buf = ssl->out_msg;
      p = buf + 4;
  
      /*
       * Supported certificate types
       *
       *     ClientCertificateType certificate_types<1..2^8-1>;
       *     enum { (255) } ClientCertificateType;
       */
      ct_len = 0;
  
  #if defined(MBEDTLS_RSA_C)
      p[1 + ct_len++] = MBEDTLS_SSL_CERT_TYPE_RSA_SIGN;
  #endif
  #if defined(MBEDTLS_ECDSA_C)
      p[1 + ct_len++] = MBEDTLS_SSL_CERT_TYPE_ECDSA_SIGN;
  #endif
  
      p[0] = (unsigned char) ct_len++;
      p += ct_len;
  
      sa_len = 0;
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
      /*
       * Add signature_algorithms for verify (TLS 1.2)
       *
       *     SignatureAndHashAlgorithm supported_signature_algorithms<2..2^16-2>;
       *
       *     struct {
       *           HashAlgorithm hash;
       *           SignatureAlgorithm signature;
       *     } SignatureAndHashAlgorithm;
       *
       *     enum { (255) } HashAlgorithm;
       *     enum { (255) } SignatureAlgorithm;
       */
      if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
      {
          const uint8_t *cur;
  
          /*
           * Supported signature algorithms
           */
          for( cur = ssl->conf->sig_hashes; *cur != MBEDTLS_MD_NONE; cur++ )
          {
              unsigned char hash = mbedtls_ssl_hash_from_md_alg( *cur );
  
              if( MBEDTLS_SSL_HASH_NONE == hash || mbedtls_ssl_set_calc_verify_md( ssl, hash ) )
                  continue;
  
  #if defined(MBEDTLS_RSA_C)
              p[2 + sa_len++] = hash;
              p[2 + sa_len++] = MBEDTLS_SSL_SIG_RSA;
  #endif
  #if defined(MBEDTLS_ECDSA_C)
              p[2 + sa_len++] = hash;
              p[2 + sa_len++] = MBEDTLS_SSL_SIG_ECDSA;
  #endif
          }
  
          p[0] = (unsigned char)( sa_len >> 8 );
          p[1] = (unsigned char)( sa_len      );
          sa_len += 2;
          p += sa_len;
      }
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
  
      /*
       * DistinguishedName certificate_authorities<0..2^16-1>;
       * opaque DistinguishedName<1..2^16-1>;
       */
      p += 2;
  
      total_dn_size = 0;
  
      if( ssl->conf->cert_req_ca_list ==  MBEDTLS_SSL_CERT_REQ_CA_LIST_ENABLED )
      {
          /* NOTE: If trusted certificates are provisioned
           *       via a CA callback (configured through
           *       `mbedtls_ssl_conf_ca_cb()`, then the
           *       CertificateRequest is currently left empty. */
  
  #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
          if( ssl->handshake->sni_ca_chain != NULL )
              crt = ssl->handshake->sni_ca_chain;
          else
  #endif
              crt = ssl->conf->ca_chain;
  
          while( crt != NULL && crt->version != 0 )
          {
              /* It follows from RFC 5280 A.1 that this length
               * can be represented in at most 11 bits. */
              dn_size = (uint16_t) crt->subject_raw.len;
  
              if( end < p || (size_t)( end - p ) < 2 + (size_t) dn_size )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "skipping CAs: buffer too short" ) );
                  break;
              }
  
              *p++ = (unsigned char)( dn_size >> 8 );
              *p++ = (unsigned char)( dn_size      );
              memcpy( p, crt->subject_raw.p, dn_size );
              p += dn_size;
  
              MBEDTLS_SSL_DEBUG_BUF( 3, "requested DN", p - dn_size, dn_size );
  
              total_dn_size += 2 + dn_size;
              crt = crt->next;
          }
      }
  
      ssl->out_msglen  = p - buf;
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_CERTIFICATE_REQUEST;
      ssl->out_msg[4 + ct_len + sa_len] = (unsigned char)( total_dn_size  >> 8 );
      ssl->out_msg[5 + ct_len + sa_len] = (unsigned char)( total_dn_size       );
  
      ret = mbedtls_ssl_write_handshake_msg( ssl );
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write certificate request" ) );
  
      return( ret );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
  static int ssl_get_ecdh_params_from_cert( mbedtls_ssl_context *ssl )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
  
      if( ! mbedtls_pk_can_do( mbedtls_ssl_own_key( ssl ), MBEDTLS_PK_ECKEY ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "server key not ECDH capable" ) );
          return( MBEDTLS_ERR_SSL_PK_TYPE_MISMATCH );
      }
  
      if( ( ret = mbedtls_ecdh_get_params( &ssl->handshake->ecdh_ctx,
                                   mbedtls_pk_ec( *mbedtls_ssl_own_key( ssl ) ),
                                   MBEDTLS_ECDH_OURS ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, ( "mbedtls_ecdh_get_params" ), ret );
          return( ret );
      }
  
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) ||
            MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED) && \
      defined(MBEDTLS_SSL_ASYNC_PRIVATE)
  static int ssl_resume_server_key_exchange( mbedtls_ssl_context *ssl,
                                             size_t *signature_len )
  {
      /* Append the signature to ssl->out_msg, leaving 2 bytes for the
       * signature length which will be added in ssl_write_server_key_exchange
       * after the call to ssl_prepare_server_key_exchange.
       * ssl_write_server_key_exchange also takes care of incrementing
       * ssl->out_msglen. */
      unsigned char *sig_start = ssl->out_msg + ssl->out_msglen + 2;
      size_t sig_max_len = ( ssl->out_buf + MBEDTLS_SSL_OUT_CONTENT_LEN
                             - sig_start );
      int ret = ssl->conf->f_async_resume( ssl,
                                           sig_start, signature_len, sig_max_len );
      if( ret != MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS )
      {
          ssl->handshake->async_in_progress = 0;
          mbedtls_ssl_set_async_operation_data( ssl, NULL );
      }
      MBEDTLS_SSL_DEBUG_RET( 2, "ssl_resume_server_key_exchange", ret );
      return( ret );
  }
  #endif /* defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED) &&
            defined(MBEDTLS_SSL_ASYNC_PRIVATE) */
  
