library/ssl_tls.c

/*
 *  TLS shared functions
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
/*
 *  http://www.ietf.org/rfc/rfc2246.txt
 *  http://www.ietf.org/rfc/rfc4346.txt
 */

#include "common.h"

#if defined(MBEDTLS_SSL_TLS_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/ssl.h"
#include "ssl_misc.h"
#include "mbedtls/debug.h"
#include "mbedtls/error.h"
#include "mbedtls/platform_util.h"
#include "mbedtls/version.h"

#include <string.h>

#if defined(MBEDTLS_USE_PSA_CRYPTO)
#include "mbedtls/psa_util.h"
#include "psa/crypto.h"
#endif

#if defined(MBEDTLS_X509_CRT_PARSE_C)
#include "mbedtls/oid.h"
#endif

#if defined(MBEDTLS_SSL_PROTO_DTLS)

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

int mbedtls_ssl_conf_cid( mbedtls_ssl_config *conf,
                          size_t len,
                          int ignore_other_cid )
{
    if( len > MBEDTLS_SSL_CID_IN_LEN_MAX )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    if( ignore_other_cid != MBEDTLS_SSL_UNEXPECTED_CID_FAIL &&
        ignore_other_cid != MBEDTLS_SSL_UNEXPECTED_CID_IGNORE )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    conf->ignore_unexpected_cid = ignore_other_cid;
    conf->cid_len = len;
    return( 0 );
}

int mbedtls_ssl_set_cid( mbedtls_ssl_context *ssl,
                         int enable,
                         unsigned char const *own_cid,
                         size_t own_cid_len )
{
    if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl->negotiate_cid = enable;
    if( enable == MBEDTLS_SSL_CID_DISABLED )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Disable use of CID extension." ) );
        return( 0 );
    }
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "Enable use of CID extension." ) );
    MBEDTLS_SSL_DEBUG_BUF( 3, "Own CID", own_cid, own_cid_len );

    if( own_cid_len != ssl->conf->cid_len )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "CID length %u does not match CID length %u in config",
                                    (unsigned) own_cid_len,
                                    (unsigned) ssl->conf->cid_len ) );
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    memcpy( ssl->own_cid, own_cid, own_cid_len );
    /* Truncation is not an issue here because
     * MBEDTLS_SSL_CID_IN_LEN_MAX at most 255. */
    ssl->own_cid_len = (uint8_t) own_cid_len;

    return( 0 );
}

int mbedtls_ssl_get_peer_cid( mbedtls_ssl_context *ssl,
                     int *enabled,
                     unsigned char peer_cid[ MBEDTLS_SSL_CID_OUT_LEN_MAX ],
                     size_t *peer_cid_len )
{
    *enabled = MBEDTLS_SSL_CID_DISABLED;

    if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM ||
        ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    /* We report MBEDTLS_SSL_CID_DISABLED in case the CID extensions
     * were used, but client and server requested the empty CID.
     * This is indistinguishable from not using the CID extension
     * in the first place. */
    if( ssl->transform_in->in_cid_len  == 0 &&
        ssl->transform_in->out_cid_len == 0 )
    {
        return( 0 );
    }

    if( peer_cid_len != NULL )
    {
        *peer_cid_len = ssl->transform_in->out_cid_len;
        if( peer_cid != NULL )
        {
            memcpy( peer_cid, ssl->transform_in->out_cid,
                    ssl->transform_in->out_cid_len );
        }
    }

    *enabled = MBEDTLS_SSL_CID_ENABLED;

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

#endif /* MBEDTLS_SSL_PROTO_DTLS */

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

int mbedtls_ssl_session_copy( mbedtls_ssl_session *dst,
                              const mbedtls_ssl_session *src )
{
    mbedtls_ssl_session_free( dst );
    memcpy( dst, src, sizeof( mbedtls_ssl_session ) );

#if defined(MBEDTLS_X509_CRT_PARSE_C)

#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    if( src->peer_cert != NULL )
    {
        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

        dst->peer_cert = mbedtls_calloc( 1, sizeof(mbedtls_x509_crt) );
        if( dst->peer_cert == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

        mbedtls_x509_crt_init( dst->peer_cert );

        if( ( ret = mbedtls_x509_crt_parse_der( dst->peer_cert, src->peer_cert->raw.p,
                                        src->peer_cert->raw.len ) ) != 0 )
        {
            mbedtls_free( dst->peer_cert );
            dst->peer_cert = NULL;
            return( ret );
        }
    }
#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    if( src->peer_cert_digest != NULL )
    {
        dst->peer_cert_digest =
            mbedtls_calloc( 1, src->peer_cert_digest_len );
        if( dst->peer_cert_digest == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

        memcpy( dst->peer_cert_digest, src->peer_cert_digest,
                src->peer_cert_digest_len );
        dst->peer_cert_digest_type = src->peer_cert_digest_type;
        dst->peer_cert_digest_len = src->peer_cert_digest_len;
    }
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

#endif /* MBEDTLS_X509_CRT_PARSE_C */

#if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
    if( src->ticket != NULL )
    {
        dst->ticket = mbedtls_calloc( 1, src->ticket_len );
        if( dst->ticket == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_FAILED );

        memcpy( dst->ticket, src->ticket, src->ticket_len );
    }
#endif /* MBEDTLS_SSL_SESSION_TICKETS && MBEDTLS_SSL_CLI_C */

    return( 0 );
}

#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
static int resize_buffer( unsigned char **buffer, size_t len_new, size_t *len_old )
{
    unsigned char* resized_buffer = mbedtls_calloc( 1, len_new );
    if( resized_buffer == NULL )
        return -1;

    /* We want to copy len_new bytes when downsizing the buffer, and
     * len_old bytes when upsizing, so we choose the smaller of two sizes,
     * to fit one buffer into another. Size checks, ensuring that no data is
     * lost, are done outside of this function. */
    memcpy( resized_buffer, *buffer,
            ( len_new < *len_old ) ? len_new : *len_old );
    mbedtls_platform_zeroize( *buffer, *len_old );
    mbedtls_free( *buffer );

    *buffer = resized_buffer;
    *len_old = len_new;

    return 0;
}

static void handle_buffer_resizing( mbedtls_ssl_context *ssl, int downsizing,
                                    size_t in_buf_new_len,
                                    size_t out_buf_new_len )
{
    int modified = 0;
    size_t written_in = 0, iv_offset_in = 0, len_offset_in = 0;
    size_t written_out = 0, iv_offset_out = 0, len_offset_out = 0;
    if( ssl->in_buf != NULL )
    {
        written_in = ssl->in_msg - ssl->in_buf;
        iv_offset_in = ssl->in_iv - ssl->in_buf;
        len_offset_in = ssl->in_len - ssl->in_buf;
        if( downsizing ?
            ssl->in_buf_len > in_buf_new_len && ssl->in_left < in_buf_new_len :
            ssl->in_buf_len < in_buf_new_len )
        {
            if( resize_buffer( &ssl->in_buf, in_buf_new_len, &ssl->in_buf_len ) != 0 )
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "input buffer resizing failed - out of memory" ) );
            }
            else
            {
                MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reallocating in_buf to %" MBEDTLS_PRINTF_SIZET,
                                            in_buf_new_len ) );
                modified = 1;
            }
        }
    }

    if( ssl->out_buf != NULL )
    {
        written_out = ssl->out_msg - ssl->out_buf;
        iv_offset_out = ssl->out_iv - ssl->out_buf;
        len_offset_out = ssl->out_len - ssl->out_buf;
        if( downsizing ?
            ssl->out_buf_len > out_buf_new_len && ssl->out_left < out_buf_new_len :
            ssl->out_buf_len < out_buf_new_len )
        {
            if( resize_buffer( &ssl->out_buf, out_buf_new_len, &ssl->out_buf_len ) != 0 )
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "output buffer resizing failed - out of memory" ) );
            }
            else
            {
                MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reallocating out_buf to %" MBEDTLS_PRINTF_SIZET,
                                            out_buf_new_len ) );
                modified = 1;
            }
        }
    }
    if( modified )
    {
        /* Update pointers here to avoid doing it twice. */
        mbedtls_ssl_reset_in_out_pointers( ssl );
        /* Fields below might not be properly updated with record
         * splitting or with CID, so they are manually updated here. */
        ssl->out_msg = ssl->out_buf + written_out;
        ssl->out_len = ssl->out_buf + len_offset_out;
        ssl->out_iv = ssl->out_buf + iv_offset_out;

        ssl->in_msg = ssl->in_buf + written_in;
        ssl->in_len = ssl->in_buf + len_offset_in;
        ssl->in_iv = ssl->in_buf + iv_offset_in;
    }
}
#endif /* MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_USE_PSA_CRYPTO)

static psa_status_t setup_psa_key_derivation( psa_key_derivation_operation_t* derivation,
                                              psa_key_id_t key,
                                              psa_algorithm_t alg,
                                              const unsigned char* seed, size_t seed_length,
                                              const unsigned char* label, size_t label_length,
                                              size_t capacity )
{
    psa_status_t status;

    status = psa_key_derivation_setup( derivation, alg );
    if( status != PSA_SUCCESS )
        return( status );

    if( PSA_ALG_IS_TLS12_PRF( alg ) || PSA_ALG_IS_TLS12_PSK_TO_MS( alg ) )
    {
        status = psa_key_derivation_input_bytes( derivation,
                                                 PSA_KEY_DERIVATION_INPUT_SEED,
                                                 seed, seed_length );
        if( status != PSA_SUCCESS )
            return( status );

        if( mbedtls_svc_key_id_is_null( key ) )
        {
            status = psa_key_derivation_input_bytes(
                derivation, PSA_KEY_DERIVATION_INPUT_SECRET,
                NULL, 0 );
        }
        else
        {
            status = psa_key_derivation_input_key(
                derivation, PSA_KEY_DERIVATION_INPUT_SECRET, key );
        }
        if( status != PSA_SUCCESS )
            return( status );

        status = psa_key_derivation_input_bytes( derivation,
                                                 PSA_KEY_DERIVATION_INPUT_LABEL,
                                                 label, label_length );
        if( status != PSA_SUCCESS )
            return( status );
    }
    else
    {
        return( PSA_ERROR_NOT_SUPPORTED );
    }

    status = psa_key_derivation_set_capacity( derivation, capacity );
    if( status != PSA_SUCCESS )
        return( status );

    return( PSA_SUCCESS );
}

static int tls_prf_generic( mbedtls_md_type_t md_type,
                            const unsigned char *secret, size_t slen,
                            const char *label,
                            const unsigned char *random, size_t rlen,
                            unsigned char *dstbuf, size_t dlen )
{
    psa_status_t status;
    psa_algorithm_t alg;
    psa_key_id_t master_key = MBEDTLS_SVC_KEY_ID_INIT;
    psa_key_derivation_operation_t derivation =
        PSA_KEY_DERIVATION_OPERATION_INIT;

    if( md_type == MBEDTLS_MD_SHA384 )
        alg = PSA_ALG_TLS12_PRF(PSA_ALG_SHA_384);
    else
        alg = PSA_ALG_TLS12_PRF(PSA_ALG_SHA_256);

    /* Normally a "secret" should be long enough to be impossible to
     * find by brute force, and in particular should not be empty. But
     * this PRF is also used to derive an IV, in particular in EAP-TLS,
     * and for this use case it makes sense to have a 0-length "secret".
     * Since the key API doesn't allow importing a key of length 0,
     * keep master_key=0, which setup_psa_key_derivation() understands
     * to mean a 0-length "secret" input. */
    if( slen != 0 )
    {
        psa_key_attributes_t key_attributes = psa_key_attributes_init();
        psa_set_key_usage_flags( &key_attributes, PSA_KEY_USAGE_DERIVE );
        psa_set_key_algorithm( &key_attributes, alg );
        psa_set_key_type( &key_attributes, PSA_KEY_TYPE_DERIVE );

        status = psa_import_key( &key_attributes, secret, slen, &master_key );
        if( status != PSA_SUCCESS )
            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
    }

    status = setup_psa_key_derivation( &derivation,
                                       master_key, alg,
                                       random, rlen,
                                       (unsigned char const *) label,
                                       (size_t) strlen( label ),
                                       dlen );
    if( status != PSA_SUCCESS )
    {
        psa_key_derivation_abort( &derivation );
        psa_destroy_key( master_key );
        return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
    }

    status = psa_key_derivation_output_bytes( &derivation, dstbuf, dlen );
    if( status != PSA_SUCCESS )
    {
        psa_key_derivation_abort( &derivation );
        psa_destroy_key( master_key );
        return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
    }

    status = psa_key_derivation_abort( &derivation );
    if( status != PSA_SUCCESS )
    {
        psa_destroy_key( master_key );
        return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
    }

    if( ! mbedtls_svc_key_id_is_null( master_key ) )
        status = psa_destroy_key( master_key );
    if( status != PSA_SUCCESS )
        return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );

    return( 0 );
}

#else /* MBEDTLS_USE_PSA_CRYPTO */

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

    mbedtls_md_init( &md_ctx );

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

    md_len = mbedtls_md_get_size( md_info );

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

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

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

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

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

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

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

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

exit:
    mbedtls_md_free( &md_ctx );

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

    mbedtls_free( tmp );

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

#if defined(MBEDTLS_SHA384_C)
static int tls_prf_sha384( const unsigned char *secret, size_t slen,
                           const char *label,
                           const unsigned char *random, size_t rlen,
                           unsigned char *dstbuf, size_t dlen )
{
    return( tls_prf_generic( MBEDTLS_MD_SHA384, secret, slen,
                             label, random, rlen, dstbuf, dlen ) );
}
#endif /* MBEDTLS_SHA384_C */
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

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

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

#if defined(MBEDTLS_SHA384_C)
static void ssl_update_checksum_sha384( mbedtls_ssl_context *, const unsigned char *, size_t );
static void ssl_calc_verify_tls_sha384( const mbedtls_ssl_context *, unsigned char*, size_t * );
static void ssl_calc_finished_tls_sha384( mbedtls_ssl_context *, unsigned char *, int );
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

#if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED) && \
    defined(MBEDTLS_USE_PSA_CRYPTO)
static int ssl_use_opaque_psk( mbedtls_ssl_context const *ssl )
{
    if( ssl->conf->f_psk != NULL )
    {
        /* If we've used a callback to select the PSK,
         * the static configuration is irrelevant. */
        if( ! mbedtls_svc_key_id_is_null( ssl->handshake->psk_opaque ) )
            return( 1 );

        return( 0 );
    }

    if( ! mbedtls_svc_key_id_is_null( ssl->conf->psk_opaque ) )
        return( 1 );

    return( 0 );
}
#endif /* MBEDTLS_USE_PSA_CRYPTO &&
          MBEDTLS_KEY_EXCHANGE_PSK_ENABLED */

#if defined(MBEDTLS_SSL_EXPORT_KEYS)
static mbedtls_tls_prf_types tls_prf_get_type( mbedtls_ssl_tls_prf_cb *tls_prf )
{
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA384_C)
    if( tls_prf == tls_prf_sha384 )
    {
        return( MBEDTLS_SSL_TLS_PRF_SHA384 );
    }
    else
#endif
#if defined(MBEDTLS_SHA256_C)
    if( tls_prf == tls_prf_sha256 )
    {
        return( MBEDTLS_SSL_TLS_PRF_SHA256 );
    }
    else
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    return( MBEDTLS_SSL_TLS_PRF_NONE );
}
#endif /* MBEDTLS_SSL_EXPORT_KEYS */

int  mbedtls_ssl_tls_prf( const mbedtls_tls_prf_types prf,
                          const unsigned char *secret, size_t slen,
                          const char *label,
                          const unsigned char *random, size_t rlen,
                          unsigned char *dstbuf, size_t dlen )
{
    mbedtls_ssl_tls_prf_cb *tls_prf = NULL;

    switch( prf )
    {
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA384_C)
        case MBEDTLS_SSL_TLS_PRF_SHA384:
            tls_prf = tls_prf_sha384;
        break;
#endif /* MBEDTLS_SHA384_C */
#if defined(MBEDTLS_SHA256_C)
        case MBEDTLS_SSL_TLS_PRF_SHA256:
            tls_prf = tls_prf_sha256;
        break;
#endif /* MBEDTLS_SHA256_C */
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    default:
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
    }

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

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

/*
 * Populate a transform structure with session keys and all the other
 * necessary information.
 *
 * Parameters:
 * - [in/out]: transform: structure to populate
 *      [in] must be just initialised with mbedtls_ssl_transform_init()
 *      [out] fully populated, ready for use by mbedtls_ssl_{en,de}crypt_buf()
 * - [in] ciphersuite
 * - [in] master
 * - [in] encrypt_then_mac
 * - [in] compression
 * - [in] tls_prf: pointer to PRF to use for key derivation
 * - [in] randbytes: buffer holding ServerHello.random + ClientHello.random
 * - [in] minor_ver: SSL/TLS minor version
 * - [in] endpoint: client or server
 * - [in] ssl: optionally used for:
 *        - MBEDTLS_SSL_EXPORT_KEYS: ssl->conf->{f,p}_export_keys
 *        - MBEDTLS_DEBUG_C: ssl->conf->{f,p}_dbg
 */
static int ssl_tls12_populate_transform( mbedtls_ssl_transform *transform,
                                   int ciphersuite,
                                   const unsigned char master[48],
#if defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC) && \
    defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                                   int encrypt_then_mac,
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC &&
          MBEDTLS_SSL_SOME_SUITES_USE_MAC */
                                   ssl_tls_prf_t tls_prf,
                                   const unsigned char randbytes[64],
                                   int minor_ver,
                                   unsigned endpoint,
                                   const mbedtls_ssl_context *ssl )
{
    int ret = 0;
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    int psa_fallthrough;
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    unsigned char keyblk[256];
    unsigned char *key1;
    unsigned char *key2;
    unsigned char *mac_enc;
    unsigned char *mac_dec;
    size_t mac_key_len = 0;
    size_t iv_copy_len;
    unsigned keylen;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
    const mbedtls_cipher_info_t *cipher_info;
    const mbedtls_md_info_t *md_info;

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

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

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

#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
    if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_4 )
    {
        /* At the moment, we keep TLS <= 1.2 and TLS 1.3 transform
         * generation separate. This should never happen. */
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */

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

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

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

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

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

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

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

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

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

    keylen = cipher_info->key_bitlen / 8;

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

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

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

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

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

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

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

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
            if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
            {
                transform->minlen += transform->ivlen;
            }
            else
#endif
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
                ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
                goto end;
            }
        }
    }
    else
#endif /* MBEDTLS_SSL_SOME_SUITES_USE_MAC */
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

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

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

        mac_enc = keyblk;
        mac_dec = keyblk + mac_key_len;

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

        mac_enc = keyblk + mac_key_len;
        mac_dec = keyblk;

