text: /*
   *  SSLv3/TLSv1 client-side functions
   *
   *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
   *  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.
   *
   *  This file is part of mbed TLS (https://tls.mbed.org)
   */
  
  #if !defined(MBEDTLS_CONFIG_FILE)
  #include "mbedtls/config.h"
  #else
  #include MBEDTLS_CONFIG_FILE
  #endif
  
  #if defined(MBEDTLS_SSL_CLI_C)
  
  #if defined(MBEDTLS_PLATFORM_C)
  #include "mbedtls/platform.h"
  #else
  #include <stdlib.h>
  #define mbedtls_calloc    calloc
  #define mbedtls_free      free
  #endif
  
  #include "mbedtls/debug.h"
  #include "mbedtls/ssl.h"
  #include "mbedtls/ssl_internal.h"
  
  #if defined(MBEDTLS_USE_PSA_CRYPTO)
  #include "mbedtls/psa_util.h"
  #endif /* MBEDTLS_USE_PSA_CRYPTO */
  
  #include <string.h>
  
  #include <stdint.h>
  
  #if defined(MBEDTLS_HAVE_TIME)
  #include "mbedtls/platform_time.h"
  #endif
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
  #include "mbedtls/platform_util.h"
  #endif
  
  #if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
  static int ssl_conf_has_static_psk( mbedtls_ssl_config const *conf )
  {
      if( conf->psk_identity     == NULL ||
          conf->psk_identity_len == 0     )
      {
          return( 0 );
      }
  
      if( conf->psk != NULL && conf->psk_len != 0 )
          return( 1 );
  
  #if defined(MBEDTLS_USE_PSA_CRYPTO)
      if( conf->psk_opaque != 0 )
          return( 1 );
  #endif /* MBEDTLS_USE_PSA_CRYPTO */
  
      return( 0 );
  }
  
  #if defined(MBEDTLS_USE_PSA_CRYPTO)
  static int ssl_conf_has_static_raw_psk( mbedtls_ssl_config const *conf )
  {
      if( conf->psk_identity     == NULL ||
          conf->psk_identity_len == 0     )
      {
          return( 0 );
      }
  
      if( conf->psk != NULL && conf->psk_len != 0 )
          return( 1 );
  
      return( 0 );
  }
  #endif /* MBEDTLS_USE_PSA_CRYPTO */
  
  #endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
  
  #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
  static void ssl_write_hostname_ext( mbedtls_ssl_context *ssl,
                                      unsigned char *buf,
                                      size_t *olen )
  {
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
      size_t hostname_len;
  
      *olen = 0;
  
      if( ssl->hostname == NULL )
          return;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding server name extension: %s",
                     ssl->hostname ) );
  
      hostname_len = strlen( ssl->hostname );
  
      if( end < p || (size_t)( end - p ) < hostname_len + 9 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      /*
       * Sect. 3, RFC 6066 (TLS Extensions Definitions)
       *
       * In order to provide any of the server names, clients MAY include an
       * extension of type "server_name" in the (extended) client hello. The
       * "extension_data" field of this extension SHALL contain
       * "ServerNameList" where:
       *
       * struct {
       *     NameType name_type;
       *     select (name_type) {
       *         case host_name: HostName;
       *     } name;
       * } ServerName;
       *
       * enum {
       *     host_name(0), (255)
       * } NameType;
       *
       * opaque HostName<1..2^16-1>;
       *
       * struct {
       *     ServerName server_name_list<1..2^16-1>
       * } ServerNameList;
       *
       */
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SERVERNAME >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SERVERNAME      ) & 0xFF );
  
      *p++ = (unsigned char)( ( (hostname_len + 5) >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( (hostname_len + 5)      ) & 0xFF );
  
      *p++ = (unsigned char)( ( (hostname_len + 3) >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( (hostname_len + 3)      ) & 0xFF );
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SERVERNAME_HOSTNAME ) & 0xFF );
      *p++ = (unsigned char)( ( hostname_len >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( hostname_len      ) & 0xFF );
  
      memcpy( p, ssl->hostname, hostname_len );
  
      *olen = hostname_len + 9;
  }
  #endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
  
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
  static void ssl_write_renegotiation_ext( mbedtls_ssl_context *ssl,
                                           unsigned char *buf,
                                           size_t *olen )
  {
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
  
      *olen = 0;
  
      /* We're always including an TLS_EMPTY_RENEGOTIATION_INFO_SCSV in the
       * initial ClientHello, in which case also adding the renegotiation
       * info extension is NOT RECOMMENDED as per RFC 5746 Section 3.4. */
      if( ssl->renego_status != MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
          return;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding renegotiation extension" ) );
  
      if( end < p || (size_t)( end - p ) < 5 + ssl->verify_data_len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      /*
       * Secure renegotiation
       */
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_RENEGOTIATION_INFO >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_RENEGOTIATION_INFO      ) & 0xFF );
  
      *p++ = 0x00;
      *p++ = ( ssl->verify_data_len + 1 ) & 0xFF;
      *p++ = ssl->verify_data_len & 0xFF;
  
      memcpy( p, ssl->own_verify_data, ssl->verify_data_len );
  
      *olen = 5 + ssl->verify_data_len;
  }
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
  
  /*
   * Only if we handle at least one key exchange that needs signatures.
   */
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
      defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
  static void ssl_write_signature_algorithms_ext( mbedtls_ssl_context *ssl,
                                                  unsigned char *buf,
                                                  size_t *olen )
  {
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
      size_t sig_alg_len = 0;
      const int *md;
  #if defined(MBEDTLS_RSA_C) || defined(MBEDTLS_ECDSA_C)
      unsigned char *sig_alg_list = buf + 6;
  #endif
  
      *olen = 0;
  
      if( ssl->conf->max_minor_ver != MBEDTLS_SSL_MINOR_VERSION_3 )
          return;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding signature_algorithms extension" ) );
  
      for( md = ssl->conf->sig_hashes; *md != MBEDTLS_MD_NONE; md++ )
      {
  #if defined(MBEDTLS_ECDSA_C)
          sig_alg_len += 2;
  #endif
  #if defined(MBEDTLS_RSA_C)
          sig_alg_len += 2;
  #endif
      }
  
      if( end < p || (size_t)( end - p ) < sig_alg_len + 6 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      /*
       * Prepare signature_algorithms extension (TLS 1.2)
       */
      sig_alg_len = 0;
  
      for( md = ssl->conf->sig_hashes; *md != MBEDTLS_MD_NONE; md++ )
      {
  #if defined(MBEDTLS_ECDSA_C)
          sig_alg_list[sig_alg_len++] = mbedtls_ssl_hash_from_md_alg( *md );
          sig_alg_list[sig_alg_len++] = MBEDTLS_SSL_SIG_ECDSA;
  #endif
  #if defined(MBEDTLS_RSA_C)
          sig_alg_list[sig_alg_len++] = mbedtls_ssl_hash_from_md_alg( *md );
          sig_alg_list[sig_alg_len++] = MBEDTLS_SSL_SIG_RSA;
  #endif
      }
  
      /*
       * enum {
       *     none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5),
       *     sha512(6), (255)
       * } HashAlgorithm;
       *
       * enum { anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) }
       *   SignatureAlgorithm;
       *
       * struct {
       *     HashAlgorithm hash;
       *     SignatureAlgorithm signature;
       * } SignatureAndHashAlgorithm;
       *
       * SignatureAndHashAlgorithm
       *   supported_signature_algorithms<2..2^16-2>;
       */
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SIG_ALG >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SIG_ALG      ) & 0xFF );
  
      *p++ = (unsigned char)( ( ( sig_alg_len + 2 ) >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( ( sig_alg_len + 2 )      ) & 0xFF );
  
      *p++ = (unsigned char)( ( sig_alg_len >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( sig_alg_len      ) & 0xFF );
  
      *olen = 6 + sig_alg_len;
  }
  #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 void ssl_write_supported_elliptic_curves_ext( mbedtls_ssl_context *ssl,
                                                       unsigned char *buf,
                                                       size_t *olen )
  {
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
      unsigned char *elliptic_curve_list = p + 6;
      size_t elliptic_curve_len = 0;
      const mbedtls_ecp_curve_info *info;
  #if defined(MBEDTLS_ECP_C)
      const mbedtls_ecp_group_id *grp_id;
  #else
      ((void) ssl);
  #endif
  
      *olen = 0;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding supported_elliptic_curves extension" ) );
  
  #if defined(MBEDTLS_ECP_C)
      for( grp_id = ssl->conf->curve_list; *grp_id != MBEDTLS_ECP_DP_NONE; grp_id++ )
  #else
      for( info = mbedtls_ecp_curve_list(); info->grp_id != MBEDTLS_ECP_DP_NONE; info++ )
  #endif
      {
  #if defined(MBEDTLS_ECP_C)
          info = mbedtls_ecp_curve_info_from_grp_id( *grp_id );
  #endif
          if( info == NULL )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid curve in ssl configuration" ) );
              return;
          }
  
          elliptic_curve_len += 2;
      }
  
      if( end < p || (size_t)( end - p ) < 6 + elliptic_curve_len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      elliptic_curve_len = 0;
  
  #if defined(MBEDTLS_ECP_C)
      for( grp_id = ssl->conf->curve_list; *grp_id != MBEDTLS_ECP_DP_NONE; grp_id++ )
  #else
      for( info = mbedtls_ecp_curve_list(); info->grp_id != MBEDTLS_ECP_DP_NONE; info++ )
  #endif
      {
  #if defined(MBEDTLS_ECP_C)
          info = mbedtls_ecp_curve_info_from_grp_id( *grp_id );
  #endif
          elliptic_curve_list[elliptic_curve_len++] = info->tls_id >> 8;
          elliptic_curve_list[elliptic_curve_len++] = info->tls_id & 0xFF;
      }
  
      if( elliptic_curve_len == 0 )
          return;
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SUPPORTED_ELLIPTIC_CURVES >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SUPPORTED_ELLIPTIC_CURVES      ) & 0xFF );
  
      *p++ = (unsigned char)( ( ( elliptic_curve_len + 2 ) >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( ( elliptic_curve_len + 2 )      ) & 0xFF );
  
      *p++ = (unsigned char)( ( ( elliptic_curve_len     ) >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( ( elliptic_curve_len     )      ) & 0xFF );
  
      *olen = 6 + elliptic_curve_len;
  }
  
  static void ssl_write_supported_point_formats_ext( mbedtls_ssl_context *ssl,
                                                     unsigned char *buf,
                                                     size_t *olen )
  {
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
  
      *olen = 0;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding supported_point_formats extension" ) );
  
      if( end < p || (size_t)( end - p ) < 6 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      *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;
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
      size_t kkpp_len;
  
      *olen = 0;
  
      /* Skip costly extension if we can't use EC J-PAKE anyway */
      if( mbedtls_ecjpake_check( &ssl->handshake->ecjpake_ctx ) != 0 )
          return;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding 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 );
  
      /*
       * We may need to send ClientHello multiple times for Hello verification.
       * We don't want to compute fresh values every time (both for performance
       * and consistency reasons), so cache the extension content.
       */
      if( ssl->handshake->ecjpake_cache == NULL ||
          ssl->handshake->ecjpake_cache_len == 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "generating new ecjpake parameters" ) );
  