  /* Prepare the ServerKeyExchange message, up to and including
   * calculating the signature if any, but excluding formatting the
   * signature and sending the message. */
  static int ssl_prepare_server_key_exchange( mbedtls_ssl_context *ssl,
                                              size_t *signature_len )
  {
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PFS_ENABLED)
  #if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED)
      unsigned char *dig_signed = NULL;
  #endif /* MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED */
  #endif /* MBEDTLS_KEY_EXCHANGE_SOME_PFS_ENABLED */
      (void) ciphersuite_info; /* unused in some configurations */
  #if !defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED)
      (void) signature_len;
  #endif /* MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED */
      ssl->out_msglen = 4; /* header (type:1, length:3) to be written later */
      /*
       *
       * Part 1: Provide key exchange parameters for chosen ciphersuite.
       *
       */
      /*
       * - ECJPAKE key exchanges
       */
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE )
      {
          int ret = MBEDTLS_ERR_THIS_CORRUPTION;
          size_t len = 0;
          ret = mbedtls_ecjpake_write_round_two(
              &ssl->handshake->ecjpake_ctx,
              ssl->out_msg + ssl->out_msglen,
              MBEDTLS_SSL_OUT_CONTENT_LEN - ssl->out_msglen, &len,
              ssl->conf->f_rng, ssl->conf->p_rng );
          if( ret != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecjpake_write_round_two", ret );
              return( ret );
          }
          ssl->out_msglen += len;
      }
  #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
      /*
       * For (EC)DHE key exchanges with PSK, parameters are prefixed by support
       * identity hint (RFC 4279, Sec. 3). Until someone needs this feature,
       * we use empty support identity hints here.
       **/
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)   || \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK )
      {
          ssl->out_msg[ssl->out_msglen++] = 0x00;
          ssl->out_msg[ssl->out_msglen++] = 0x00;
      }
  #endif /* MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
      /*
       * - DHE key exchanges
       */
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_DHE_ENABLED)
      if( mbedtls_ssl_ciphersuite_uses_dhe( ciphersuite_info ) )
      {
          int ret = MBEDTLS_ERR_THIS_CORRUPTION;
          size_t len = 0;
          if( ssl->conf->dhm_P.p == NULL || ssl->conf->dhm_G.p == NULL )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "no DH parameters set" ) );
              return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
          }
          /*
           * Ephemeral DH parameters:
           *
           * struct {
           *     opaque dh_p<1..2^16-1>;
           *     opaque dh_g<1..2^16-1>;
           *     opaque dh_Ys<1..2^16-1>;
           * } ServerDHParams;
           */
          if( ( ret = mbedtls_dhm_set_group( &ssl->handshake->dhm_ctx,
                                             &ssl->conf->dhm_P,
                                             &ssl->conf->dhm_G ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_dhm_set_group", ret );
              return( ret );
          }
          if( ( ret = mbedtls_dhm_make_params(
                    &ssl->handshake->dhm_ctx,
                    (int) mbedtls_mpi_size( &ssl->handshake->dhm_ctx.P ),
                    ssl->out_msg + ssl->out_msglen, &len,
                    ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_dhm_make_params", ret );
              return( ret );
          }
  #if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED)
          dig_signed = ssl->out_msg + ssl->out_msglen;
  #endif
          ssl->out_msglen += len;
          MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: X ", &ssl->handshake->dhm_ctx.X  );
          MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: P ", &ssl->handshake->dhm_ctx.P  );
          MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: G ", &ssl->handshake->dhm_ctx.G  );
          MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: GX", &ssl->handshake->dhm_ctx.GX );
      }
  #endif /* MBEDTLS_KEY_EXCHANGE_SOME_DHE_ENABLED */
      /*
       * - ECDHE key exchanges
       */
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_ECDHE_ENABLED)
      if( mbedtls_ssl_ciphersuite_uses_ecdhe( ciphersuite_info ) )
      {
          /*
           * Ephemeral ECDH parameters:
           *
           * struct {
           *     ECParameters curve_params;
           *     ECPoint      public;
           * } ServerECDHParams;
           */
          const mbedtls_ecp_curve_info **curve = NULL;
          const mbedtls_ecp_group_id *gid;
          int ret = MBEDTLS_ERR_THIS_CORRUPTION;
          size_t len = 0;
          /* Match our preference list against the offered curves */
          for( gid = ssl->conf->curve_list; *gid != MBEDTLS_ECP_DP_NONE; gid++ )
              for( curve = ssl->handshake->curves; *curve != NULL; curve++ )
                  if( (*curve)->grp_id == *gid )
                      goto curve_matching_done;
  curve_matching_done:
          if( curve == NULL || *curve == NULL )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "no matching curve for ECDHE" ) );
              return( MBEDTLS_ERR_SSL_NO_CIPHER_CHOSEN );
          }
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "ECDHE curve: %s", (*curve)->name ) );
          ssl->curve = *curve;
          if( ( ret = mbedtls_ecdh_setup( &ssl->handshake->ecdh_ctx,
                                          (*curve)->grp_id ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecp_group_load", ret );
              return( ret );
          }
          if( ( ret = mbedtls_ecdh_make_params(
                    &ssl->handshake->ecdh_ctx, &len,
                    ssl->out_msg + ssl->out_msglen,
                    MBEDTLS_SSL_OUT_CONTENT_LEN - ssl->out_msglen,
                    ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_make_params", ret );
              return( ret );
          }
  #if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED)
          dig_signed = ssl->out_msg + ssl->out_msglen;
  #endif
          ssl->out_msglen += len;
          MBEDTLS_SSL_DEBUG_ECDH( 3, &ssl->handshake->ecdh_ctx,
                                  MBEDTLS_DEBUG_ECDH_Q );
      }
  #endif /* MBEDTLS_KEY_EXCHANGE_SOME_ECDHE_ENABLED */
      /*
       *
       * Part 2: For key exchanges involving the server signing the
       *         exchange parameters, compute and add the signature here.
       *
       */
  #if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED)
      if( mbedtls_ssl_ciphersuite_uses_server_signature( ciphersuite_info ) )
      {
          size_t dig_signed_len = ssl->out_msg + ssl->out_msglen - dig_signed;