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

#if defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC)
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
    /* For HMAC-based ciphersuites, initialize the HMAC transforms.
       For AEAD-based ciphersuites, there is nothing to do here. */
    if( mac_key_len != 0 )
    {
        mbedtls_md_hmac_starts( &transform->md_ctx_enc, mac_enc, mac_key_len );
        mbedtls_md_hmac_starts( &transform->md_ctx_dec, mac_dec, mac_key_len );
    }
#endif
#endif /* MBEDTLS_SSL_SOME_SUITES_USE_MAC */

    ((void) mac_dec);
    ((void) mac_enc);

#if defined(MBEDTLS_SSL_EXPORT_KEYS)
    if( ssl->f_export_keys != NULL )
    {
        ssl->f_export_keys( ssl->p_export_keys,
                            MBEDTLS_SSL_KEY_EXPORT_TLS12_MASTER_SECRET,
                            master, 48,
                            randbytes + 32,
                            randbytes,
                            tls_prf_get_type( tls_prf ) );
    }
#endif

#if defined(MBEDTLS_USE_PSA_CRYPTO)

    /* Only use PSA-based ciphers for TLS-1.2.
     * That's relevant at least for TLS-1.0, where
     * we assume that mbedtls_cipher_crypt() updates
     * the structure field for the IV, which the PSA-based
     * implementation currently doesn't. */
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
    if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
    {
        ret = mbedtls_cipher_setup_psa( &transform->cipher_ctx_enc,
                                        cipher_info, transform->taglen );
        if( ret != 0 && ret != MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_setup_psa", ret );
            goto end;
        }

        if( ret == 0 )
        {
            MBEDTLS_SSL_DEBUG_MSG( 3, ( "Successfully setup PSA-based encryption cipher context" ) );
            psa_fallthrough = 0;
        }
        else
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "Failed to setup PSA-based cipher context for record encryption - fall through to default setup." ) );
            psa_fallthrough = 1;
        }
    }
    else
        psa_fallthrough = 1;
#else
    psa_fallthrough = 1;
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

    if( psa_fallthrough == 1 )
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    if( ( ret = mbedtls_cipher_setup( &transform->cipher_ctx_enc,
                                 cipher_info ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_setup", ret );
        goto end;
    }

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    /* Only use PSA-based ciphers for TLS-1.2.
     * That's relevant at least for TLS-1.0, where
     * we assume that mbedtls_cipher_crypt() updates
     * the structure field for the IV, which the PSA-based
     * implementation currently doesn't. */
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
    if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
    {
        ret = mbedtls_cipher_setup_psa( &transform->cipher_ctx_dec,
                                        cipher_info, transform->taglen );
        if( ret != 0 && ret != MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_setup_psa", ret );
            goto end;
        }

        if( ret == 0 )
        {
            MBEDTLS_SSL_DEBUG_MSG( 3, ( "Successfully setup PSA-based decryption cipher context" ) );
            psa_fallthrough = 0;
        }
        else
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "Failed to setup PSA-based cipher context for record decryption - fall through to default setup." ) );
            psa_fallthrough = 1;
        }
    }
    else
        psa_fallthrough = 1;
#else
    psa_fallthrough = 1;
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

    if( psa_fallthrough == 1 )
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    if( ( ret = mbedtls_cipher_setup( &transform->cipher_ctx_dec,
                                 cipher_info ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_setup", ret );
        goto end;
    }

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

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

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

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


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

/*
 * Set appropriate PRF function and other SSL / TLS1.2 functions
 *
 * Inputs:
 * - SSL/TLS minor version
 * - hash associated with the ciphersuite (only used by TLS 1.2)
 *
 * Outputs:
 * - the tls_prf, calc_verify and calc_finished members of handshake structure
 */
static int ssl_set_handshake_prfs( mbedtls_ssl_handshake_params *handshake,
                                   int minor_ver,
                                   mbedtls_md_type_t hash )
{
#if !defined(MBEDTLS_SSL_PROTO_TLS1_2) || !defined(MBEDTLS_SHA384_C)
    (void) hash;
#endif

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA384_C)
    if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 &&
        hash == MBEDTLS_MD_SHA384 )
    {
        handshake->tls_prf = tls_prf_sha384;
        handshake->calc_verify = ssl_calc_verify_tls_sha384;
        handshake->calc_finished = ssl_calc_finished_tls_sha384;
    }
    else
#endif
#if defined(MBEDTLS_SHA256_C)
    if( minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 )
    {
        handshake->tls_prf = tls_prf_sha256;
        handshake->calc_verify = ssl_calc_verify_tls_sha256;
        handshake->calc_finished = ssl_calc_finished_tls_sha256;
    }
    else
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    {
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

    return( 0 );
}

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

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

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

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

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

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

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

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

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

#if defined(MBEDTLS_USE_PSA_CRYPTO) &&          \
    defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
    if( handshake->ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK &&
        ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3 &&
        ssl_use_opaque_psk( ssl ) == 1 )
    {
        /* Perform PSK-to-MS expansion in a single step. */
        psa_status_t status;
        psa_algorithm_t alg;
        psa_key_id_t psk;
        psa_key_derivation_operation_t derivation =
            PSA_KEY_DERIVATION_OPERATION_INIT;
        mbedtls_md_type_t hash_alg = handshake->ciphersuite_info->mac;

        MBEDTLS_SSL_DEBUG_MSG( 2, ( "perform PSA-based PSK-to-MS expansion" ) );

        psk = mbedtls_ssl_get_opaque_psk( ssl );

        if( hash_alg == MBEDTLS_MD_SHA384 )
            alg = PSA_ALG_TLS12_PSK_TO_MS(PSA_ALG_SHA_384);
        else
            alg = PSA_ALG_TLS12_PSK_TO_MS(PSA_ALG_SHA_256);

        status = setup_psa_key_derivation( &derivation, psk, alg,
                                           salt, salt_len,
                                           (unsigned char const *) lbl,
                                           (size_t) strlen( lbl ),
                                           master_secret_len );
        if( status != PSA_SUCCESS )
        {
            psa_key_derivation_abort( &derivation );
            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
        }

        status = psa_key_derivation_output_bytes( &derivation,
                                                  master,
                                                  master_secret_len );
        if( status != PSA_SUCCESS )
        {
            psa_key_derivation_abort( &derivation );
            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
        }

        status = psa_key_derivation_abort( &derivation );
        if( status != PSA_SUCCESS )
            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
    }
    else
#endif
    {
        ret = handshake->tls_prf( handshake->premaster, handshake->pmslen,
                                  lbl, salt, salt_len,
                                  master,
                                  master_secret_len );
        if( ret != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "prf", ret );
            return( ret );
        }

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

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

    return( 0 );
}

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

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

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

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

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

    /* Populate transform structure */
    ret = ssl_tls12_populate_transform( ssl->transform_negotiate,
                                        ssl->session_negotiate->ciphersuite,
                                        ssl->session_negotiate->master,
#if defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC) && \
    defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                                        ssl->session_negotiate->encrypt_then_mac,
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC &&
          MBEDTLS_SSL_SOME_SUITES_USE_MAC */
                                        ssl->handshake->tls_prf,
                                        ssl->handshake->randbytes,
                                        ssl->minor_ver,
                                        ssl->conf->endpoint,
                                        ssl );
    if( ret != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "ssl_tls12_populate_transform", ret );
        return( ret );
    }

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

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

    return( 0 );
}

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
void ssl_calc_verify_tls_sha256( const mbedtls_ssl_context *ssl,
                                 unsigned char *hash,
                                 size_t *hlen )
{
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    size_t hash_size;
    psa_status_t status;
    psa_hash_operation_t sha256_psa = psa_hash_operation_init();

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> PSA calc verify sha256" ) );
    status = psa_hash_clone( &ssl->handshake->fin_sha256_psa, &sha256_psa );
    if( status != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "PSA hash clone failed" ) );
        return;
    }

    status = psa_hash_finish( &sha256_psa, hash, 32, &hash_size );
    if( status != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "PSA hash finish failed" ) );
        return;
    }

    *hlen = 32;
    MBEDTLS_SSL_DEBUG_BUF( 3, "PSA calculated verify result", hash, *hlen );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= PSA calc verify" ) );
#else
    mbedtls_sha256_context sha256;

    mbedtls_sha256_init( &sha256 );

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc verify sha256" ) );

    mbedtls_sha256_clone( &sha256, &ssl->handshake->fin_sha256 );
    mbedtls_sha256_finish( &sha256, hash );

    *hlen = 32;

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

    mbedtls_sha256_free( &sha256 );
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    return;
}
#endif /* MBEDTLS_SHA256_C */

#if defined(MBEDTLS_SHA384_C)
void ssl_calc_verify_tls_sha384( const mbedtls_ssl_context *ssl,
                                 unsigned char *hash,
                                 size_t *hlen )
{
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    size_t hash_size;
    psa_status_t status;
    psa_hash_operation_t sha384_psa = psa_hash_operation_init();

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> PSA calc verify sha384" ) );
    status = psa_hash_clone( &ssl->handshake->fin_sha384_psa, &sha384_psa );
    if( status != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "PSA hash clone failed" ) );
        return;
    }

    status = psa_hash_finish( &sha384_psa, hash, 48, &hash_size );
    if( status != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "PSA hash finish failed" ) );
        return;
    }

    *hlen = 48;
    MBEDTLS_SSL_DEBUG_BUF( 3, "PSA calculated verify result", hash, *hlen );
    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= PSA calc verify" ) );
#else
    mbedtls_sha512_context sha512;

    mbedtls_sha512_init( &sha512 );

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc verify sha384" ) );

    mbedtls_sha512_clone( &sha512, &ssl->handshake->fin_sha512 );
    mbedtls_sha512_finish( &sha512, hash );

    *hlen = 48;

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

    mbedtls_sha512_free( &sha512 );
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    return;
}
#endif /* MBEDTLS_SHA384_C */
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

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

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

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

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

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

        memset( p, 0, psk_len );
        p += psk_len;
    }
    else
#endif /* MBEDTLS_KEY_EXCHANGE_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
    if( key_ex == MBEDTLS_KEY_EXCHANGE_RSA_PSK )
    {
        /*
         * other_secret already set by the ClientKeyExchange message,
         * and is 48 bytes long
         */
        if( end - p < 2 )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

/*
 * Handshake functions
 */
#if !defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/* No certificate support -> dummy functions */
int mbedtls_ssl_write_certificate( mbedtls_ssl_context *ssl )
{
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate" ) );

    if( !mbedtls_ssl_ciphersuite_uses_srv_cert( ciphersuite_info ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate" ) );
        ssl->state++;
        return( 0 );
    }

    MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
    return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}

int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
{
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate" ) );

    if( !mbedtls_ssl_ciphersuite_uses_srv_cert( ciphersuite_info ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
        ssl->state++;
        return( 0 );
    }

    MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
    return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}

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

int mbedtls_ssl_write_certificate( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
    size_t i, n;
    const mbedtls_x509_crt *crt;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write certificate" ) );

    if( !mbedtls_ssl_ciphersuite_uses_srv_cert( ciphersuite_info ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate" ) );
        ssl->state++;
        return( 0 );
    }

#if defined(MBEDTLS_SSL_CLI_C)
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
    {
        if( ssl->client_auth == 0 )
        {
            MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip write certificate" ) );
            ssl->state++;
            return( 0 );
        }
    }
#endif /* MBEDTLS_SSL_CLI_C */
#if defined(MBEDTLS_SSL_SRV_C)
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        if( mbedtls_ssl_own_cert( ssl ) == NULL )
        {
            /* Should never happen because we shouldn't have picked the
             * ciphersuite if we don't have a certificate. */
            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
        }
    }
#endif

    MBEDTLS_SSL_DEBUG_CRT( 3, "own certificate", mbedtls_ssl_own_cert( ssl ) );

    /*
     *     0  .  0    handshake type
     *     1  .  3    handshake length
     *     4  .  6    length of all certs
     *     7  .  9    length of cert. 1
     *    10  . n-1   peer certificate
     *     n  . n+2   length of cert. 2
     *    n+3 . ...   upper level cert, etc.
     */
    i = 7;
    crt = mbedtls_ssl_own_cert( ssl );

    while( crt != NULL )
    {
        n = crt->raw.len;
        if( n > MBEDTLS_SSL_OUT_CONTENT_LEN - 3 - i )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "certificate too large, %" MBEDTLS_PRINTF_SIZET
                                        " > %" MBEDTLS_PRINTF_SIZET,
                           i + 3 + n, (size_t) MBEDTLS_SSL_OUT_CONTENT_LEN ) );
            return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
        }

        ssl->out_msg[i    ] = (unsigned char)( n >> 16 );
        ssl->out_msg[i + 1] = (unsigned char)( n >>  8 );
        ssl->out_msg[i + 2] = (unsigned char)( n       );

        i += 3; memcpy( ssl->out_msg + i, crt->raw.p, n );
        i += n; crt = crt->next;
    }

    ssl->out_msg[4]  = (unsigned char)( ( i - 7 ) >> 16 );
    ssl->out_msg[5]  = (unsigned char)( ( i - 7 ) >>  8 );
    ssl->out_msg[6]  = (unsigned char)( ( i - 7 )       );

    ssl->out_msglen  = i;
    ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
    ssl->out_msg[0]  = MBEDTLS_SSL_HS_CERTIFICATE;

    ssl->state++;

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

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write certificate" ) );

    return( ret );
}

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

#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
                                         unsigned char *crt_buf,
                                         size_t crt_buf_len )
{
    mbedtls_x509_crt const * const peer_crt = ssl->session->peer_cert;

    if( peer_crt == NULL )
        return( -1 );

    if( peer_crt->raw.len != crt_buf_len )
        return( -1 );

    return( memcmp( peer_crt->raw.p, crt_buf, peer_crt->raw.len ) );
}
#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
                                         unsigned char *crt_buf,
                                         size_t crt_buf_len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char const * const peer_cert_digest =
        ssl->session->peer_cert_digest;
    mbedtls_md_type_t const peer_cert_digest_type =
        ssl->session->peer_cert_digest_type;
    mbedtls_md_info_t const * const digest_info =
        mbedtls_md_info_from_type( peer_cert_digest_type );
    unsigned char tmp_digest[MBEDTLS_SSL_PEER_CERT_DIGEST_MAX_LEN];
    size_t digest_len;

    if( peer_cert_digest == NULL || digest_info == NULL )
        return( -1 );

    digest_len = mbedtls_md_get_size( digest_info );
    if( digest_len > MBEDTLS_SSL_PEER_CERT_DIGEST_MAX_LEN )
        return( -1 );

    ret = mbedtls_md( digest_info, crt_buf, crt_buf_len, tmp_digest );
    if( ret != 0 )
        return( -1 );

    return( memcmp( tmp_digest, peer_cert_digest, digest_len ) );
}
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_SSL_RENEGOTIATION && MBEDTLS_SSL_CLI_C */

/*
 * Once the certificate message is read, parse it into a cert chain and
 * perform basic checks, but leave actual verification to the caller
 */
static int ssl_parse_certificate_chain( mbedtls_ssl_context *ssl,
                                        mbedtls_x509_crt *chain )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
#if defined(MBEDTLS_SSL_RENEGOTIATION) && defined(MBEDTLS_SSL_CLI_C)
    int crt_cnt=0;
#endif
    size_t i, n;
    uint8_t alert;

    if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
        return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
    }

    if( ssl->in_msg[0] != MBEDTLS_SSL_HS_CERTIFICATE  )
    {
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
        return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
    }

    if( ssl->in_hslen < mbedtls_ssl_hs_hdr_len( ssl ) + 3 + 3 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
        return( MBEDTLS_ERR_SSL_DECODE_ERROR );
    }

    i = mbedtls_ssl_hs_hdr_len( ssl );

    /*
     * Same message structure as in mbedtls_ssl_write_certificate()
     */
    n = ( ssl->in_msg[i+1] << 8 ) | ssl->in_msg[i+2];

    if( ssl->in_msg[i] != 0 ||
        ssl->in_hslen != n + 3 + mbedtls_ssl_hs_hdr_len( ssl ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
        return( MBEDTLS_ERR_SSL_DECODE_ERROR );
    }

    /* Make &ssl->in_msg[i] point to the beginning of the CRT chain. */
    i += 3;

    /* Iterate through and parse the CRTs in the provided chain. */
    while( i < ssl->in_hslen )
    {
        /* Check that there's room for the next CRT's length fields. */
        if ( i + 3 > ssl->in_hslen ) {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
            mbedtls_ssl_send_alert_message( ssl,
                              MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                              MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
            return( MBEDTLS_ERR_SSL_DECODE_ERROR );
        }
        /* In theory, the CRT can be up to 2**24 Bytes, but we don't support
         * anything beyond 2**16 ~ 64K. */
        if( ssl->in_msg[i] != 0 )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
            mbedtls_ssl_send_alert_message( ssl,
                            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT );
            return( MBEDTLS_ERR_SSL_BAD_CERTIFICATE );
        }

        /* Read length of the next CRT in the chain. */
        n = ( (unsigned int) ssl->in_msg[i + 1] << 8 )
            | (unsigned int) ssl->in_msg[i + 2];
        i += 3;

        if( n < 128 || i + n > ssl->in_hslen )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate message" ) );
            mbedtls_ssl_send_alert_message( ssl,
                                 MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                 MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
            return( MBEDTLS_ERR_SSL_DECODE_ERROR );
        }

        /* Check if we're handling the first CRT in the chain. */
#if defined(MBEDTLS_SSL_RENEGOTIATION) && defined(MBEDTLS_SSL_CLI_C)
        if( crt_cnt++ == 0 &&
            ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT &&
            ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
        {
            /* During client-side renegotiation, check that the server's
             * end-CRTs hasn't changed compared to the initial handshake,
             * mitigating the triple handshake attack. On success, reuse
             * the original end-CRT instead of parsing it again. */
            MBEDTLS_SSL_DEBUG_MSG( 3, ( "Check that peer CRT hasn't changed during renegotiation" ) );
            if( ssl_check_peer_crt_unchanged( ssl,
                                              &ssl->in_msg[i],
                                              n ) != 0 )
            {
                MBEDTLS_SSL_DEBUG_MSG( 1, ( "new server cert during renegotiation" ) );
                mbedtls_ssl_send_alert_message( ssl,
                                                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                                MBEDTLS_SSL_ALERT_MSG_ACCESS_DENIED );
                return( MBEDTLS_ERR_SSL_BAD_CERTIFICATE );
            }

            /* Now we can safely free the original chain. */
            ssl_clear_peer_cert( ssl->session );
        }
#endif /* MBEDTLS_SSL_RENEGOTIATION && MBEDTLS_SSL_CLI_C */

