library/ssl_tls12_client.c

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

#include "common.h"

#if defined(MBEDTLS_SSL_CLI_C) && defined(MBEDTLS_SSL_PROTO_TLS1_2)

#include "mbedtls/platform.h"

#include "mbedtls/ssl.h"
#include "ssl_client.h"
#include "ssl_misc.h"
#include "mbedtls/debug.h"
#include "mbedtls/error.h"
#include "mbedtls/constant_time.h"

#if defined(MBEDTLS_USE_PSA_CRYPTO)
#include "psa_util_internal.h"
#include "psa/crypto.h"
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
/* Define a local translating function to save code size by not using too many
 * arguments in each translating place. */
static int local_err_translation(psa_status_t status)
{
    return psa_status_to_mbedtls(status, psa_to_ssl_errors,
                                 ARRAY_LENGTH(psa_to_ssl_errors),
                                 psa_generic_status_to_mbedtls);
}
#define PSA_TO_MBEDTLS_ERR(status) local_err_translation(status)
#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
#endif /* MBEDTLS_USE_PSA_CRYPTO */

#include <string.h>

#include <stdint.h>

#if defined(MBEDTLS_HAVE_TIME)
#include "mbedtls/platform_time.h"
#endif

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
#include "mbedtls/platform_util.h"
#endif

#if defined(MBEDTLS_SSL_RENEGOTIATION)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_renegotiation_ext(mbedtls_ssl_context *ssl,
                                       unsigned char *buf,
                                       const unsigned char *end,
                                       size_t *olen)
{
    unsigned char *p = buf;

    *olen = 0;

    /* We're always including a TLS_EMPTY_RENEGOTIATION_INFO_SCSV in the
     * initial ClientHello, in which case also adding the renegotiation
     * info extension is NOT RECOMMENDED as per RFC 5746 Section 3.4. */
    if (ssl->renego_status != MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS) {
        return 0;
    }

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("client hello, adding renegotiation extension"));

    MBEDTLS_SSL_CHK_BUF_PTR(p, end, 5 + ssl->verify_data_len);

    /*
     * Secure renegotiation
     */
    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_RENEGOTIATION_INFO, p, 0);
    p += 2;

    *p++ = 0x00;
    *p++ = MBEDTLS_BYTE_0(ssl->verify_data_len + 1);
    *p++ = MBEDTLS_BYTE_0(ssl->verify_data_len);

    memcpy(p, ssl->own_verify_data, ssl->verify_data_len);

    *olen = 5 + ssl->verify_data_len;

    return 0;
}
#endif /* MBEDTLS_SSL_RENEGOTIATION */

#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)

MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_supported_point_formats_ext(mbedtls_ssl_context *ssl,
                                                 unsigned char *buf,
                                                 const unsigned char *end,
                                                 size_t *olen)
{
    unsigned char *p = buf;
    (void) ssl; /* ssl used for debugging only */

    *olen = 0;

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("client hello, adding supported_point_formats extension"));
    MBEDTLS_SSL_CHK_BUF_PTR(p, end, 6);

    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS, p, 0);
    p += 2;

    *p++ = 0x00;
    *p++ = 2;

    *p++ = 1;
    *p++ = MBEDTLS_ECP_PF_UNCOMPRESSED;

    *olen = 6;

    return 0;
}
#endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C ||
          MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */

#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_ecjpake_kkpp_ext(mbedtls_ssl_context *ssl,
                                      unsigned char *buf,
                                      const unsigned char *end,
                                      size_t *olen)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char *p = buf;
    size_t kkpp_len = 0;

    *olen = 0;

    /* Skip costly extension if we can't use EC J-PAKE anyway */
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    if (ssl->handshake->psa_pake_ctx_is_ok != 1) {
        return 0;
    }
#else
    if (mbedtls_ecjpake_check(&ssl->handshake->ecjpake_ctx) != 0) {
        return 0;
    }
#endif /* MBEDTLS_USE_PSA_CRYPTO */

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("client hello, adding ecjpake_kkpp extension"));

    MBEDTLS_SSL_CHK_BUF_PTR(p, end, 4);

    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_ECJPAKE_KKPP, p, 0);
    p += 2;

    /*
     * We may need to send ClientHello multiple times for Hello verification.
     * We don't want to compute fresh values every time (both for performance
     * and consistency reasons), so cache the extension content.
     */
    if (ssl->handshake->ecjpake_cache == NULL ||
        ssl->handshake->ecjpake_cache_len == 0) {
        MBEDTLS_SSL_DEBUG_MSG(3, ("generating new ecjpake parameters"));

#if defined(MBEDTLS_USE_PSA_CRYPTO)
        ret = mbedtls_psa_ecjpake_write_round(&ssl->handshake->psa_pake_ctx,
                                              p + 2, end - p - 2, &kkpp_len,
                                              MBEDTLS_ECJPAKE_ROUND_ONE);
        if (ret != 0) {
            psa_destroy_key(ssl->handshake->psa_pake_password);
            psa_pake_abort(&ssl->handshake->psa_pake_ctx);
            MBEDTLS_SSL_DEBUG_RET(1, "psa_pake_output", ret);
            return ret;
        }
#else
        ret = mbedtls_ecjpake_write_round_one(&ssl->handshake->ecjpake_ctx,
                                              p + 2, end - p - 2, &kkpp_len,
                                              ssl->conf->f_rng, ssl->conf->p_rng);
        if (ret != 0) {
            MBEDTLS_SSL_DEBUG_RET(1,
                                  "mbedtls_ecjpake_write_round_one", ret);
            return ret;
        }
#endif /* MBEDTLS_USE_PSA_CRYPTO */

        ssl->handshake->ecjpake_cache = mbedtls_calloc(1, kkpp_len);
        if (ssl->handshake->ecjpake_cache == NULL) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("allocation failed"));
            return MBEDTLS_ERR_SSL_ALLOC_FAILED;
        }

        memcpy(ssl->handshake->ecjpake_cache, p + 2, kkpp_len);
        ssl->handshake->ecjpake_cache_len = kkpp_len;
    } else {
        MBEDTLS_SSL_DEBUG_MSG(3, ("re-using cached ecjpake parameters"));

        kkpp_len = ssl->handshake->ecjpake_cache_len;
        MBEDTLS_SSL_CHK_BUF_PTR(p + 2, end, kkpp_len);

        memcpy(p + 2, ssl->handshake->ecjpake_cache, kkpp_len);
    }

    MBEDTLS_PUT_UINT16_BE(kkpp_len, p, 0);
    p += 2;

    *olen = kkpp_len + 4;

    return 0;
}
#endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_cid_ext(mbedtls_ssl_context *ssl,
                             unsigned char *buf,
                             const unsigned char *end,
                             size_t *olen)
{
    unsigned char *p = buf;
    size_t ext_len;

    /*
     *   struct {
     *      opaque cid<0..2^8-1>;
     *   } ConnectionId;
     */

    *olen = 0;
    if (ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM ||
        ssl->negotiate_cid == MBEDTLS_SSL_CID_DISABLED) {
        return 0;
    }
    MBEDTLS_SSL_DEBUG_MSG(3, ("client hello, adding CID extension"));

    /* ssl->own_cid_len is at most MBEDTLS_SSL_CID_IN_LEN_MAX
     * which is at most 255, so the increment cannot overflow. */
    MBEDTLS_SSL_CHK_BUF_PTR(p, end, (unsigned) (ssl->own_cid_len + 5));

    /* Add extension ID + size */
    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_CID, p, 0);
    p += 2;
    ext_len = (size_t) ssl->own_cid_len + 1;
    MBEDTLS_PUT_UINT16_BE(ext_len, p, 0);
    p += 2;

    *p++ = (uint8_t) ssl->own_cid_len;
    memcpy(p, ssl->own_cid, ssl->own_cid_len);