          size_t hashlen = 0;
          unsigned char hash[MBEDTLS_MD_MAX_SIZE];
          int ret = MBEDTLS_ERR_THIS_CORRUPTION;
          /*
           * 2.1: Choose hash algorithm:
           * A: For TLS 1.2, obey signature-hash-algorithm extension
           *    to choose appropriate hash.
           * B: For SSL3, TLS1.0, TLS1.1 and ECDHE_ECDSA, use SHA1
           *    (RFC 4492, Sec. 5.4)
           * C: Otherwise, use MD5 + SHA1 (RFC 4346, Sec. 7.4.3)
           */
          mbedtls_md_type_t md_alg;
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
          mbedtls_pk_type_t sig_alg =
              mbedtls_ssl_get_ciphersuite_sig_pk_alg( ciphersuite_info );
          if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
          {
              /* A: For TLS 1.2, obey signature-hash-algorithm extension
               *    (RFC 5246, Sec. 7.4.1.4.1). */
              if( sig_alg == MBEDTLS_PK_NONE ||
                  ( md_alg = mbedtls_ssl_sig_hash_set_find( &ssl->handshake->hash_algs,
                                                            sig_alg ) ) == MBEDTLS_MD_NONE )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
                  /* (... because we choose a cipher suite
                   *      only if there is a matching hash.) */
                  return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
              }
          }
          else
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
  #if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
      defined(MBEDTLS_SSL_PROTO_TLS1_1)
          if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA )
          {
              /* B: Default hash SHA1 */
              md_alg = MBEDTLS_MD_SHA1;
          }
          else
  #endif /* MBEDTLS_SSL_PROTO_SSL3 || MBEDTLS_SSL_PROTO_TLS1 || \
            MBEDTLS_SSL_PROTO_TLS1_1 */
          {
              /* C: MD5 + SHA1 */
              md_alg = MBEDTLS_MD_NONE;
          }
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "pick hash algorithm %u for signing", (unsigned) md_alg ) );
          /*
           * 2.2: Compute the hash to be signed
           */
  #if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
      defined(MBEDTLS_SSL_PROTO_TLS1_1)
          if( md_alg == MBEDTLS_MD_NONE )
          {
              hashlen = 36;
              ret = mbedtls_ssl_get_key_exchange_md_ssl_tls( ssl, hash,
                                                             dig_signed,
                                                             dig_signed_len );
              if( ret != 0 )
                  return( ret );
          }
          else
  #endif /* MBEDTLS_SSL_PROTO_SSL3 || MBEDTLS_SSL_PROTO_TLS1 || \
            MBEDTLS_SSL_PROTO_TLS1_1 */
  #if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
      defined(MBEDTLS_SSL_PROTO_TLS1_2)
          if( md_alg != MBEDTLS_MD_NONE )
          {
              ret = mbedtls_ssl_get_key_exchange_md_tls1_2( ssl, hash, &hashlen,
                                                            dig_signed,
                                                            dig_signed_len,
                                                            md_alg );
              if( ret != 0 )
                  return( ret );
          }
          else
  #endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
            MBEDTLS_SSL_PROTO_TLS1_2 */
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
              return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
          }
          MBEDTLS_SSL_DEBUG_BUF( 3, "parameters hash", hash, hashlen );
          /*
           * 2.3: Compute and add the signature
           */
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
          if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
          {
              /*
               * For TLS 1.2, we need to specify signature and hash algorithm
               * explicitly through a prefix to the signature.
               *
               * struct {
               *    HashAlgorithm hash;
               *    SignatureAlgorithm signature;
               * } SignatureAndHashAlgorithm;
               *
               * struct {
               *    SignatureAndHashAlgorithm algorithm;
               *    opaque signature<0..2^16-1>;
               * } DigitallySigned;
               *
               */
              ssl->out_msg[ssl->out_msglen++] =
                  mbedtls_ssl_hash_from_md_alg( md_alg );
              ssl->out_msg[ssl->out_msglen++] =
                  mbedtls_ssl_sig_from_pk_alg( sig_alg );
          }
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
  #if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
          if( ssl->conf->f_async_sign_start != NULL )
          {
              ret = ssl->conf->f_async_sign_start( ssl,
                                                   mbedtls_ssl_own_cert( ssl ),
                                                   md_alg, hash, hashlen );
              switch( ret )
              {
              case MBEDTLS_ERR_SSL_HW_ACCEL_FALLTHROUGH:
                  /* act as if f_async_sign was null */
                  break;
              case 0:
                  ssl->handshake->async_in_progress = 1;
                  return( ssl_resume_server_key_exchange( ssl, signature_len ) );
              case MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS:
                  ssl->handshake->async_in_progress = 1;
                  return( MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS );
              default:
                  MBEDTLS_SSL_DEBUG_RET( 1, "f_async_sign_start", ret );
                  return( ret );
              }
          }
  #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
          if( mbedtls_ssl_own_key( ssl ) == NULL )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no private key" ) );
              return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
          }
          /* Append the signature to ssl->out_msg, leaving 2 bytes for the
           * signature length which will be added in ssl_write_server_key_exchange
           * after the call to ssl_prepare_server_key_exchange.
           * ssl_write_server_key_exchange also takes care of incrementing
           * ssl->out_msglen. */
          if( ( ret = mbedtls_pk_sign( mbedtls_ssl_own_key( ssl ),
                                       md_alg, hash, hashlen,
                                       ssl->out_msg + ssl->out_msglen + 2,
                                       signature_len,
                                       ssl->conf->f_rng,
                                       ssl->conf->p_rng ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_pk_sign", ret );
              return( ret );
          }
      }
  #endif /* MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED */
      return( 0 );
  }
  