        /* Parse the next certificate in the chain. */
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
        ret = mbedtls_x509_crt_parse_der( chain, ssl->in_msg + i, n );
#else
        /* If we don't need to store the CRT chain permanently, parse
         * it in-place from the input buffer instead of making a copy. */
        ret = mbedtls_x509_crt_parse_der_nocopy( chain, ssl->in_msg + i, n );
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
        switch( ret )
        {
            case 0: /*ok*/
            case MBEDTLS_ERR_X509_UNKNOWN_SIG_ALG + MBEDTLS_ERR_OID_NOT_FOUND:
                /* Ignore certificate with an unknown algorithm: maybe a
                   prior certificate was already trusted. */
                break;

            case MBEDTLS_ERR_X509_ALLOC_FAILED:
                alert = MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR;
                goto crt_parse_der_failed;

            case MBEDTLS_ERR_X509_UNKNOWN_VERSION:
                alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
                goto crt_parse_der_failed;

            default:
                alert = MBEDTLS_SSL_ALERT_MSG_BAD_CERT;
            crt_parse_der_failed:
                mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL, alert );
                MBEDTLS_SSL_DEBUG_RET( 1, " mbedtls_x509_crt_parse_der", ret );
                return( ret );
        }

        i += n;
    }

    MBEDTLS_SSL_DEBUG_CRT( 3, "peer certificate", chain );
    return( 0 );
}

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

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

    return( -1 );
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
}
#endif /* MBEDTLS_SSL_SRV_C */

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

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

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

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

    return( SSL_CERTIFICATE_EXPECTED );
}

static int ssl_parse_certificate_verify( mbedtls_ssl_context *ssl,
                                         int authmode,
                                         mbedtls_x509_crt *chain,
                                         void *rs_ctx )
{
    int ret = 0;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    int have_ca_chain = 0;

    int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *);
    void *p_vrfy;

    if( authmode == MBEDTLS_SSL_VERIFY_NONE )
        return( 0 );

    if( ssl->f_vrfy != NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Use context-specific verification callback" ) );
        f_vrfy = ssl->f_vrfy;
        p_vrfy = ssl->p_vrfy;
    }
    else
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Use configuration-specific verification callback" ) );
        f_vrfy = ssl->conf->f_vrfy;
        p_vrfy = ssl->conf->p_vrfy;
    }

    /*
     * Main check: verify certificate
     */
#if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
    if( ssl->conf->f_ca_cb != NULL )
    {
        ((void) rs_ctx);
        have_ca_chain = 1;

        MBEDTLS_SSL_DEBUG_MSG( 3, ( "use CA callback for X.509 CRT verification" ) );
        ret = mbedtls_x509_crt_verify_with_ca_cb(
            chain,
            ssl->conf->f_ca_cb,
            ssl->conf->p_ca_cb,
            ssl->conf->cert_profile,
            ssl->hostname,
            &ssl->session_negotiate->verify_result,
            f_vrfy, p_vrfy );
    }
    else
#endif /* MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK */
    {
        mbedtls_x509_crt *ca_chain;
        mbedtls_x509_crl *ca_crl;

#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
        if( ssl->handshake->sni_ca_chain != NULL )
        {
            ca_chain = ssl->handshake->sni_ca_chain;
            ca_crl   = ssl->handshake->sni_ca_crl;
        }
        else
#endif
        {
            ca_chain = ssl->conf->ca_chain;
            ca_crl   = ssl->conf->ca_crl;
        }

        if( ca_chain != NULL )
            have_ca_chain = 1;

        ret = mbedtls_x509_crt_verify_restartable(
            chain,
            ca_chain, ca_crl,
            ssl->conf->cert_profile,
            ssl->hostname,
            &ssl->session_negotiate->verify_result,
            f_vrfy, p_vrfy, rs_ctx );
    }

    if( ret != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "x509_verify_cert", ret );
    }

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if( ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
        return( MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS );
#endif

    /*
     * Secondary checks: always done, but change 'ret' only if it was 0
     */

#if defined(MBEDTLS_ECP_C)
    {
        const mbedtls_pk_context *pk = &chain->pk;

        /* If certificate uses an EC key, make sure the curve is OK */
        if( mbedtls_pk_can_do( pk, MBEDTLS_PK_ECKEY ) &&
            mbedtls_ssl_check_curve( ssl, mbedtls_pk_ec( *pk )->grp.id ) != 0 )
        {
            ssl->session_negotiate->verify_result |= MBEDTLS_X509_BADCERT_BAD_KEY;

            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate (EC key curve)" ) );
            if( ret == 0 )
                ret = MBEDTLS_ERR_SSL_BAD_CERTIFICATE;
        }
    }
#endif /* MBEDTLS_ECP_C */

    if( mbedtls_ssl_check_cert_usage( chain,
                                      ciphersuite_info,
                                      ! ssl->conf->endpoint,
                                      &ssl->session_negotiate->verify_result ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate (usage extensions)" ) );
        if( ret == 0 )
            ret = MBEDTLS_ERR_SSL_BAD_CERTIFICATE;
    }

    /* mbedtls_x509_crt_verify_with_profile is supposed to report a
     * verification failure through MBEDTLS_ERR_X509_CERT_VERIFY_FAILED,
     * with details encoded in the verification flags. All other kinds
     * of error codes, including those from the user provided f_vrfy
     * functions, are treated as fatal and lead to a failure of
     * ssl_parse_certificate even if verification was optional. */
    if( authmode == MBEDTLS_SSL_VERIFY_OPTIONAL &&
        ( ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED ||
          ret == MBEDTLS_ERR_SSL_BAD_CERTIFICATE ) )
    {
        ret = 0;
    }

    if( have_ca_chain == 0 && authmode == MBEDTLS_SSL_VERIFY_REQUIRED )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "got no CA chain" ) );
        ret = MBEDTLS_ERR_SSL_CA_CHAIN_REQUIRED;
    }

    if( ret != 0 )
    {
        uint8_t alert;

        /* The certificate may have been rejected for several reasons.
           Pick one and send the corresponding alert. Which alert to send
           may be a subject of debate in some cases. */
        if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_OTHER )
            alert = MBEDTLS_SSL_ALERT_MSG_ACCESS_DENIED;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_CN_MISMATCH )
            alert = MBEDTLS_SSL_ALERT_MSG_BAD_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_KEY_USAGE )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_EXT_KEY_USAGE )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_NS_CERT_TYPE )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_BAD_PK )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_BAD_KEY )
            alert = MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_CERT;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_EXPIRED )
            alert = MBEDTLS_SSL_ALERT_MSG_CERT_EXPIRED;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_REVOKED )
            alert = MBEDTLS_SSL_ALERT_MSG_CERT_REVOKED;
        else if( ssl->session_negotiate->verify_result & MBEDTLS_X509_BADCERT_NOT_TRUSTED )
            alert = MBEDTLS_SSL_ALERT_MSG_UNKNOWN_CA;
        else
            alert = MBEDTLS_SSL_ALERT_MSG_CERT_UNKNOWN;
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        alert );
    }

#if defined(MBEDTLS_DEBUG_C)
    if( ssl->session_negotiate->verify_result != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "! Certificate verification flags %08x",
                                    (unsigned int) ssl->session_negotiate->verify_result ) );
    }
    else
    {
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "Certificate verification flags clear" ) );
    }
#endif /* MBEDTLS_DEBUG_C */

    return( ret );
}

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

        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
    }

    ret = mbedtls_md( mbedtls_md_info_from_type(
                          MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_TYPE ),
                      start, len,
                      ssl->session_negotiate->peer_cert_digest );

    ssl->session_negotiate->peer_cert_digest_type =
        MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_TYPE;
    ssl->session_negotiate->peer_cert_digest_len =
        MBEDTLS_SSL_PEER_CERT_DIGEST_DFL_LEN;

    return( ret );
}

static int ssl_remember_peer_pubkey( mbedtls_ssl_context *ssl,
                                     unsigned char *start, size_t len )
{
    unsigned char *end = start + len;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    /* Make a copy of the peer's raw public key. */
    mbedtls_pk_init( &ssl->handshake->peer_pubkey );
    ret = mbedtls_pk_parse_subpubkey( &start, end,
                                      &ssl->handshake->peer_pubkey );
    if( ret != 0 )
    {
        /* We should have parsed the public key before. */
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

    return( 0 );
}
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl )
{
    int ret = 0;
    int crt_expected;
#if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
    const int authmode = ssl->handshake->sni_authmode != MBEDTLS_SSL_VERIFY_UNSET
                       ? ssl->handshake->sni_authmode
                       : ssl->conf->authmode;
#else
    const int authmode = ssl->conf->authmode;
#endif
    void *rs_ctx = NULL;
    mbedtls_x509_crt *chain = NULL;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse certificate" ) );

    crt_expected = ssl_parse_certificate_coordinate( ssl, authmode );
    if( crt_expected == SSL_CERTIFICATE_SKIP )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= skip parse certificate" ) );
        goto exit;
    }

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if( ssl->handshake->ecrs_enabled &&
        ssl->handshake->ecrs_state == ssl_ecrs_crt_verify )
    {
        chain = ssl->handshake->ecrs_peer_cert;
        ssl->handshake->ecrs_peer_cert = NULL;
        goto crt_verify;
    }
#endif

    if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
    {
        /* mbedtls_ssl_read_record may have sent an alert already. We
           let it decide whether to alert. */
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
        goto exit;
    }

#if defined(MBEDTLS_SSL_SRV_C)
    if( ssl_srv_check_client_no_crt_notification( ssl ) == 0 )
    {
        ssl->session_negotiate->verify_result = MBEDTLS_X509_BADCERT_MISSING;

        if( authmode != MBEDTLS_SSL_VERIFY_OPTIONAL )
            ret = MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE;

        goto exit;
    }
#endif /* MBEDTLS_SSL_SRV_C */

    /* Clear existing peer CRT structure in case we tried to
     * reuse a session but it failed, and allocate a new one. */
    ssl_clear_peer_cert( ssl->session_negotiate );

    chain = mbedtls_calloc( 1, sizeof( mbedtls_x509_crt ) );
    if( chain == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%" MBEDTLS_PRINTF_SIZET " bytes) failed",
                                    sizeof( mbedtls_x509_crt ) ) );
        mbedtls_ssl_send_alert_message( ssl,
                                        MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );

        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto exit;
    }
    mbedtls_x509_crt_init( chain );

    ret = ssl_parse_certificate_chain( ssl, chain );
    if( ret != 0 )
        goto exit;

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if( ssl->handshake->ecrs_enabled)
        ssl->handshake->ecrs_state = ssl_ecrs_crt_verify;

crt_verify:
    if( ssl->handshake->ecrs_enabled)
        rs_ctx = &ssl->handshake->ecrs_ctx;
#endif

    ret = ssl_parse_certificate_verify( ssl, authmode,
                                        chain, rs_ctx );
    if( ret != 0 )
        goto exit;

#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    {
        unsigned char *crt_start, *pk_start;
        size_t crt_len, pk_len;

        /* We parse the CRT chain without copying, so
         * these pointers point into the input buffer,
         * and are hence still valid after freeing the
         * CRT chain. */

        crt_start = chain->raw.p;
        crt_len   = chain->raw.len;

        pk_start = chain->pk_raw.p;
        pk_len   = chain->pk_raw.len;

        /* Free the CRT structures before computing
         * digest and copying the peer's public key. */
        mbedtls_x509_crt_free( chain );
        mbedtls_free( chain );
        chain = NULL;

        ret = ssl_remember_peer_crt_digest( ssl, crt_start, crt_len );
        if( ret != 0 )
            goto exit;

        ret = ssl_remember_peer_pubkey( ssl, pk_start, pk_len );
        if( ret != 0 )
            goto exit;
    }
#else /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    /* Pass ownership to session structure. */
    ssl->session_negotiate->peer_cert = chain;
    chain = NULL;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse certificate" ) );

exit:

    if( ret == 0 )
        ssl->state++;

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if( ret == MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS )
    {
        ssl->handshake->ecrs_peer_cert = chain;
        chain = NULL;
    }
#endif

    if( chain != NULL )
    {
        mbedtls_x509_crt_free( chain );
        mbedtls_free( chain );
    }

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

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

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA384_C)
    if( ciphersuite_info->mac == MBEDTLS_MD_SHA384 )
        ssl->handshake->update_checksum = ssl_update_checksum_sha384;
    else
#endif
#if defined(MBEDTLS_SHA256_C)
    if( ciphersuite_info->mac != MBEDTLS_MD_SHA384 )
        ssl->handshake->update_checksum = ssl_update_checksum_sha256;
    else
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
        return;
    }
}

void mbedtls_ssl_reset_checksum( mbedtls_ssl_context *ssl )
{
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_hash_abort( &ssl->handshake->fin_sha256_psa );
    psa_hash_setup( &ssl->handshake->fin_sha256_psa, PSA_ALG_SHA_256 );
#else
    mbedtls_sha256_starts( &ssl->handshake->fin_sha256, 0 );
#endif
#endif
#if defined(MBEDTLS_SHA384_C)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_hash_abort( &ssl->handshake->fin_sha384_psa );
    psa_hash_setup( &ssl->handshake->fin_sha384_psa, PSA_ALG_SHA_384 );
#else
    mbedtls_sha512_starts( &ssl->handshake->fin_sha512, 1 );
#endif
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
}

static void ssl_update_checksum_start( mbedtls_ssl_context *ssl,
                                       const unsigned char *buf, size_t len )
{
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_hash_update( &ssl->handshake->fin_sha256_psa, buf, len );
#else
    mbedtls_sha256_update( &ssl->handshake->fin_sha256, buf, len );
#endif
#endif
#if defined(MBEDTLS_SHA384_C)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_hash_update( &ssl->handshake->fin_sha384_psa, buf, len );
#else
    mbedtls_sha512_update( &ssl->handshake->fin_sha512, buf, len );
#endif
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
}

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
static void ssl_update_checksum_sha256( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf, size_t len )
{
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_hash_update( &ssl->handshake->fin_sha256_psa, buf, len );
#else
    mbedtls_sha256_update( &ssl->handshake->fin_sha256, buf, len );
#endif
}
#endif

#if defined(MBEDTLS_SHA384_C)
static void ssl_update_checksum_sha384( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf, size_t len )
{
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_hash_update( &ssl->handshake->fin_sha384_psa, buf, len );
#else
    mbedtls_sha512_update( &ssl->handshake->fin_sha512, buf, len );
#endif
}
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
static void ssl_calc_finished_tls_sha256(
                mbedtls_ssl_context *ssl, unsigned char *buf, int from )
{
    int len = 12;
    const char *sender;
    unsigned char padbuf[32];
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    size_t hash_size;
    psa_hash_operation_t sha256_psa = PSA_HASH_OPERATION_INIT;
    psa_status_t status;
#else
    mbedtls_sha256_context sha256;
#endif

    mbedtls_ssl_session *session = ssl->session_negotiate;
    if( !session )
        session = ssl->session;

    sender = ( from == MBEDTLS_SSL_IS_CLIENT )
             ? "client finished"
             : "server finished";

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    sha256_psa = psa_hash_operation_init();

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc PSA finished tls sha256" ) );

    status = psa_hash_clone( &ssl->handshake->fin_sha256_psa, &sha256_psa );
    if( status != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "PSA hash clone failed" ) );
        return;
    }

    status = psa_hash_finish( &sha256_psa, padbuf, sizeof( padbuf ), &hash_size );
    if( status != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "PSA hash finish failed" ) );
        return;
    }
    MBEDTLS_SSL_DEBUG_BUF( 3, "PSA calculated padbuf", padbuf, 32 );
#else

    mbedtls_sha256_init( &sha256 );

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc  finished tls sha256" ) );

    mbedtls_sha256_clone( &sha256, &ssl->handshake->fin_sha256 );

    /*
     * TLSv1.2:
     *   hash = PRF( master, finished_label,
     *               Hash( handshake ) )[0.11]
     */

#if !defined(MBEDTLS_SHA256_ALT)
    MBEDTLS_SSL_DEBUG_BUF( 4, "finished sha2 state", (unsigned char *)
                   sha256.state, sizeof( sha256.state ) );
#endif

    mbedtls_sha256_finish( &sha256, padbuf );
    mbedtls_sha256_free( &sha256 );
#endif /* MBEDTLS_USE_PSA_CRYPTO */

    ssl->handshake->tls_prf( session->master, 48, sender,
                             padbuf, 32, buf, len );

    MBEDTLS_SSL_DEBUG_BUF( 3, "calc finished result", buf, len );

    mbedtls_platform_zeroize(  padbuf, sizeof(  padbuf ) );

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc  finished" ) );
}
#endif /* MBEDTLS_SHA256_C */

#if defined(MBEDTLS_SHA384_C)

static void ssl_calc_finished_tls_sha384(
                mbedtls_ssl_context *ssl, unsigned char *buf, int from )
{
    int len = 12;
    const char *sender;
    unsigned char padbuf[48];
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    size_t hash_size;
    psa_hash_operation_t sha384_psa = PSA_HASH_OPERATION_INIT;
    psa_status_t status;
#else
    mbedtls_sha512_context sha512;
#endif

    mbedtls_ssl_session *session = ssl->session_negotiate;
    if( !session )
        session = ssl->session;

    sender = ( from == MBEDTLS_SSL_IS_CLIENT )
                ? "client finished"
                : "server finished";

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    sha384_psa = psa_hash_operation_init();

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc PSA finished tls sha384" ) );

    status = psa_hash_clone( &ssl->handshake->fin_sha384_psa, &sha384_psa );
    if( status != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "PSA hash clone failed" ) );
        return;
    }

    status = psa_hash_finish( &sha384_psa, padbuf, sizeof( padbuf ), &hash_size );
    if( status != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_MSG( 2, ( "PSA hash finish failed" ) );
        return;
    }
    MBEDTLS_SSL_DEBUG_BUF( 3, "PSA calculated padbuf", padbuf, 48 );
#else
    mbedtls_sha512_init( &sha512 );

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> calc  finished tls sha384" ) );

    mbedtls_sha512_clone( &sha512, &ssl->handshake->fin_sha512 );

    /*
     * TLSv1.2:
     *   hash = PRF( master, finished_label,
     *               Hash( handshake ) )[0.11]
     */

#if !defined(MBEDTLS_SHA512_ALT)
    MBEDTLS_SSL_DEBUG_BUF( 4, "finished sha512 state", (unsigned char *)
                   sha512.state, sizeof( sha512.state ) );
#endif
    mbedtls_sha512_finish( &sha512, padbuf );

    mbedtls_sha512_free( &sha512 );
#endif

    ssl->handshake->tls_prf( session->master, 48, sender,
                             padbuf, 48, buf, len );

    MBEDTLS_SSL_DEBUG_BUF( 3, "calc finished result", buf, len );

    mbedtls_platform_zeroize(  padbuf, sizeof( padbuf ) );

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= calc  finished" ) );
}
#endif /* MBEDTLS_SHA384_C */
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

void mbedtls_ssl_handshake_wrapup_free_hs_transform( mbedtls_ssl_context *ssl )
{
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "=> handshake wrapup: final free" ) );