          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;
          }
  
          ssl->handshake->ecjpake_cache = mbedtls_calloc( 1, kkpp_len );
          if( ssl->handshake->ecjpake_cache == NULL )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "allocation failed" ) );
              return;
          }
  
          memcpy( ssl->handshake->ecjpake_cache, p + 2, kkpp_len );
          ssl->handshake->ecjpake_cache_len = kkpp_len;
      }
      else
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "re-using cached ecjpake parameters" ) );
  
          kkpp_len = ssl->handshake->ecjpake_cache_len;
  
          if( (size_t)( end - p - 2 ) < kkpp_len )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
              return;
          }
  
          memcpy( p + 2, ssl->handshake->ecjpake_cache, kkpp_len );
      }
  
      *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_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;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
  
      *olen = 0;
  
      if( ssl->conf->mfl_code == MBEDTLS_SSL_MAX_FRAG_LEN_NONE ) {
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding max_fragment_length extension" ) );
  
      if( end < p || (size_t)( end - p ) < 5 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      *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->conf->mfl_code;
  
      *olen = 5;
  }
  #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
  
  #if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
  static void ssl_write_truncated_hmac_ext( mbedtls_ssl_context *ssl,
                                            unsigned char *buf, size_t *olen )
  {
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
  
      *olen = 0;
  
      if( ssl->conf->trunc_hmac == MBEDTLS_SSL_TRUNC_HMAC_DISABLED )
      {
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding truncated_hmac extension" ) );
  
      if( end < p || (size_t)( end - p ) < 4 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_TRUNCATED_HMAC >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_TRUNCATED_HMAC      ) & 0xFF );
  
      *p++ = 0x00;
      *p++ = 0x00;
  
      *olen = 4;
  }
  #endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
  
  #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 unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
  
      *olen = 0;
  
      if( ssl->conf->encrypt_then_mac == MBEDTLS_SSL_ETM_DISABLED ||
          ssl->conf->max_minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
      {
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding encrypt_then_mac "
                          "extension" ) );
  
      if( end < p || (size_t)( end - p ) < 4 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      *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;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
  
      *olen = 0;
  
      if( ssl->conf->extended_ms == MBEDTLS_SSL_EXTENDED_MS_DISABLED ||
          ssl->conf->max_minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
      {
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding extended_master_secret "
                          "extension" ) );
  
      if( end < p || (size_t)( end - p ) < 4 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      *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;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
      size_t tlen = ssl->session_negotiate->ticket_len;
  
      *olen = 0;
  
      if( ssl->conf->session_tickets == MBEDTLS_SSL_SESSION_TICKETS_DISABLED )
      {
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding session ticket extension" ) );
  
      if( end < p || (size_t)( end - p ) < 4 + tlen )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SESSION_TICKET >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SESSION_TICKET      ) & 0xFF );
  
      *p++ = (unsigned char)( ( tlen >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( tlen      ) & 0xFF );
  
      *olen = 4;
  
      if( ssl->session_negotiate->ticket == NULL || tlen == 0 )
      {
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "sending session ticket of length %d", tlen ) );
  
      memcpy( p, ssl->session_negotiate->ticket, tlen );
  
      *olen += tlen;
  }
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  #if defined(MBEDTLS_SSL_ALPN)
  static void ssl_write_alpn_ext( mbedtls_ssl_context *ssl,
                                  unsigned char *buf, size_t *olen )
  {
      unsigned char *p = buf;
      const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
      size_t alpnlen = 0;
      const char **cur;
  
      *olen = 0;
  
      if( ssl->conf->alpn_list == NULL )
      {
          return;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding alpn extension" ) );
  
      for( cur = ssl->conf->alpn_list; *cur != NULL; cur++ )
          alpnlen += (unsigned char)( strlen( *cur ) & 0xFF ) + 1;
  
      if( end < p || (size_t)( end - p ) < 6 + alpnlen )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
          return;
      }
  
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ALPN >> 8 ) & 0xFF );
      *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ALPN      ) & 0xFF );
  
      /*
       * opaque ProtocolName<1..2^8-1>;
       *
       * struct {
       *     ProtocolName protocol_name_list<2..2^16-1>
       * } ProtocolNameList;
       */
  
      /* Skip writing extension and list length for now */
      p += 4;
  
      for( cur = ssl->conf->alpn_list; *cur != NULL; cur++ )
      {
          *p = (unsigned char)( strlen( *cur ) & 0xFF );
          memcpy( p + 1, *cur, *p );
          p += 1 + *p;
      }
  
      *olen = p - buf;
  
      /* List length = olen - 2 (ext_type) - 2 (ext_len) - 2 (list_len) */
      buf[4] = (unsigned char)( ( ( *olen - 6 ) >> 8 ) & 0xFF );
      buf[5] = (unsigned char)( ( ( *olen - 6 )      ) & 0xFF );
  
      /* Extension length = olen - 2 (ext_type) - 2 (ext_len) */
      buf[2] = (unsigned char)( ( ( *olen - 4 ) >> 8 ) & 0xFF );
      buf[3] = (unsigned char)( ( ( *olen - 4 )      ) & 0xFF );
  }
  #endif /* MBEDTLS_SSL_ALPN */
  
  /*
   * Generate random bytes for ClientHello
   */
  static int ssl_generate_random( mbedtls_ssl_context *ssl )
  {
      int ret;
      unsigned char *p = ssl->handshake->randbytes;
  #if defined(MBEDTLS_HAVE_TIME)
      mbedtls_time_t t;
  #endif
  
      /*
       * When responding to a verify request, MUST reuse random (RFC 6347 4.2.1)
       */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
          ssl->handshake->verify_cookie != NULL )
      {
          return( 0 );
      }
  #endif
  
  #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, ( "client hello, current time: %lu", 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 );
  
      return( 0 );
  }
  
  /**
   * \brief           Validate cipher suite against config in SSL context.
   *
   * \param suite_info    cipher suite to validate
   * \param ssl           SSL context
   * \param min_minor_ver Minimal minor version to accept a cipher suite
   * \param max_minor_ver Maximal minor version to accept a cipher suite
   *
   * \return          0 if valid, else 1
   */
  static int ssl_validate_ciphersuite( const mbedtls_ssl_ciphersuite_t * suite_info,
                                       const mbedtls_ssl_context * ssl,
                                       int min_minor_ver, int max_minor_ver )
  {
      (void) ssl;
      if( suite_info == NULL )
          return( 1 );
  
      if( suite_info->min_minor_ver > max_minor_ver ||
              suite_info->max_minor_ver < min_minor_ver )
          return( 1 );
  
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
              ( suite_info->flags & MBEDTLS_CIPHERSUITE_NODTLS ) )
          return( 1 );
  #endif
  
  #if defined(MBEDTLS_ARC4_C)
      if( ssl->conf->arc4_disabled == MBEDTLS_SSL_ARC4_DISABLED &&
              suite_info->cipher == MBEDTLS_CIPHER_ARC4_128 )
          return( 1 );
  #endif
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
      if( suite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE &&
              mbedtls_ecjpake_check( &ssl->handshake->ecjpake_ctx ) != 0 )
          return( 1 );
  #endif
  
      /* Don't suggest PSK-based ciphersuite if no PSK is available. */
  #if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
      if( mbedtls_ssl_ciphersuite_uses_psk( suite_info ) &&
          ssl_conf_has_static_psk( ssl->conf ) == 0 )
      {
          return( 1 );
      }
  #endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
  
      return( 0 );
  }
  
  static int ssl_write_client_hello( mbedtls_ssl_context *ssl )
  {
      int ret;
      size_t i, n, olen, ext_len = 0;
      unsigned char *buf;
      unsigned char *p, *q;
      unsigned char offer_compress;
      const int *ciphersuites;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
      int uses_ec = 0;
  #endif
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write client hello" ) );
  
      if( ssl->conf->f_rng == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided") );
          return( MBEDTLS_ERR_SSL_NO_RNG );
      }
  
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status == MBEDTLS_SSL_INITIAL_HANDSHAKE )
  #endif
      {
          ssl->major_ver = ssl->conf->min_major_ver;
          ssl->minor_ver = ssl->conf->min_minor_ver;
      }
  
      if( ssl->conf->max_major_ver == 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "configured max major version is invalid, "
                              "consider using mbedtls_ssl_config_defaults()" ) );
          return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
      }
  
      /*
       *     0  .   0   handshake type
       *     1  .   3   handshake length
       *     4  .   5   highest version supported
       *     6  .   9   current UNIX time
       *    10  .  37   random bytes
       */
      buf = ssl->out_msg;
      p = buf + 4;
  
      mbedtls_ssl_write_version( ssl->conf->max_major_ver, ssl->conf->max_minor_ver,
                         ssl->conf->transport, p );
      p += 2;
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, max version: [%d:%d]",
                     buf[4], buf[5] ) );
  
      if( ( ret = ssl_generate_random( ssl ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "ssl_generate_random", ret );
          return( ret );
      }
  
      memcpy( p, ssl->handshake->randbytes, 32 );
      MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, random bytes", p, 32 );
      p += 32;
  
      /*
       *    38  .  38   session id length
       *    39  . 39+n  session id
       *   39+n . 39+n  DTLS only: cookie length (1 byte)
       *   40+n .  ..   DTSL only: cookie
       *   ..   . ..    ciphersuitelist length (2 bytes)
       *   ..   . ..    ciphersuitelist
       *   ..   . ..    compression methods length (1 byte)
       *   ..   . ..    compression methods
       *   ..   . ..    extensions length (2 bytes)
       *   ..   . ..    extensions
       */
      n = ssl->session_negotiate->id_len;
  
      if( n < 16 || n > 32 ||
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
          ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE ||
  #endif
          ssl->handshake->resume == 0 )
      {
          n = 0;
      }
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
      /*
       * RFC 5077 section 3.4: "When presenting a ticket, the client MAY
       * generate and include a Session ID in the TLS ClientHello."
       */
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status == MBEDTLS_SSL_INITIAL_HANDSHAKE )
  #endif
      {
          if( ssl->session_negotiate->ticket != NULL &&
                  ssl->session_negotiate->ticket_len != 0 )
          {
              ret = ssl->conf->f_rng( ssl->conf->p_rng, ssl->session_negotiate->id, 32 );
  
              if( ret != 0 )
                  return( ret );
  
              ssl->session_negotiate->id_len = n = 32;
          }
      }
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
      *p++ = (unsigned char) n;
  
      for( i = 0; i < n; i++ )
          *p++ = ssl->session_negotiate->id[i];
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, session id len.: %d", n ) );
      MBEDTLS_SSL_DEBUG_BUF( 3,   "client hello, session id", buf + 39, n );
  
      /*
       * DTLS cookie
       */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
      {
          if( ssl->handshake->verify_cookie == NULL )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "no verify cookie to send" ) );
              *p++ = 0;
          }
          else
          {
              MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, cookie",
                                ssl->handshake->verify_cookie,
                                ssl->handshake->verify_cookie_len );
  
              *p++ = ssl->handshake->verify_cookie_len;
              memcpy( p, ssl->handshake->verify_cookie,
                         ssl->handshake->verify_cookie_len );
              p += ssl->handshake->verify_cookie_len;
          }
      }
  #endif
  
      /*
       * Ciphersuite list
       */
      ciphersuites = ssl->conf->ciphersuite_list[ssl->minor_ver];
  