  /* Prepare the ServerKeyExchange message and send it. For ciphersuites
   * that do not include a ServerKeyExchange message, do nothing. Either
   * way, if successful, move on to the next step in the SSL state
   * machine. */
  static int ssl_write_server_key_exchange( mbedtls_ssl_context *ssl )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      size_t signature_len = 0;
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_NON_PFS_ENABLED)
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
                              ssl->handshake->ciphersuite_info;
  #endif /* MBEDTLS_KEY_EXCHANGE_SOME_NON_PFS_ENABLED */
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write server key exchange" ) );
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_NON_PFS_ENABLED)
      /* Extract static ECDH parameters and abort if ServerKeyExchange
       * is not needed. */
      if( mbedtls_ssl_ciphersuite_no_pfs( ciphersuite_info ) )
      {
          /* For suites involving ECDH, extract DH parameters
           * from certificate at this point. */
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_ECDH_ENABLED)
          if( mbedtls_ssl_ciphersuite_uses_ecdh( ciphersuite_info ) )
          {
              ssl_get_ecdh_params_from_cert( ssl );
          }
  #endif /* MBEDTLS_KEY_EXCHANGE_SOME_ECDH_ENABLED */
          /* Key exchanges not involving ephemeral keys don't use
           * ServerKeyExchange, so end here. */
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write server key exchange" ) );
          ssl->state++;
          return( 0 );
      }
  #endif /* MBEDTLS_KEY_EXCHANGE_SOME_NON_PFS_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED) && \
      defined(MBEDTLS_SSL_ASYNC_PRIVATE)
      /* If we have already prepared the message and there is an ongoing
       * signature operation, resume signing. */
      if( ssl->handshake->async_in_progress != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "resuming signature operation" ) );
          ret = ssl_resume_server_key_exchange( ssl, &signature_len );
      }
      else
  #endif /* defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED) &&
            defined(MBEDTLS_SSL_ASYNC_PRIVATE) */
      {
          /* ServerKeyExchange is needed. Prepare the message. */
          ret = ssl_prepare_server_key_exchange( ssl, &signature_len );
      }
      if( ret != 0 )
      {
          /* If we're starting to write a new message, set ssl->out_msglen
           * to 0. But if we're resuming after an asynchronous message,
           * out_msglen is the amount of data written so far and mst be
           * preserved. */
          if( ret == MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS )
              MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write server key exchange (pending)" ) );
          else
              ssl->out_msglen = 0;
          return( ret );
      }
      /* If there is a signature, write its length.
       * ssl_prepare_server_key_exchange already wrote the signature
       * itself at its proper place in the output buffer. */
  #if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED)
      if( signature_len != 0 )
      {
          ssl->out_msg[ssl->out_msglen++] = (unsigned char)( signature_len >> 8 );
          ssl->out_msg[ssl->out_msglen++] = (unsigned char)( signature_len      );
          MBEDTLS_SSL_DEBUG_BUF( 3, "my signature",
                                 ssl->out_msg + ssl->out_msglen,
                                 signature_len );
          /* Skip over the already-written signature */
          ssl->out_msglen += signature_len;
      }
  #endif /* MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED */
      /* Add header and send. */
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_SERVER_KEY_EXCHANGE;
      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 server key exchange" ) );
      return( 0 );
  }
  