    *olen = ssl->own_cid_len + 5;

    return 0;
}
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_max_fragment_length_ext(mbedtls_ssl_context *ssl,
                                             unsigned char *buf,
                                             const unsigned char *end,
                                             size_t *olen)
{
    unsigned char *p = buf;

    *olen = 0;

    if (ssl->conf->mfl_code == MBEDTLS_SSL_MAX_FRAG_LEN_NONE) {
        return 0;
    }

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("client hello, adding max_fragment_length extension"));

    MBEDTLS_SSL_CHK_BUF_PTR(p, end, 5);

    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH, p, 0);
    p += 2;

    *p++ = 0x00;
    *p++ = 1;

    *p++ = ssl->conf->mfl_code;

    *olen = 5;

    return 0;
}
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_encrypt_then_mac_ext(mbedtls_ssl_context *ssl,
                                          unsigned char *buf,
                                          const unsigned char *end,
                                          size_t *olen)
{
    unsigned char *p = buf;

    *olen = 0;

    if (ssl->conf->encrypt_then_mac == MBEDTLS_SSL_ETM_DISABLED) {
        return 0;
    }

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("client hello, adding encrypt_then_mac extension"));

    MBEDTLS_SSL_CHK_BUF_PTR(p, end, 4);

    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC, p, 0);
    p += 2;

    *p++ = 0x00;
    *p++ = 0x00;

    *olen = 4;

    return 0;
}
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_extended_ms_ext(mbedtls_ssl_context *ssl,
                                     unsigned char *buf,
                                     const unsigned char *end,
                                     size_t *olen)
{
    unsigned char *p = buf;

    *olen = 0;

    if (ssl->conf->extended_ms == MBEDTLS_SSL_EXTENDED_MS_DISABLED) {
        return 0;
    }

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("client hello, adding extended_master_secret extension"));

    MBEDTLS_SSL_CHK_BUF_PTR(p, end, 4);

    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET, p, 0);
    p += 2;

    *p++ = 0x00;
    *p++ = 0x00;

    *olen = 4;

    return 0;
}
#endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_session_ticket_ext(mbedtls_ssl_context *ssl,
                                        unsigned char *buf,
                                        const unsigned char *end,
                                        size_t *olen)
{
    unsigned char *p = buf;
    size_t tlen = ssl->session_negotiate->ticket_len;

    *olen = 0;

    if (ssl->conf->session_tickets == MBEDTLS_SSL_SESSION_TICKETS_DISABLED) {
        return 0;
    }

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("client hello, adding session ticket extension"));

    /* The addition is safe here since the ticket length is 16 bit. */
    MBEDTLS_SSL_CHK_BUF_PTR(p, end, 4 + tlen);

    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_SESSION_TICKET, p, 0);
    p += 2;

    MBEDTLS_PUT_UINT16_BE(tlen, p, 0);
    p += 2;

    *olen = 4;

    if (ssl->session_negotiate->ticket == NULL || tlen == 0) {
        return 0;
    }

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("sending session ticket of length %" MBEDTLS_PRINTF_SIZET, tlen));

    memcpy(p, ssl->session_negotiate->ticket, tlen);

    *olen += tlen;

    return 0;
}
#endif /* MBEDTLS_SSL_SESSION_TICKETS */

#if defined(MBEDTLS_SSL_DTLS_SRTP)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_use_srtp_ext(mbedtls_ssl_context *ssl,
                                  unsigned char *buf,
                                  const unsigned char *end,
                                  size_t *olen)
{
    unsigned char *p = buf;
    size_t protection_profiles_index = 0, ext_len = 0;
    uint16_t mki_len = 0, profile_value = 0;

    *olen = 0;

    if ((ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM) ||
        (ssl->conf->dtls_srtp_profile_list == NULL) ||
        (ssl->conf->dtls_srtp_profile_list_len == 0)) {
        return 0;
    }

    /* RFC 5764 section 4.1.1
     * uint8 SRTPProtectionProfile[2];
     *
     * struct {
     *   SRTPProtectionProfiles SRTPProtectionProfiles;
     *   opaque srtp_mki<0..255>;
     * } UseSRTPData;
     * SRTPProtectionProfile SRTPProtectionProfiles<2..2^16-1>;
     */
    if (ssl->conf->dtls_srtp_mki_support == MBEDTLS_SSL_DTLS_SRTP_MKI_SUPPORTED) {
        mki_len = ssl->dtls_srtp_info.mki_len;
    }
    /* Extension length = 2 bytes for profiles length,
     *                    ssl->conf->dtls_srtp_profile_list_len * 2 (each profile is 2 bytes length ),
     *                    1 byte for srtp_mki vector length and the mki_len value
     */
    ext_len = 2 + 2 * (ssl->conf->dtls_srtp_profile_list_len) + 1 + mki_len;

    MBEDTLS_SSL_DEBUG_MSG(3, ("client hello, adding use_srtp extension"));

    /* Check there is room in the buffer for the extension + 4 bytes
     * - the extension tag (2 bytes)
     * - the extension length (2 bytes)
     */
    MBEDTLS_SSL_CHK_BUF_PTR(p, end, ext_len + 4);

    MBEDTLS_PUT_UINT16_BE(MBEDTLS_TLS_EXT_USE_SRTP, p, 0);
    p += 2;

    MBEDTLS_PUT_UINT16_BE(ext_len, p, 0);
    p += 2;

    /* protection profile length: 2*(ssl->conf->dtls_srtp_profile_list_len) */
    /* micro-optimization:
     * the list size is limited to MBEDTLS_TLS_SRTP_MAX_PROFILE_LIST_LENGTH
     * which is lower than 127, so the upper byte of the length is always 0
     * For the documentation, the more generic code is left in comments
     * *p++ = (unsigned char)( ( ( 2 * ssl->conf->dtls_srtp_profile_list_len )
     *                        >> 8 ) & 0xFF );
     */
    *p++ = 0;
    *p++ = MBEDTLS_BYTE_0(2 * ssl->conf->dtls_srtp_profile_list_len);

    for (protection_profiles_index = 0;
         protection_profiles_index < ssl->conf->dtls_srtp_profile_list_len;
         protection_profiles_index++) {
        profile_value = mbedtls_ssl_check_srtp_profile_value
                            (ssl->conf->dtls_srtp_profile_list[protection_profiles_index]);
        if (profile_value != MBEDTLS_TLS_SRTP_UNSET) {
            MBEDTLS_SSL_DEBUG_MSG(3, ("ssl_write_use_srtp_ext, add profile: %04x",
                                      profile_value));
            MBEDTLS_PUT_UINT16_BE(profile_value, p, 0);
            p += 2;
        } else {
            /*
             * Note: we shall never arrive here as protection profiles
             * is checked by mbedtls_ssl_conf_dtls_srtp_protection_profiles function
             */
            MBEDTLS_SSL_DEBUG_MSG(3,
                                  ("client hello, "
                                   "illegal DTLS-SRTP protection profile %d",
                                   ssl->conf->dtls_srtp_profile_list[protection_profiles_index]
                                  ));
            return MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
        }
    }

    *p++ = mki_len & 0xFF;

    if (mki_len != 0) {
        memcpy(p, ssl->dtls_srtp_info.mki_value, mki_len);
        /*
         * Increment p to point to the current position.
         */
        p += mki_len;
        MBEDTLS_SSL_DEBUG_BUF(3, "sending mki",  ssl->dtls_srtp_info.mki_value,
                              ssl->dtls_srtp_info.mki_len);
    }