    /*
     * Free our handshake params
     */
    mbedtls_ssl_handshake_free( ssl );
    mbedtls_free( ssl->handshake );
    ssl->handshake = NULL;

    /*
     * Free the previous transform and swith in the current one
     */
    if( ssl->transform )
    {
        mbedtls_ssl_transform_free( ssl->transform );
        mbedtls_free( ssl->transform );
    }
    ssl->transform = ssl->transform_negotiate;
    ssl->transform_negotiate = NULL;

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "<= handshake wrapup: final free" ) );
}

void mbedtls_ssl_handshake_wrapup( mbedtls_ssl_context *ssl )
{
    int resume = ssl->handshake->resume;

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "=> handshake wrapup" ) );

#if defined(MBEDTLS_SSL_RENEGOTIATION)
    if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS )
    {
        ssl->renego_status =  MBEDTLS_SSL_RENEGOTIATION_DONE;
        ssl->renego_records_seen = 0;
    }
#endif

    /*
     * Free the previous session and switch in the current one
     */
    if( ssl->session )
    {
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
        /* RFC 7366 3.1: keep the EtM state */
        ssl->session_negotiate->encrypt_then_mac =
                  ssl->session->encrypt_then_mac;
#endif

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

    /*
     * Add cache entry
     */
    if( ssl->conf->f_set_cache != NULL &&
        ssl->session->id_len != 0 &&
        resume == 0 )
    {
        if( ssl->conf->f_set_cache( ssl->conf->p_cache,
                                    ssl->session->id,
                                    ssl->session->id_len,
                                    ssl->session ) != 0 )
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "cache did not store session" ) );
    }

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
        ssl->handshake->flight != NULL )
    {
        /* Cancel handshake timer */
        mbedtls_ssl_set_timer( ssl, 0 );

        /* Keep last flight around in case we need to resend it:
         * we need the handshake and transform structures for that */
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "skip freeing handshake and transform" ) );
    }
    else
#endif
        mbedtls_ssl_handshake_wrapup_free_hs_transform( ssl );

    ssl->state++;

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "<= handshake wrapup" ) );
}

int mbedtls_ssl_write_finished( mbedtls_ssl_context *ssl )
{
    int ret, hash_len;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write finished" ) );

    mbedtls_ssl_update_out_pointers( ssl, ssl->transform_negotiate );

    ssl->handshake->calc_finished( ssl, ssl->out_msg + 4, ssl->conf->endpoint );

    /*
     * RFC 5246 7.4.9 (Page 63) says 12 is the default length and ciphersuites
     * may define some other value. Currently (early 2016), no defined
     * ciphersuite does this (and this is unlikely to change as activity has
     * moved to TLS 1.3 now) so we can keep the hardcoded 12 here.
     */
    hash_len = 12;

#if defined(MBEDTLS_SSL_RENEGOTIATION)
    ssl->verify_data_len = hash_len;
    memcpy( ssl->own_verify_data, ssl->out_msg + 4, hash_len );
#endif

    ssl->out_msglen  = 4 + hash_len;
    ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
    ssl->out_msg[0]  = MBEDTLS_SSL_HS_FINISHED;

    /*
     * In case of session resuming, invert the client and server
     * ChangeCipherSpec messages order.
     */
    if( ssl->handshake->resume != 0 )
    {
#if defined(MBEDTLS_SSL_CLI_C)
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
            ssl->state = MBEDTLS_SSL_HANDSHAKE_WRAPUP;
#endif
#if defined(MBEDTLS_SSL_SRV_C)
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
            ssl->state = MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC;
#endif
    }
    else
        ssl->state++;

    /*
     * Switch to our negotiated transform and session parameters for outbound
     * data.
     */
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "switching to new transform spec for outbound data" ) );

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
    {
        unsigned char i;

        /* Remember current epoch settings for resending */
        ssl->handshake->alt_transform_out = ssl->transform_out;
        memcpy( ssl->handshake->alt_out_ctr, ssl->cur_out_ctr, 8 );

        /* Set sequence_number to zero */
        memset( ssl->cur_out_ctr + 2, 0, 6 );

        /* Increment epoch */
        for( i = 2; i > 0; i-- )
            if( ++ssl->cur_out_ctr[i - 1] != 0 )
                break;

        /* The loop goes to its end iff the counter is wrapping */
        if( i == 0 )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "DTLS epoch would wrap" ) );
            return( MBEDTLS_ERR_SSL_COUNTER_WRAPPING );
        }
    }
    else
#endif /* MBEDTLS_SSL_PROTO_DTLS */
    memset( ssl->cur_out_ctr, 0, 8 );

    ssl->transform_out = ssl->transform_negotiate;
    ssl->session_out = ssl->session_negotiate;

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
        mbedtls_ssl_send_flight_completed( ssl );
#endif

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

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
        ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
        return( ret );
    }
#endif

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write finished" ) );

    return( 0 );
}

#define SSL_MAX_HASH_LEN 12

int mbedtls_ssl_parse_finished( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned int hash_len;
    unsigned char buf[SSL_MAX_HASH_LEN];

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse finished" ) );

    ssl->handshake->calc_finished( ssl, buf, ssl->conf->endpoint ^ 1 );

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

    if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad finished message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
        return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
    }

    hash_len = 12;

    if( ssl->in_msg[0] != MBEDTLS_SSL_HS_FINISHED  )
    {
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
        return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
    }

    if( ssl->in_hslen  != mbedtls_ssl_hs_hdr_len( ssl ) + hash_len )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad finished message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
        return( MBEDTLS_ERR_SSL_DECODE_ERROR );
    }

    if( mbedtls_ssl_safer_memcmp( ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl ),
                      buf, hash_len ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad finished message" ) );
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_DECRYPT_ERROR );
        return( MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE );
    }

#if defined(MBEDTLS_SSL_RENEGOTIATION)
    ssl->verify_data_len = hash_len;
    memcpy( ssl->peer_verify_data, buf, hash_len );
#endif

    if( ssl->handshake->resume != 0 )
    {
#if defined(MBEDTLS_SSL_CLI_C)
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
            ssl->state = MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC;
#endif
#if defined(MBEDTLS_SSL_SRV_C)
        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
            ssl->state = MBEDTLS_SSL_HANDSHAKE_WRAPUP;
#endif
    }
    else
        ssl->state++;

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
        mbedtls_ssl_recv_flight_completed( ssl );
#endif

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse finished" ) );

    return( 0 );
}

static void ssl_handshake_params_init( mbedtls_ssl_handshake_params *handshake )
{
    memset( handshake, 0, sizeof( mbedtls_ssl_handshake_params ) );

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    handshake->fin_sha256_psa = psa_hash_operation_init();
    psa_hash_setup( &handshake->fin_sha256_psa, PSA_ALG_SHA_256 );
#else
    mbedtls_sha256_init(   &handshake->fin_sha256    );
    mbedtls_sha256_starts( &handshake->fin_sha256, 0 );
#endif
#endif
#if defined(MBEDTLS_SHA384_C)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    handshake->fin_sha384_psa = psa_hash_operation_init();
    psa_hash_setup( &handshake->fin_sha384_psa, PSA_ALG_SHA_384 );
#else
    mbedtls_sha512_init(   &handshake->fin_sha512    );
    mbedtls_sha512_starts( &handshake->fin_sha512, 1 );
#endif
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

    handshake->update_checksum = ssl_update_checksum_start;

#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
    defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
    mbedtls_ssl_sig_hash_set_init( &handshake->hash_algs );
#endif

#if defined(MBEDTLS_DHM_C)
    mbedtls_dhm_init( &handshake->dhm_ctx );
#endif
#if defined(MBEDTLS_ECDH_C)
    mbedtls_ecdh_init( &handshake->ecdh_ctx );
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    mbedtls_ecjpake_init( &handshake->ecjpake_ctx );
#if defined(MBEDTLS_SSL_CLI_C)
    handshake->ecjpake_cache = NULL;
    handshake->ecjpake_cache_len = 0;
#endif
#endif

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    mbedtls_x509_crt_restart_init( &handshake->ecrs_ctx );
#endif

#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
    handshake->sni_authmode = MBEDTLS_SSL_VERIFY_UNSET;
#endif

#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
    !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    mbedtls_pk_init( &handshake->peer_pubkey );
#endif
}

void mbedtls_ssl_transform_init( mbedtls_ssl_transform *transform )
{
    memset( transform, 0, sizeof(mbedtls_ssl_transform) );

    mbedtls_cipher_init( &transform->cipher_ctx_enc );
    mbedtls_cipher_init( &transform->cipher_ctx_dec );

#if defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC)
    mbedtls_md_init( &transform->md_ctx_enc );
    mbedtls_md_init( &transform->md_ctx_dec );
#endif
}

void mbedtls_ssl_session_init( mbedtls_ssl_session *session )
{
    memset( session, 0, sizeof(mbedtls_ssl_session) );
}

static int ssl_handshake_init( mbedtls_ssl_context *ssl )
{
    /* Clear old handshake information if present */
    if( ssl->transform_negotiate )
        mbedtls_ssl_transform_free( ssl->transform_negotiate );
    if( ssl->session_negotiate )
        mbedtls_ssl_session_free( ssl->session_negotiate );
    if( ssl->handshake )
        mbedtls_ssl_handshake_free( ssl );

    /*
     * Either the pointers are now NULL or cleared properly and can be freed.
     * Now allocate missing structures.
     */
    if( ssl->transform_negotiate == NULL )
    {
        ssl->transform_negotiate = mbedtls_calloc( 1, sizeof(mbedtls_ssl_transform) );
    }

    if( ssl->session_negotiate == NULL )
    {
        ssl->session_negotiate = mbedtls_calloc( 1, sizeof(mbedtls_ssl_session) );
    }

    if( ssl->handshake == NULL )
    {
        ssl->handshake = mbedtls_calloc( 1, sizeof(mbedtls_ssl_handshake_params) );
    }
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    /* If the buffers are too small - reallocate */

    handle_buffer_resizing( ssl, 0, MBEDTLS_SSL_IN_BUFFER_LEN,
                                    MBEDTLS_SSL_OUT_BUFFER_LEN );
#endif

    /* All pointers should exist and can be directly freed without issue */
    if( ssl->handshake == NULL ||
        ssl->transform_negotiate == NULL ||
        ssl->session_negotiate == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc() of ssl sub-contexts failed" ) );

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

        ssl->handshake = NULL;
        ssl->transform_negotiate = NULL;
        ssl->session_negotiate = NULL;

        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
    }

    /* Initialize structures */
    mbedtls_ssl_session_init( ssl->session_negotiate );
    mbedtls_ssl_transform_init( ssl->transform_negotiate );
    ssl_handshake_params_init( ssl->handshake );

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
    {
        ssl->handshake->alt_transform_out = ssl->transform_out;

        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
            ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_PREPARING;
        else
            ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_WAITING;

        mbedtls_ssl_set_timer( ssl, 0 );
    }
#endif

    return( 0 );
}

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

    return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
}

static int ssl_cookie_check_dummy( void *ctx,
                      const unsigned char *cookie, size_t cookie_len,
                      const unsigned char *cli_id, size_t cli_id_len )
{
    ((void) ctx);
    ((void) cookie);
    ((void) cookie_len);
    ((void) cli_id);
    ((void) cli_id_len);

    return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
}
#endif /* MBEDTLS_SSL_DTLS_HELLO_VERIFY && MBEDTLS_SSL_SRV_C */

/*
 * Initialize an SSL context
 */
void mbedtls_ssl_init( mbedtls_ssl_context *ssl )
{
    memset( ssl, 0, sizeof( mbedtls_ssl_context ) );
}

static int ssl_conf_version_check( const mbedtls_ssl_context *ssl )
{
#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
    if( mbedtls_ssl_conf_is_tls13_only( ssl->conf ) )
    {
        if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
        {
             MBEDTLS_SSL_DEBUG_MSG( 1, ( "DTLS 1.3 is not yet supported" ) );
             return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
        }
        MBEDTLS_SSL_DEBUG_MSG( 4, ( "The SSL configuration is tls13 only." ) );
        return( 0 );
    }
#endif

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
    if( mbedtls_ssl_conf_is_tls12_only( ssl->conf ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 4, ( "The SSL configuration is tls12 only." ) );
        return( 0 );
    }
#endif

#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
    if( mbedtls_ssl_conf_is_hybrid_tls12_tls13( ssl->conf ) )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Hybrid TLS 1.2 + TLS 1.3 configurations are not yet supported" ) );
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
    }
#endif

    MBEDTLS_SSL_DEBUG_MSG( 1, ( "The SSL configuration is invalid." ) );
    return( MBEDTLS_ERR_SSL_BAD_CONFIG );
}

static int ssl_conf_check(const mbedtls_ssl_context *ssl)
{
    int ret;
    ret = ssl_conf_version_check( ssl );
    if( ret != 0 )
        return( ret );

    /* Space for further checks */

    return( 0 );
}

/*
 * Setup an SSL context
 */

int mbedtls_ssl_setup( mbedtls_ssl_context *ssl,
                       const mbedtls_ssl_config *conf )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;

    ssl->conf = conf;

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

    /*
     * Prepare base structures
     */

    /* Set to NULL in case of an error condition */
    ssl->out_buf = NULL;

#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    ssl->in_buf_len = in_buf_len;
#endif
    ssl->in_buf = mbedtls_calloc( 1, in_buf_len );
    if( ssl->in_buf == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%" MBEDTLS_PRINTF_SIZET " bytes) failed", in_buf_len ) );
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto error;
    }

#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    ssl->out_buf_len = out_buf_len;
#endif
    ssl->out_buf = mbedtls_calloc( 1, out_buf_len );
    if( ssl->out_buf == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc(%" MBEDTLS_PRINTF_SIZET " bytes) failed", out_buf_len ) );
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto error;
    }

    mbedtls_ssl_reset_in_out_pointers( ssl );

#if defined(MBEDTLS_SSL_DTLS_SRTP)
    memset( &ssl->dtls_srtp_info, 0, sizeof(ssl->dtls_srtp_info) );
#endif

    if( ( ret = ssl_handshake_init( ssl ) ) != 0 )
        goto error;

    return( 0 );

error:
    mbedtls_free( ssl->in_buf );
    mbedtls_free( ssl->out_buf );

    ssl->conf = NULL;

#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    ssl->in_buf_len = 0;
    ssl->out_buf_len = 0;
#endif
    ssl->in_buf = NULL;
    ssl->out_buf = NULL;

    ssl->in_hdr = NULL;
    ssl->in_ctr = NULL;
    ssl->in_len = NULL;
    ssl->in_iv = NULL;
    ssl->in_msg = NULL;

    ssl->out_hdr = NULL;
    ssl->out_ctr = NULL;
    ssl->out_len = NULL;
    ssl->out_iv = NULL;
    ssl->out_msg = NULL;

    return( ret );
}

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

#if !defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) || !defined(MBEDTLS_SSL_SRV_C)
    partial = 0;
#endif

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

    mbedtls_ssl_reset_in_out_pointers( ssl );

    /* Reset incoming message parsing */
    ssl->in_offt    = NULL;
    ssl->nb_zero    = 0;
    ssl->in_msgtype = 0;
    ssl->in_msglen  = 0;
    ssl->in_hslen   = 0;
    ssl->keep_current_message = 0;
    ssl->transform_in  = NULL;

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    ssl->next_record_offset = 0;
    ssl->in_epoch = 0;
#endif

    /* Keep current datagram if partial == 1 */
    if( partial == 0 )
    {
        ssl->in_left = 0;
        memset( ssl->in_buf, 0, in_buf_len );
    }

    /* Reset outgoing message writing */
    ssl->out_msgtype = 0;
    ssl->out_msglen  = 0;
    ssl->out_left    = 0;
    memset( ssl->out_buf, 0, out_buf_len );
    memset( ssl->cur_out_ctr, 0, sizeof( ssl->cur_out_ctr ) );
    ssl->transform_out = NULL;

#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
    mbedtls_ssl_dtls_replay_reset( ssl );
#endif

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

int mbedtls_ssl_session_reset_int( mbedtls_ssl_context *ssl, int partial )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    ssl->state = MBEDTLS_SSL_HELLO_REQUEST;

    ssl_session_reset_msg_layer( ssl, partial );

    /* Reset renegotiation state */
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    ssl->renego_status = MBEDTLS_SSL_INITIAL_HANDSHAKE;
    ssl->renego_records_seen = 0;

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

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

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

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

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

    return( 0 );
}

/*
 * Reset an initialized and used SSL context for re-use while retaining
 * all application-set variables, function pointers and data.
 */
int mbedtls_ssl_session_reset( mbedtls_ssl_context *ssl )
{
    return( mbedtls_ssl_session_reset_int( ssl, 0 ) );
}

/*
 * SSL set accessors
 */
void mbedtls_ssl_conf_endpoint( mbedtls_ssl_config *conf, int endpoint )
{
    conf->endpoint   = endpoint;
}

void mbedtls_ssl_conf_transport( mbedtls_ssl_config *conf, int transport )
{
    conf->transport = transport;
}

#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
void mbedtls_ssl_conf_dtls_anti_replay( mbedtls_ssl_config *conf, char mode )
{
    conf->anti_replay = mode;
}
#endif

void mbedtls_ssl_conf_dtls_badmac_limit( mbedtls_ssl_config *conf, unsigned limit )
{
    conf->badmac_limit = limit;
}

#if defined(MBEDTLS_SSL_PROTO_DTLS)

void mbedtls_ssl_set_datagram_packing( mbedtls_ssl_context *ssl,
                                       unsigned allow_packing )
{
    ssl->disable_datagram_packing = !allow_packing;
}

void mbedtls_ssl_conf_handshake_timeout( mbedtls_ssl_config *conf,
                                         uint32_t min, uint32_t max )
{
    conf->hs_timeout_min = min;
    conf->hs_timeout_max = max;
}
#endif

void mbedtls_ssl_conf_authmode( mbedtls_ssl_config *conf, int authmode )
{
    conf->authmode   = authmode;
}

#if defined(MBEDTLS_X509_CRT_PARSE_C)
void mbedtls_ssl_conf_verify( mbedtls_ssl_config *conf,
                     int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
                     void *p_vrfy )
{
    conf->f_vrfy      = f_vrfy;
    conf->p_vrfy      = p_vrfy;
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

void mbedtls_ssl_conf_rng( mbedtls_ssl_config *conf,
                  int (*f_rng)(void *, unsigned char *, size_t),
                  void *p_rng )
{
    conf->f_rng      = f_rng;
    conf->p_rng      = p_rng;
}

void mbedtls_ssl_conf_dbg( mbedtls_ssl_config *conf,
                  void (*f_dbg)(void *, int, const char *, int, const char *),
                  void  *p_dbg )
{
    conf->f_dbg      = f_dbg;
    conf->p_dbg      = p_dbg;
}

void mbedtls_ssl_set_bio( mbedtls_ssl_context *ssl,
        void *p_bio,
        mbedtls_ssl_send_t *f_send,
        mbedtls_ssl_recv_t *f_recv,
        mbedtls_ssl_recv_timeout_t *f_recv_timeout )
{
    ssl->p_bio          = p_bio;
    ssl->f_send         = f_send;
    ssl->f_recv         = f_recv;
    ssl->f_recv_timeout = f_recv_timeout;
}