  static int ssl_write_server_hello_done( mbedtls_ssl_context *ssl )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write server hello done" ) );
      ssl->out_msglen  = 4;
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_SERVER_HELLO_DONE;
      ssl->state++;
  #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_PROTO_DTLS */
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write server hello done" ) );
      return( 0 );
  }
  
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
      defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
  static int ssl_parse_client_dh_public( mbedtls_ssl_context *ssl, unsigned char **p,
                                         const unsigned char *end )
  {
      int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
      size_t n;
      /*
       * Receive G^Y mod P, premaster = (G^Y)^X mod P
       */
      if( *p + 2 > end )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
      }
      n = ( (*p)[0] << 8 ) | (*p)[1];
      *p += 2;
      if( *p + n > end )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
      }
      if( ( ret = mbedtls_dhm_read_public( &ssl->handshake->dhm_ctx, *p, n ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_dhm_read_public", ret );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_RP );
      }
      *p += n;
      MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: GY", &ssl->handshake->dhm_ctx.GY );
      return( ret );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED) ||                           \
      defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
  
  #if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
  static int ssl_resume_decrypt_pms( mbedtls_ssl_context *ssl,
                                     unsigned char *peer_pms,
                                     size_t *peer_pmslen,
                                     size_t peer_pmssize )
  {
      int ret = ssl->conf->f_async_resume( ssl,
                                           peer_pms, peer_pmslen, peer_pmssize );
      if( ret != MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS )
      {
          ssl->handshake->async_in_progress = 0;
          mbedtls_ssl_set_async_operation_data( ssl, NULL );
      }
      MBEDTLS_SSL_DEBUG_RET( 2, "ssl_decrypt_encrypted_pms", ret );
      return( ret );
  }
  #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
  