      /* Skip writing ciphersuite length for now */
      n = 0;
      q = p;
      p += 2;
  
      for( i = 0; ciphersuites[i] != 0; i++ )
      {
          ciphersuite_info = mbedtls_ssl_ciphersuite_from_id( ciphersuites[i] );
  
          if( ssl_validate_ciphersuite( ciphersuite_info, ssl,
                                        ssl->conf->min_minor_ver,
                                        ssl->conf->max_minor_ver ) != 0 )
              continue;
  
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, add ciphersuite: %04x",
                                      ciphersuites[i] ) );
  
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
          uses_ec |= mbedtls_ssl_ciphersuite_uses_ec( ciphersuite_info );
  #endif
  
          n++;
          *p++ = (unsigned char)( ciphersuites[i] >> 8 );
          *p++ = (unsigned char)( ciphersuites[i]      );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, got %d ciphersuites (excluding SCSVs)", n ) );
  
      /*
       * Add TLS_EMPTY_RENEGOTIATION_INFO_SCSV
       */
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      if( ssl->renego_status == MBEDTLS_SSL_INITIAL_HANDSHAKE )
  #endif
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "adding EMPTY_RENEGOTIATION_INFO_SCSV" ) );
          *p++ = (unsigned char)( MBEDTLS_SSL_EMPTY_RENEGOTIATION_INFO >> 8 );
          *p++ = (unsigned char)( MBEDTLS_SSL_EMPTY_RENEGOTIATION_INFO      );
          n++;
      }
  
      /* Some versions of OpenSSL don't handle it correctly if not at end */
  #if defined(MBEDTLS_SSL_FALLBACK_SCSV)
      if( ssl->conf->fallback == MBEDTLS_SSL_IS_FALLBACK )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "adding FALLBACK_SCSV" ) );
          *p++ = (unsigned char)( MBEDTLS_SSL_FALLBACK_SCSV_VALUE >> 8 );
          *p++ = (unsigned char)( MBEDTLS_SSL_FALLBACK_SCSV_VALUE      );
          n++;
      }
  #endif
  
      *q++ = (unsigned char)( n >> 7 );
      *q++ = (unsigned char)( n << 1 );
  
  #if defined(MBEDTLS_ZLIB_SUPPORT)
      offer_compress = 1;
  #else
      offer_compress = 0;
  #endif
  
      /*
       * We don't support compression with DTLS right now: if many records come
       * in the same datagram, uncompressing one could overwrite the next one.
       * We don't want to add complexity for handling that case unless there is
       * an actual need for it.
       */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
          offer_compress = 0;
  #endif
  
      if( offer_compress )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, compress len.: %d", 2 ) );
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, compress alg.: %d %d",
                              MBEDTLS_SSL_COMPRESS_DEFLATE, MBEDTLS_SSL_COMPRESS_NULL ) );
  
          *p++ = 2;
          *p++ = MBEDTLS_SSL_COMPRESS_DEFLATE;
          *p++ = MBEDTLS_SSL_COMPRESS_NULL;
      }
      else
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, compress len.: %d", 1 ) );
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, compress alg.: %d",
                              MBEDTLS_SSL_COMPRESS_NULL ) );
  
          *p++ = 1;
          *p++ = MBEDTLS_SSL_COMPRESS_NULL;
      }
  
      // First write extensions, then the total length
      //
  #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
      ssl_write_hostname_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
      /* Note that TLS_EMPTY_RENEGOTIATION_INFO_SCSV is always added
       * even if MBEDTLS_SSL_RENEGOTIATION is not defined. */
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      ssl_write_renegotiation_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
      defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
      ssl_write_signature_algorithms_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( uses_ec )
      {
          ssl_write_supported_elliptic_curves_ext( ssl, p + 2 + ext_len, &olen );
          ext_len += olen;
  
          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_MAX_FRAGMENT_LENGTH)
      ssl_write_max_fragment_length_ext( ssl, p + 2 + ext_len, &olen );
      ext_len += olen;
  #endif
  
  #if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
      ssl_write_truncated_hmac_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_ALPN)
      ssl_write_alpn_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
  
      /* olen unused if all extensions are disabled */
      ((void) olen);
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, total extension length: %d",
                     ext_len ) );
  
      if( ext_len > 0 )
      {
          *p++ = (unsigned char)( ( ext_len >> 8 ) & 0xFF );
          *p++ = (unsigned char)( ( ext_len      ) & 0xFF );
          p += ext_len;
      }
  
      ssl->out_msglen  = p - buf;
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_CLIENT_HELLO;
  
      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 client hello" ) );
  
      return( 0 );
  }
  
  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 * 2 ||
              buf[0] !=     ssl->verify_data_len * 2 ||
              mbedtls_ssl_safer_memcmp( buf + 1,
                            ssl->own_verify_data, ssl->verify_data_len ) != 0 ||
              mbedtls_ssl_safer_memcmp( buf + 1 + ssl->verify_data_len,
                            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_SERVER_HELLO );
          }
      }
      else
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
      {
          if( len != 1 || buf[0] != 0x00 )
          {
              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_SERVER_HELLO );
          }
  
          ssl->secure_renegotiation = MBEDTLS_SSL_SECURE_RENEGOTIATION;
      }
  
      return( 0 );
  }
  
  #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 )
  {
      /*
       * server should use the extension only if we did,
       * and if so the server's value should match ours (and len is always 1)
       */
      if( ssl->conf->mfl_code == MBEDTLS_SSL_MAX_FRAG_LEN_NONE ||
          len != 1 ||
          buf[0] != ssl->conf->mfl_code )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-matching max fragment length extension" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
      }
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
  
  #if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
  static int ssl_parse_truncated_hmac_ext( mbedtls_ssl_context *ssl,
                                           const unsigned char *buf,
                                           size_t len )
  {
      if( ssl->conf->trunc_hmac == MBEDTLS_SSL_TRUNC_HMAC_DISABLED ||
          len != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-matching truncated HMAC extension" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
      }
  
      ((void) buf);
  
      ssl->session_negotiate->trunc_hmac = MBEDTLS_SSL_TRUNC_HMAC_ENABLED;
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
  
  #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( ssl->conf->encrypt_then_mac == MBEDTLS_SSL_ETM_DISABLED ||
          ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 ||
          len != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-matching encrypt-then-MAC extension" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
      }
  
      ((void) buf);
  
      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( ssl->conf->extended_ms == MBEDTLS_SSL_EXTENDED_MS_DISABLED ||
          ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 ||
          len != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-matching extended master secret extension" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
      }
  
      ((void) buf);
  
      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,
                                           const unsigned char *buf,
                                           size_t len )
  {
      if( ssl->conf->session_tickets == MBEDTLS_SSL_SESSION_TICKETS_DISABLED ||
          len != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-matching session ticket extension" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
      }
  
      ((void) buf);
  
      ssl->handshake->new_session_ticket = 1;
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
  static int ssl_parse_supported_point_formats_ext( 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 server 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_SERVER_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++;
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 1, ( "no point format in common" ) );
      mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                      MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
      return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
  }
  #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;
  
      if( ssl->handshake->ciphersuite_info->key_exchange !=
          MBEDTLS_KEY_EXCHANGE_ECJPAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 3, ( "skip ecjpake kkpp extension" ) );
          return( 0 );
      }
  
      /* If we got here, we no longer need our cached extension */
      mbedtls_free( ssl->handshake->ecjpake_cache );
      ssl->handshake->ecjpake_cache = NULL;
      ssl->handshake->ecjpake_cache_len = 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_HANDSHAKE_FAILURE );
          return( ret );
      }
  
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
  
  #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, name_len;
      const char **p;
  
      /* If we didn't send it, the server shouldn't send it */
      if( ssl->conf->alpn_list == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-matching ALPN extension" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
      }
  
      /*
       * opaque ProtocolName<1..2^8-1>;
       *
       * struct {
       *     ProtocolName protocol_name_list<2..2^16-1>
       * } ProtocolNameList;
       *
       * the "ProtocolNameList" MUST contain exactly one "ProtocolName"
       */
  
      /* 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_SERVER_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_SERVER_HELLO );
      }
  
      name_len = buf[2];
      if( name_len != list_len - 1 )
      {
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
      }
  
      /* Check that the server chosen protocol was in our list and save it */
      for( p = ssl->conf->alpn_list; *p != NULL; p++ )
      {
          if( name_len == strlen( *p ) &&
              memcmp( buf + 3, *p, name_len ) == 0 )
          {
              ssl->alpn_chosen = *p;
              return( 0 );
          }
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 1, ( "ALPN extension: no matching protocol" ) );
      mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                      MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
      return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
  }
  #endif /* MBEDTLS_SSL_ALPN */
  
  /*
   * Parse HelloVerifyRequest.  Only called after verifying the HS type.
   */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
  static int ssl_parse_hello_verify_request( mbedtls_ssl_context *ssl )
  {
      const unsigned char *p = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
      int major_ver, minor_ver;
      unsigned char cookie_len;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse hello verify request" ) );
  
      /*
       * struct {
       *   ProtocolVersion server_version;
       *   opaque cookie<0..2^8-1>;
       * } HelloVerifyRequest;
       */
      MBEDTLS_SSL_DEBUG_BUF( 3, "server version", p, 2 );
      mbedtls_ssl_read_version( &major_ver, &minor_ver, ssl->conf->transport, p );
      p += 2;
  
      /*
       * Since the RFC is not clear on this point, accept DTLS 1.0 (TLS 1.1)
       * even is lower than our min version.
       */
      if( major_ver < MBEDTLS_SSL_MAJOR_VERSION_3 ||
          minor_ver < MBEDTLS_SSL_MINOR_VERSION_2 ||
          major_ver > ssl->conf->max_major_ver  ||
          minor_ver > ssl->conf->max_minor_ver  )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server version" ) );
  
          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 );
      }
  
      cookie_len = *p++;
      MBEDTLS_SSL_DEBUG_BUF( 3, "cookie", p, cookie_len );
  
      if( ( ssl->in_msg + ssl->in_msglen ) - p < cookie_len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1,
              ( "cookie length does not match incoming message size" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                      MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
      }
  
      mbedtls_free( ssl->handshake->verify_cookie );
  
      ssl->handshake->verify_cookie = mbedtls_calloc( 1, cookie_len );
      if( ssl->handshake->verify_cookie  == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc failed (%d bytes)", cookie_len ) );
          return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
      }
  
      memcpy( ssl->handshake->verify_cookie, p, cookie_len );
      ssl->handshake->verify_cookie_len = cookie_len;
  
      /* Start over at ClientHello */
      ssl->state = MBEDTLS_SSL_CLIENT_HELLO;
      mbedtls_ssl_reset_checksum( ssl );
  
      mbedtls_ssl_recv_flight_completed( ssl );
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse hello verify request" ) );
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_PROTO_DTLS */
  
  static int ssl_parse_server_hello( mbedtls_ssl_context *ssl )
  {
      int ret, i;
      size_t n;
      size_t ext_len;
      unsigned char *buf, *ext;
      unsigned char comp;
  #if defined(MBEDTLS_ZLIB_SUPPORT)
      int accept_comp;
  #endif
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
      int renegotiation_info_seen = 0;
  #endif
      int handshake_failure = 0;
      const mbedtls_ssl_ciphersuite_t *suite_info;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse server hello" ) );
  
      buf = ssl->in_msg;
  
      if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
      {
          /* No alert on a read error. */
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
          return( ret );
      }
  
      if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
      {
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
          if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
          {
              ssl->renego_records_seen++;
  
              if( ssl->conf->renego_max_records >= 0 &&
                  ssl->renego_records_seen > ssl->conf->renego_max_records )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "renegotiation requested, "
                                      "but not honored by server" ) );
                  return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
              }
  