#if defined(MBEDTLS_SSL_PROTO_DTLS)
void mbedtls_ssl_set_mtu( mbedtls_ssl_context *ssl, uint16_t mtu )
{
    ssl->mtu = mtu;
}
#endif

void mbedtls_ssl_conf_read_timeout( mbedtls_ssl_config *conf, uint32_t timeout )
{
    conf->read_timeout   = timeout;
}

void mbedtls_ssl_set_timer_cb( mbedtls_ssl_context *ssl,
                               void *p_timer,
                               mbedtls_ssl_set_timer_t *f_set_timer,
                               mbedtls_ssl_get_timer_t *f_get_timer )
{
    ssl->p_timer        = p_timer;
    ssl->f_set_timer    = f_set_timer;
    ssl->f_get_timer    = f_get_timer;

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

#if defined(MBEDTLS_SSL_SRV_C)
void mbedtls_ssl_conf_session_cache( mbedtls_ssl_config *conf,
                                     void *p_cache,
                                     mbedtls_ssl_cache_get_t *f_get_cache,
                                     mbedtls_ssl_cache_set_t *f_set_cache )
{
    conf->p_cache = p_cache;
    conf->f_get_cache = f_get_cache;
    conf->f_set_cache = f_set_cache;
}
#endif /* MBEDTLS_SSL_SRV_C */

#if defined(MBEDTLS_SSL_CLI_C)
int mbedtls_ssl_set_session( mbedtls_ssl_context *ssl, const mbedtls_ssl_session *session )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

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

    if( ssl->handshake->resume == 1 )
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );

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

    ssl->handshake->resume = 1;

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

void mbedtls_ssl_conf_ciphersuites( mbedtls_ssl_config *conf,
                                    const int *ciphersuites )
{
    conf->ciphersuite_list = ciphersuites;
}

#if defined(MBEDTLS_X509_CRT_PARSE_C)
void mbedtls_ssl_conf_cert_profile( mbedtls_ssl_config *conf,
                                    const mbedtls_x509_crt_profile *profile )
{
    conf->cert_profile = profile;
}

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

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

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

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

    return( 0 );
}

int mbedtls_ssl_conf_own_cert( mbedtls_ssl_config *conf,
                              mbedtls_x509_crt *own_cert,
                              mbedtls_pk_context *pk_key )
{
    return( ssl_append_key_cert( &conf->key_cert, own_cert, pk_key ) );
}

void mbedtls_ssl_conf_ca_chain( mbedtls_ssl_config *conf,
                               mbedtls_x509_crt *ca_chain,
                               mbedtls_x509_crl *ca_crl )
{
    conf->ca_chain   = ca_chain;
    conf->ca_crl     = ca_crl;

#if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
    /* mbedtls_ssl_conf_ca_chain() and mbedtls_ssl_conf_ca_cb()
     * cannot be used together. */
    conf->f_ca_cb = NULL;
    conf->p_ca_cb = NULL;
#endif /* MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK */
}

#if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
void mbedtls_ssl_conf_ca_cb( mbedtls_ssl_config *conf,
                             mbedtls_x509_crt_ca_cb_t f_ca_cb,
                             void *p_ca_cb )
{
    conf->f_ca_cb = f_ca_cb;
    conf->p_ca_cb = p_ca_cb;

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

#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
int mbedtls_ssl_set_hs_own_cert( mbedtls_ssl_context *ssl,
                                 mbedtls_x509_crt *own_cert,
                                 mbedtls_pk_context *pk_key )
{
    return( ssl_append_key_cert( &ssl->handshake->sni_key_cert,
                                 own_cert, pk_key ) );
}

void mbedtls_ssl_set_hs_ca_chain( mbedtls_ssl_context *ssl,
                                  mbedtls_x509_crt *ca_chain,
                                  mbedtls_x509_crl *ca_crl )
{
    ssl->handshake->sni_ca_chain   = ca_chain;
    ssl->handshake->sni_ca_crl     = ca_crl;
}

void mbedtls_ssl_set_hs_authmode( mbedtls_ssl_context *ssl,
                                  int authmode )
{
    ssl->handshake->sni_authmode = authmode;
}
#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */

#if defined(MBEDTLS_X509_CRT_PARSE_C)
void mbedtls_ssl_set_verify( mbedtls_ssl_context *ssl,
                     int (*f_vrfy)(void *, mbedtls_x509_crt *, int, uint32_t *),
                     void *p_vrfy )
{
    ssl->f_vrfy = f_vrfy;
    ssl->p_vrfy = p_vrfy;
}
#endif

#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
/*
 * Set EC J-PAKE password for current handshake
 */
int mbedtls_ssl_set_hs_ecjpake_password( mbedtls_ssl_context *ssl,
                                         const unsigned char *pw,
                                         size_t pw_len )
{
    mbedtls_ecjpake_role role;

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

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

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

#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)

static int ssl_conf_psk_is_configured( mbedtls_ssl_config const *conf )
{
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    if( !mbedtls_svc_key_id_is_null( conf->psk_opaque ) )
        return( 1 );
#endif /* MBEDTLS_USE_PSA_CRYPTO */

    if( conf->psk != NULL )
        return( 1 );

    return( 0 );
}

static void ssl_conf_remove_psk( mbedtls_ssl_config *conf )
{
    /* Remove reference to existing PSK, if any. */
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    if( ! mbedtls_svc_key_id_is_null( conf->psk_opaque ) )
    {
        /* The maintenance of the PSK key slot is the
         * user's responsibility. */
        conf->psk_opaque = MBEDTLS_SVC_KEY_ID_INIT;
    }
    /* This and the following branch should never
     * be taken simultaenously as we maintain the
     * invariant that raw and opaque PSKs are never
     * configured simultaneously. As a safeguard,
     * though, `else` is omitted here. */
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    if( conf->psk != NULL )
    {
        mbedtls_platform_zeroize( conf->psk, conf->psk_len );

        mbedtls_free( conf->psk );
        conf->psk = NULL;
        conf->psk_len = 0;
    }

    /* Remove reference to PSK identity, if any. */
    if( conf->psk_identity != NULL )
    {
        mbedtls_free( conf->psk_identity );
        conf->psk_identity = NULL;
        conf->psk_identity_len = 0;
    }
}

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

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

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

    return( 0 );
}

int mbedtls_ssl_conf_psk( mbedtls_ssl_config *conf,
                const unsigned char *psk, size_t psk_len,
                const unsigned char *psk_identity, size_t psk_identity_len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    /* We currently only support one PSK, raw or opaque. */
    if( ssl_conf_psk_is_configured( conf ) )
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );

    /* Check and set raw PSK */
    if( psk == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    if( psk_len == 0 )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    if( psk_len > MBEDTLS_PSK_MAX_LEN )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    if( ( conf->psk = mbedtls_calloc( 1, psk_len ) ) == NULL )
        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
    conf->psk_len = psk_len;
    memcpy( conf->psk, psk, conf->psk_len );

    /* Check and set PSK Identity */
    ret = ssl_conf_set_psk_identity( conf, psk_identity, psk_identity_len );
    if( ret != 0 )
        ssl_conf_remove_psk( conf );

    return( ret );
}

static void ssl_remove_psk( mbedtls_ssl_context *ssl )
{
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    if( ! mbedtls_svc_key_id_is_null( ssl->handshake->psk_opaque ) )
    {
        ssl->handshake->psk_opaque = MBEDTLS_SVC_KEY_ID_INIT;
    }
    else
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    if( ssl->handshake->psk != NULL )
    {
        mbedtls_platform_zeroize( ssl->handshake->psk,
                                  ssl->handshake->psk_len );
        mbedtls_free( ssl->handshake->psk );
        ssl->handshake->psk_len = 0;
    }
}

int mbedtls_ssl_set_hs_psk( mbedtls_ssl_context *ssl,
                            const unsigned char *psk, size_t psk_len )
{
    if( psk == NULL || ssl->handshake == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    if( psk_len > MBEDTLS_PSK_MAX_LEN )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl_remove_psk( ssl );

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

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

    return( 0 );
}

#if defined(MBEDTLS_USE_PSA_CRYPTO)
int mbedtls_ssl_conf_psk_opaque( mbedtls_ssl_config *conf,
                                 psa_key_id_t psk,
                                 const unsigned char *psk_identity,
                                 size_t psk_identity_len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    /* We currently only support one PSK, raw or opaque. */
    if( ssl_conf_psk_is_configured( conf ) )
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );

    /* Check and set opaque PSK */
    if( mbedtls_svc_key_id_is_null( psk ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    conf->psk_opaque = psk;

    /* Check and set PSK Identity */
    ret = ssl_conf_set_psk_identity( conf, psk_identity,
                                     psk_identity_len );
    if( ret != 0 )
        ssl_conf_remove_psk( conf );

    return( ret );
}

int mbedtls_ssl_set_hs_psk_opaque( mbedtls_ssl_context *ssl,
                                   psa_key_id_t psk )
{
    if( ( mbedtls_svc_key_id_is_null( psk ) ) ||
        ( ssl->handshake == NULL ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ssl_remove_psk( ssl );
    ssl->handshake->psk_opaque = psk;
    return( 0 );
}
#endif /* MBEDTLS_USE_PSA_CRYPTO */

void mbedtls_ssl_conf_psk_cb( mbedtls_ssl_config *conf,
                     int (*f_psk)(void *, mbedtls_ssl_context *, const unsigned char *,
                     size_t),
                     void *p_psk )
{
    conf->f_psk = f_psk;
    conf->p_psk = p_psk;
}
#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */

#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C)
int mbedtls_ssl_conf_dh_param_bin( mbedtls_ssl_config *conf,
                                   const unsigned char *dhm_P, size_t P_len,
                                   const unsigned char *dhm_G, size_t G_len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

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

    return( 0 );
}

int mbedtls_ssl_conf_dh_param_ctx( mbedtls_ssl_config *conf, mbedtls_dhm_context *dhm_ctx )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if( ( ret = mbedtls_dhm_get_value( dhm_ctx, MBEDTLS_DHM_PARAM_P,
                                       &conf->dhm_P ) ) != 0 ||
        ( ret = mbedtls_dhm_get_value( dhm_ctx, MBEDTLS_DHM_PARAM_G,
                                       &conf->dhm_G ) ) != 0 )
    {
        mbedtls_mpi_free( &conf->dhm_P );
        mbedtls_mpi_free( &conf->dhm_G );
        return( ret );
    }

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

#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_CLI_C)
/*
 * Set the minimum length for Diffie-Hellman parameters
 */
void mbedtls_ssl_conf_dhm_min_bitlen( mbedtls_ssl_config *conf,
                                      unsigned int bitlen )
{
    conf->dhm_min_bitlen = bitlen;
}
#endif /* MBEDTLS_DHM_C && MBEDTLS_SSL_CLI_C */

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/*
 * Set allowed/preferred hashes for handshake signatures
 */
void mbedtls_ssl_conf_sig_hashes( mbedtls_ssl_config *conf,
                                  const int *hashes )
{
    conf->sig_hashes = hashes;
}

#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
/* Configure allowed signature algorithms for use in TLS 1.3 */
void mbedtls_ssl_conf_sig_algs( mbedtls_ssl_config *conf,
                                const uint16_t* sig_algs )
{
    conf->tls13_sig_algs = sig_algs;
}
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */

#if defined(MBEDTLS_ECP_C)
/*
 * Set the allowed elliptic curves
 */
void mbedtls_ssl_conf_curves( mbedtls_ssl_config *conf,
                             const mbedtls_ecp_group_id *curve_list )
{
    conf->curve_list = curve_list;
}
#endif /* MBEDTLS_ECP_C */

#if defined(MBEDTLS_X509_CRT_PARSE_C)
int mbedtls_ssl_set_hostname( mbedtls_ssl_context *ssl, const char *hostname )
{
    /* Initialize to suppress unnecessary compiler warning */
    size_t hostname_len = 0;

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

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

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

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

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

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

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

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

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

#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
void mbedtls_ssl_conf_sni( mbedtls_ssl_config *conf,
                  int (*f_sni)(void *, mbedtls_ssl_context *,
                                const unsigned char *, size_t),
                  void *p_sni )
{
    conf->f_sni = f_sni;
    conf->p_sni = p_sni;
}
#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */

#if defined(MBEDTLS_SSL_ALPN)
int mbedtls_ssl_conf_alpn_protocols( mbedtls_ssl_config *conf, const char **protos )
{
    size_t cur_len, tot_len;
    const char **p;

    /*
     * RFC 7301 3.1: "Empty strings MUST NOT be included and byte strings
     * MUST NOT be truncated."
     * We check lengths now rather than later.
     */
    tot_len = 0;
    for( p = protos; *p != NULL; p++ )
    {
        cur_len = strlen( *p );
        tot_len += cur_len;

        if( ( cur_len == 0 ) ||
            ( cur_len > MBEDTLS_SSL_MAX_ALPN_NAME_LEN ) ||
            ( tot_len > MBEDTLS_SSL_MAX_ALPN_LIST_LEN ) )
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    conf->alpn_list = protos;

    return( 0 );
}

const char *mbedtls_ssl_get_alpn_protocol( const mbedtls_ssl_context *ssl )
{
    return( ssl->alpn_chosen );
}
#endif /* MBEDTLS_SSL_ALPN */

#if defined(MBEDTLS_SSL_DTLS_SRTP)
void mbedtls_ssl_conf_srtp_mki_value_supported( mbedtls_ssl_config *conf,
                                                int support_mki_value )
{
    conf->dtls_srtp_mki_support = support_mki_value;
}

int mbedtls_ssl_dtls_srtp_set_mki_value( mbedtls_ssl_context *ssl,
                                         unsigned char *mki_value,
                                         uint16_t mki_len )
{
    if( mki_len > MBEDTLS_TLS_SRTP_MAX_MKI_LENGTH )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    if( ssl->conf->dtls_srtp_mki_support == MBEDTLS_SSL_DTLS_SRTP_MKI_UNSUPPORTED )
    {
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
    }

    memcpy( ssl->dtls_srtp_info.mki_value, mki_value, mki_len );
    ssl->dtls_srtp_info.mki_len = mki_len;
    return( 0 );
}

int mbedtls_ssl_conf_dtls_srtp_protection_profiles( mbedtls_ssl_config *conf,
                                                    const mbedtls_ssl_srtp_profile *profiles )
{
    const mbedtls_ssl_srtp_profile *p;
    size_t list_size = 0;

    /* check the profiles list: all entry must be valid,
     * its size cannot be more than the total number of supported profiles, currently 4 */
    for( p = profiles; *p != MBEDTLS_TLS_SRTP_UNSET &&
                       list_size <= MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH;
         p++ )
    {
        if( mbedtls_ssl_check_srtp_profile_value( *p ) != MBEDTLS_TLS_SRTP_UNSET )
        {
            list_size++;
        }
        else
        {
            /* unsupported value, stop parsing and set the size to an error value */
            list_size = MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH + 1;
        }
    }

    if( list_size > MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH )
    {
                conf->dtls_srtp_profile_list = NULL;
                conf->dtls_srtp_profile_list_len = 0;
                return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    conf->dtls_srtp_profile_list = profiles;
    conf->dtls_srtp_profile_list_len = list_size;

    return( 0 );
}

void mbedtls_ssl_get_dtls_srtp_negotiation_result( const mbedtls_ssl_context *ssl,
                                                   mbedtls_dtls_srtp_info *dtls_srtp_info )
{
    dtls_srtp_info->chosen_dtls_srtp_profile = ssl->dtls_srtp_info.chosen_dtls_srtp_profile;
    /* do not copy the mki value if there is no chosen profile */
    if( dtls_srtp_info->chosen_dtls_srtp_profile == MBEDTLS_TLS_SRTP_UNSET )
    {
        dtls_srtp_info->mki_len = 0;
    }
    else
    {
        dtls_srtp_info->mki_len = ssl->dtls_srtp_info.mki_len;
        memcpy( dtls_srtp_info->mki_value, ssl->dtls_srtp_info.mki_value,
                ssl->dtls_srtp_info.mki_len );
    }
}
#endif /* MBEDTLS_SSL_DTLS_SRTP */

void mbedtls_ssl_conf_max_version( mbedtls_ssl_config *conf, int major, int minor )
{
    conf->max_major_ver = major;
    conf->max_minor_ver = minor;
}

void mbedtls_ssl_conf_min_version( mbedtls_ssl_config *conf, int major, int minor )
{
    conf->min_major_ver = major;
    conf->min_minor_ver = minor;
}

#if defined(MBEDTLS_SSL_SRV_C)
void mbedtls_ssl_conf_cert_req_ca_list( mbedtls_ssl_config *conf,
                                          char cert_req_ca_list )
{
    conf->cert_req_ca_list = cert_req_ca_list;
}
#endif

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
void mbedtls_ssl_conf_encrypt_then_mac( mbedtls_ssl_config *conf, char etm )
{
    conf->encrypt_then_mac = etm;
}
#endif

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
void mbedtls_ssl_conf_extended_master_secret( mbedtls_ssl_config *conf, char ems )
{
    conf->extended_ms = ems;
}
#endif

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
int mbedtls_ssl_conf_max_frag_len( mbedtls_ssl_config *conf, unsigned char mfl_code )
{
    if( mfl_code >= MBEDTLS_SSL_MAX_FRAG_LEN_INVALID ||
        ssl_mfl_code_to_length( mfl_code ) > MBEDTLS_TLS_EXT_ADV_CONTENT_LEN )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    conf->mfl_code = mfl_code;

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

void mbedtls_ssl_conf_legacy_renegotiation( mbedtls_ssl_config *conf, int allow_legacy )
{
    conf->allow_legacy_renegotiation = allow_legacy;
}

#if defined(MBEDTLS_SSL_RENEGOTIATION)
void mbedtls_ssl_conf_renegotiation( mbedtls_ssl_config *conf, int renegotiation )
{
    conf->disable_renegotiation = renegotiation;
}

void mbedtls_ssl_conf_renegotiation_enforced( mbedtls_ssl_config *conf, int max_records )
{
    conf->renego_max_records = max_records;
}

void mbedtls_ssl_conf_renegotiation_period( mbedtls_ssl_config *conf,
                                   const unsigned char period[8] )
{
    memcpy( conf->renego_period, period, 8 );
}
#endif /* MBEDTLS_SSL_RENEGOTIATION */

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
#if defined(MBEDTLS_SSL_CLI_C)
void mbedtls_ssl_conf_session_tickets( mbedtls_ssl_config *conf, int use_tickets )
{
    conf->session_tickets = use_tickets;
}
#endif