  static int ssl_decrypt_encrypted_pms( mbedtls_ssl_context *ssl,
                                        const unsigned char *p,
                                        const unsigned char *end,
                                        unsigned char *peer_pms,
                                        size_t *peer_pmslen,
                                        size_t peer_pmssize )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      mbedtls_pk_context *private_key = mbedtls_ssl_own_key( ssl );
      mbedtls_pk_context *public_key = &mbedtls_ssl_own_cert( ssl )->pk;
      size_t len = mbedtls_pk_get_len( public_key );
  #if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
      /* If we have already started decoding the message and there is an ongoing
       * decryption operation, resume signing. */
      if( ssl->handshake->async_in_progress != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "resuming decryption operation" ) );
          return( ssl_resume_decrypt_pms( ssl,
                                          peer_pms, peer_pmslen, peer_pmssize ) );
      }
  #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
      /*
       * Prepare to decrypt the premaster using own private RSA key
       */
  #if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
      defined(MBEDTLS_SSL_PROTO_TLS1_2)
      if( ssl->minor_ver != MBEDTLS_SSL_MINOR_VERSION_0 )
      {
          if ( p + 2 > end ) {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
          }
          if( *p++ != ( ( len >> 8 ) & 0xFF ) ||
              *p++ != ( ( len      ) & 0xFF ) )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
          }
      }
  #endif
      if( p + len != end )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
      }
      /*
       * Decrypt the premaster secret
       */
  #if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
      if( ssl->conf->f_async_decrypt_start != NULL )
      {
          ret = ssl->conf->f_async_decrypt_start( ssl,
                                                  mbedtls_ssl_own_cert( ssl ),
                                                  p, len );
          switch( ret )
          {
          case MBEDTLS_ERR_SSL_HW_ACCEL_FALLTHROUGH:
              /* act as if f_async_decrypt_start was null */
              break;
          case 0:
              ssl->handshake->async_in_progress = 1;
              return( ssl_resume_decrypt_pms( ssl,
                                              peer_pms,
                                              peer_pmslen,
                                              peer_pmssize ) );
          case MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS:
              ssl->handshake->async_in_progress = 1;
              return( MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS );
          default:
              MBEDTLS_SSL_DEBUG_RET( 1, "f_async_decrypt_start", ret );
              return( ret );
          }
      }
  #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
      if( ! mbedtls_pk_can_do( private_key, MBEDTLS_PK_RSA ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no RSA private key" ) );
          return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
      }
      ret = mbedtls_pk_decrypt( private_key, p, len,
                                peer_pms, peer_pmslen, peer_pmssize,
                                ssl->conf->f_rng, ssl->conf->p_rng );
      return( ret );
  }
  
  static int ssl_parse_encrypted_pms( mbedtls_ssl_context *ssl,
                                      const unsigned char *p,
                                      const unsigned char *end,
                                      size_t pms_offset )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      unsigned char *pms = ssl->handshake->premaster + pms_offset;
      unsigned char ver[2];
      unsigned char fake_pms[48], peer_pms[48];
      unsigned char mask;
      size_t i, peer_pmslen;
      unsigned int diff;
      /* In case of a failure in decryption, the decryption may write less than
       * 2 bytes of output, but we always read the first two bytes. It doesn't
       * matter in the end because diff will be nonzero in that case due to
       * ret being nonzero, and we only care whether diff is 0.
       * But do initialize peer_pms and peer_pmslen for robustness anyway. This
       * also makes memory analyzers happy (don't access uninitialized memory,
       * even if it's an unsigned char). */
      peer_pms[0] = peer_pms[1] = ~0;
      peer_pmslen = 0;
      ret = ssl_decrypt_encrypted_pms( ssl, p, end,
                                       peer_pms,
                                       &peer_pmslen,
                                       sizeof( peer_pms ) );
  #if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
      if ( ret == MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS )
          return( ret );
  #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
      mbedtls_ssl_write_version( ssl->handshake->max_major_ver,
                                 ssl->handshake->max_minor_ver,
                                 ssl->conf->transport, ver );
      /* Avoid data-dependent branches while checking for invalid
       * padding, to protect against timing-based Bleichenbacher-type
       * attacks. */
      diff  = (unsigned int) ret;
      diff |= peer_pmslen ^ 48;
      diff |= peer_pms[0] ^ ver[0];
      diff |= peer_pms[1] ^ ver[1];
      /* mask = diff ? 0xff : 0x00 using bit operations to avoid branches */
      /* MSVC has a warning about unary minus on unsigned, but this is
       * well-defined and precisely what we want to do here */
  #if defined(_MSC_VER)
  #pragma warning( push )
  #pragma warning( disable : 4146 )
  #endif
      mask = - ( ( diff | - diff ) >> ( sizeof( unsigned int ) * 8 - 1 ) );
  #if defined(_MSC_VER)
  #pragma warning( pop )
  #endif
      /*
       * Protection against Bleichenbacher's attack: invalid PKCS#1 v1.5 padding
       * must not cause the connection to end immediately; instead, send a
       * bad_record_mac later in the handshake.
       * To protect against timing-based variants of the attack, we must
       * not have any branch that depends on whether the decryption was
       * successful. In particular, always generate the fake premaster secret,
       * regardless of whether it will ultimately influence the output or not.
       */
      ret = ssl->conf->f_rng( ssl->conf->p_rng, fake_pms, sizeof( fake_pms ) );
      if( ret != 0 )
      {
          /* It's ok to abort on an RNG failure, since this does not reveal
           * anything about the RSA decryption. */
          return( ret );
      }
  #if defined(MBEDTLS_SSL_DEBUG_ALL)
      if( diff != 0 )
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
  #endif
      if( sizeof( ssl->handshake->premaster ) < pms_offset ||
          sizeof( ssl->handshake->premaster ) - pms_offset < 48 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
      ssl->handshake->pmslen = 48;
      /* Set pms to either the true or the fake PMS, without
       * data-dependent branches. */
      for( i = 0; i < ssl->handshake->pmslen; i++ )
          pms[i] = ( mask & fake_pms[i] ) | ( (~mask) & peer_pms[i] );
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
  static int ssl_parse_client_psk_identity( mbedtls_ssl_context *ssl, unsigned char **p,
                                            const unsigned char *end )
  {
      int ret = 0;
      uint16_t n;
      if( ssl_conf_has_psk_or_cb( ssl->conf ) == 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no pre-shared key" ) );
          return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
      }
      /*
       * Receive client pre-shared key identity name
       */
      if( end - *p < 2 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
      }
      n = ( (*p)[0] << 8 ) | (*p)[1];
      *p += 2;
      if( n == 0 || n > end - *p )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
      }
      if( ssl->conf->f_psk != NULL )
      {
          if( ssl->conf->f_psk( ssl->conf->p_psk, ssl, *p, n ) != 0 )
              ret = MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY;
      }
      else
      {
          /* Identity is not a big secret since clients send it in the clear,
           * but treat it carefully anyway, just in case */
          if( n != ssl->conf->psk_identity_len ||
              timingsafe_bcmp( ssl->conf->psk_identity, *p, n ) != 0 )
          {
              ret = MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY;
          }
      }
      if( ret == MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY )
      {
          MBEDTLS_SSL_DEBUG_BUF( 3, "Unknown PSK identity", *p, n );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_UNKNOWN_PSK_IDENTITY );
          return( MBEDTLS_ERR_SSL_UNKNOWN_IDENTITY );
      }
      *p += n;
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
  