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "non-handshake message during renego" ) );
  
              ssl->keep_current_message = 1;
              return( MBEDTLS_ERR_SSL_WAITING_SERVER_HELLO_RENEGO );
          }
  #endif /* MBEDTLS_SSL_RENEGOTIATION */
  
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server hello message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
          return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
      }
  
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
      {
          if( buf[0] == MBEDTLS_SSL_HS_HELLO_VERIFY_REQUEST )
          {
              MBEDTLS_SSL_DEBUG_MSG( 2, ( "received hello verify request" ) );
              MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse server hello" ) );
              return( ssl_parse_hello_verify_request( ssl ) );
          }
          else
          {
              /* We made it through the verification process */
              mbedtls_free( ssl->handshake->verify_cookie );
              ssl->handshake->verify_cookie = NULL;
              ssl->handshake->verify_cookie_len = 0;
          }
      }
  #endif /* MBEDTLS_SSL_PROTO_DTLS */
  
      if( ssl->in_hslen < 38 + mbedtls_ssl_hs_hdr_len( ssl ) ||
          buf[0] != MBEDTLS_SSL_HS_SERVER_HELLO )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server 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_SERVER_HELLO );
      }
  
      /*
       *  0   .  1    server_version
       *  2   . 33    random (maybe including 4 bytes of Unix time)
       * 34   . 34    session_id length = n
       * 35   . 34+n  session_id
       * 35+n . 36+n  cipher_suite
       * 37+n . 37+n  compression_method
       *
       * 38+n . 39+n  extensions length (optional)
       * 40+n .  ..   extensions
       */
      buf += mbedtls_ssl_hs_hdr_len( ssl );
  
      MBEDTLS_SSL_DEBUG_BUF( 3, "server hello, version", buf + 0, 2 );
      mbedtls_ssl_read_version( &ssl->major_ver, &ssl->minor_ver,
                        ssl->conf->transport, buf + 0 );
  
      if( ssl->major_ver < ssl->conf->min_major_ver ||
          ssl->minor_ver < ssl->conf->min_minor_ver ||
          ssl->major_ver > ssl->conf->max_major_ver ||
          ssl->minor_ver > ssl->conf->max_minor_ver )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "server version out of bounds - "
                              " min: [%d:%d], server: [%d:%d], max: [%d:%d]",
                              ssl->conf->min_major_ver, ssl->conf->min_minor_ver,
                              ssl->major_ver, ssl->minor_ver,
                              ssl->conf->max_major_ver, ssl->conf->max_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 );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, current time: %lu",
                             ( (uint32_t) buf[2] << 24 ) |
                             ( (uint32_t) buf[3] << 16 ) |
                             ( (uint32_t) buf[4] <<  8 ) |
                             ( (uint32_t) buf[5]       ) ) );
  
      memcpy( ssl->handshake->randbytes + 32, buf + 2, 32 );
  
      n = buf[34];
  
      MBEDTLS_SSL_DEBUG_BUF( 3,   "server hello, random bytes", buf + 2, 32 );
  
      if( n > 32 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server 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_SERVER_HELLO );
      }
  
      if( ssl->in_hslen > mbedtls_ssl_hs_hdr_len( ssl ) + 39 + n )
      {
          ext_len = ( ( buf[38 + n] <<  8 )
                    | ( buf[39 + n]       ) );
  
          if( ( ext_len > 0 && ext_len < 4 ) ||
              ssl->in_hslen != mbedtls_ssl_hs_hdr_len( ssl ) + 40 + n + ext_len )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server 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_SERVER_HELLO );
          }
      }
      else if( ssl->in_hslen == mbedtls_ssl_hs_hdr_len( ssl ) + 38 + n )
      {
          ext_len = 0;
      }
      else
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server 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_SERVER_HELLO );
      }
  
      /* ciphersuite (used later) */
      i = ( buf[35 + n] << 8 ) | buf[36 + n];
  
      /*
       * Read and check compression
       */
      comp = buf[37 + n];
  
  #if defined(MBEDTLS_ZLIB_SUPPORT)
      /* See comments in ssl_write_client_hello() */
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
          accept_comp = 0;
      else
  #endif
          accept_comp = 1;
  
      if( comp != MBEDTLS_SSL_COMPRESS_NULL &&
          ( comp != MBEDTLS_SSL_COMPRESS_DEFLATE || accept_comp == 0 ) )
  #else /* MBEDTLS_ZLIB_SUPPORT */
      if( comp != MBEDTLS_SSL_COMPRESS_NULL )
  #endif/* MBEDTLS_ZLIB_SUPPORT */
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "server hello, bad compression: %d", comp ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
          return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
      }
  
      /*
       * Initialize update checksum functions
       */
      ssl->handshake->ciphersuite_info = mbedtls_ssl_ciphersuite_from_id( i );
      if( ssl->handshake->ciphersuite_info == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "ciphersuite info for %04x not found", i ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
      }
  
      mbedtls_ssl_optimize_checksum( ssl, ssl->handshake->ciphersuite_info );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, session id len.: %d", n ) );
      MBEDTLS_SSL_DEBUG_BUF( 3,   "server hello, session id", buf + 35, n );
  
      /*
       * Check if the session can be resumed
       */
      if( ssl->handshake->resume == 0 || n == 0 ||
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
          ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE ||
  #endif
          ssl->session_negotiate->ciphersuite != i ||
          ssl->session_negotiate->compression != comp ||
          ssl->session_negotiate->id_len != n ||
          memcmp( ssl->session_negotiate->id, buf + 35, n ) != 0 )
      {
          ssl->state++;
          ssl->handshake->resume = 0;
  #if defined(MBEDTLS_HAVE_TIME)
          ssl->session_negotiate->start = mbedtls_time( NULL );
  #endif
          ssl->session_negotiate->ciphersuite = i;
          ssl->session_negotiate->compression = comp;
          ssl->session_negotiate->id_len = n;
          memcpy( ssl->session_negotiate->id, buf + 35, n );
      }
      else
      {
          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 );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
              return( ret );
          }
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "%s session has been resumed",
                     ssl->handshake->resume ? "a" : "no" ) );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, chosen ciphersuite: %04x", i ) );
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, compress alg.: %d", buf[37 + n] ) );
  
      /*
       * Perform cipher suite validation in same way as in ssl_write_client_hello.
       */
      i = 0;
      while( 1 )
      {
          if( ssl->conf->ciphersuite_list[ssl->minor_ver][i] == 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server 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_SERVER_HELLO );
          }
  
          if( ssl->conf->ciphersuite_list[ssl->minor_ver][i++] ==
              ssl->session_negotiate->ciphersuite )
          {
              break;
          }
      }
  
      suite_info = mbedtls_ssl_ciphersuite_from_id( ssl->session_negotiate->ciphersuite );
      if( ssl_validate_ciphersuite( suite_info, ssl, ssl->minor_ver, ssl->minor_ver ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server 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_SERVER_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, chosen ciphersuite: %s", suite_info->name ) );
  
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
      if( suite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA &&
          ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
      {
          ssl->handshake->ecrs_enabled = 1;
      }
  #endif
  
      if( comp != MBEDTLS_SSL_COMPRESS_NULL
  #if defined(MBEDTLS_ZLIB_SUPPORT)
          && comp != MBEDTLS_SSL_COMPRESS_DEFLATE
  #endif
        )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server 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_SERVER_HELLO );
      }
      ssl->session_negotiate->compression = comp;
  
      ext = buf + 40 + n;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "server hello, total extension length: %d", ext_len ) );
  
      while( ext_len )
      {
          unsigned int ext_id   = ( ( ext[0] <<  8 )
                                  | ( ext[1]       ) );
          unsigned int ext_size = ( ( ext[2] <<  8 )
                                  | ( ext[3]       ) );
  
          if( ext_size + 4 > ext_len )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server 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_SERVER_HELLO );
          }
  
          switch( ext_id )
          {
          case MBEDTLS_TLS_EXT_RENEGOTIATION_INFO:
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "found renegotiation extension" ) );
  #if defined(MBEDTLS_SSL_RENEGOTIATION)
              renegotiation_info_seen = 1;
  #endif
  
              if( ( ret = ssl_parse_renegotiation_info( ssl, ext + 4,
                                                        ext_size ) ) != 0 )
                  return( ret );
  
              break;
  
  #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
          case MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH:
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "found max_fragment_length extension" ) );
  
              if( ( ret = ssl_parse_max_fragment_length_ext( ssl,
                              ext + 4, ext_size ) ) != 0 )
              {
                  return( ret );
              }
  
              break;
  #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
  
  #if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
          case MBEDTLS_TLS_EXT_TRUNCATED_HMAC:
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "found truncated_hmac extension" ) );
  
              if( ( ret = ssl_parse_truncated_hmac_ext( ssl,
                              ext + 4, ext_size ) ) != 0 )
              {
                  return( ret );
              }
  
              break;
  #endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
  
  #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
          case MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC:
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "found encrypt_then_mac extension" ) );
  
              if( ( ret = ssl_parse_encrypt_then_mac_ext( ssl,
                              ext + 4, ext_size ) ) != 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" ) );
  
              if( ( ret = ssl_parse_extended_ms_ext( ssl,
                              ext + 4, ext_size ) ) != 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" ) );
  
              if( ( ret = ssl_parse_session_ticket_ext( ssl,
                              ext + 4, ext_size ) ) != 0 )
              {
                  return( ret );
              }
  
              break;
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
          case MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS:
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "found supported_point_formats extension" ) );
  
              if( ( ret = ssl_parse_supported_point_formats_ext( ssl,
                              ext + 4, ext_size ) ) != 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" ) );
  
              if( ( ret = ssl_parse_ecjpake_kkpp( ssl,
                              ext + 4, ext_size ) ) != 0 )
              {
                  return( ret );
              }
  
              break;
  #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
  
  #if defined(MBEDTLS_SSL_ALPN)
          case MBEDTLS_TLS_EXT_ALPN:
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "found alpn extension" ) );
  
              if( ( ret = ssl_parse_alpn_ext( ssl, ext + 4, ext_size ) ) != 0 )
                  return( ret );
  
              break;
  #endif /* MBEDTLS_SSL_ALPN */
  
          default:
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "unknown extension found: %d (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 server hello message" ) );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
          }
      }
  
      /*
       * 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" ) );
          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_SERVER_HELLO );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse server hello" ) );
  
      return( 0 );
  }
  
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
      defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
  static int ssl_parse_server_dh_params( mbedtls_ssl_context *ssl, unsigned char **p,
                                         unsigned char *end )
  {
      int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
  
      /*
       * 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_read_params( &ssl->handshake->dhm_ctx, p, end ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 2, ( "mbedtls_dhm_read_params" ), ret );
          return( ret );
      }
  
      if( ssl->handshake->dhm_ctx.len * 8 < ssl->conf->dhm_min_bitlen )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "DHM prime too short: %d < %d",
                                      ssl->handshake->dhm_ctx.len * 8,
                                      ssl->conf->dhm_min_bitlen ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
      }
  