#if defined(MBEDTLS_SSL_SRV_C)
void mbedtls_ssl_conf_session_tickets_cb( mbedtls_ssl_config *conf,
        mbedtls_ssl_ticket_write_t *f_ticket_write,
        mbedtls_ssl_ticket_parse_t *f_ticket_parse,
        void *p_ticket )
{
    conf->f_ticket_write = f_ticket_write;
    conf->f_ticket_parse = f_ticket_parse;
    conf->p_ticket       = p_ticket;
}
#endif
#endif /* MBEDTLS_SSL_SESSION_TICKETS */

#if defined(MBEDTLS_SSL_EXPORT_KEYS)
void mbedtls_ssl_set_export_keys_cb( mbedtls_ssl_context *ssl,
                                     mbedtls_ssl_export_keys_t *f_export_keys,
                                     void *p_export_keys )
{
    ssl->f_export_keys = f_export_keys;
    ssl->p_export_keys = p_export_keys;
}
#endif

#if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
void mbedtls_ssl_conf_async_private_cb(
    mbedtls_ssl_config *conf,
    mbedtls_ssl_async_sign_t *f_async_sign,
    mbedtls_ssl_async_decrypt_t *f_async_decrypt,
    mbedtls_ssl_async_resume_t *f_async_resume,
    mbedtls_ssl_async_cancel_t *f_async_cancel,
    void *async_config_data )
{
    conf->f_async_sign_start = f_async_sign;
    conf->f_async_decrypt_start = f_async_decrypt;
    conf->f_async_resume = f_async_resume;
    conf->f_async_cancel = f_async_cancel;
    conf->p_async_config_data = async_config_data;
}

void *mbedtls_ssl_conf_get_async_config_data( const mbedtls_ssl_config *conf )
{
    return( conf->p_async_config_data );
}

void *mbedtls_ssl_get_async_operation_data( const mbedtls_ssl_context *ssl )
{
    if( ssl->handshake == NULL )
        return( NULL );
    else
        return( ssl->handshake->user_async_ctx );
}

void mbedtls_ssl_set_async_operation_data( mbedtls_ssl_context *ssl,
                                 void *ctx )
{
    if( ssl->handshake != NULL )
        ssl->handshake->user_async_ctx = ctx;
}
#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */

/*
 * SSL get accessors
 */
uint32_t mbedtls_ssl_get_verify_result( const mbedtls_ssl_context *ssl )
{
    if( ssl->session != NULL )
        return( ssl->session->verify_result );

    if( ssl->session_negotiate != NULL )
        return( ssl->session_negotiate->verify_result );

    return( 0xFFFFFFFF );
}

const char *mbedtls_ssl_get_ciphersuite( const mbedtls_ssl_context *ssl )
{
    if( ssl == NULL || ssl->session == NULL )
        return( NULL );

    return mbedtls_ssl_get_ciphersuite_name( ssl->session->ciphersuite );
}

const char *mbedtls_ssl_get_version( const mbedtls_ssl_context *ssl )
{
#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
    {
        switch( ssl->minor_ver )
        {
            case MBEDTLS_SSL_MINOR_VERSION_3:
                return( "DTLSv1.2" );

            default:
                return( "unknown (DTLS)" );
        }
    }
#endif

    switch( ssl->minor_ver )
    {
        case MBEDTLS_SSL_MINOR_VERSION_3:
            return( "TLSv1.2" );

        default:
            return( "unknown" );
    }
}

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
size_t mbedtls_ssl_get_input_max_frag_len( const mbedtls_ssl_context *ssl )
{
    size_t max_len = MBEDTLS_SSL_IN_CONTENT_LEN;
    size_t read_mfl;

    /* Use the configured MFL for the client if we're past SERVER_HELLO_DONE */
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT &&
        ssl->state >= MBEDTLS_SSL_SERVER_HELLO_DONE )
    {
        return ssl_mfl_code_to_length( ssl->conf->mfl_code );
    }

    /* Check if a smaller max length was negotiated */
    if( ssl->session_out != NULL )
    {
        read_mfl = ssl_mfl_code_to_length( ssl->session_out->mfl_code );
        if( read_mfl < max_len )
        {
            max_len = read_mfl;
        }
    }

    // During a handshake, use the value being negotiated
    if( ssl->session_negotiate != NULL )
    {
        read_mfl = ssl_mfl_code_to_length( ssl->session_negotiate->mfl_code );
        if( read_mfl < max_len )
        {
            max_len = read_mfl;
        }
    }

    return( max_len );
}

size_t mbedtls_ssl_get_output_max_frag_len( const mbedtls_ssl_context *ssl )
{
    size_t max_len;

    /*
     * Assume mfl_code is correct since it was checked when set
     */
    max_len = ssl_mfl_code_to_length( ssl->conf->mfl_code );

    /* Check if a smaller max length was negotiated */
    if( ssl->session_out != NULL &&
        ssl_mfl_code_to_length( ssl->session_out->mfl_code ) < max_len )
    {
        max_len = ssl_mfl_code_to_length( ssl->session_out->mfl_code );
    }

    /* During a handshake, use the value being negotiated */
    if( ssl->session_negotiate != NULL &&
        ssl_mfl_code_to_length( ssl->session_negotiate->mfl_code ) < max_len )
    {
        max_len = ssl_mfl_code_to_length( ssl->session_negotiate->mfl_code );
    }

    return( max_len );
}
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */

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

    if( ssl->handshake == NULL || ssl->handshake->mtu == 0 )
        return( ssl->mtu );

    if( ssl->mtu == 0 )
        return( ssl->handshake->mtu );

    return( ssl->mtu < ssl->handshake->mtu ?
            ssl->mtu : ssl->handshake->mtu );
}
#endif /* MBEDTLS_SSL_PROTO_DTLS */

int mbedtls_ssl_get_max_out_record_payload( const mbedtls_ssl_context *ssl )
{
    size_t max_len = MBEDTLS_SSL_OUT_CONTENT_LEN;

#if !defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH) && \
    !defined(MBEDTLS_SSL_PROTO_DTLS)
    (void) ssl;
#endif

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
    const size_t mfl = mbedtls_ssl_get_output_max_frag_len( ssl );

    if( max_len > mfl )
        max_len = mfl;
#endif

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( mbedtls_ssl_get_current_mtu( ssl ) != 0 )
    {
        const size_t mtu = mbedtls_ssl_get_current_mtu( ssl );
        const int ret = mbedtls_ssl_get_record_expansion( ssl );
        const size_t overhead = (size_t) ret;

        if( ret < 0 )
            return( ret );

        if( mtu <= overhead )
        {
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "MTU too low for record expansion" ) );
            return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
        }

        if( max_len > mtu - overhead )
            max_len = mtu - overhead;
    }
#endif /* MBEDTLS_SSL_PROTO_DTLS */

#if !defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH) &&        \
    !defined(MBEDTLS_SSL_PROTO_DTLS)
    ((void) ssl);
#endif

    return( (int) max_len );
}

int mbedtls_ssl_get_max_in_record_payload( const mbedtls_ssl_context *ssl )
{
    size_t max_len = MBEDTLS_SSL_IN_CONTENT_LEN;

#if !defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
    (void) ssl;
#endif

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
    const size_t mfl = mbedtls_ssl_get_input_max_frag_len( ssl );

    if( max_len > mfl )
        max_len = mfl;
#endif

    return( (int) max_len );
}

#if defined(MBEDTLS_X509_CRT_PARSE_C)
const mbedtls_x509_crt *mbedtls_ssl_get_peer_cert( const mbedtls_ssl_context *ssl )
{
    if( ssl == NULL || ssl->session == NULL )
        return( NULL );

#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    return( ssl->session->peer_cert );
#else
    return( NULL );
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

#if defined(MBEDTLS_SSL_CLI_C)
int mbedtls_ssl_get_session( const mbedtls_ssl_context *ssl,
                             mbedtls_ssl_session *dst )
{
    int ret;

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

    /* Since Mbed TLS 3.0, mbedtls_ssl_get_session() is no longer
     * idempotent: Each session can only be exported once.
     *
     * (This is in preparation for TLS 1.3 support where we will
     * need the ability to export multiple sessions (aka tickets),
     * which will be achieved by calling mbedtls_ssl_get_session()
     * multiple times until it fails.)
     *
     * Check whether we have already exported the current session,
     * and fail if so.
     */
    if( ssl->session->exported == 1 )
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );

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

    /* Remember that we've exported the session. */
    ssl->session->exported = 1;
    return( 0 );
}
#endif /* MBEDTLS_SSL_CLI_C */

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

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

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

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

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

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

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

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

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

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

static unsigned char ssl_serialized_session_header[] = {
    MBEDTLS_VERSION_MAJOR,
    MBEDTLS_VERSION_MINOR,
    MBEDTLS_VERSION_PATCH,
    MBEDTLS_BYTE_1( SSL_SERIALIZED_SESSION_CONFIG_BITFLAG ),
    MBEDTLS_BYTE_0( SSL_SERIALIZED_SESSION_CONFIG_BITFLAG ),
};

/*
 * Serialize a session in the following format:
 * (in the presentation language of TLS, RFC 8446 section 3)
 *
 *  struct {
 *
 *    opaque mbedtls_version[3];   // library version: major, minor, patch
 *    opaque session_format[2];    // library-version specific 16-bit field
 *                                 // determining the format of the remaining
 *                                 // serialized data.
 *
 *          Note: When updating the format, remember to keep
 *          these version+format bytes.
 *
 *                                 // In this version, `session_format` determines
 *                                 // the setting of those compile-time
 *                                 // configuration options which influence
 *                                 // the structure of mbedtls_ssl_session.
 *
 *    uint8_t minor_ver;           // Protocol-version. Possible values:
 *                                 // - TLS 1.2 (MBEDTLS_SSL_MINOR_VERSION_3)
 *
 *    select (serialized_session.minor_ver) {
 *
 *      case MBEDTLS_SSL_MINOR_VERSION_3: // TLS 1.2
 *        serialized_session_tls12 data;
 *
 *   };
 *
 * } serialized_session;
 *
 */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
/* Serialization of TLS 1.2 sessions:
 *
 * struct {
 *    uint64 start_time;
 *    uint8 ciphersuite[2];           // defined by the standard
 *    uint8 compression;              // 0 or 1
 *    uint8 session_id_len;           // at most 32
 *    opaque session_id[32];
 *    opaque master[48];              // fixed length in the standard
 *    uint32 verify_result;
 *    opaque peer_cert<0..2^24-1>;    // length 0 means no peer cert
 *    opaque ticket<0..2^24-1>;       // length 0 means no ticket
 *    uint32 ticket_lifetime;
 *    uint8 mfl_code;                 // up to 255 according to standard
 *    uint8 encrypt_then_mac;         // 0 or 1
 * } serialized_session_tls12;
 *
 */
static size_t ssl_session_save_tls12( const mbedtls_ssl_session *session,
                                      unsigned char *buf,
                                      size_t buf_len )
{
    unsigned char *p = buf;
    size_t used = 0;

#if defined(MBEDTLS_HAVE_TIME)
    uint64_t start;
#endif
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    size_t cert_len;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */

    /*
     * Time
     */
#if defined(MBEDTLS_HAVE_TIME)
    used += 8;

    if( used <= buf_len )
    {
        start = (uint64_t) session->start;

        *p++ = MBEDTLS_BYTE_7( start );
        *p++ = MBEDTLS_BYTE_6( start );
        *p++ = MBEDTLS_BYTE_5( start );
        *p++ = MBEDTLS_BYTE_4( start );
        *p++ = MBEDTLS_BYTE_3( start );
        *p++ = MBEDTLS_BYTE_2( start );
        *p++ = MBEDTLS_BYTE_1( start );
        *p++ = MBEDTLS_BYTE_0( start );
    }
#endif /* MBEDTLS_HAVE_TIME */

    /*
     * Basic mandatory fields
     */
    used += 2   /* ciphersuite */
          + 1   /* compression */
          + 1   /* id_len */
          + sizeof( session->id )
          + sizeof( session->master )
          + 4;  /* verify_result */

    if( used <= buf_len )
    {
        *p++ = MBEDTLS_BYTE_1( session->ciphersuite );
        *p++ = MBEDTLS_BYTE_0( session->ciphersuite );

        *p++ = MBEDTLS_BYTE_0( session->compression );

        *p++ = MBEDTLS_BYTE_0( session->id_len );
        memcpy( p, session->id, 32 );
        p += 32;

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

        *p++ = MBEDTLS_BYTE_3( session->verify_result );
        *p++ = MBEDTLS_BYTE_2( session->verify_result );
        *p++ = MBEDTLS_BYTE_1( session->verify_result );
        *p++ = MBEDTLS_BYTE_0( session->verify_result );
    }

    /*
     * Peer's end-entity certificate
     */
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    if( session->peer_cert == NULL )
        cert_len = 0;
    else
        cert_len = session->peer_cert->raw.len;

    used += 3 + cert_len;

    if( used <= buf_len )
    {
        *p++ = MBEDTLS_BYTE_2( cert_len );
        *p++ = MBEDTLS_BYTE_1( cert_len );
        *p++ = MBEDTLS_BYTE_0( cert_len );

        if( session->peer_cert != NULL )
        {
            memcpy( p, session->peer_cert->raw.p, cert_len );
            p += cert_len;
        }
    }
#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    if( session->peer_cert_digest != NULL )
    {
        used += 1 /* type */ + 1 /* length */ + session->peer_cert_digest_len;
        if( used <= buf_len )
        {
            *p++ = (unsigned char) session->peer_cert_digest_type;
            *p++ = (unsigned char) session->peer_cert_digest_len;
            memcpy( p, session->peer_cert_digest,
                    session->peer_cert_digest_len );
            p += session->peer_cert_digest_len;
        }
    }
    else
    {
        used += 2;
        if( used <= buf_len )
        {
            *p++ = (unsigned char) MBEDTLS_MD_NONE;
            *p++ = 0;
        }
    }
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */

    /*
     * Session ticket if any, plus associated data
     */
#if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
    used += 3 + session->ticket_len + 4; /* len + ticket + lifetime */

    if( used <= buf_len )
    {
        *p++ = MBEDTLS_BYTE_2( session->ticket_len );
        *p++ = MBEDTLS_BYTE_1( session->ticket_len );
        *p++ = MBEDTLS_BYTE_0( session->ticket_len );

        if( session->ticket != NULL )
        {
            memcpy( p, session->ticket, session->ticket_len );
            p += session->ticket_len;
        }

        *p++ = MBEDTLS_BYTE_3( session->ticket_lifetime );
        *p++ = MBEDTLS_BYTE_2( session->ticket_lifetime );
        *p++ = MBEDTLS_BYTE_1( session->ticket_lifetime );
        *p++ = MBEDTLS_BYTE_0( session->ticket_lifetime );
    }
#endif /* MBEDTLS_SSL_SESSION_TICKETS && MBEDTLS_SSL_CLI_C */

    /*
     * Misc extension-related info
     */
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
    used += 1;

    if( used <= buf_len )
        *p++ = session->mfl_code;
#endif

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
    used += 1;

    if( used <= buf_len )
        *p++ = MBEDTLS_BYTE_0( session->encrypt_then_mac );
#endif

    return( used );
}
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

static int ssl_session_save( const mbedtls_ssl_session *session,
                             unsigned char omit_header,
                             unsigned char *buf,
                             size_t buf_len,
                             size_t *olen )
{
    unsigned char *p = buf;
    size_t used = 0;

    if( !omit_header )
    {
        /*
         * Add Mbed TLS version identifier
         */

        used += sizeof( ssl_serialized_session_header );

        if( used <= buf_len )
        {
            memcpy( p, ssl_serialized_session_header,
                    sizeof( ssl_serialized_session_header ) );
            p += sizeof( ssl_serialized_session_header );
        }
    }

    /*
     * TLS version identifier
     */
    used += 1;
    if( used <= buf_len )
    {
        *p++ = session->minor_ver;
    }

    /* Forward to version-specific serialization routine. */
    switch( session->minor_ver )
    {
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
    case MBEDTLS_SSL_MINOR_VERSION_3:
    {
        size_t remaining_len = used <= buf_len ? buf_len - used : 0;
        used += ssl_session_save_tls12( session, p, remaining_len );
        break;
    }
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

    default:
        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
    }

    *olen = used;
    if( used > buf_len )
        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );

    return( 0 );
}

/*
 * Public wrapper for ssl_session_save()
 */
int mbedtls_ssl_session_save( const mbedtls_ssl_session *session,
                              unsigned char *buf,
                              size_t buf_len,
                              size_t *olen )
{
    return( ssl_session_save( session, 0, buf, buf_len, olen ) );
}

/*
 * Deserialize session, see mbedtls_ssl_session_save() for format.
 *
 * This internal version is wrapped by a public function that cleans up in
 * case of error, and has an extra option omit_header.
 */
static int ssl_session_load_tls12( mbedtls_ssl_session *session,
                                   const unsigned char *buf,
                                   size_t len )
{
#if defined(MBEDTLS_HAVE_TIME)
    uint64_t start;
#endif
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    size_t cert_len;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
#endif /* MBEDTLS_X509_CRT_PARSE_C */

    const unsigned char *p = buf;
    const unsigned char * const end = buf + len;

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

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

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

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

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

    session->compression = *p++;

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

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

    session->verify_result = ( (uint32_t) p[0] << 24 ) |
                             ( (uint32_t) p[1] << 16 ) |
                             ( (uint32_t) p[2] <<  8 ) |
                             ( (uint32_t) p[3]       );
    p += 4;

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

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

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

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

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

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

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

        mbedtls_x509_crt_init( session->peer_cert );

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

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

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

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

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

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

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

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

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

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

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

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

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

    session->ticket_lifetime = ( (uint32_t) p[0] << 24 ) |
                               ( (uint32_t) p[1] << 16 ) |
                               ( (uint32_t) p[2] <<  8 ) |
                               ( (uint32_t) p[3]       );
    p += 4;
#endif /* MBEDTLS_SSL_SESSION_TICKETS && MBEDTLS_SSL_CLI_C */

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

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

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

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

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

    return( 0 );
}

static int ssl_session_load( mbedtls_ssl_session *session,
                             unsigned char omit_header,
                             const unsigned char *buf,
                             size_t len )
{
    const unsigned char *p = buf;
    const unsigned char * const end = buf + len;

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

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

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

    /*
     * TLS version identifier
     */
    if( 1 > (size_t)( end - p ) )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    session->minor_ver = *p++;

    /* Dispatch according to TLS version. */
    switch( session->minor_ver )
    {
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
    case MBEDTLS_SSL_MINOR_VERSION_3: /* TLS 1.2 */
    {
        size_t remaining_len = ( end - p );
        return( ssl_session_load_tls12( session, p, remaining_len ) );
    }
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

    default:
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }
}

/*
 * Deserialize session: public wrapper for error cleaning
 */
int mbedtls_ssl_session_load( mbedtls_ssl_session *session,
                              const unsigned char *buf,
                              size_t len )
{
    int ret = ssl_session_load( session, 0, buf, len );