  static int ssl_parse_client_key_exchange( mbedtls_ssl_context *ssl )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
      unsigned char *p, *end;
      ciphersuite_info = ssl->handshake->ciphersuite_info;
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse client key exchange" ) );
  #if defined(MBEDTLS_SSL_ASYNC_PRIVATE) && \
      ( defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED) || \
        defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED) )
      if( ( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK ||
            ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA ) &&
          ( ssl->handshake->async_in_progress != 0 ) )
      {
          /* We've already read a record and there is an asynchronous
           * operation in progress to decrypt it. So skip reading the
           * record. */
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "will resume decryption of previously-read record" ) );
      }
      else
  #endif
      if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
          return( ret );
      }
      p = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
      end = ssl->in_msg + ssl->in_hslen;
      if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
      }
      if( ssl->in_msg[0] != MBEDTLS_SSL_HS_CLIENT_KEY_EXCHANGE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
      }
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_RSA )
      {
          if( ( ret = ssl_parse_client_dh_public( ssl, &p, end ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_dh_public" ), ret );
              return( ret );
          }
          if( p != end )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
          }
          if( ( ret = mbedtls_dhm_calc_secret( &ssl->handshake->dhm_ctx,
                                        ssl->handshake->premaster,
                                        MBEDTLS_PREMASTER_SIZE,
                                       &ssl->handshake->pmslen,
                                        ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_dhm_calc_secret", ret );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_CS );
          }
          MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: K ", &ssl->handshake->dhm_ctx.K  );
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||                     \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) ||                   \
      defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) ||                      \
      defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_RSA ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_RSA ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA )
      {
        if( ( ret = mbedtls_ecdh_read_public( &ssl->handshake->ecdh_ctx,
                                              p, end - p) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_read_public", ret );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_RP );
          }
          MBEDTLS_SSL_DEBUG_ECDH( 3, &ssl->handshake->ecdh_ctx,
                                  MBEDTLS_DEBUG_ECDH_QP );
          if( ( ret = mbedtls_ecdh_calc_secret( &ssl->handshake->ecdh_ctx,
                                                        &ssl->handshake->pmslen,
                                                        ssl->handshake->premaster,
                                                        MBEDTLS_MPI_MAX_SIZE,
                                                        ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_calc_secret", ret );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_CS );
          }
          MBEDTLS_SSL_DEBUG_ECDH( 3, &ssl->handshake->ecdh_ctx,
                                  MBEDTLS_DEBUG_ECDH_Z );
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK )
      {
          if( ( ret = ssl_parse_client_psk_identity( ssl, &p, end ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_psk_identity" ), ret );
              return( ret );
          }
          if( p != end )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
          }
          if( ( ret = mbedtls_ssl_psk_derive_premaster( ssl,
                          ciphersuite_info->key_exchange ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_psk_derive_premaster", ret );
              return( ret );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_PSK_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
      {
  #if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
          if ( ssl->handshake->async_in_progress != 0 )
          {
              /* There is an asynchronous operation in progress to
               * decrypt the encrypted premaster secret, so skip
               * directly to resuming this operation. */
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "PSK identity already parsed" ) );
              /* Update p to skip the PSK identity. ssl_parse_encrypted_pms
               * won't actually use it, but maintain p anyway for robustness. */
              p += ssl->conf->psk_identity_len + 2;
          }
          else
  #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
          if( ( ret = ssl_parse_client_psk_identity( ssl, &p, end ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_psk_identity" ), ret );
              return( ret );
          }
          if( ( ret = ssl_parse_encrypted_pms( ssl, p, end, 2 ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_encrypted_pms" ), ret );
              return( ret );
          }
          if( ( ret = mbedtls_ssl_psk_derive_premaster( ssl,
                          ciphersuite_info->key_exchange ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_psk_derive_premaster", ret );
              return( ret );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK )
      {
          if( ( ret = ssl_parse_client_psk_identity( ssl, &p, end ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_psk_identity" ), ret );
              return( ret );
          }
          if( ( ret = ssl_parse_client_dh_public( ssl, &p, end ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_dh_public" ), ret );
              return( ret );
          }
          if( p != end )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
          }
          if( ( ret = mbedtls_ssl_psk_derive_premaster( ssl,
                          ciphersuite_info->key_exchange ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_psk_derive_premaster", ret );
              return( ret );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK )
      {
          if( ( ret = ssl_parse_client_psk_identity( ssl, &p, end ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_client_psk_identity" ), ret );
              return( ret );
          }
          if( ( ret = mbedtls_ecdh_read_public( &ssl->handshake->ecdh_ctx,
                                         p, end - p ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_read_public", ret );
              return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_RP );
          }
          MBEDTLS_SSL_DEBUG_ECDH( 3, &ssl->handshake->ecdh_ctx,
                                  MBEDTLS_DEBUG_ECDH_QP );
          if( ( ret = mbedtls_ssl_psk_derive_premaster( ssl,
                          ciphersuite_info->key_exchange ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_psk_derive_premaster", ret );
              return( ret );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA )
      {
          if( ( ret = ssl_parse_encrypted_pms( ssl, p, end, 0 ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_parse_parse_encrypted_pms_secret" ), ret );
              return( ret );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_RSA_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE )
      {
          ret = mbedtls_ecjpake_read_round_two( &ssl->handshake->ecjpake_ctx,
                                                p, end - p );
          if( ret != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecjpake_read_round_two", ret );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
          }
          ret = mbedtls_ecjpake_derive_secret( &ssl->handshake->ecjpake_ctx,
                  ssl->handshake->premaster, 32, &ssl->handshake->pmslen,
                  ssl->conf->f_rng, ssl->conf->p_rng );
          if( ret != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecjpake_derive_secret", ret );
              return( ret );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
      if( ( ret = mbedtls_ssl_derive_keys( ssl ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_derive_keys", ret );
          return( ret );
      }
      ssl->state++;
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse client key exchange" ) );
      return( 0 );
  }
  