      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: 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_ECDHE_RSA_ENABLED) ||                     \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) ||                   \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED) ||                     \
      defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) ||                      \
      defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
  static int ssl_check_server_ecdh_params( const mbedtls_ssl_context *ssl )
  {
      const mbedtls_ecp_curve_info *curve_info;
      mbedtls_ecp_group_id grp_id;
  #if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
      grp_id = ssl->handshake->ecdh_ctx.grp.id;
  #else
      grp_id = ssl->handshake->ecdh_ctx.grp_id;
  #endif
  
      curve_info = mbedtls_ecp_curve_info_from_grp_id( grp_id );
      if( curve_info == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "ECDH curve: %s", curve_info->name ) );
  
  #if defined(MBEDTLS_ECP_C)
      if( mbedtls_ssl_check_curve( ssl, grp_id ) != 0 )
  #else
      if( ssl->handshake->ecdh_ctx.grp.nbits < 163 ||
          ssl->handshake->ecdh_ctx.grp.nbits > 521 )
  #endif
          return( -1 );
  
      MBEDTLS_SSL_DEBUG_ECDH( 3, &ssl->handshake->ecdh_ctx,
                              MBEDTLS_DEBUG_ECDH_QP );
  
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */
  
  #if defined(MBEDTLS_USE_PSA_CRYPTO) &&                           \
          ( defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||     \
            defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) )
  static int ssl_parse_server_ecdh_params_psa( mbedtls_ssl_context *ssl,
                                               unsigned char **p,
                                               unsigned char *end )
  {
      uint16_t tls_id;
      uint8_t ecpoint_len;
      mbedtls_ssl_handshake_params *handshake = ssl->handshake;
  
      /*
       * Parse ECC group
       */
  
      if( end - *p < 4 )
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
  
      /* First byte is curve_type; only named_curve is handled */
      if( *(*p)++ != MBEDTLS_ECP_TLS_NAMED_CURVE )
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
  
      /* Next two bytes are the namedcurve value */
      tls_id = *(*p)++;
      tls_id <<= 8;
      tls_id |= *(*p)++;
  
      /* Convert EC group to PSA key type. */
      if( ( handshake->ecdh_psa_curve =
            mbedtls_psa_parse_tls_ecc_group( tls_id ) ) == 0 )
      {
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
      }
  
      /*
       * Put peer's ECDH public key in the format understood by PSA.
       */
  
      ecpoint_len = *(*p)++;
      if( (size_t)( end - *p ) < ecpoint_len )
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
  
      if( mbedtls_psa_tls_ecpoint_to_psa_ec( handshake->ecdh_psa_curve,
                                      *p, ecpoint_len,
                                      handshake->ecdh_psa_peerkey,
                                      sizeof( handshake->ecdh_psa_peerkey ),
                                      &handshake->ecdh_psa_peerkey_len ) != 0 )
      {
          return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
      }
  
      *p += ecpoint_len;
      return( 0 );
  }
  #endif /* MBEDTLS_USE_PSA_CRYPTO &&
              ( MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
                MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ) */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||                     \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) ||                   \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
  static int ssl_parse_server_ecdh_params( mbedtls_ssl_context *ssl,
                                           unsigned char **p,
                                           unsigned char *end )
  {
      int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
  
      /*
       * Ephemeral ECDH parameters:
       *
       * struct {
       *     ECParameters curve_params;
       *     ECPoint      public;
       * } ServerECDHParams;
       */
      if( ( ret = mbedtls_ecdh_read_params( &ssl->handshake->ecdh_ctx,
                                    (const unsigned char **) p, end ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, ( "mbedtls_ecdh_read_params" ), ret );
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
          if( ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
              ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
  #endif
          return( ret );
      }
  
      if( ssl_check_server_ecdh_params( ssl ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message (ECDHE curve)" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
      }
  
      return( ret );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
  static int ssl_parse_server_psk_hint( mbedtls_ssl_context *ssl,
                                        unsigned char **p,
                                        unsigned char *end )
  {
      int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
      size_t  len;
      ((void) ssl);
  
      /*
       * PSK parameters:
       *
       * opaque psk_identity_hint<0..2^16-1>;
       */
      if( end - (*p) < 2 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message "
                                      "(psk_identity_hint length)" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
      }
      len = (*p)[0] << 8 | (*p)[1];
      *p += 2;
  
      if( end - (*p) < (int) len )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message "
                                      "(psk_identity_hint length)" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
      }
  
      /*
       * Note: we currently ignore the PKS identity hint, as we only allow one
       * PSK to be provisionned on the client. This could be changed later if
       * someone needs that feature.
       */
      *p += len;
      ret = 0;
  
      return( ret );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED) ||                           \
      defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
  /*
   * Generate a pre-master secret and encrypt it with the server's RSA key
   */
  static int ssl_write_encrypted_pms( mbedtls_ssl_context *ssl,
                                      size_t offset, size_t *olen,
                                      size_t pms_offset )
  {
      int ret;
      size_t len_bytes = ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 ? 0 : 2;
      unsigned char *p = ssl->handshake->premaster + pms_offset;
      mbedtls_pk_context * peer_pk;
  
      if( offset + len_bytes > MBEDTLS_SSL_OUT_CONTENT_LEN )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small for encrypted pms" ) );
          return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
      }
  
      /*
       * Generate (part of) the pre-master as
       *  struct {
       *      ProtocolVersion client_version;
       *      opaque random[46];
       *  } PreMasterSecret;
       */
      mbedtls_ssl_write_version( ssl->conf->max_major_ver, ssl->conf->max_minor_ver,
                         ssl->conf->transport, p );
  
      if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng, p + 2, 46 ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "f_rng", ret );
          return( ret );
      }
  
      ssl->handshake->pmslen = 48;
  
  #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 */
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
      peer_pk = &ssl->session_negotiate->peer_cert->pk;
  #endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
  
      /*
       * Now write it out, encrypted
       */
      if( ! mbedtls_pk_can_do( peer_pk, MBEDTLS_PK_RSA ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "certificate key type mismatch" ) );
          return( MBEDTLS_ERR_SSL_PK_TYPE_MISMATCH );
      }
  
      if( ( ret = mbedtls_pk_encrypt( peer_pk,
                              p, ssl->handshake->pmslen,
                              ssl->out_msg + offset + len_bytes, olen,
                              MBEDTLS_SSL_OUT_CONTENT_LEN - offset - len_bytes,
                              ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_rsa_pkcs1_encrypt", ret );
          return( ret );
      }
  
  #if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
      defined(MBEDTLS_SSL_PROTO_TLS1_2)
      if( len_bytes == 2 )
      {
          ssl->out_msg[offset+0] = (unsigned char)( *olen >> 8 );
          ssl->out_msg[offset+1] = (unsigned char)( *olen      );
          *olen += 2;
      }
  #endif
  
  #if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
      /* We don't need the peer's public key anymore. Free it. */
      mbedtls_pk_free( peer_pk );
  #endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
  
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||                     \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
  static int ssl_parse_signature_algorithm( mbedtls_ssl_context *ssl,
                                            unsigned char **p,
                                            unsigned char *end,
                                            mbedtls_md_type_t *md_alg,
                                            mbedtls_pk_type_t *pk_alg )
  {
      ((void) ssl);
      *md_alg = MBEDTLS_MD_NONE;
      *pk_alg = MBEDTLS_PK_NONE;
  
      /* Only in TLS 1.2 */
      if( ssl->minor_ver != MBEDTLS_SSL_MINOR_VERSION_3 )
      {
          return( 0 );
      }
  
      if( (*p) + 2 > end )
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
  
      /*
       * Get hash algorithm
       */
      if( ( *md_alg = mbedtls_ssl_md_alg_from_hash( (*p)[0] ) ) == MBEDTLS_MD_NONE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "Server used unsupported "
                              "HashAlgorithm %d", *(p)[0] ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
      }
  
      /*
       * Get signature algorithm
       */
      if( ( *pk_alg = mbedtls_ssl_pk_alg_from_sig( (*p)[1] ) ) == MBEDTLS_PK_NONE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "server used unsupported "
                              "SignatureAlgorithm %d", (*p)[1] ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
      }
  
      /*
       * Check if the hash is acceptable
       */
      if( mbedtls_ssl_check_sig_hash( ssl, *md_alg ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "server used HashAlgorithm %d that was not offered",
                                      *(p)[0] ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "Server used SignatureAlgorithm %d", (*p)[1] ) );
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "Server used HashAlgorithm %d", (*p)[0] ) );
      *p += 2;
  
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED */
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
  
  #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;
      const mbedtls_ecp_keypair *peer_key;
      mbedtls_pk_context * peer_pk;
  
  #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 */
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
      peer_pk = &ssl->session_negotiate->peer_cert->pk;
  #endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
  
      if( ! mbedtls_pk_can_do( peer_pk, MBEDTLS_PK_ECKEY ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "server key not ECDH capable" ) );
          return( MBEDTLS_ERR_SSL_PK_TYPE_MISMATCH );
      }
  
      peer_key = mbedtls_pk_ec( *peer_pk );
  
      if( ( ret = mbedtls_ecdh_get_params( &ssl->handshake->ecdh_ctx, peer_key,
                                   MBEDTLS_ECDH_THEIRS ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, ( "mbedtls_ecdh_get_params" ), ret );
          return( ret );
      }
  
      if( ssl_check_server_ecdh_params( ssl ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server certificate (ECDH curve)" ) );
          return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE );
      }
  
  #if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
      /* We don't need the peer's public key anymore. Free it,
       * so that more RAM is available for upcoming expensive
       * operations like ECDHE. */
      mbedtls_pk_free( peer_pk );
  #endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
  
      return( ret );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) ||
            MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */
  
  static int ssl_parse_server_key_exchange( mbedtls_ssl_context *ssl )
  {
      int ret;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
      unsigned char *p = NULL, *end = NULL;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse server key exchange" ) );
  
  #if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse server key exchange" ) );
          ssl->state++;
          return( 0 );
      }
      ((void) p);
      ((void) end);
  #endif
  
  #if defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) || \
      defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_RSA ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA )
      {
          if( ( ret = ssl_get_ecdh_params_from_cert( ssl ) ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "ssl_get_ecdh_params_from_cert", ret );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
              return( ret );
          }
  
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse server key exchange" ) );
          ssl->state++;
          return( 0 );
      }
      ((void) p);
      ((void) end);
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */
  
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
      if( ssl->handshake->ecrs_enabled &&
          ssl->handshake->ecrs_state == ssl_ecrs_ske_start_processing )
      {
          goto start_processing;
      }
  #endif
  
      if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
          return( ret );
      }
  
      if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
          return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
      }
  
      /*
       * ServerKeyExchange may be skipped with PSK and RSA-PSK when the server
       * doesn't use a psk_identity_hint
       */
      if( ssl->in_msg[0] != MBEDTLS_SSL_HS_SERVER_KEY_EXCHANGE )
      {
          if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK ||
              ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
          {
              /* Current message is probably either
               * CertificateRequest or ServerHelloDone */
              ssl->keep_current_message = 1;
              goto exit;
          }
  
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "server key exchange message must "
                                      "not be skipped" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
  
          return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
      }
  
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
      if( ssl->handshake->ecrs_enabled )
          ssl->handshake->ecrs_state = ssl_ecrs_ske_start_processing;
  
  start_processing:
  #endif
      p   = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
      end = ssl->in_msg + ssl->in_hslen;
      MBEDTLS_SSL_DEBUG_BUF( 3,   "server key exchange", p, end - p );
  