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

    return( ret );
}

/*
 * Perform a single step of the SSL handshake
 */
static int ssl_prepare_handshake_step( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    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 */

    return( ret );
}

int mbedtls_ssl_handshake_step( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if( ssl            == NULL                       ||
        ssl->conf      == NULL                       ||
        ssl->handshake == NULL                       ||
        ssl->state     == MBEDTLS_SSL_HANDSHAKE_OVER )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

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

#if defined(MBEDTLS_SSL_CLI_C)
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
    {
#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
        if( mbedtls_ssl_conf_is_tls13_only( ssl->conf ) )
            ret = mbedtls_ssl_handshake_client_step_tls1_3( ssl );
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
        if( mbedtls_ssl_conf_is_tls12_only( ssl->conf ) )
            ret = mbedtls_ssl_handshake_client_step( ssl );
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    }
#endif
#if defined(MBEDTLS_SSL_SRV_C)
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
    {
#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
        if( mbedtls_ssl_conf_is_tls13_only( ssl->conf ) )
            ret = mbedtls_ssl_handshake_server_step_tls1_3( ssl );
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
        if( mbedtls_ssl_conf_is_tls12_only( ssl->conf ) )
            ret = mbedtls_ssl_handshake_server_step( ssl );
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
    }
#endif

    return( ret );
}

/*
 * Perform the SSL handshake
 */
int mbedtls_ssl_handshake( mbedtls_ssl_context *ssl )
{
    int ret = 0;

    /* Sanity checks */

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

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

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

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

        if( ret != 0 )
            break;
    }

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

    return( ret );
}

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

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

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

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

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

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

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

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

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

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

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

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

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

    return( 0 );
}

/*
 * Renegotiate current connection on client,
 * or request renegotiation on server
 */
int mbedtls_ssl_renegotiate( mbedtls_ssl_context *ssl )
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;

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

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

        ssl->renego_status = MBEDTLS_SSL_RENEGOTIATION_PENDING;

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

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

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

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

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

#if defined(MBEDTLS_X509_CRT_PARSE_C)
static void ssl_key_cert_free( mbedtls_ssl_key_cert *key_cert )
{
    mbedtls_ssl_key_cert *cur = key_cert, *next;

    while( cur != NULL )
    {
        next = cur->next;
        mbedtls_free( cur );
        cur = next;
    }
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */

void mbedtls_ssl_handshake_free( mbedtls_ssl_context *ssl )
{
    mbedtls_ssl_handshake_params *handshake = ssl->handshake;

    if( handshake == NULL )
        return;

#if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
    if( ssl->conf->f_async_cancel != NULL && handshake->async_in_progress != 0 )
    {
        ssl->conf->f_async_cancel( ssl );
        handshake->async_in_progress = 0;
    }
#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
#if defined(MBEDTLS_SHA256_C)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_hash_abort( &handshake->fin_sha256_psa );
#else
    mbedtls_sha256_free(   &handshake->fin_sha256    );
#endif
#endif
#if defined(MBEDTLS_SHA384_C)
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_hash_abort( &handshake->fin_sha384_psa );
#else
    mbedtls_sha512_free(   &handshake->fin_sha512    );
#endif
#endif
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

#if defined(MBEDTLS_DHM_C)
    mbedtls_dhm_free( &handshake->dhm_ctx );
#endif
#if defined(MBEDTLS_ECDH_C)
    mbedtls_ecdh_free( &handshake->ecdh_ctx );
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    mbedtls_ecjpake_free( &handshake->ecjpake_ctx );
#if defined(MBEDTLS_SSL_CLI_C)
    mbedtls_free( handshake->ecjpake_cache );
    handshake->ecjpake_cache = NULL;
    handshake->ecjpake_cache_len = 0;
#endif
#endif

#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    /* explicit void pointer cast for buggy MS compiler */
    mbedtls_free( (void *) handshake->curves );
#endif

#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
    if( handshake->psk != NULL )
    {
        mbedtls_platform_zeroize( handshake->psk, handshake->psk_len );
        mbedtls_free( handshake->psk );
    }
#endif

#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
    defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
    /*
     * Free only the linked list wrapper, not the keys themselves
     * since the belong to the SNI callback
     */
    if( handshake->sni_key_cert != NULL )
    {
        mbedtls_ssl_key_cert *cur = handshake->sni_key_cert, *next;

        while( cur != NULL )
        {
            next = cur->next;
            mbedtls_free( cur );
            cur = next;
        }
    }
#endif /* MBEDTLS_X509_CRT_PARSE_C && MBEDTLS_SSL_SERVER_NAME_INDICATION */

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    mbedtls_x509_crt_restart_free( &handshake->ecrs_ctx );
    if( handshake->ecrs_peer_cert != NULL )
    {
        mbedtls_x509_crt_free( handshake->ecrs_peer_cert );
        mbedtls_free( handshake->ecrs_peer_cert );
    }
#endif

#if defined(MBEDTLS_X509_CRT_PARSE_C) &&        \
    !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    mbedtls_pk_free( &handshake->peer_pubkey );
#endif /* MBEDTLS_X509_CRT_PARSE_C && !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    mbedtls_free( handshake->verify_cookie );
    mbedtls_ssl_flight_free( handshake->flight );
    mbedtls_ssl_buffering_free( ssl );
#endif

#if defined(MBEDTLS_ECDH_C) &&                  \
    defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_destroy_key( handshake->ecdh_psa_privkey );
#endif /* MBEDTLS_ECDH_C && MBEDTLS_USE_PSA_CRYPTO */

    mbedtls_platform_zeroize( handshake,
                              sizeof( mbedtls_ssl_handshake_params ) );

#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    /* If the buffers are too big - reallocate. Because of the way Mbed TLS
     * processes datagrams and the fact that a datagram is allowed to have
     * several records in it, it is possible that the I/O buffers are not
     * empty at this stage */
    handle_buffer_resizing( ssl, 1, mbedtls_ssl_get_input_buflen( ssl ),
                                    mbedtls_ssl_get_output_buflen( ssl ) );
#endif

#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
    mbedtls_free( handshake->transform_earlydata );
    mbedtls_free( handshake->transform_handshake );
    handshake->transform_earlydata = NULL;
    handshake->transform_handshake = NULL;
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
}

void mbedtls_ssl_session_free( mbedtls_ssl_session *session )
{
    if( session == NULL )
        return;

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

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

    mbedtls_platform_zeroize( session, sizeof( mbedtls_ssl_session ) );
}

#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)

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

#define SSL_SERIALIZED_CONTEXT_CONFIG_DTLS_BADMAC_LIMIT 1u

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

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

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

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

static unsigned char ssl_serialized_context_header[] = {
    MBEDTLS_VERSION_MAJOR,
    MBEDTLS_VERSION_MINOR,
    MBEDTLS_VERSION_PATCH,
    MBEDTLS_BYTE_1( SSL_SERIALIZED_SESSION_CONFIG_BITFLAG ),
    MBEDTLS_BYTE_0( SSL_SERIALIZED_SESSION_CONFIG_BITFLAG ),
    MBEDTLS_BYTE_2( SSL_SERIALIZED_CONTEXT_CONFIG_BITFLAG ),
    MBEDTLS_BYTE_1( SSL_SERIALIZED_CONTEXT_CONFIG_BITFLAG ),
    MBEDTLS_BYTE_0( SSL_SERIALIZED_CONTEXT_CONFIG_BITFLAG ),
};

/*
 * Serialize a full SSL context
 *
 * The format of the serialized data is:
 * (in the presentation language of TLS, RFC 8446 section 3)
 *
 *  // header
 *  opaque mbedtls_version[3];   // major, minor, patch
 *  opaque context_format[5];    // version-specific field determining
 *                               // the format of the remaining
 *                               // serialized data.
 *  Note: When updating the format, remember to keep these
 *        version+format bytes. (We may make their size part of the API.)
 *
 *  // session sub-structure
 *  opaque session<1..2^32-1>;  // see mbedtls_ssl_session_save()
 *  // transform sub-structure
 *  uint8 random[64];           // ServerHello.random+ClientHello.random
 *  uint8 in_cid<0..2^8-1>      // Connection ID: expected incoming value
 *  uint8 out_cid<0..2^8-1>     // Connection ID: outgoing value to use
 *  // fields from ssl_context
 *  uint32 badmac_seen;         // DTLS: number of records with failing MAC
 *  uint64 in_window_top;       // DTLS: last validated record seq_num
 *  uint64 in_window;           // DTLS: bitmask for replay protection
 *  uint8 disable_datagram_packing; // DTLS: only one record per datagram
 *  uint64 cur_out_ctr;         // Record layer: outgoing sequence number
 *  uint16 mtu;                 // DTLS: path mtu (max outgoing fragment size)
 *  uint8 alpn_chosen<0..2^8-1> // ALPN: negotiated application protocol
 *
 * Note that many fields of the ssl_context or sub-structures are not
 * serialized, as they fall in one of the following categories:
 *
 *  1. forced value (eg in_left must be 0)
 *  2. pointer to dynamically-allocated memory (eg session, transform)
 *  3. value can be re-derived from other data (eg session keys from MS)
 *  4. value was temporary (eg content of input buffer)
 *  5. value will be provided by the user again (eg I/O callbacks and context)
 */
int mbedtls_ssl_context_save( mbedtls_ssl_context *ssl,
                              unsigned char *buf,
                              size_t buf_len,
                              size_t *olen )
{
    unsigned char *p = buf;
    size_t used = 0;
    size_t session_len;
    int ret = 0;

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

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

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

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

    used += 4 + session_len;
    if( used <= buf_len )
    {
        *p++ = MBEDTLS_BYTE_3( session_len );
        *p++ = MBEDTLS_BYTE_2( session_len );
        *p++ = MBEDTLS_BYTE_1( session_len );
        *p++ = MBEDTLS_BYTE_0( session_len );

        ret = ssl_session_save( ssl->session, 1,
                                p, session_len, &session_len );
        if( ret != 0 )
            return( ret );

        p += session_len;
    }

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

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

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

    /*
     * Saved fields from top-level ssl_context structure
     */
    used += 4;
    if( used <= buf_len )
    {
        *p++ = MBEDTLS_BYTE_3( ssl->badmac_seen );
        *p++ = MBEDTLS_BYTE_2( ssl->badmac_seen );
        *p++ = MBEDTLS_BYTE_1( ssl->badmac_seen );
        *p++ = MBEDTLS_BYTE_0( ssl->badmac_seen );
    }

#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
    used += 16;
    if( used <= buf_len )
    {
        *p++ = MBEDTLS_BYTE_7( ssl->in_window_top );
        *p++ = MBEDTLS_BYTE_6( ssl->in_window_top );
        *p++ = MBEDTLS_BYTE_5( ssl->in_window_top );
        *p++ = MBEDTLS_BYTE_4( ssl->in_window_top );
        *p++ = MBEDTLS_BYTE_3( ssl->in_window_top );
        *p++ = MBEDTLS_BYTE_2( ssl->in_window_top );
        *p++ = MBEDTLS_BYTE_1( ssl->in_window_top );
        *p++ = MBEDTLS_BYTE_0( ssl->in_window_top );

        *p++ = MBEDTLS_BYTE_7( ssl->in_window );
        *p++ = MBEDTLS_BYTE_6( ssl->in_window );
        *p++ = MBEDTLS_BYTE_5( ssl->in_window );
        *p++ = MBEDTLS_BYTE_4( ssl->in_window );
        *p++ = MBEDTLS_BYTE_3( ssl->in_window );
        *p++ = MBEDTLS_BYTE_2( ssl->in_window );
        *p++ = MBEDTLS_BYTE_1( ssl->in_window );
        *p++ = MBEDTLS_BYTE_0( ssl->in_window );
    }
#endif /* MBEDTLS_SSL_DTLS_ANTI_REPLAY */

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

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

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    used += 2;
    if( used <= buf_len )
    {
        *p++ = MBEDTLS_BYTE_1( ssl->mtu );
        *p++ = MBEDTLS_BYTE_0( ssl->mtu );
    }
#endif /* MBEDTLS_SSL_PROTO_DTLS */

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

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

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

    /*
     * Done
     */
    *olen = used;

    if( used > buf_len )
        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );

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

    return( mbedtls_ssl_session_reset_int( ssl, 0 ) );
}

/*
 * Helper to get TLS 1.2 PRF from ciphersuite
 * (Duplicates bits of logic from ssl_set_handshake_prfs().)
 */
typedef int (*tls_prf_fn)( const unsigned char *secret, size_t slen,
                           const char *label,
                           const unsigned char *random, size_t rlen,
                           unsigned char *dstbuf, size_t dlen );
static tls_prf_fn ssl_tls12prf_from_cs( int ciphersuite_id )
{
#if defined(MBEDTLS_SHA384_C)
    const mbedtls_ssl_ciphersuite_t * const ciphersuite_info =
         mbedtls_ssl_ciphersuite_from_id( ciphersuite_id );

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

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

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

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

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

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

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

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

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

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

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

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

    p += session_len;

    /*
     * Transform
     */

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

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

    ret = ssl_tls12_populate_transform( ssl->transform,
                  ssl->session->ciphersuite,
                  ssl->session->master,
#if defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC) && \
    defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                  ssl->session->encrypt_then_mac,
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC &&
          MBEDTLS_SSL_SOME_SUITES_USE_MAC */
                  ssl_tls12prf_from_cs( ssl->session->ciphersuite ),
                  p, /* currently pointing to randbytes */
                  MBEDTLS_SSL_MINOR_VERSION_3, /* (D)TLS 1.2 is forced */
                  ssl->conf->endpoint,
                  ssl );
    if( ret != 0 )
        return( ret );

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        alpn_len = *p++;

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

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

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

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

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

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

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

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

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

    return( 0 );
}

/*
 * Deserialize context: public wrapper for error cleaning
 */
int mbedtls_ssl_context_load( mbedtls_ssl_context *context,
                              const unsigned char *buf,
                              size_t len )
{
    int ret = ssl_context_load( context, buf, len );

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

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

/*
 * Free an SSL context
 */
void mbedtls_ssl_free( mbedtls_ssl_context *ssl )
{
    if( ssl == NULL )
        return;

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

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

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

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

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

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

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

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

#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
    mbedtls_ssl_transform_free( ssl->transform_application );
    mbedtls_free( ssl->transform_application );
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */

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

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

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

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

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

/*
 * Initialze mbedtls_ssl_config
 */
void mbedtls_ssl_config_init( mbedtls_ssl_config *conf )
{
    memset( conf, 0, sizeof( mbedtls_ssl_config ) );
}

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/* The selection should be the same as mbedtls_x509_crt_profile_default in
 * x509_crt.c. Here, the order matters. Currently we favor stronger hashes,
 * for no fundamental reason.
 * See the documentation of mbedtls_ssl_conf_curves() for what we promise
 * about this list. */
static int ssl_preset_default_hashes[] = {
#if defined(MBEDTLS_SHA512_C)
    MBEDTLS_MD_SHA512,
#endif
#if defined(MBEDTLS_SHA384_C)
    MBEDTLS_MD_SHA384,
#endif
#if defined(MBEDTLS_SHA256_C)
    MBEDTLS_MD_SHA256,
#endif
    MBEDTLS_MD_NONE
};
#endif

#if defined(MBEDTLS_ECP_C)
/* The selection should be the same as mbedtls_x509_crt_profile_default in
 * x509_crt.c, plus Montgomery curves for ECDHE. Here, the order matters:
 * curves with a lower resource usage come first.
 * See the documentation of mbedtls_ssl_conf_curves() for what we promise
 * about this list.
 */
static mbedtls_ecp_group_id ssl_preset_default_curves[] = {
#if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
    MBEDTLS_ECP_DP_CURVE25519,
#endif
#if defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
    MBEDTLS_ECP_DP_SECP256R1,
#endif
#if defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
    MBEDTLS_ECP_DP_SECP384R1,
#endif
#if defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
    MBEDTLS_ECP_DP_CURVE448,
#endif
#if defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
    MBEDTLS_ECP_DP_SECP521R1,
#endif
#if defined(MBEDTLS_ECP_DP_BP256R1_ENABLED)
    MBEDTLS_ECP_DP_BP256R1,
#endif
#if defined(MBEDTLS_ECP_DP_BP384R1_ENABLED)
    MBEDTLS_ECP_DP_BP384R1,
#endif
#if defined(MBEDTLS_ECP_DP_BP512R1_ENABLED)
    MBEDTLS_ECP_DP_BP512R1,
#endif
    MBEDTLS_ECP_DP_NONE
};
#endif

static int ssl_preset_suiteb_ciphersuites[] = {
    MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
    MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
    0
};

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
static int ssl_preset_suiteb_hashes[] = {
    MBEDTLS_MD_SHA256,
    MBEDTLS_MD_SHA384,
    MBEDTLS_MD_NONE
};

#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
static uint16_t ssl_preset_default_sig_algs[] = {
    /* ECDSA algorithms */
#if defined(MBEDTLS_ECDSA_C)
#if defined(MBEDTLS_SHA256_C) && defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
    MBEDTLS_TLS13_SIG_ECDSA_SECP256R1_SHA256,
#endif /* MBEDTLS_SHA256_C && MBEDTLS_ECP_DP_SECP256R1_ENABLED */
#if defined(MBEDTLS_SHA512_C) && defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
    MBEDTLS_TLS13_SIG_ECDSA_SECP384R1_SHA384,
#endif /* MBEDTLS_SHA512_C && MBEDTLS_ECP_DP_SECP384R1_ENABLED */
#if defined(MBEDTLS_SHA512_C) && defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
    MBEDTLS_TLS13_SIG_ECDSA_SECP521R1_SHA512,
#endif /* MBEDTLS_SHA512_C && MBEDTLS_ECP_DP_SECP521R1_ENABLED */
#endif /* MBEDTLS_ECDSA_C */
    MBEDTLS_TLS13_SIG_NONE
};

static uint16_t ssl_preset_suiteb_sig_algs[] = {
    /* ECDSA algorithms */
#if defined(MBEDTLS_ECDSA_C)
#if defined(MBEDTLS_SHA256_C) && defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
    MBEDTLS_TLS13_SIG_ECDSA_SECP256R1_SHA256,
#endif /* MBEDTLS_SHA256_C && MBEDTLS_ECP_DP_SECP256R1_ENABLED */
#if defined(MBEDTLS_SHA512_C) && defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
    MBEDTLS_TLS13_SIG_ECDSA_SECP384R1_SHA384,
#endif /* MBEDTLS_SHA512_C && MBEDTLS_ECP_DP_SECP384R1_ENABLED */
#endif /* MBEDTLS_ECDSA_C */
    MBEDTLS_TLS13_SIG_NONE
};
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
#endif