  static int ssl_parse_certificate_verify( mbedtls_ssl_context *ssl )
  {
  #if !defined(MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED)
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate verify" ) );
      if( !mbedtls_ssl_ciphersuite_cert_req_allowed( ciphersuite_info ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate verify" ) );
          ssl->state++;
          return( 0 );
      }
      MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
      return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
  #else /* !MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
      int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
      size_t i, sig_len;
      unsigned char hash[48];
      unsigned char *hash_start = hash;
      size_t hashlen;
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
      mbedtls_pk_type_t pk_alg;
  #endif
      mbedtls_md_type_t md_alg;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
      mbedtls_pk_context * peer_pk;
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate verify" ) );
      if( !mbedtls_ssl_ciphersuite_cert_req_allowed( ciphersuite_info ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate verify" ) );
          ssl->state++;
          return( 0 );
      }
  #if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
      if( ssl->session_negotiate->peer_cert == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate verify" ) );
          ssl->state++;
          return( 0 );
      }
  #else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
      if( ssl->session_negotiate->peer_cert_digest == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate verify" ) );
          ssl->state++;
          return( 0 );
      }
  #endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
      /* Read the message without adding it to the checksum */
      ret = mbedtls_ssl_read_record( ssl, 0 /* no checksum update */ );
      if( 0 != ret )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, ( "mbedtls_ssl_read_record" ), ret );
          return( ret );
      }
      ssl->state++;
      /* Process the message contents */
      if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE ||
          ssl->in_msg[0] != MBEDTLS_SSL_HS_CERTIFICATE_VERIFY )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate verify message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_VERIFY );
      }
      i = mbedtls_ssl_hs_hdr_len( ssl );
  #if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
      peer_pk = &ssl->handshake->peer_pubkey;
  #else /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
      if( ssl->session_negotiate->peer_cert == NULL )
      {
          /* Should never happen */
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
      peer_pk = &ssl->session_negotiate->peer_cert->pk;
  #endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
      /*
       *  struct {
       *     SignatureAndHashAlgorithm algorithm; -- TLS 1.2 only
       *     opaque signature<0..2^16-1>;
       *  } DigitallySigned;
       */
  #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 )
      {
          md_alg = MBEDTLS_MD_NONE;
          hashlen = 36;
          /* For ECDSA, use SHA-1, not MD-5 + SHA-1 */
          if( mbedtls_pk_can_do( peer_pk, MBEDTLS_PK_ECDSA ) )
          {
              hash_start += 16;
              hashlen -= 16;
              md_alg = MBEDTLS_MD_SHA1;
          }
      }
      else
  #endif /* MBEDTLS_SSL_PROTO_SSL3 || MBEDTLS_SSL_PROTO_TLS1 ||
            MBEDTLS_SSL_PROTO_TLS1_1 */
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
      if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
      {
          if( i + 2 > ssl->in_hslen )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate verify message" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_VERIFY );
          }
          /*
           * Hash
           */
          md_alg = mbedtls_ssl_md_alg_from_hash( ssl->in_msg[i] );
          if( md_alg == MBEDTLS_MD_NONE || mbedtls_ssl_set_calc_verify_md( ssl, ssl->in_msg[i] ) )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "peer not adhering to requested sig_alg"
                                  " for verify message" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_VERIFY );
          }
  #if !defined(MBEDTLS_MD_SHA1)
          if( MBEDTLS_MD_SHA1 == md_alg )
              hash_start += 16;
  #endif
          /* Info from md_alg will be used instead */
          hashlen = 0;
          i++;
          /*
           * Signature
           */
          if( ( pk_alg = mbedtls_ssl_pk_alg_from_sig( ssl->in_msg[i] ) )
                          == MBEDTLS_PK_NONE )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "peer not adhering to requested sig_alg"
                                  " for verify message" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_VERIFY );
          }
          /*
           * Check the certificate's key type matches the signature alg
           */
          if( !mbedtls_pk_can_do( peer_pk, pk_alg ) )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "sig_alg doesn't match cert key" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_VERIFY );
          }
          i++;
      }
      else
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
      if( i + 2 > ssl->in_hslen )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate verify message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_VERIFY );
      }
      sig_len = ( ssl->in_msg[i] << 8 ) | ssl->in_msg[i+1];
      i += 2;
      if( i + sig_len != ssl->in_hslen )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate verify message" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_VERIFY );
      }
      /* Calculate hash and verify signature */
      {
          size_t dummy_hlen;
          ssl->handshake->calc_verify( ssl, hash, &dummy_hlen );
      }
      if( ( ret = mbedtls_pk_verify( peer_pk,
                             md_alg, hash_start, hashlen,
                             ssl->in_msg + i, sig_len ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_pk_verify", ret );
          return( ret );
      }
      mbedtls_ssl_update_handshake_status( ssl );
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse certificate verify" ) );
      return( ret );
  #endif /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
  }
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
  static int ssl_write_new_session_ticket( mbedtls_ssl_context *ssl )
  {
      int ret = MBEDTLS_ERR_THIS_CORRUPTION;
      size_t tlen;
      uint32_t lifetime;
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write new session ticket" ) );
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_NEW_SESSION_TICKET;
      /*
       * struct {
       *     uint32 ticket_lifetime_hint;
       *     opaque ticket<0..2^16-1>;
       * } NewSessionTicket;
       *
       * 4  .  7   ticket_lifetime_hint (0 = unspecified)
       * 8  .  9   ticket_len (n)
       * 10 .  9+n ticket content
       */
      if( ( ret = ssl->conf->f_ticket_write( ssl->conf->p_ticket,
                                  ssl->session_negotiate,
                                  ssl->out_msg + 10,
                                  ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN,
                                  &tlen, &lifetime ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_ticket_write", ret );
          tlen = 0;
      }
      ssl->out_msg[4] = ( lifetime >> 24 ) & 0xFF;
      ssl->out_msg[5] = ( lifetime >> 16 ) & 0xFF;
      ssl->out_msg[6] = ( lifetime >>  8 ) & 0xFF;
      ssl->out_msg[7] = ( lifetime       ) & 0xFF;
      ssl->out_msg[8] = (unsigned char)( ( tlen >> 8 ) & 0xFF );
      ssl->out_msg[9] = (unsigned char)( ( tlen      ) & 0xFF );
      ssl->out_msglen = 10 + tlen;
      /*
       * Morally equivalent to updating ssl->state, but NewSessionTicket and
       * ChangeCipherSpec share the same state.
       */
      ssl->handshake->new_session_ticket = 0;
      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 new session ticket" ) );
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  /**
   * \brief          Perform a single step of the SSL server 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_server_step( mbedtls_ssl_context *ssl )
  {
      int ret = 0;
      if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER || ssl->handshake == NULL )
          return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "server state: %d", ssl->state ) );
      if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
          return( ret );
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
          ssl->handshake->retransmit_state == MBEDTLS_SSL_RETRANS_SENDING )
      {
          if( ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
              return( ret );
      }
  #endif /* MBEDTLS_SSL_PROTO_DTLS */
      /* INFOF("handshake step %s", GetSslStateName(ssl->state)); */
      switch( ssl->state )
      {
          case MBEDTLS_SSL_HELLO_REQUEST:
              ssl->state = MBEDTLS_SSL_CLIENT_HELLO;
              break;
          /*
           *  <==   ClientHello
           */
          case MBEDTLS_SSL_CLIENT_HELLO:
              ret = ssl_parse_client_hello( ssl );
              break;
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
          case MBEDTLS_SSL_SERVER_HELLO_VERIFY_REQUEST_SENT:
              return( MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED );
  #endif
          /*
           *  ==>   ServerHello
           *        Certificate
           *      ( ServerKeyExchange  )
           *      ( CertificateRequest )
           *        ServerHelloDone
           */
          case MBEDTLS_SSL_SERVER_HELLO:
              ret = ssl_write_server_hello( ssl );
              break;
          case MBEDTLS_SSL_SERVER_CERTIFICATE:
              ret = mbedtls_ssl_write_certificate( ssl );
              break;
          case MBEDTLS_SSL_SERVER_KEY_EXCHANGE:
              ret = ssl_write_server_key_exchange( ssl );
              break;
          case MBEDTLS_SSL_CERTIFICATE_REQUEST:
              ret = ssl_write_certificate_request( ssl );
              break;
          case MBEDTLS_SSL_SERVER_HELLO_DONE:
              ret = ssl_write_server_hello_done( ssl );
              break;
          /*
           *  <== ( Certificate/Alert  )
           *        ClientKeyExchange
           *      ( CertificateVerify  )
           *        ChangeCipherSpec
           *        Finished
           */
          case MBEDTLS_SSL_CLIENT_CERTIFICATE:
              ret = mbedtls_ssl_parse_certificate( ssl );
              break;
          case MBEDTLS_SSL_CLIENT_KEY_EXCHANGE:
              ret = ssl_parse_client_key_exchange( ssl );
              break;
          case MBEDTLS_SSL_CERTIFICATE_VERIFY:
              ret = ssl_parse_certificate_verify( ssl );
              break;
          case MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC:
              ret = mbedtls_ssl_parse_change_cipher_spec( ssl );
              break;
          case MBEDTLS_SSL_CLIENT_FINISHED:
            ret = mbedtls_ssl_parse_finished( ssl );
              break;
          /*
           *  ==> ( NewSessionTicket )
           *        ChangeCipherSpec
           *        Finished
           */
          case MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC:
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
              if( ssl->handshake->new_session_ticket != 0 )
                  ret = ssl_write_new_session_ticket( ssl );
              else
  #endif
                  ret = mbedtls_ssl_write_change_cipher_spec( ssl );
              break;
          case MBEDTLS_SSL_SERVER_FINISHED:
              ret = mbedtls_ssl_write_finished( ssl );
              break;
          case MBEDTLS_SSL_FLUSH_BUFFERS:
              MBEDTLS_SSL_DEBUG_MSG( 2, ( "handshake: done" ) );
              ssl->state = MBEDTLS_SSL_HANDSHAKE_WRAPUP;
              break;
          case MBEDTLS_SSL_HANDSHAKE_WRAPUP:
              mbedtls_ssl_handshake_wrapup( ssl );
              break;
          default:
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid state %d", ssl->state ) );
              return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
      }
      return( ret );
  }
  