    /*
     * total extension length: extension type (2 bytes)
     *                         + extension length (2 bytes)
     *                         + protection profile length (2 bytes)
     *                         + 2 * number of protection profiles
     *                         + srtp_mki vector length(1 byte)
     *                         + mki value
     */
    *olen = p - buf;

    return 0;
}
#endif /* MBEDTLS_SSL_DTLS_SRTP */

int mbedtls_ssl_tls12_write_client_hello_exts(mbedtls_ssl_context *ssl,
                                              unsigned char *buf,
                                              const unsigned char *end,
                                              int uses_ec,
                                              size_t *out_len)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char *p = buf;
    size_t ext_len = 0;

    (void) ssl;
    (void) end;
    (void) uses_ec;
    (void) ret;
    (void) ext_len;

    *out_len = 0;

    /* Note that TLS_EMPTY_RENEGOTIATION_INFO_SCSV is always added
     * even if MBEDTLS_SSL_RENEGOTIATION is not defined. */
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    if ((ret = ssl_write_renegotiation_ext(ssl, p, end, &ext_len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_renegotiation_ext", ret);
        return ret;
    }
    p += ext_len;
#endif

#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    if (uses_ec) {
        if ((ret = ssl_write_supported_point_formats_ext(ssl, p, end,
                                                         &ext_len)) != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_supported_point_formats_ext", ret);
            return ret;
        }
        p += ext_len;
    }
#endif

#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    if ((ret = ssl_write_ecjpake_kkpp_ext(ssl, p, end, &ext_len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_ecjpake_kkpp_ext", ret);
        return ret;
    }
    p += ext_len;
#endif

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
    if ((ret = ssl_write_cid_ext(ssl, p, end, &ext_len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_cid_ext", ret);
        return ret;
    }
    p += ext_len;
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
    if ((ret = ssl_write_max_fragment_length_ext(ssl, p, end,
                                                 &ext_len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_max_fragment_length_ext", ret);
        return ret;
    }
    p += ext_len;
#endif

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
    if ((ret = ssl_write_encrypt_then_mac_ext(ssl, p, end, &ext_len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_encrypt_then_mac_ext", ret);
        return ret;
    }
    p += ext_len;
#endif

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
    if ((ret = ssl_write_extended_ms_ext(ssl, p, end, &ext_len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_extended_ms_ext", ret);
        return ret;
    }
    p += ext_len;
#endif

#if defined(MBEDTLS_SSL_DTLS_SRTP)
    if ((ret = ssl_write_use_srtp_ext(ssl, p, end, &ext_len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_use_srtp_ext", ret);
        return ret;
    }
    p += ext_len;
#endif

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
    if ((ret = ssl_write_session_ticket_ext(ssl, p, end, &ext_len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "ssl_write_session_ticket_ext", ret);
        return ret;
    }
    p += ext_len;
#endif

    *out_len = p - buf;

    return 0;
}

MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_renegotiation_info(mbedtls_ssl_context *ssl,
                                        const unsigned char *buf,
                                        size_t len)
{
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    if (ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE) {
        /* Check verify-data in constant-time. The length OTOH is no secret */
        if (len    != 1 + ssl->verify_data_len * 2 ||
            buf[0] !=     ssl->verify_data_len * 2 ||
            mbedtls_ct_memcmp(buf + 1,
                              ssl->own_verify_data, ssl->verify_data_len) != 0 ||
            mbedtls_ct_memcmp(buf + 1 + ssl->verify_data_len,
                              ssl->peer_verify_data, ssl->verify_data_len) != 0) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("non-matching renegotiation info"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
            return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
        }
    } else
#endif /* MBEDTLS_SSL_RENEGOTIATION */
    {
        if (len != 1 || buf[0] != 0x00) {
            MBEDTLS_SSL_DEBUG_MSG(1,
                                  ("non-zero length renegotiation info"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
            return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
        }

        ssl->secure_renegotiation = MBEDTLS_SSL_SECURE_RENEGOTIATION;
    }

    return 0;
}

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_max_fragment_length_ext(mbedtls_ssl_context *ssl,
                                             const unsigned char *buf,
                                             size_t len)
{
    /*
     * server should use the extension only if we did,
     * and if so the server's value should match ours (and len is always 1)
     */
    if (ssl->conf->mfl_code == MBEDTLS_SSL_MAX_FRAG_LEN_NONE ||
        len != 1 ||
        buf[0] != ssl->conf->mfl_code) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("non-matching max fragment length extension"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
        return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
    }

    return 0;
}
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_cid_ext(mbedtls_ssl_context *ssl,
                             const unsigned char *buf,
                             size_t len)
{
    size_t peer_cid_len;

    if ( /* CID extension only makes sense in DTLS */
        ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM ||
        /* The server must only send the CID extension if we have offered it. */
        ssl->negotiate_cid == MBEDTLS_SSL_CID_DISABLED) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("CID extension unexpected"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT);
        return MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION;
    }

    if (len == 0) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("CID extension invalid"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    peer_cid_len = *buf++;
    len--;

    if (peer_cid_len > MBEDTLS_SSL_CID_OUT_LEN_MAX) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("CID extension invalid"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
        return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
    }

    if (len != peer_cid_len) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("CID extension invalid"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    ssl->handshake->cid_in_use = MBEDTLS_SSL_CID_ENABLED;
    ssl->handshake->peer_cid_len = (uint8_t) peer_cid_len;
    memcpy(ssl->handshake->peer_cid, buf, peer_cid_len);

    MBEDTLS_SSL_DEBUG_MSG(3, ("Use of CID extension negotiated"));
    MBEDTLS_SSL_DEBUG_BUF(3, "Server CID", buf, peer_cid_len);

    return 0;
}
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_encrypt_then_mac_ext(mbedtls_ssl_context *ssl,
                                          const unsigned char *buf,
                                          size_t len)
{
    if (ssl->conf->encrypt_then_mac == MBEDTLS_SSL_ETM_DISABLED ||
        len != 0) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("non-matching encrypt-then-MAC extension"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT);
        return MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION;
    }

    ((void) buf);

    ssl->session_negotiate->encrypt_then_mac = MBEDTLS_SSL_ETM_ENABLED;

    return 0;
}
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_extended_ms_ext(mbedtls_ssl_context *ssl,
                                     const unsigned char *buf,
                                     size_t len)
{
    if (ssl->conf->extended_ms == MBEDTLS_SSL_EXTENDED_MS_DISABLED ||
        len != 0) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("non-matching extended master secret extension"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT);
        return MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION;
    }

    ((void) buf);

    ssl->handshake->extended_ms = MBEDTLS_SSL_EXTENDED_MS_ENABLED;

    return 0;
}
#endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_session_ticket_ext(mbedtls_ssl_context *ssl,
                                        const unsigned char *buf,
                                        size_t len)
{
    if (ssl->conf->session_tickets == MBEDTLS_SSL_SESSION_TICKETS_DISABLED ||
        len != 0) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("non-matching session ticket extension"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT);
        return MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION;
    }

    ((void) buf);

    ssl->handshake->new_session_ticket = 1;

    return 0;
}
#endif /* MBEDTLS_SSL_SESSION_TICKETS */

#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_supported_point_formats_ext(mbedtls_ssl_context *ssl,
                                                 const unsigned char *buf,
                                                 size_t len)
{
    size_t list_size;
    const unsigned char *p;

    if (len == 0 || (size_t) (buf[0] + 1) != len) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }
    list_size = buf[0];

    p = buf + 1;
    while (list_size > 0) {
        if (p[0] == MBEDTLS_ECP_PF_UNCOMPRESSED ||
            p[0] == MBEDTLS_ECP_PF_COMPRESSED) {
#if !defined(MBEDTLS_USE_PSA_CRYPTO) && defined(MBEDTLS_ECDH_C)
            ssl->handshake->ecdh_ctx.point_format = p[0];
#endif /* !MBEDTLS_USE_PSA_CRYPTO && MBEDTLS_ECDH_C */
#if !defined(MBEDTLS_USE_PSA_CRYPTO) &&                             \
            defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
            mbedtls_ecjpake_set_point_format(&ssl->handshake->ecjpake_ctx,
                                             p[0]);
#endif /* !MBEDTLS_USE_PSA_CRYPTO && MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
            MBEDTLS_SSL_DEBUG_MSG(4, ("point format selected: %d", p[0]));
            return 0;
        }

        list_size--;
        p++;
    }

    MBEDTLS_SSL_DEBUG_MSG(1, ("no point format in common"));
    mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                   MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
    return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
}
#endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C ||
          MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */

#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_ecjpake_kkpp(mbedtls_ssl_context *ssl,
                                  const unsigned char *buf,
                                  size_t len)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if (ssl->handshake->ciphersuite_info->key_exchange !=
        MBEDTLS_KEY_EXCHANGE_ECJPAKE) {
        MBEDTLS_SSL_DEBUG_MSG(3, ("skip ecjpake kkpp extension"));
        return 0;
    }

    /* If we got here, we no longer need our cached extension */
    mbedtls_free(ssl->handshake->ecjpake_cache);
    ssl->handshake->ecjpake_cache = NULL;
    ssl->handshake->ecjpake_cache_len = 0;

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    if ((ret = mbedtls_psa_ecjpake_read_round(
             &ssl->handshake->psa_pake_ctx, buf, len,
             MBEDTLS_ECJPAKE_ROUND_ONE)) != 0) {
        psa_destroy_key(ssl->handshake->psa_pake_password);
        psa_pake_abort(&ssl->handshake->psa_pake_ctx);

        MBEDTLS_SSL_DEBUG_RET(1, "psa_pake_input round one", ret);
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
        return ret;
    }

    return 0;
#else
    if ((ret = mbedtls_ecjpake_read_round_one(&ssl->handshake->ecjpake_ctx,
                                              buf, len)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ecjpake_read_round_one", ret);
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
        return ret;
    }

    return 0;
#endif /* MBEDTLS_USE_PSA_CRYPTO */
}
#endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */

#if defined(MBEDTLS_SSL_ALPN)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_alpn_ext(mbedtls_ssl_context *ssl,
                              const unsigned char *buf, size_t len)
{
    size_t list_len, name_len;
    const char **p;

    /* If we didn't send it, the server shouldn't send it */
    if (ssl->conf->alpn_list == NULL) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("non-matching ALPN extension"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT);
        return MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION;
    }

    /*
     * opaque ProtocolName<1..2^8-1>;
     *
     * struct {
     *     ProtocolName protocol_name_list<2..2^16-1>
     * } ProtocolNameList;
     *
     * the "ProtocolNameList" MUST contain exactly one "ProtocolName"
     */

    /* Min length is 2 (list_len) + 1 (name_len) + 1 (name) */
    if (len < 4) {
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    list_len = (buf[0] << 8) | buf[1];
    if (list_len != len - 2) {
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    name_len = buf[2];
    if (name_len != list_len - 1) {
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /* Check that the server chosen protocol was in our list and save it */
    for (p = ssl->conf->alpn_list; *p != NULL; p++) {
        if (name_len == strlen(*p) &&
            memcmp(buf + 3, *p, name_len) == 0) {
            ssl->alpn_chosen = *p;
            return 0;
        }
    }

    MBEDTLS_SSL_DEBUG_MSG(1, ("ALPN extension: no matching protocol"));
    mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                   MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
    return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
}
#endif /* MBEDTLS_SSL_ALPN */

#if defined(MBEDTLS_SSL_DTLS_SRTP)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_use_srtp_ext(mbedtls_ssl_context *ssl,
                                  const unsigned char *buf,
                                  size_t len)
{
    mbedtls_ssl_srtp_profile server_protection = MBEDTLS_TLS_SRTP_UNSET;
    size_t i, mki_len = 0;
    uint16_t server_protection_profile_value = 0;

    /* If use_srtp is not configured, just ignore the extension */
    if ((ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM) ||
        (ssl->conf->dtls_srtp_profile_list == NULL) ||
        (ssl->conf->dtls_srtp_profile_list_len == 0)) {
        return 0;
    }

    /* RFC 5764 section 4.1.1
     * uint8 SRTPProtectionProfile[2];
     *
     * struct {
     *   SRTPProtectionProfiles SRTPProtectionProfiles;
     *   opaque srtp_mki<0..255>;
     * } UseSRTPData;

     * SRTPProtectionProfile SRTPProtectionProfiles<2..2^16-1>;
     *
     */
    if (ssl->conf->dtls_srtp_mki_support == MBEDTLS_SSL_DTLS_SRTP_MKI_SUPPORTED) {
        mki_len = ssl->dtls_srtp_info.mki_len;
    }

    /*
     * Length is 5 + optional mki_value : one protection profile length (2 bytes)
     *                                      + protection profile (2 bytes)
     *                                      + mki_len(1 byte)
     *                                      and optional srtp_mki
     */
    if ((len < 5) || (len != (buf[4] + 5u))) {
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /*
     * get the server protection profile
     */

    /*
     * protection profile length must be 0x0002 as we must have only
     * one protection profile in server Hello
     */
    if ((buf[0] != 0) || (buf[1] != 2)) {
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    server_protection_profile_value = (buf[2] << 8) | buf[3];
    server_protection = mbedtls_ssl_check_srtp_profile_value(
        server_protection_profile_value);
    if (server_protection != MBEDTLS_TLS_SRTP_UNSET) {
        MBEDTLS_SSL_DEBUG_MSG(3, ("found srtp profile: %s",
                                  mbedtls_ssl_get_srtp_profile_as_string(
                                      server_protection)));
    }

    ssl->dtls_srtp_info.chosen_dtls_srtp_profile = MBEDTLS_TLS_SRTP_UNSET;

    /*
     * Check we have the server profile in our list
     */
    for (i = 0; i < ssl->conf->dtls_srtp_profile_list_len; i++) {
        if (server_protection == ssl->conf->dtls_srtp_profile_list[i]) {
            ssl->dtls_srtp_info.chosen_dtls_srtp_profile = ssl->conf->dtls_srtp_profile_list[i];
            MBEDTLS_SSL_DEBUG_MSG(3, ("selected srtp profile: %s",
                                      mbedtls_ssl_get_srtp_profile_as_string(
                                          server_protection)));
            break;
        }
    }

    /* If no match was found : server problem, it shall never answer with incompatible profile */
    if (ssl->dtls_srtp_info.chosen_dtls_srtp_profile == MBEDTLS_TLS_SRTP_UNSET) {
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }

    /* If server does not use mki in its reply, make sure the client won't keep
     * one as negotiated */
    if (len == 5) {
        ssl->dtls_srtp_info.mki_len = 0;
    }

    /*
     * RFC5764:
     *  If the client detects a nonzero-length MKI in the server's response
     *  that is different than the one the client offered, then the client
     *  MUST abort the handshake and SHOULD send an invalid_parameter alert.
     */
    if (len > 5  && (buf[4] != mki_len ||
                     (memcmp(ssl->dtls_srtp_info.mki_value, &buf[5], mki_len)))) {
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
        return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
    }
#if defined(MBEDTLS_DEBUG_C)
    if (len > 5) {
        MBEDTLS_SSL_DEBUG_BUF(3, "received mki", ssl->dtls_srtp_info.mki_value,
                              ssl->dtls_srtp_info.mki_len);
    }
#endif
    return 0;
}
#endif /* MBEDTLS_SSL_DTLS_SRTP */

/*
 * Parse HelloVerifyRequest.  Only called after verifying the HS type.
 */
#if defined(MBEDTLS_SSL_PROTO_DTLS)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_hello_verify_request(mbedtls_ssl_context *ssl)
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
    const unsigned char *p = ssl->in_msg + mbedtls_ssl_hs_hdr_len(ssl);
    uint16_t dtls_legacy_version;