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

/*
 * Load default in mbedtls_ssl_config
 */
int mbedtls_ssl_config_defaults( mbedtls_ssl_config *conf,
                                 int endpoint, int transport, int preset )
{
#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C)
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
#endif

    /* Use the functions here so that they are covered in tests,
     * but otherwise access member directly for efficiency */
    mbedtls_ssl_conf_endpoint( conf, endpoint );
    mbedtls_ssl_conf_transport( conf, transport );

    /*
     * Things that are common to all presets
     */
#if defined(MBEDTLS_SSL_CLI_C)
    if( endpoint == MBEDTLS_SSL_IS_CLIENT )
    {
        conf->authmode = MBEDTLS_SSL_VERIFY_REQUIRED;
#if defined(MBEDTLS_SSL_SESSION_TICKETS)
        conf->session_tickets = MBEDTLS_SSL_SESSION_TICKETS_ENABLED;
#endif
    }
#endif

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
    conf->encrypt_then_mac = MBEDTLS_SSL_ETM_ENABLED;
#endif

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
    conf->extended_ms = MBEDTLS_SSL_EXTENDED_MS_ENABLED;
#endif

#if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY) && defined(MBEDTLS_SSL_SRV_C)
    conf->f_cookie_write = ssl_cookie_write_dummy;
    conf->f_cookie_check = ssl_cookie_check_dummy;
#endif

#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
    conf->anti_replay = MBEDTLS_SSL_ANTI_REPLAY_ENABLED;
#endif

#if defined(MBEDTLS_SSL_SRV_C)
    conf->cert_req_ca_list = MBEDTLS_SSL_CERT_REQ_CA_LIST_ENABLED;
    conf->respect_cli_pref = MBEDTLS_SSL_SRV_CIPHERSUITE_ORDER_SERVER;
#endif

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    conf->hs_timeout_min = MBEDTLS_SSL_DTLS_TIMEOUT_DFL_MIN;
    conf->hs_timeout_max = MBEDTLS_SSL_DTLS_TIMEOUT_DFL_MAX;
#endif

#if defined(MBEDTLS_SSL_RENEGOTIATION)
    conf->renego_max_records = MBEDTLS_SSL_RENEGO_MAX_RECORDS_DEFAULT;
    memset( conf->renego_period,     0x00, 2 );
    memset( conf->renego_period + 2, 0xFF, 6 );
#endif

#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C)
            if( endpoint == MBEDTLS_SSL_IS_SERVER )
            {
                const unsigned char dhm_p[] =
                    MBEDTLS_DHM_RFC3526_MODP_2048_P_BIN;
                const unsigned char dhm_g[] =
                    MBEDTLS_DHM_RFC3526_MODP_2048_G_BIN;

                if ( ( ret = mbedtls_ssl_conf_dh_param_bin( conf,
                                               dhm_p, sizeof( dhm_p ),
                                               dhm_g, sizeof( dhm_g ) ) ) != 0 )
                {
                    return( ret );
                }
            }
#endif

    /*
     * Preset-specific defaults
     */
    switch( preset )
    {
        /*
         * NSA Suite B
         */
        case MBEDTLS_SSL_PRESET_SUITEB:
            conf->min_major_ver = MBEDTLS_SSL_MAJOR_VERSION_3;
            conf->min_minor_ver = MBEDTLS_SSL_MINOR_VERSION_3; /* TLS 1.2 */
            conf->max_major_ver = MBEDTLS_SSL_MAX_MAJOR_VERSION;
            conf->max_minor_ver = MBEDTLS_SSL_MAX_MINOR_VERSION;

            conf->ciphersuite_list = ssl_preset_suiteb_ciphersuites;

#if defined(MBEDTLS_X509_CRT_PARSE_C)
            conf->cert_profile = &mbedtls_x509_crt_profile_suiteb;
#endif

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
            conf->sig_hashes = ssl_preset_suiteb_hashes;
#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
            conf->tls13_sig_algs = ssl_preset_suiteb_sig_algs;
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
#endif

#if defined(MBEDTLS_ECP_C)
            conf->curve_list = ssl_preset_suiteb_curves;
#endif
            break;

        /*
         * Default
         */
        default:
            conf->min_major_ver = ( MBEDTLS_SSL_MIN_MAJOR_VERSION >
                                    MBEDTLS_SSL_MIN_VALID_MAJOR_VERSION ) ?
                                    MBEDTLS_SSL_MIN_MAJOR_VERSION :
                                    MBEDTLS_SSL_MIN_VALID_MAJOR_VERSION;
            conf->min_minor_ver = ( MBEDTLS_SSL_MIN_MINOR_VERSION >
                                    MBEDTLS_SSL_MIN_VALID_MINOR_VERSION ) ?
                                    MBEDTLS_SSL_MIN_MINOR_VERSION :
                                    MBEDTLS_SSL_MIN_VALID_MINOR_VERSION;
            conf->max_major_ver = MBEDTLS_SSL_MAX_MAJOR_VERSION;
            conf->max_minor_ver = MBEDTLS_SSL_MAX_MINOR_VERSION;

#if defined(MBEDTLS_SSL_PROTO_DTLS)
            if( transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
                conf->min_minor_ver = MBEDTLS_SSL_MINOR_VERSION_3;
#endif
            conf->ciphersuite_list = mbedtls_ssl_list_ciphersuites();

#if defined(MBEDTLS_X509_CRT_PARSE_C)
            conf->cert_profile = &mbedtls_x509_crt_profile_default;
#endif

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
            conf->sig_hashes = ssl_preset_default_hashes;
#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
            conf->tls13_sig_algs = ssl_preset_default_sig_algs;
#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */

#if defined(MBEDTLS_ECP_C)
            conf->curve_list = ssl_preset_default_curves;
#endif

#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_CLI_C)
            conf->dhm_min_bitlen = 1024;
#endif
    }

    return( 0 );
}

/*
 * Free mbedtls_ssl_config
 */
void mbedtls_ssl_config_free( mbedtls_ssl_config *conf )
{
#if defined(MBEDTLS_DHM_C)
    mbedtls_mpi_free( &conf->dhm_P );
    mbedtls_mpi_free( &conf->dhm_G );
#endif

#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
    if( conf->psk != NULL )
    {
        mbedtls_platform_zeroize( conf->psk, conf->psk_len );
        mbedtls_free( conf->psk );
        conf->psk = NULL;
        conf->psk_len = 0;
    }

    if( conf->psk_identity != NULL )
    {
        mbedtls_platform_zeroize( conf->psk_identity, conf->psk_identity_len );
        mbedtls_free( conf->psk_identity );
        conf->psk_identity = NULL;
        conf->psk_identity_len = 0;
    }
#endif

#if defined(MBEDTLS_X509_CRT_PARSE_C)
    ssl_key_cert_free( conf->key_cert );
#endif

    mbedtls_platform_zeroize( conf, sizeof( mbedtls_ssl_config ) );
}

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

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

mbedtls_pk_type_t mbedtls_ssl_pk_alg_from_sig( unsigned char sig )
{
    switch( sig )
    {
#if defined(MBEDTLS_RSA_C)
        case MBEDTLS_SSL_SIG_RSA:
            return( MBEDTLS_PK_RSA );
#endif
#if defined(MBEDTLS_ECDSA_C)
        case MBEDTLS_SSL_SIG_ECDSA:
            return( MBEDTLS_PK_ECDSA );
#endif
        default:
            return( MBEDTLS_PK_NONE );
    }
}
#endif /* MBEDTLS_PK_C && ( MBEDTLS_RSA_C || MBEDTLS_ECDSA_C ) */

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

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

/* Add a signature-hash-pair to a signature-hash set */
void mbedtls_ssl_sig_hash_set_add( mbedtls_ssl_sig_hash_set_t *set,
                                   mbedtls_pk_type_t sig_alg,
                                   mbedtls_md_type_t md_alg )
{
    switch( sig_alg )
    {
        case MBEDTLS_PK_RSA:
            if( set->rsa == MBEDTLS_MD_NONE )
                set->rsa = md_alg;
            break;

        case MBEDTLS_PK_ECDSA:
            if( set->ecdsa == MBEDTLS_MD_NONE )
                set->ecdsa = md_alg;
            break;

        default:
            break;
    }
}

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

#endif /* MBEDTLS_SSL_PROTO_TLS1_2) &&
          MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */

/*
 * Convert from MBEDTLS_SSL_HASH_XXX to MBEDTLS_MD_XXX
 */
mbedtls_md_type_t mbedtls_ssl_md_alg_from_hash( unsigned char hash )
{
    switch( hash )
    {
#if defined(MBEDTLS_MD5_C)
        case MBEDTLS_SSL_HASH_MD5:
            return( MBEDTLS_MD_MD5 );
#endif
#if defined(MBEDTLS_SHA1_C)
        case MBEDTLS_SSL_HASH_SHA1:
            return( MBEDTLS_MD_SHA1 );
#endif
#if defined(MBEDTLS_SHA224_C)
        case MBEDTLS_SSL_HASH_SHA224:
            return( MBEDTLS_MD_SHA224 );
#endif
#if defined(MBEDTLS_SHA256_C)
        case MBEDTLS_SSL_HASH_SHA256:
            return( MBEDTLS_MD_SHA256 );
#endif
#if defined(MBEDTLS_SHA384_C)
        case MBEDTLS_SSL_HASH_SHA384:
            return( MBEDTLS_MD_SHA384 );
#endif
#if defined(MBEDTLS_SHA512_C)
        case MBEDTLS_SSL_HASH_SHA512:
            return( MBEDTLS_MD_SHA512 );
#endif
        default:
            return( MBEDTLS_MD_NONE );
    }
}

/*
 * Convert from MBEDTLS_MD_XXX to MBEDTLS_SSL_HASH_XXX
 */
unsigned char mbedtls_ssl_hash_from_md_alg( int md )
{
    switch( md )
    {
#if defined(MBEDTLS_MD5_C)
        case MBEDTLS_MD_MD5:
            return( MBEDTLS_SSL_HASH_MD5 );
#endif
#if defined(MBEDTLS_SHA1_C)
        case MBEDTLS_MD_SHA1:
            return( MBEDTLS_SSL_HASH_SHA1 );
#endif
#if defined(MBEDTLS_SHA224_C)
        case MBEDTLS_MD_SHA224:
            return( MBEDTLS_SSL_HASH_SHA224 );
#endif
#if defined(MBEDTLS_SHA256_C)
        case MBEDTLS_MD_SHA256:
            return( MBEDTLS_SSL_HASH_SHA256 );
#endif
#if defined(MBEDTLS_SHA384_C)
        case MBEDTLS_MD_SHA384:
            return( MBEDTLS_SSL_HASH_SHA384 );
#endif
#if defined(MBEDTLS_SHA512_C)
        case MBEDTLS_MD_SHA512:
            return( MBEDTLS_SSL_HASH_SHA512 );
#endif
        default:
            return( MBEDTLS_SSL_HASH_NONE );
    }
}

#if defined(MBEDTLS_ECP_C)
/*
 * Check if a curve proposed by the peer is in our list.
 * Return 0 if we're willing to use it, -1 otherwise.
 */
int mbedtls_ssl_check_curve( const mbedtls_ssl_context *ssl, mbedtls_ecp_group_id grp_id )
{
    const mbedtls_ecp_group_id *gid;

    if( ssl->conf->curve_list == NULL )
        return( -1 );

    for( gid = ssl->conf->curve_list; *gid != MBEDTLS_ECP_DP_NONE; gid++ )
        if( *gid == grp_id )
            return( 0 );

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

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
/*
 * Check if a hash proposed by the peer is in our list.
 * Return 0 if we're willing to use it, -1 otherwise.
 */
int mbedtls_ssl_check_sig_hash( const mbedtls_ssl_context *ssl,
                                mbedtls_md_type_t md )
{
    const int *cur;

    if( ssl->conf->sig_hashes == NULL )
        return( -1 );

    for( cur = ssl->conf->sig_hashes; *cur != MBEDTLS_MD_NONE; cur++ )
        if( *cur == (int) md )
            return( 0 );

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

#if defined(MBEDTLS_X509_CRT_PARSE_C)
int mbedtls_ssl_check_cert_usage( const mbedtls_x509_crt *cert,
                          const mbedtls_ssl_ciphersuite_t *ciphersuite,
                          int cert_endpoint,
                          uint32_t *flags )
{
    int ret = 0;
    int usage = 0;
    const char *ext_oid;
    size_t ext_len;

    if( cert_endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        /* Server part of the key exchange */
        switch( ciphersuite->key_exchange )
        {
            case MBEDTLS_KEY_EXCHANGE_RSA:
            case MBEDTLS_KEY_EXCHANGE_RSA_PSK:
                usage = MBEDTLS_X509_KU_KEY_ENCIPHERMENT;
                break;

            case MBEDTLS_KEY_EXCHANGE_DHE_RSA:
            case MBEDTLS_KEY_EXCHANGE_ECDHE_RSA:
            case MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA:
                usage = MBEDTLS_X509_KU_DIGITAL_SIGNATURE;
                break;

            case MBEDTLS_KEY_EXCHANGE_ECDH_RSA:
            case MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA:
                usage = MBEDTLS_X509_KU_KEY_AGREEMENT;
                break;

            /* Don't use default: we want warnings when adding new values */
            case MBEDTLS_KEY_EXCHANGE_NONE:
            case MBEDTLS_KEY_EXCHANGE_PSK:
            case MBEDTLS_KEY_EXCHANGE_DHE_PSK:
            case MBEDTLS_KEY_EXCHANGE_ECDHE_PSK:
            case MBEDTLS_KEY_EXCHANGE_ECJPAKE:
                usage = 0;
        }
    }
    else
    {
        /* Client auth: we only implement rsa_sign and mbedtls_ecdsa_sign for now */
        usage = MBEDTLS_X509_KU_DIGITAL_SIGNATURE;
    }

    if( mbedtls_x509_crt_check_key_usage( cert, usage ) != 0 )
    {
        *flags |= MBEDTLS_X509_BADCERT_KEY_USAGE;
        ret = -1;
    }

    if( cert_endpoint == MBEDTLS_SSL_IS_SERVER )
    {
        ext_oid = MBEDTLS_OID_SERVER_AUTH;
        ext_len = MBEDTLS_OID_SIZE( MBEDTLS_OID_SERVER_AUTH );
    }
    else
    {
        ext_oid = MBEDTLS_OID_CLIENT_AUTH;
        ext_len = MBEDTLS_OID_SIZE( MBEDTLS_OID_CLIENT_AUTH );
    }

    if( mbedtls_x509_crt_check_extended_key_usage( cert, ext_oid, ext_len ) != 0 )
    {
        *flags |= MBEDTLS_X509_BADCERT_EXT_KEY_USAGE;
        ret = -1;
    }

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

int mbedtls_ssl_set_calc_verify_md( mbedtls_ssl_context *ssl, int md )
{
#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
    if( ssl->minor_ver != MBEDTLS_SSL_MINOR_VERSION_3 )
        return( -1 );

    switch( md )
    {
#if defined(MBEDTLS_SHA384_C)
        case MBEDTLS_SSL_HASH_SHA384:
            ssl->handshake->calc_verify = ssl_calc_verify_tls_sha384;
            break;
#endif
#if defined(MBEDTLS_SHA256_C)
        case MBEDTLS_SSL_HASH_SHA256:
            ssl->handshake->calc_verify = ssl_calc_verify_tls_sha256;
            break;
#endif
        default:
            return( -1 );
    }

    return 0;
#else /* !MBEDTLS_SSL_PROTO_TLS1_2 */
    (void) ssl;
    (void) md;

    return( -1 );
#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
}

#if defined(MBEDTLS_SSL_PROTO_TLS1_2)

#if defined(MBEDTLS_USE_PSA_CRYPTO)
int mbedtls_ssl_get_key_exchange_md_tls1_2( mbedtls_ssl_context *ssl,
                                            unsigned char *hash, size_t *hashlen,
                                            unsigned char *data, size_t data_len,
                                            mbedtls_md_type_t md_alg )
{
    psa_status_t status;
    psa_hash_operation_t hash_operation = PSA_HASH_OPERATION_INIT;
    psa_algorithm_t hash_alg = mbedtls_psa_translate_md( md_alg );

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "Perform PSA-based computation of digest of ServerKeyExchange" ) );

    if( ( status = psa_hash_setup( &hash_operation,
                                   hash_alg ) ) != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "psa_hash_setup", status );
        goto exit;
    }

    if( ( status = psa_hash_update( &hash_operation, ssl->handshake->randbytes,
                                    64 ) ) != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "psa_hash_update", status );
        goto exit;
    }

    if( ( status = psa_hash_update( &hash_operation,
                                    data, data_len ) ) != PSA_SUCCESS )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "psa_hash_update", status );
        goto exit;
    }

    if( ( status = psa_hash_finish( &hash_operation, hash, MBEDTLS_MD_MAX_SIZE,
                                    hashlen ) ) != PSA_SUCCESS )
    {
         MBEDTLS_SSL_DEBUG_RET( 1, "psa_hash_finish", status );
         goto exit;
    }

exit:
    if( status != PSA_SUCCESS )
    {
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
        switch( status )
        {
            case PSA_ERROR_NOT_SUPPORTED:
                return( MBEDTLS_ERR_MD_FEATURE_UNAVAILABLE );
            case PSA_ERROR_BAD_STATE: /* Intentional fallthrough */
            case PSA_ERROR_BUFFER_TOO_SMALL:
                return( MBEDTLS_ERR_MD_BAD_INPUT_DATA );
            case PSA_ERROR_INSUFFICIENT_MEMORY:
                return( MBEDTLS_ERR_MD_ALLOC_FAILED );
            default:
                return( MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED );
        }
    }
    return( 0 );
}

#else

int mbedtls_ssl_get_key_exchange_md_tls1_2( mbedtls_ssl_context *ssl,
                                            unsigned char *hash, size_t *hashlen,
                                            unsigned char *data, size_t data_len,
                                            mbedtls_md_type_t md_alg )
{
    int ret = 0;
    mbedtls_md_context_t ctx;
    const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type( md_alg );
    *hashlen = mbedtls_md_get_size( md_info );

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "Perform mbedtls-based computation of digest of ServerKeyExchange" ) );

    mbedtls_md_init( &ctx );

    /*
     * digitally-signed struct {
     *     opaque client_random[32];
     *     opaque server_random[32];
     *     ServerDHParams params;
     * };
     */
    if( ( ret = mbedtls_md_setup( &ctx, md_info, 0 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_setup", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md_starts( &ctx ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_starts", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md_update( &ctx, ssl->handshake->randbytes, 64 ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_update", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md_update( &ctx, data, data_len ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_update", ret );
        goto exit;
    }
    if( ( ret = mbedtls_md_finish( &ctx, hash ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_md_finish", ret );
        goto exit;
    }

exit:
    mbedtls_md_free( &ctx );

    if( ret != 0 )
        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                        MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );

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

#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */

#endif /* MBEDTLS_SSL_TLS_C */