  #if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK )
      {
          if( ssl_parse_server_psk_hint( ssl, &p, end ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
          }
      } /* FALLTROUGH */
  #endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
  
  #if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED) ||                       \
      defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
          ; /* nothing more to do */
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_PSK_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
      defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_RSA ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK )
      {
          if( ssl_parse_server_dh_params( ssl, &p, end ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */
  #if defined(MBEDTLS_USE_PSA_CRYPTO) &&                           \
          ( defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||     \
            defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) )
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_RSA ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA )
      {
          if( ssl_parse_server_ecdh_params_psa( ssl, &p, end ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
          }
      }
      else
  #endif /* MBEDTLS_USE_PSA_CRYPTO &&
              ( MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
                MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ) */
  #if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||                     \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED) ||                     \
      defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_RSA ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA )
      {
          if( ssl_parse_server_ecdh_params( ssl, &p, end ) != 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED ||
            MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_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 );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
          }
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
  
  #if defined(MBEDTLS_KEY_EXCHANGE__WITH_SERVER_SIGNATURE__ENABLED)
      if( mbedtls_ssl_ciphersuite_uses_server_signature( ciphersuite_info ) )
      {
          size_t sig_len, hashlen;
          unsigned char hash[64];
          mbedtls_md_type_t md_alg = MBEDTLS_MD_NONE;
          mbedtls_pk_type_t pk_alg = MBEDTLS_PK_NONE;
          unsigned char *params = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
          size_t params_len = p - params;
          void *rs_ctx = NULL;
  
          mbedtls_pk_context * peer_pk;
  
          /*
           * Handle the digitally-signed structure
           */
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
          if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
          {
              if( ssl_parse_signature_algorithm( ssl, &p, end,
                                                 &md_alg, &pk_alg ) != 0 )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
                  return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
              }
  
              if( pk_alg != mbedtls_ssl_get_ciphersuite_sig_pk_alg( ciphersuite_info ) )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
                  return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
              }
          }
          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( ssl->minor_ver < MBEDTLS_SSL_MINOR_VERSION_3 )
          {
              pk_alg = mbedtls_ssl_get_ciphersuite_sig_pk_alg( ciphersuite_info );
  
              /* Default hash for ECDSA is SHA-1 */
              if( pk_alg == MBEDTLS_PK_ECDSA && md_alg == MBEDTLS_MD_NONE )
                  md_alg = MBEDTLS_MD_SHA1;
          }
          else
  #endif
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
              return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
          }
  
          /*
           * Read signature
           */
  
          if( p > end - 2 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
          }
          sig_len = ( p[0] << 8 ) | p[1];
          p += 2;
  
          if( p != end - sig_len )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
              return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
          }
  
          MBEDTLS_SSL_DEBUG_BUF( 3, "signature", p, sig_len );
  
          /*
           * Compute the hash that has been 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, params,
                                                             params_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,
                                                            params, params_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 );
  
  #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 */
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
              return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
          }
          peer_pk = &ssl->session_negotiate->peer_cert->pk;
  #endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
  
          /*
           * Verify signature
           */
          if( !mbedtls_pk_can_do( peer_pk, pk_alg ) )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
              return( MBEDTLS_ERR_SSL_PK_TYPE_MISMATCH );
          }
  
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
          if( ssl->handshake->ecrs_enabled )
              rs_ctx = &ssl->handshake->ecrs_ctx.pk;
  #endif
  
          if( ( ret = mbedtls_pk_verify_restartable( peer_pk,
                          md_alg, hash, hashlen, p, sig_len, rs_ctx ) ) != 0 )
          {
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
              if( ret != MBEDTLS_ERR_ECP_IN_PROGRESS )
  #endif
                  mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                  MBEDTLS_SSL_ALERT_MSG_DECRYPT_ERROR );
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_pk_verify", ret );
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
              if( ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
                  ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
  #endif
              return( ret );
          }
  
  #if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
          /* We don't need the peer's public key anymore. Free it,
           * so that more RAM is available for upcoming expensive
           * operations like ECDHE. */
          mbedtls_pk_free( peer_pk );
  #endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
      }
  #endif /* MBEDTLS_KEY_EXCHANGE__WITH_SERVER_SIGNATURE__ENABLED */
  
  exit:
      ssl->state++;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse server key exchange" ) );
  
      return( 0 );
  }
  
  #if ! defined(MBEDTLS_KEY_EXCHANGE__CERT_REQ_ALLOWED__ENABLED)
  static int ssl_parse_certificate_request( mbedtls_ssl_context *ssl )
  {
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate request" ) );
  
      if( ! mbedtls_ssl_ciphersuite_cert_req_allowed( ciphersuite_info ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse 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_parse_certificate_request( mbedtls_ssl_context *ssl )
  {
      int ret;
      unsigned char *buf;
      size_t n = 0;
      size_t cert_type_len = 0, dn_len = 0;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate request" ) );
  
      if( ! mbedtls_ssl_ciphersuite_cert_req_allowed( ciphersuite_info ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate request" ) );
          ssl->state++;
          return( 0 );
      }
  
      if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
          return( ret );
      }
  
      if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate request message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
          return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
      }
  
      ssl->state++;
      ssl->client_auth = ( ssl->in_msg[0] == MBEDTLS_SSL_HS_CERTIFICATE_REQUEST );
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "got %s certificate request",
                          ssl->client_auth ? "a" : "no" ) );
  
      if( ssl->client_auth == 0 )
      {
          /* Current message is probably the ServerHelloDone */
          ssl->keep_current_message = 1;
          goto exit;
      }
  
      /*
       *  struct {
       *      ClientCertificateType certificate_types<1..2^8-1>;
       *      SignatureAndHashAlgorithm
       *        supported_signature_algorithms<2^16-1>; -- TLS 1.2 only
       *      DistinguishedName certificate_authorities<0..2^16-1>;
       *  } CertificateRequest;
       *
       *  Since we only support a single certificate on clients, let's just
       *  ignore all the information that's supposed to help us pick a
       *  certificate.
       *
       *  We could check that our certificate matches the request, and bail out
       *  if it doesn't, but it's simpler to just send the certificate anyway,
       *  and give the server the opportunity to decide if it should terminate
       *  the connection when it doesn't like our certificate.
       *
       *  Same goes for the hash in TLS 1.2's signature_algorithms: at this
       *  point we only have one hash available (see comments in
       *  write_certificate_verify), so let's just use what we have.
       *
       *  However, we still minimally parse the message to check it is at least
       *  superficially sane.
       */
      buf = ssl->in_msg;
  
      /* certificate_types */
      if( ssl->in_hslen <= mbedtls_ssl_hs_hdr_len( ssl ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate request message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_REQUEST );
      }
      cert_type_len = buf[mbedtls_ssl_hs_hdr_len( ssl )];
      n = cert_type_len;
  
      /*
       * In the subsequent code there are two paths that read from buf:
       *     * the length of the signature algorithms field (if minor version of
       *       SSL is 3),
       *     * distinguished name length otherwise.
       * Both reach at most the index:
       *    ...hdr_len + 2 + n,
       * therefore the buffer length at this point must be greater than that
       * regardless of the actual code path.
       */
      if( ssl->in_hslen <= mbedtls_ssl_hs_hdr_len( ssl ) + 2 + n )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate request message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_REQUEST );
      }
  
      /* supported_signature_algorithms */
  #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
      if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
      {
          size_t sig_alg_len = ( ( buf[mbedtls_ssl_hs_hdr_len( ssl ) + 1 + n] <<  8 )
                               | ( buf[mbedtls_ssl_hs_hdr_len( ssl ) + 2 + n]       ) );
  #if defined(MBEDTLS_DEBUG_C)
          unsigned char* sig_alg;
          size_t i;
  #endif
  
          /*
           * The furthest access in buf is in the loop few lines below:
           *     sig_alg[i + 1],
           * where:
           *     sig_alg = buf + ...hdr_len + 3 + n,
           *     max(i) = sig_alg_len - 1.
           * Therefore the furthest access is:
           *     buf[...hdr_len + 3 + n + sig_alg_len - 1 + 1],
           * which reduces to:
           *     buf[...hdr_len + 3 + n + sig_alg_len],
           * which is one less than we need the buf to be.
           */
          if( ssl->in_hslen <= mbedtls_ssl_hs_hdr_len( ssl ) + 3 + n + sig_alg_len )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate request message" ) );
              mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                              MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
              return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_REQUEST );
          }
  
  #if defined(MBEDTLS_DEBUG_C)
          sig_alg = buf + mbedtls_ssl_hs_hdr_len( ssl ) + 3 + n;
          for( i = 0; i < sig_alg_len; i += 2 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 3, ( "Supported Signature Algorithm found: %d"
                                          ",%d", sig_alg[i], sig_alg[i + 1]  ) );
          }
  #endif
  
          n += 2 + sig_alg_len;
      }
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
  
      /* certificate_authorities */
      dn_len = ( ( buf[mbedtls_ssl_hs_hdr_len( ssl ) + 1 + n] <<  8 )
               | ( buf[mbedtls_ssl_hs_hdr_len( ssl ) + 2 + n]       ) );
  
      n += dn_len;
      if( ssl->in_hslen != mbedtls_ssl_hs_hdr_len( ssl ) + 3 + n )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate request message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_CERTIFICATE_REQUEST );
      }
  
  exit:
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse certificate request" ) );
  
      return( 0 );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE__CERT_REQ_ALLOWED__ENABLED */
  
  static int ssl_parse_server_hello_done( mbedtls_ssl_context *ssl )
  {
      int ret;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse server hello done" ) );
  
      if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
          return( ret );
      }
  
      if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server hello done message" ) );
          return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
      }
  
      if( ssl->in_hslen  != mbedtls_ssl_hs_hdr_len( ssl ) ||
          ssl->in_msg[0] != MBEDTLS_SSL_HS_SERVER_HELLO_DONE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server hello done message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO_DONE );
      }
  
      ssl->state++;
  
  #if defined(MBEDTLS_SSL_PROTO_DTLS)
      if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
          mbedtls_ssl_recv_flight_completed( ssl );
  #endif
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse server hello done" ) );
  
      return( 0 );
  }
  
  static int ssl_write_client_key_exchange( mbedtls_ssl_context *ssl )
  {
      int ret;
  
      size_t header_len;
      size_t content_len;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write client key exchange" ) );
  
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_RSA )
      {
          /*
           * DHM key exchange -- send G^X mod P
           */
          content_len = ssl->handshake->dhm_ctx.len;
  
          ssl->out_msg[4] = (unsigned char)( content_len >> 8 );
          ssl->out_msg[5] = (unsigned char)( content_len      );
          header_len = 6;
  
          ret = mbedtls_dhm_make_public( &ssl->handshake->dhm_ctx,
                             (int) mbedtls_mpi_size( &ssl->handshake->dhm_ctx.P ),
                             &ssl->out_msg[header_len], content_len,
                             ssl->conf->f_rng, ssl->conf->p_rng );
          if( ret != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_dhm_make_public", ret );
              return( ret );
          }
  
          MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: X ", &ssl->handshake->dhm_ctx.X  );
          MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: GX", &ssl->handshake->dhm_ctx.GX );
  