#if !defined(MBEDTLS_SSL_PROTO_TLS1_3)
    uint8_t cookie_len;
#else
    uint16_t cookie_len;
#endif

    MBEDTLS_SSL_DEBUG_MSG(2, ("=> parse hello verify request"));

    /* Check that there is enough room for:
     * - 2 bytes of version
     * - 1 byte of cookie_len
     */
    if (mbedtls_ssl_hs_hdr_len(ssl) + 3 > ssl->in_msglen) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("incoming HelloVerifyRequest message is too short"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /*
     * struct {
     *   ProtocolVersion server_version;
     *   opaque cookie<0..2^8-1>;
     * } HelloVerifyRequest;
     */
    MBEDTLS_SSL_DEBUG_BUF(3, "server version", p, 2);
    dtls_legacy_version = MBEDTLS_GET_UINT16_BE(p, 0);
    p += 2;

    /*
     * Since the RFC is not clear on this point, accept DTLS 1.0 (0xfeff)
     * The DTLS 1.3 (current draft) renames ProtocolVersion server_version to
     * legacy_version and locks the value of legacy_version to 0xfefd (DTLS 1.2)
     */
    if (dtls_legacy_version != 0xfefd && dtls_legacy_version != 0xfeff) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server version"));

        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION);

        return MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION;
    }

    cookie_len = *p++;
    if ((ssl->in_msg + ssl->in_msglen) - p < cookie_len) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("cookie length does not match incoming message size"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }
    MBEDTLS_SSL_DEBUG_BUF(3, "cookie", p, cookie_len);

    mbedtls_free(ssl->handshake->cookie);

    ssl->handshake->cookie = mbedtls_calloc(1, cookie_len);
    if (ssl->handshake->cookie  == NULL) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("alloc failed (%d bytes)", cookie_len));
        return MBEDTLS_ERR_SSL_ALLOC_FAILED;
    }

    memcpy(ssl->handshake->cookie, p, cookie_len);
    ssl->handshake->cookie_len = cookie_len;

    /* Start over at ClientHello */
    ssl->state = MBEDTLS_SSL_CLIENT_HELLO;
    ret = mbedtls_ssl_reset_checksum(ssl);
    if (0 != ret) {
        MBEDTLS_SSL_DEBUG_RET(1, ("mbedtls_ssl_reset_checksum"), ret);
        return ret;
    }

    mbedtls_ssl_recv_flight_completed(ssl);

    MBEDTLS_SSL_DEBUG_MSG(2, ("<= parse hello verify request"));

    return 0;
}
#endif /* MBEDTLS_SSL_PROTO_DTLS */

MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_server_hello(mbedtls_ssl_context *ssl)
{
    int ret, i;
    size_t n;
    size_t ext_len;
    unsigned char *buf, *ext;
    unsigned char comp;
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    int renegotiation_info_seen = 0;
#endif
    int handshake_failure = 0;
    const mbedtls_ssl_ciphersuite_t *suite_info;

    MBEDTLS_SSL_DEBUG_MSG(2, ("=> parse server hello"));

    if ((ret = mbedtls_ssl_read_record(ssl, 1)) != 0) {
        /* No alert on a read error. */
        MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ssl_read_record", ret);
        return ret;
    }

    buf = ssl->in_msg;

    if (ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE) {
#if defined(MBEDTLS_SSL_RENEGOTIATION)
        if (ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS) {
            ssl->renego_records_seen++;

            if (ssl->conf->renego_max_records >= 0 &&
                ssl->renego_records_seen > ssl->conf->renego_max_records) {
                MBEDTLS_SSL_DEBUG_MSG(1,
                                      ("renegotiation requested, but not honored by server"));
                return MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE;
            }

            MBEDTLS_SSL_DEBUG_MSG(1,
                                  ("non-handshake message during renegotiation"));

            ssl->keep_current_message = 1;
            return MBEDTLS_ERR_SSL_WAITING_SERVER_HELLO_RENEGO;
        }
#endif /* MBEDTLS_SSL_RENEGOTIATION */

        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE);
        return MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE;
    }

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if (ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM) {
        if (buf[0] == MBEDTLS_SSL_HS_HELLO_VERIFY_REQUEST) {
            MBEDTLS_SSL_DEBUG_MSG(2, ("received hello verify request"));
            MBEDTLS_SSL_DEBUG_MSG(2, ("<= parse server hello"));
            return ssl_parse_hello_verify_request(ssl);
        } else {
            /* We made it through the verification process */
            mbedtls_free(ssl->handshake->cookie);
            ssl->handshake->cookie = NULL;
            ssl->handshake->cookie_len = 0;
        }
    }
#endif /* MBEDTLS_SSL_PROTO_DTLS */

    if (ssl->in_hslen < 38 + mbedtls_ssl_hs_hdr_len(ssl) ||
        buf[0] != MBEDTLS_SSL_HS_SERVER_HELLO) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /*
     *  0   .  1    server_version
     *  2   . 33    random (maybe including 4 bytes of Unix time)
     * 34   . 34    session_id length = n
     * 35   . 34+n  session_id
     * 35+n . 36+n  cipher_suite
     * 37+n . 37+n  compression_method
     *
     * 38+n . 39+n  extensions length (optional)
     * 40+n .  ..   extensions
     */
    buf += mbedtls_ssl_hs_hdr_len(ssl);

    MBEDTLS_SSL_DEBUG_BUF(3, "server hello, version", buf, 2);
    ssl->tls_version = mbedtls_ssl_read_version(buf, ssl->conf->transport);
    ssl->session_negotiate->tls_version = ssl->tls_version;

    if (ssl->tls_version < ssl->conf->min_tls_version ||
        ssl->tls_version > ssl->conf->max_tls_version) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              (
                                  "server version out of bounds -  min: [0x%x], server: [0x%x], max: [0x%x]",
                                  (unsigned) ssl->conf->min_tls_version,
                                  (unsigned) ssl->tls_version,
                                  (unsigned) ssl->conf->max_tls_version));

        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION);

        return MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION;
    }

    MBEDTLS_SSL_DEBUG_MSG(3, ("server hello, current time: %lu",
                              ((unsigned long) buf[2] << 24) |
                              ((unsigned long) buf[3] << 16) |
                              ((unsigned long) buf[4] <<  8) |
                              ((unsigned long) buf[5])));

    memcpy(ssl->handshake->randbytes + 32, buf + 2, 32);

    n = buf[34];

    MBEDTLS_SSL_DEBUG_BUF(3,   "server hello, random bytes", buf + 2, 32);

    if (n > 32) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    if (ssl->in_hslen > mbedtls_ssl_hs_hdr_len(ssl) + 39 + n) {
        ext_len = ((buf[38 + n] <<  8)
                   | (buf[39 + n]));

        if ((ext_len > 0 && ext_len < 4) ||
            ssl->in_hslen != mbedtls_ssl_hs_hdr_len(ssl) + 40 + n + ext_len) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
            return MBEDTLS_ERR_SSL_DECODE_ERROR;
        }
    } else if (ssl->in_hslen == mbedtls_ssl_hs_hdr_len(ssl) + 38 + n) {
        ext_len = 0;
    } else {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /* ciphersuite (used later) */
    i = (buf[35 + n] << 8) | buf[36 + n];

    /*
     * Read and check compression
     */
    comp = buf[37 + n];

    if (comp != MBEDTLS_SSL_COMPRESS_NULL) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("server hello, bad compression: %d", comp));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
        return MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
    }

    /*
     * Initialize update checksum functions
     */
    ssl->handshake->ciphersuite_info = mbedtls_ssl_ciphersuite_from_id(i);
    if (ssl->handshake->ciphersuite_info == NULL) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("ciphersuite info for %04x not found", (unsigned int) i));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR);
        return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
    }

    mbedtls_ssl_optimize_checksum(ssl, ssl->handshake->ciphersuite_info);

    MBEDTLS_SSL_DEBUG_MSG(3, ("server hello, session id len.: %" MBEDTLS_PRINTF_SIZET, n));
    MBEDTLS_SSL_DEBUG_BUF(3,   "server hello, session id", buf + 35, n);

    /*
     * Check if the session can be resumed
     */
    if (ssl->handshake->resume == 0 || n == 0 ||
#if defined(MBEDTLS_SSL_RENEGOTIATION)
        ssl->renego_status != MBEDTLS_SSL_INITIAL_HANDSHAKE ||
#endif
        ssl->session_negotiate->ciphersuite != i ||
        ssl->session_negotiate->id_len != n ||
        memcmp(ssl->session_negotiate->id, buf + 35, n) != 0) {
        ssl->state++;
        ssl->handshake->resume = 0;
#if defined(MBEDTLS_HAVE_TIME)
        ssl->session_negotiate->start = mbedtls_time(NULL);
#endif
        ssl->session_negotiate->ciphersuite = i;
        ssl->session_negotiate->id_len = n;
        memcpy(ssl->session_negotiate->id, buf + 35, n);
    } else {
        ssl->state = MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC;
    }

    MBEDTLS_SSL_DEBUG_MSG(3, ("%s session has been resumed",
                              ssl->handshake->resume ? "a" : "no"));

    MBEDTLS_SSL_DEBUG_MSG(3, ("server hello, chosen ciphersuite: %04x", (unsigned) i));
    MBEDTLS_SSL_DEBUG_MSG(3, ("server hello, compress alg.: %d",
                              buf[37 + n]));

    /*
     * Perform cipher suite validation in same way as in ssl_write_client_hello.
     */
    i = 0;
    while (1) {
        if (ssl->conf->ciphersuite_list[i] == 0) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
            return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
        }

        if (ssl->conf->ciphersuite_list[i++] ==
            ssl->session_negotiate->ciphersuite) {
            break;
        }
    }

    suite_info = mbedtls_ssl_ciphersuite_from_id(
        ssl->session_negotiate->ciphersuite);
    if (mbedtls_ssl_validate_ciphersuite(ssl, suite_info, ssl->tls_version,
                                         ssl->tls_version) != 0) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }

    MBEDTLS_SSL_DEBUG_MSG(3,
                          ("server hello, chosen ciphersuite: %s", suite_info->name));

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if (suite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA &&
        ssl->tls_version == MBEDTLS_SSL_VERSION_TLS1_2) {
        ssl->handshake->ecrs_enabled = 1;
    }
#endif

    if (comp != MBEDTLS_SSL_COMPRESS_NULL) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
        return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
    }

    ext = buf + 40 + n;

    MBEDTLS_SSL_DEBUG_MSG(2,
                          ("server hello, total extension length: %" MBEDTLS_PRINTF_SIZET,
                           ext_len));

    while (ext_len) {
        unsigned int ext_id   = ((ext[0] <<  8)
                                 | (ext[1]));
        unsigned int ext_size = ((ext[2] <<  8)
                                 | (ext[3]));

        if (ext_size + 4 > ext_len) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
            mbedtls_ssl_send_alert_message(
                ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
            return MBEDTLS_ERR_SSL_DECODE_ERROR;
        }

        switch (ext_id) {
            case MBEDTLS_TLS_EXT_RENEGOTIATION_INFO:
                MBEDTLS_SSL_DEBUG_MSG(3, ("found renegotiation extension"));
#if defined(MBEDTLS_SSL_RENEGOTIATION)
                renegotiation_info_seen = 1;
#endif

                if ((ret = ssl_parse_renegotiation_info(ssl, ext + 4,
                                                        ext_size)) != 0) {
                    return ret;
                }

                break;

#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
            case MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH:
                MBEDTLS_SSL_DEBUG_MSG(3,
                                      ("found max_fragment_length extension"));

                if ((ret = ssl_parse_max_fragment_length_ext(ssl,
                                                             ext + 4, ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */

#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
            case MBEDTLS_TLS_EXT_CID:
                MBEDTLS_SSL_DEBUG_MSG(3, ("found CID extension"));

                if ((ret = ssl_parse_cid_ext(ssl,
                                             ext + 4,
                                             ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */

#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
            case MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC:
                MBEDTLS_SSL_DEBUG_MSG(3, ("found encrypt_then_mac extension"));

                if ((ret = ssl_parse_encrypt_then_mac_ext(ssl,
                                                          ext + 4, ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */

#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
            case MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET:
                MBEDTLS_SSL_DEBUG_MSG(3,
                                      ("found extended_master_secret extension"));

                if ((ret = ssl_parse_extended_ms_ext(ssl,
                                                     ext + 4, ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
            case MBEDTLS_TLS_EXT_SESSION_TICKET:
                MBEDTLS_SSL_DEBUG_MSG(3, ("found session_ticket extension"));

                if ((ret = ssl_parse_session_ticket_ext(ssl,
                                                        ext + 4, ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_SSL_SESSION_TICKETS */

#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
                defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
            case MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS:
                MBEDTLS_SSL_DEBUG_MSG(3,
                                      ("found supported_point_formats extension"));

                if ((ret = ssl_parse_supported_point_formats_ext(ssl,
                                                                 ext + 4, ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C ||
          MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */

#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
            case MBEDTLS_TLS_EXT_ECJPAKE_KKPP:
                MBEDTLS_SSL_DEBUG_MSG(3, ("found ecjpake_kkpp extension"));

                if ((ret = ssl_parse_ecjpake_kkpp(ssl,
                                                  ext + 4, ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */

#if defined(MBEDTLS_SSL_ALPN)
            case MBEDTLS_TLS_EXT_ALPN:
                MBEDTLS_SSL_DEBUG_MSG(3, ("found alpn extension"));

                if ((ret = ssl_parse_alpn_ext(ssl, ext + 4, ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_SSL_ALPN */

#if defined(MBEDTLS_SSL_DTLS_SRTP)
            case MBEDTLS_TLS_EXT_USE_SRTP:
                MBEDTLS_SSL_DEBUG_MSG(3, ("found use_srtp extension"));

                if ((ret = ssl_parse_use_srtp_ext(ssl, ext + 4, ext_size)) != 0) {
                    return ret;
                }

                break;
#endif /* MBEDTLS_SSL_DTLS_SRTP */

            default:
                MBEDTLS_SSL_DEBUG_MSG(3,
                                      ("unknown extension found: %u (ignoring)", ext_id));
        }

        ext_len -= 4 + ext_size;
        ext += 4 + ext_size;

        if (ext_len > 0 && ext_len < 4) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello message"));
            return MBEDTLS_ERR_SSL_DECODE_ERROR;
        }
    }

    /*
     * mbedtls_ssl_derive_keys() has to be called after the parsing of the
     * extensions. It sets the transform data for the resumed session which in
     * case of DTLS includes the server CID extracted from the CID extension.
     */
    if (ssl->handshake->resume) {
        if ((ret = mbedtls_ssl_derive_keys(ssl)) != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ssl_derive_keys", ret);
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR);
            return ret;
        }
    }

    /*
     * Renegotiation security checks
     */
    if (ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
        ssl->conf->allow_legacy_renegotiation ==
        MBEDTLS_SSL_LEGACY_BREAK_HANDSHAKE) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("legacy renegotiation, breaking off handshake"));
        handshake_failure = 1;
    }
#if defined(MBEDTLS_SSL_RENEGOTIATION)
    else if (ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
             ssl->secure_renegotiation == MBEDTLS_SSL_SECURE_RENEGOTIATION &&
             renegotiation_info_seen == 0) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("renegotiation_info extension missing (secure)"));
        handshake_failure = 1;
    } else if (ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
               ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
               ssl->conf->allow_legacy_renegotiation ==
               MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("legacy renegotiation not allowed"));
        handshake_failure = 1;
    } else if (ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
               ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
               renegotiation_info_seen == 1) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("renegotiation_info extension present (legacy)"));
        handshake_failure = 1;
    }
#endif /* MBEDTLS_SSL_RENEGOTIATION */

    if (handshake_failure == 1) {
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }

    MBEDTLS_SSL_DEBUG_MSG(2, ("<= parse server hello"));

    return 0;
}

#if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
    defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_server_dh_params(mbedtls_ssl_context *ssl,
                                      unsigned char **p,
                                      unsigned char *end)
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
    size_t dhm_actual_bitlen;

    /*
     * Ephemeral DH parameters:
     *
     * struct {
     *     opaque dh_p<1..2^16-1>;
     *     opaque dh_g<1..2^16-1>;
     *     opaque dh_Ys<1..2^16-1>;
     * } ServerDHParams;
     */
    if ((ret = mbedtls_dhm_read_params(&ssl->handshake->dhm_ctx,
                                       p, end)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(2, ("mbedtls_dhm_read_params"), ret);
        return ret;
    }

    dhm_actual_bitlen = mbedtls_dhm_get_bitlen(&ssl->handshake->dhm_ctx);
    if (dhm_actual_bitlen < ssl->conf->dhm_min_bitlen) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("DHM prime too short: %" MBEDTLS_PRINTF_SIZET " < %u",
                                  dhm_actual_bitlen,
                                  ssl->conf->dhm_min_bitlen));
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }

    MBEDTLS_SSL_DEBUG_MPI(3, "DHM: P ", &ssl->handshake->dhm_ctx.P);
    MBEDTLS_SSL_DEBUG_MPI(3, "DHM: G ", &ssl->handshake->dhm_ctx.G);
    MBEDTLS_SSL_DEBUG_MPI(3, "DHM: GY", &ssl->handshake->dhm_ctx.GY);

    return ret;
}
#endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */

#if defined(MBEDTLS_USE_PSA_CRYPTO)
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)   ||   \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)   ||   \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_server_ecdh_params(mbedtls_ssl_context *ssl,
                                        unsigned char **p,
                                        unsigned char *end)
{
    uint16_t tls_id;
    uint8_t ecpoint_len;
    mbedtls_ssl_handshake_params *handshake = ssl->handshake;
    psa_key_type_t key_type = PSA_KEY_TYPE_NONE;
    size_t ec_bits = 0;

    /*
     * struct {
     *     ECParameters curve_params;
     *     ECPoint      public;
     * } ServerECDHParams;
     *
     *  1       curve_type (must be "named_curve")
     *  2..3    NamedCurve
     *  4       ECPoint.len
     *  5+      ECPoint contents
     */
    if (end - *p < 4) {
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /* First byte is curve_type; only named_curve is handled */
    if (*(*p)++ != MBEDTLS_ECP_TLS_NAMED_CURVE) {
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }

    /* Next two bytes are the namedcurve value */
    tls_id = *(*p)++;
    tls_id <<= 8;
    tls_id |= *(*p)++;

    /* Check it's a curve we offered */
    if (mbedtls_ssl_check_curve_tls_id(ssl, tls_id) != 0) {
        MBEDTLS_SSL_DEBUG_MSG(2,
                              ("bad server key exchange message (ECDHE curve): %u",
                               (unsigned) tls_id));
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }

    /* Convert EC's TLS ID to PSA key type. */
    if (mbedtls_ssl_get_psa_curve_info_from_tls_id(tls_id, &key_type,
                                                   &ec_bits) == PSA_ERROR_NOT_SUPPORTED) {
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }
    handshake->xxdh_psa_type = key_type;
    handshake->xxdh_bits = ec_bits;

    /* Keep a copy of the peer's public key */
    ecpoint_len = *(*p)++;
    if ((size_t) (end - *p) < ecpoint_len) {
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /* When FFDH is enabled, the array handshake->xxdh_psa_peer_key size takes into account
       the sizes of the FFDH keys which are at least 2048 bits.
       The size of the array is thus greater than 256 bytes which is greater than any
       possible value of ecpoint_len (type uint8_t) and the check below can be skipped.*/
#if !defined(PSA_WANT_ALG_FFDH)
    if (ecpoint_len > sizeof(handshake->xxdh_psa_peerkey)) {
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }
#else
    MBEDTLS_STATIC_ASSERT(sizeof(handshake->xxdh_psa_peerkey) >= UINT8_MAX,
                          "peer key buffer too small");
#endif

    memcpy(handshake->xxdh_psa_peerkey, *p, ecpoint_len);
    handshake->xxdh_psa_peerkey_len = ecpoint_len;
    *p += ecpoint_len;

    return 0;
}
#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED   ||
          MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED   ||
          MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED */
#else
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)   ||   \
    defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED)    ||   \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)   ||   \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) ||   \
    defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_check_server_ecdh_params(const mbedtls_ssl_context *ssl)
{
    uint16_t tls_id;
    mbedtls_ecp_group_id grp_id;
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
    grp_id = ssl->handshake->ecdh_ctx.grp.id;
#else
    grp_id = ssl->handshake->ecdh_ctx.grp_id;
#endif

    tls_id = mbedtls_ssl_get_tls_id_from_ecp_group_id(grp_id);
    if (tls_id == 0) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
        return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
    }

    MBEDTLS_SSL_DEBUG_MSG(2, ("ECDH curve: %s",
                              mbedtls_ssl_get_curve_name_from_tls_id(tls_id)));

    if (mbedtls_ssl_check_curve(ssl, grp_id) != 0) {
        return -1;
    }

    MBEDTLS_SSL_DEBUG_ECDH(3, &ssl->handshake->ecdh_ctx,
                           MBEDTLS_DEBUG_ECDH_QP);

    return 0;
}

#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED   ||
          MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED    ||
          MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED   ||
          MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */

#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||     \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED) ||     \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_server_ecdh_params(mbedtls_ssl_context *ssl,
                                        unsigned char **p,
                                        unsigned char *end)
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;

    /*
     * Ephemeral ECDH parameters:
     *
     * struct {
     *     ECParameters curve_params;
     *     ECPoint      public;
     * } ServerECDHParams;
     */
    if ((ret = mbedtls_ecdh_read_params(&ssl->handshake->ecdh_ctx,
                                        (const unsigned char **) p, end)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, ("mbedtls_ecdh_read_params"), ret);
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
        if (ret == MBEDTLS_ERR_ECP_IN_PROGRESS) {
            ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
        }
#endif
        return ret;
    }

    if (ssl_check_server_ecdh_params(ssl) != 0) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("bad server key exchange message (ECDHE curve)"));
        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
    }

    return ret;
}
#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED || \
          MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED || \
          MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED */
#endif /* !MBEDTLS_USE_PSA_CRYPTO */
#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_server_psk_hint(mbedtls_ssl_context *ssl,
                                     unsigned char **p,
                                     unsigned char *end)
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
    uint16_t  len;
    ((void) ssl);

    /*
     * PSK parameters:
     *
     * opaque psk_identity_hint<0..2^16-1>;
     */
    if (end - (*p) < 2) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("bad server key exchange message (psk_identity_hint length)"));
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }
    len = (*p)[0] << 8 | (*p)[1];
    *p += 2;

    if (end - (*p) < len) {
        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("bad server key exchange message (psk_identity_hint length)"));
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /*
     * Note: we currently ignore the PSK identity hint, as we only allow one
     * PSK to be provisioned on the client. This could be changed later if
     * someone needs that feature.
     */
    *p += len;
    ret = 0;

    return ret;
}
#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */

#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED) ||                           \
    defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
/*
 * Generate a pre-master secret and encrypt it with the server's RSA key
 */
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_encrypted_pms(mbedtls_ssl_context *ssl,
                                   size_t offset, size_t *olen,
                                   size_t pms_offset)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len_bytes = 2;
    unsigned char *p = ssl->handshake->premaster + pms_offset;
    mbedtls_pk_context *peer_pk;

    if (offset + len_bytes > MBEDTLS_SSL_OUT_CONTENT_LEN) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("buffer too small for encrypted pms"));
        return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;
    }