          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( ret );
          }
  
          MBEDTLS_SSL_DEBUG_MPI( 3, "DHM: K ", &ssl->handshake->dhm_ctx.K  );
      }
      else
  #endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED */
  #if defined(MBEDTLS_USE_PSA_CRYPTO) &&                           \
          ( defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||     \
            defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) )
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_RSA ||
          ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA )
      {
          psa_status_t status;
          psa_key_policy_t policy;
  
          mbedtls_ssl_handshake_params *handshake = ssl->handshake;
  
          unsigned char own_pubkey[MBEDTLS_PSA_MAX_EC_PUBKEY_LENGTH];
          size_t own_pubkey_len;
          unsigned char *own_pubkey_ecpoint;
          size_t own_pubkey_ecpoint_len;
  
          psa_crypto_generator_t generator = PSA_CRYPTO_GENERATOR_INIT;
  
          header_len = 4;
  
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "Perform PSA-based ECDH computation." ) );
  
          /*
           * Generate EC private key for ECDHE exchange.
           */
  
          /* Allocate a new key slot for the private key. */
  
          status = psa_allocate_key( &handshake->ecdh_psa_privkey );
          if( status != PSA_SUCCESS )
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
  
          /* The master secret is obtained from the shared ECDH secret by
           * applying the TLS 1.2 PRF with a specific salt and label. While
           * the PSA Crypto API encourages combining key agreement schemes
           * such as ECDH with fixed KDFs such as TLS 1.2 PRF, it does not
           * yet support the provisioning of salt + label to the KDF.
           * For the time being, we therefore need to split the computation
           * of the ECDH secret and the application of the TLS 1.2 PRF. */
          policy = psa_key_policy_init();
          psa_key_policy_set_usage( &policy,
                                    PSA_KEY_USAGE_DERIVE,
                                    PSA_ALG_ECDH( PSA_ALG_SELECT_RAW ) );
          status = psa_set_key_policy( handshake->ecdh_psa_privkey, &policy );
          if( status != PSA_SUCCESS )
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
  
          /* Generate ECDH private key. */
          status = psa_generate_key( handshake->ecdh_psa_privkey,
                            PSA_KEY_TYPE_ECC_KEYPAIR( handshake->ecdh_psa_curve ),
                            MBEDTLS_PSA_ECC_KEY_BITS_OF_CURVE( handshake->ecdh_psa_curve ),
                            NULL, 0 );
          if( status != PSA_SUCCESS )
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
  
          /* Export the public part of the ECDH private key from PSA
           * and convert it to ECPoint format used in ClientKeyExchange. */
          status = psa_export_public_key( handshake->ecdh_psa_privkey,
                                          own_pubkey, sizeof( own_pubkey ),
                                          &own_pubkey_len );
          if( status != PSA_SUCCESS )
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
  
          if( mbedtls_psa_tls_psa_ec_to_ecpoint( own_pubkey,
                                                 own_pubkey_len,
                                                 &own_pubkey_ecpoint,
                                                 &own_pubkey_ecpoint_len ) != 0 )
          {
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
          }
  
          /* Copy ECPoint structure to outgoing message buffer. */
          ssl->out_msg[header_len] = own_pubkey_ecpoint_len;
          memcpy( ssl->out_msg + header_len + 1,
                  own_pubkey_ecpoint, own_pubkey_ecpoint_len );
          content_len = own_pubkey_ecpoint_len + 1;
  
          /* Compute ECDH shared secret. */
          status = psa_key_agreement( &generator,
                                      handshake->ecdh_psa_privkey,
                                      handshake->ecdh_psa_peerkey,
                                      handshake->ecdh_psa_peerkey_len,
                                      PSA_ALG_ECDH( PSA_ALG_SELECT_RAW ) );
          if( status != PSA_SUCCESS )
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
  
          /* The ECDH secret is the premaster secret used for key derivation. */
  
          ssl->handshake->pmslen =
              MBEDTLS_PSA_ECC_KEY_BYTES_OF_CURVE( handshake->ecdh_psa_curve );
  
          status = psa_generator_read( &generator,
                                       ssl->handshake->premaster,
                                       ssl->handshake->pmslen );
          if( status != PSA_SUCCESS )
          {
              psa_generator_abort( &generator );
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
          }
  
          status = psa_generator_abort( &generator );
          if( status != PSA_SUCCESS )
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
  
          status = psa_destroy_key( handshake->ecdh_psa_privkey );
          if( status != PSA_SUCCESS )
              return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
          handshake->ecdh_psa_privkey = 0;
      }
      else
  #endif /* MBEDTLS_USE_PSA_CRYPTO &&
              ( MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
                MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_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 )
      {
          /*
           * ECDH key exchange -- send client public value
           */
          header_len = 4;
  
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
          if( ssl->handshake->ecrs_enabled )
          {
              if( ssl->handshake->ecrs_state == ssl_ecrs_cke_ecdh_calc_secret )
                  goto ecdh_calc_secret;
  
              mbedtls_ecdh_enable_restart( &ssl->handshake->ecdh_ctx );
          }
  #endif
  
          ret = mbedtls_ecdh_make_public( &ssl->handshake->ecdh_ctx,
                                  &content_len,
                                  &ssl->out_msg[header_len], 1000,
                                  ssl->conf->f_rng, ssl->conf->p_rng );
          if( ret != 0 )
          {
              MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_make_public", ret );
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
              if( ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
                  ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
  #endif
              return( ret );
          }
  
          MBEDTLS_SSL_DEBUG_ECDH( 3, &ssl->handshake->ecdh_ctx,
                                  MBEDTLS_DEBUG_ECDH_Q );
  
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
          if( ssl->handshake->ecrs_enabled )
          {
              ssl->handshake->ecrs_n = content_len;
              ssl->handshake->ecrs_state = ssl_ecrs_cke_ecdh_calc_secret;
          }
  
  ecdh_calc_secret:
          if( ssl->handshake->ecrs_enabled )
              content_len = ssl->handshake->ecrs_n;
  #endif
          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 );
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
              if( ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
                  ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
  #endif
              return( ret );
          }
  
          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__SOME__PSK_ENABLED)
      if( mbedtls_ssl_ciphersuite_uses_psk( ciphersuite_info ) )
      {
          /*
           * opaque psk_identity<0..2^16-1>;
           */
          if( ssl_conf_has_static_psk( ssl->conf ) == 0 )
          {
              /* We don't offer PSK suites if we don't have a PSK,
               * and we check that the server's choice is among the
               * ciphersuites we offered, so this should never happen. */
              return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
          }
  
          header_len = 4;
          content_len = ssl->conf->psk_identity_len;
  
          if( header_len + 2 + content_len > MBEDTLS_SSL_OUT_CONTENT_LEN )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "psk identity too long or "
                                          "SSL buffer too short" ) );
              return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
          }
  
          ssl->out_msg[header_len++] = (unsigned char)( content_len >> 8 );
          ssl->out_msg[header_len++] = (unsigned char)( content_len      );
  
          memcpy( ssl->out_msg + header_len,
                  ssl->conf->psk_identity,
                  ssl->conf->psk_identity_len );
          header_len += ssl->conf->psk_identity_len;
  
  #if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
          if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK )
          {
              content_len = 0;
          }
          else
  #endif
  #if defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
          if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
          {
  #if defined(MBEDTLS_USE_PSA_CRYPTO)
              /* Opaque PSKs are currently only supported for PSK-only suites. */
              if( ssl_conf_has_static_raw_psk( ssl->conf ) == 0 )
                  return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
  #endif /* MBEDTLS_USE_PSA_CRYPTO */
  
              if( ( ret = ssl_write_encrypted_pms( ssl, header_len,
                                                   &content_len, 2 ) ) != 0 )
                  return( ret );
          }
          else
  #endif
  #if defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
          if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK )
          {
  #if defined(MBEDTLS_USE_PSA_CRYPTO)
              /* Opaque PSKs are currently only supported for PSK-only suites. */
              if( ssl_conf_has_static_raw_psk( ssl->conf ) == 0 )
                  return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
  #endif /* MBEDTLS_USE_PSA_CRYPTO */
  
              /*
               * ClientDiffieHellmanPublic public (DHM send G^X mod P)
               */
              content_len = ssl->handshake->dhm_ctx.len;
  
              if( header_len + 2 + content_len >
                  MBEDTLS_SSL_OUT_CONTENT_LEN )
              {
                  MBEDTLS_SSL_DEBUG_MSG( 1, ( "psk identity or DHM size too long"
                                              " or SSL buffer too short" ) );
                  return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
              }
  
              ssl->out_msg[header_len++] = (unsigned char)( content_len >> 8 );
              ssl->out_msg[header_len++] = (unsigned char)( content_len      );
  
              ret = mbedtls_dhm_make_public( &ssl->handshake->dhm_ctx,
                      (int) mbedtls_mpi_size( &ssl->handshake->dhm_ctx.P ),
                      &ssl->out_msg[header_len], content_len,
                      ssl->conf->f_rng, ssl->conf->p_rng );
              if( ret != 0 )
              {
                  MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_dhm_make_public", 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 defined(MBEDTLS_USE_PSA_CRYPTO)
              /* Opaque PSKs are currently only supported for PSK-only suites. */
              if( ssl_conf_has_static_raw_psk( ssl->conf ) == 0 )
                  return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
  #endif /* MBEDTLS_USE_PSA_CRYPTO */
  
              /*
               * ClientECDiffieHellmanPublic public;
               */
              ret = mbedtls_ecdh_make_public( &ssl->handshake->ecdh_ctx,
                      &content_len,
                      &ssl->out_msg[header_len],
                      MBEDTLS_SSL_OUT_CONTENT_LEN - header_len,
                      ssl->conf->f_rng, ssl->conf->p_rng );
              if( ret != 0 )
              {
                  MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_make_public", ret );
                  return( ret );
              }
  
              MBEDTLS_SSL_DEBUG_ECDH( 3, &ssl->handshake->ecdh_ctx,
                                      MBEDTLS_DEBUG_ECDH_Q );
          }
          else
  #endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
              return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
          }
  
  #if defined(MBEDTLS_USE_PSA_CRYPTO) &&          \
      defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
          if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK &&
              ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 &&
              ssl_conf_has_static_raw_psk( ssl->conf ) == 0 )
          {
              MBEDTLS_SSL_DEBUG_MSG( 1, ( "skip PMS generation for opaque PSK" ) );
          }
          else
  #endif /* MBEDTLS_USE_PSA_CRYPTO &&
            MBEDTLS_KEY_EXCHANGE_PSK_ENABLED */
          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__SOME__PSK_ENABLED */
  #if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)
      if( ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA )
      {
          header_len = 4;
          if( ( ret = ssl_write_encrypted_pms( ssl, header_len,
                                               &content_len, 0 ) ) != 0 )
              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 )
      {
          header_len = 4;
  
          ret = mbedtls_ecjpake_write_round_two( &ssl->handshake->ecjpake_ctx,
                  ssl->out_msg + header_len,
                  MBEDTLS_SSL_OUT_CONTENT_LEN - header_len,
                  &content_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 );
          }
  
          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_RSA_ENABLED */
      {
          ((void) ciphersuite_info);
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
  
      ssl->out_msglen  = header_len + content_len;
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_CLIENT_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 client key exchange" ) );
  
      return( 0 );
  }
  
  #if !defined(MBEDTLS_KEY_EXCHANGE__CERT_REQ_ALLOWED__ENABLED)
  static int ssl_write_certificate_verify( mbedtls_ssl_context *ssl )
  {
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
      int ret;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate verify" ) );
  
      if( ( ret = mbedtls_ssl_derive_keys( ssl ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_derive_keys", ret );
          return( ret );
      }
  
      if( !mbedtls_ssl_ciphersuite_cert_req_allowed( ciphersuite_info ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write 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 */
  static int ssl_write_certificate_verify( mbedtls_ssl_context *ssl )
  {
      int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
      const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
          ssl->handshake->ciphersuite_info;
      size_t n = 0, offset = 0;
      unsigned char hash[48];
      unsigned char *hash_start = hash;
      mbedtls_md_type_t md_alg = MBEDTLS_MD_NONE;
      unsigned int hashlen;
      void *rs_ctx = NULL;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate verify" ) );
  
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
      if( ssl->handshake->ecrs_enabled &&
          ssl->handshake->ecrs_state == ssl_ecrs_crt_vrfy_sign )
      {
          goto sign;
      }
  #endif
  
      if( ( ret = mbedtls_ssl_derive_keys( ssl ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_derive_keys", ret );
          return( ret );
      }
  
      if( !mbedtls_ssl_ciphersuite_cert_req_allowed( ciphersuite_info ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate verify" ) );
          ssl->state++;
          return( 0 );
      }
  
      if( ssl->client_auth == 0 || mbedtls_ssl_own_cert( ssl ) == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate verify" ) );
          ssl->state++;
          return( 0 );
      }
  
      if( mbedtls_ssl_own_key( ssl ) == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no private key for certificate" ) );
          return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
      }
  
      /*
       * Make a signature of the handshake digests
       */
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
      if( ssl->handshake->ecrs_enabled )
          ssl->handshake->ecrs_state = ssl_ecrs_crt_vrfy_sign;
  
  sign:
  #endif
  
      ssl->handshake->calc_verify( ssl, hash );
  
  #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 )
      {
          /*
           * digitally-signed struct {
           *     opaque md5_hash[16];
           *     opaque sha_hash[20];
           * };
           *
           * md5_hash
           *     MD5(handshake_messages);
           *
           * sha_hash
           *     SHA(handshake_messages);
           */
          hashlen = 36;
          md_alg = MBEDTLS_MD_NONE;
  
          /*
           * For ECDSA, default hash is SHA-1 only
           */
          if( mbedtls_pk_can_do( mbedtls_ssl_own_key( ssl ), 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 )
      {
          /*
           * digitally-signed struct {
           *     opaque handshake_messages[handshake_messages_length];
           * };
           *
           * Taking shortcut here. We assume that the server always allows the
           * PRF Hash function and has sent it in the allowed signature
           * algorithms list received in the Certificate Request message.
           *
           * Until we encounter a server that does not, we will take this
           * shortcut.
           *
           * Reason: Otherwise we should have running hashes for SHA512 and SHA224
           *         in order to satisfy 'weird' needs from the server side.
           */
          if( ssl->handshake->ciphersuite_info->mac == MBEDTLS_MD_SHA384 )
          {
              md_alg = MBEDTLS_MD_SHA384;
              ssl->out_msg[4] = MBEDTLS_SSL_HASH_SHA384;
          }
          else
          {
              md_alg = MBEDTLS_MD_SHA256;
              ssl->out_msg[4] = MBEDTLS_SSL_HASH_SHA256;
          }
          ssl->out_msg[5] = mbedtls_ssl_sig_from_pk( mbedtls_ssl_own_key( ssl ) );
  
          /* Info from md_alg will be used instead */
          hashlen = 0;
          offset = 2;
      }
      else
  #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
  
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
      if( ssl->handshake->ecrs_enabled )
          rs_ctx = &ssl->handshake->ecrs_ctx.pk;
  #endif
  
      if( ( ret = mbedtls_pk_sign_restartable( mbedtls_ssl_own_key( ssl ),
                           md_alg, hash_start, hashlen,
                           ssl->out_msg + 6 + offset, &n,
                           ssl->conf->f_rng, ssl->conf->p_rng, rs_ctx ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_pk_sign", ret );
  #if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
          if( ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
              ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
  #endif
          return( ret );
      }
  
      ssl->out_msg[4 + offset] = (unsigned char)( n >> 8 );
      ssl->out_msg[5 + offset] = (unsigned char)( n      );
  
      ssl->out_msglen  = 6 + n + offset;
      ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
      ssl->out_msg[0]  = MBEDTLS_SSL_HS_CERTIFICATE_VERIFY;
  
      ssl->state++;
  
      if( ( ret = mbedtls_ssl_write_handshake_msg( ssl ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_handshake_msg", ret );
          return( ret );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write certificate verify" ) );
  
      return( ret );
  }
  #endif /* MBEDTLS_KEY_EXCHANGE__CERT_REQ_ALLOWED__ENABLED */
  
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
  static int ssl_parse_new_session_ticket( mbedtls_ssl_context *ssl )
  {
      int ret;
      uint32_t lifetime;
      size_t ticket_len;
      unsigned char *ticket;
      const unsigned char *msg;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse new session ticket" ) );
  
      if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
      {
          MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
          return( ret );
      }
  
      if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad new session ticket message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
          return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
      }
  
      /*
       * struct {
       *     uint32 ticket_lifetime_hint;
       *     opaque ticket<0..2^16-1>;
       * } NewSessionTicket;
       *
       * 0  .  3   ticket_lifetime_hint
       * 4  .  5   ticket_len (n)
       * 6  .  5+n ticket content
       */
      if( ssl->in_msg[0] != MBEDTLS_SSL_HS_NEW_SESSION_TICKET ||
          ssl->in_hslen < 6 + mbedtls_ssl_hs_hdr_len( ssl ) )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad new session ticket message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_NEW_SESSION_TICKET );
      }
  
      msg = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
  
      lifetime = ( ((uint32_t) msg[0]) << 24 ) | ( msg[1] << 16 ) |
                 ( msg[2] << 8 ) | ( msg[3] );
  
      ticket_len = ( msg[4] << 8 ) | ( msg[5] );
  
      if( ticket_len + 6 + mbedtls_ssl_hs_hdr_len( ssl ) != ssl->in_hslen )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad new session ticket message" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
          return( MBEDTLS_ERR_SSL_BAD_HS_NEW_SESSION_TICKET );
      }
  
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "ticket length: %d", ticket_len ) );
  
      /* We're not waiting for a NewSessionTicket message any more */
      ssl->handshake->new_session_ticket = 0;
      ssl->state = MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC;
  
      /*
       * Zero-length ticket means the server changed his mind and doesn't want
       * to send a ticket after all, so just forget it
       */
      if( ticket_len == 0 )
          return( 0 );
  
      if( ssl->session != NULL && ssl->session->ticket != NULL )
      {
          mbedtls_platform_zeroize( ssl->session->ticket,
                                    ssl->session->ticket_len );
          mbedtls_free( ssl->session->ticket );
          ssl->session->ticket = NULL;
          ssl->session->ticket_len = 0;
      }
  
      mbedtls_platform_zeroize( ssl->session_negotiate->ticket,
                                ssl->session_negotiate->ticket_len );
      mbedtls_free( ssl->session_negotiate->ticket );
      ssl->session_negotiate->ticket = NULL;
      ssl->session_negotiate->ticket_len = 0;
  
      if( ( ticket = mbedtls_calloc( 1, ticket_len ) ) == NULL )
      {
          MBEDTLS_SSL_DEBUG_MSG( 1, ( "ticket alloc failed" ) );
          mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                          MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
          return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
      }
  
      memcpy( ticket, msg + 6, ticket_len );
  
      ssl->session_negotiate->ticket = ticket;
      ssl->session_negotiate->ticket_len = ticket_len;
      ssl->session_negotiate->ticket_lifetime = lifetime;
  
      /*
       * RFC 5077 section 3.4:
       * "If the client receives a session ticket from the server, then it
       * discards any Session ID that was sent in the ServerHello."
       */
      MBEDTLS_SSL_DEBUG_MSG( 3, ( "ticket in use, discarding session id" ) );
      ssl->session_negotiate->id_len = 0;
  
      MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse new session ticket" ) );
  
      return( 0 );
  }
  #endif /* MBEDTLS_SSL_SESSION_TICKETS */
  
  /*
   * SSL handshake -- client side -- single step
   */
  int mbedtls_ssl_handshake_client_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, ( "client 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 */
  
      /* Change state now, so that it is right in mbedtls_ssl_read_record(), used
       * by DTLS for dropping out-of-sequence ChangeCipherSpec records */
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
      if( ssl->state == MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC &&
          ssl->handshake->new_session_ticket != 0 )
      {
          ssl->state = MBEDTLS_SSL_SERVER_NEW_SESSION_TICKET;
      }
  #endif
  
      switch( ssl->state )
      {
          case MBEDTLS_SSL_HELLO_REQUEST:
              ssl->state = MBEDTLS_SSL_CLIENT_HELLO;
              break;
  
         /*
          *  ==>   ClientHello
          */
         case MBEDTLS_SSL_CLIENT_HELLO:
             ret = ssl_write_client_hello( ssl );
             break;
  
         /*
          *  <==   ServerHello
          *        Certificate
          *      ( ServerKeyExchange  )
          *      ( CertificateRequest )
          *        ServerHelloDone
          */
         case MBEDTLS_SSL_SERVER_HELLO:
             ret = ssl_parse_server_hello( ssl );
             break;
  
         case MBEDTLS_SSL_SERVER_CERTIFICATE:
             ret = mbedtls_ssl_parse_certificate( ssl );
             break;
  
         case MBEDTLS_SSL_SERVER_KEY_EXCHANGE:
             ret = ssl_parse_server_key_exchange( ssl );
             break;
  
         case MBEDTLS_SSL_CERTIFICATE_REQUEST:
             ret = ssl_parse_certificate_request( ssl );
             break;
  
         case MBEDTLS_SSL_SERVER_HELLO_DONE:
             ret = ssl_parse_server_hello_done( ssl );
             break;
  
         /*
          *  ==> ( Certificate/Alert  )
          *        ClientKeyExchange
          *      ( CertificateVerify  )
          *        ChangeCipherSpec
          *        Finished
          */
         case MBEDTLS_SSL_CLIENT_CERTIFICATE:
             ret = mbedtls_ssl_write_certificate( ssl );
             break;
  
         case MBEDTLS_SSL_CLIENT_KEY_EXCHANGE:
             ret = ssl_write_client_key_exchange( ssl );
             break;
  
         case MBEDTLS_SSL_CERTIFICATE_VERIFY:
             ret = ssl_write_certificate_verify( ssl );
             break;
  
         case MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC:
             ret = mbedtls_ssl_write_change_cipher_spec( ssl );
             break;
  
         case MBEDTLS_SSL_CLIENT_FINISHED:
             ret = mbedtls_ssl_write_finished( ssl );
             break;
  
         /*
          *  <==   ( NewSessionTicket )
          *        ChangeCipherSpec
          *        Finished
          */
  #if defined(MBEDTLS_SSL_SESSION_TICKETS)
         case MBEDTLS_SSL_SERVER_NEW_SESSION_TICKET:
             ret = ssl_parse_new_session_ticket( ssl );
             break;
  #endif
  
         case MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC:
             ret = mbedtls_ssl_parse_change_cipher_spec( ssl );
             break;
  
         case MBEDTLS_SSL_SERVER_FINISHED:
             ret = mbedtls_ssl_parse_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 );
  }
  #endif /* MBEDTLS_SSL_CLI_C */
  