    /*
     * Generate (part of) the pre-master as
     *  struct {
     *      ProtocolVersion client_version;
     *      opaque random[46];
     *  } PreMasterSecret;
     */
    mbedtls_ssl_write_version(p, ssl->conf->transport,
                              MBEDTLS_SSL_VERSION_TLS1_2);

    if ((ret = ssl->conf->f_rng(ssl->conf->p_rng, p + 2, 46)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "f_rng", ret);
        return ret;
    }

    ssl->handshake->pmslen = 48;

#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    peer_pk = &ssl->handshake->peer_pubkey;
#else /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    if (ssl->session_negotiate->peer_cert == NULL) {
        /* Should never happen */
        MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
        return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
    }
    peer_pk = &ssl->session_negotiate->peer_cert->pk;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

    /*
     * Now write it out, encrypted
     */
    if (!mbedtls_pk_can_do(peer_pk, MBEDTLS_PK_RSA)) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("certificate key type mismatch"));
        return MBEDTLS_ERR_SSL_PK_TYPE_MISMATCH;
    }

    if ((ret = mbedtls_pk_encrypt(peer_pk,
                                  p, ssl->handshake->pmslen,
                                  ssl->out_msg + offset + len_bytes, olen,
                                  MBEDTLS_SSL_OUT_CONTENT_LEN - offset - len_bytes,
                                  ssl->conf->f_rng, ssl->conf->p_rng)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_rsa_pkcs1_encrypt", ret);
        return ret;
    }

    if (len_bytes == 2) {
        MBEDTLS_PUT_UINT16_BE(*olen, ssl->out_msg, offset);
        *olen += 2;
    }

#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    /* We don't need the peer's public key anymore. Free it. */
    mbedtls_pk_free(peer_pk);
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    return 0;
}
#endif /* MBEDTLS_KEY_EXCHANGE_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */

#if defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) || \
    defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_get_ecdh_params_from_cert(mbedtls_ssl_context *ssl)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_pk_context *peer_pk;

#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    peer_pk = &ssl->handshake->peer_pubkey;
#else /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    if (ssl->session_negotiate->peer_cert == NULL) {
        /* Should never happen */
        MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
        return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
    }
    peer_pk = &ssl->session_negotiate->peer_cert->pk;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

    /* This is a public key, so it can't be opaque, so can_do() is a good
     * enough check to ensure pk_ec() is safe to use below. */
    if (!mbedtls_pk_can_do(peer_pk, MBEDTLS_PK_ECKEY)) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("server key not ECDH capable"));
        return MBEDTLS_ERR_SSL_PK_TYPE_MISMATCH;
    }

#if defined(MBEDTLS_ECP_C)
    const mbedtls_ecp_keypair *peer_key = mbedtls_pk_ec_ro(*peer_pk);
#endif /* MBEDTLS_ECP_C */

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    uint16_t tls_id = 0;
    psa_key_type_t key_type = PSA_KEY_TYPE_NONE;
    mbedtls_ecp_group_id grp_id = mbedtls_pk_get_group_id(peer_pk);

    if (mbedtls_ssl_check_curve(ssl, grp_id) != 0) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server certificate (ECDH curve)"));
        return MBEDTLS_ERR_SSL_BAD_CERTIFICATE;
    }

    tls_id = mbedtls_ssl_get_tls_id_from_ecp_group_id(grp_id);
    if (tls_id == 0) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("ECC group %u not suported",
                                  grp_id));
        return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
    }

    /* If the above conversion to TLS ID was fine, then also this one will be,
       so there is no need to check the return value here */
    mbedtls_ssl_get_psa_curve_info_from_tls_id(tls_id, &key_type,
                                               &ssl->handshake->xxdh_bits);

    ssl->handshake->xxdh_psa_type = key_type;

    /* Store peer's public key in psa format. */
#if defined(MBEDTLS_PK_USE_PSA_EC_DATA)
    memcpy(ssl->handshake->xxdh_psa_peerkey, peer_pk->pub_raw, peer_pk->pub_raw_len);
    ssl->handshake->xxdh_psa_peerkey_len = peer_pk->pub_raw_len;
    ret = 0;
#else /* MBEDTLS_PK_USE_PSA_EC_DATA */
    size_t olen = 0;
    ret = mbedtls_ecp_point_write_binary(&peer_key->grp, &peer_key->Q,
                                         MBEDTLS_ECP_PF_UNCOMPRESSED, &olen,
                                         ssl->handshake->xxdh_psa_peerkey,
                                         MBEDTLS_PSA_MAX_EC_PUBKEY_LENGTH);

    if (ret != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, ("mbedtls_ecp_point_write_binary"), ret);
        return ret;
    }
    ssl->handshake->xxdh_psa_peerkey_len = olen;
#endif /* MBEDTLS_PK_USE_PSA_EC_DATA */
#else /* MBEDTLS_USE_PSA_CRYPTO */
    if ((ret = mbedtls_ecdh_get_params(&ssl->handshake->ecdh_ctx, peer_key,
                                       MBEDTLS_ECDH_THEIRS)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, ("mbedtls_ecdh_get_params"), ret);
        return ret;
    }

    if (ssl_check_server_ecdh_params(ssl) != 0) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server certificate (ECDH curve)"));
        return MBEDTLS_ERR_SSL_BAD_CERTIFICATE;
    }
#endif /* MBEDTLS_USE_PSA_CRYPTO */
#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    /* We don't need the peer's public key anymore. Free it,
     * so that more RAM is available for upcoming expensive
     * operations like ECDHE. */
    mbedtls_pk_free(peer_pk);
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

    return ret;
}
#endif /* MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) ||
          MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */

MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_server_key_exchange(mbedtls_ssl_context *ssl)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    unsigned char *p = NULL, *end = NULL;

    MBEDTLS_SSL_DEBUG_MSG(2, ("=> parse server key exchange"));

#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA) {
        MBEDTLS_SSL_DEBUG_MSG(2, ("<= skip parse server key exchange"));
        ssl->state++;
        return 0;
    }
    ((void) p);
    ((void) end);
#endif

#if defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) || \
    defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_RSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA) {
        if ((ret = ssl_get_ecdh_params_from_cert(ssl)) != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "ssl_get_ecdh_params_from_cert", ret);
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
            return ret;
        }

        MBEDTLS_SSL_DEBUG_MSG(2, ("<= skip parse server key exchange"));
        ssl->state++;
        return 0;
    }
    ((void) p);
    ((void) end);
#endif /* MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if (ssl->handshake->ecrs_enabled &&
        ssl->handshake->ecrs_state == ssl_ecrs_ske_start_processing) {
        goto start_processing;
    }
#endif

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

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

    /*
     * ServerKeyExchange may be skipped with PSK and RSA-PSK when the server
     * doesn't use a psk_identity_hint
     */
    if (ssl->in_msg[0] != MBEDTLS_SSL_HS_SERVER_KEY_EXCHANGE) {
        if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK ||
            ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK) {
            /* Current message is probably either
             * CertificateRequest or ServerHelloDone */
            ssl->keep_current_message = 1;
            goto exit;
        }

        MBEDTLS_SSL_DEBUG_MSG(1,
                              ("server key exchange message must not be skipped"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE);

        return MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE;
    }

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if (ssl->handshake->ecrs_enabled) {
        ssl->handshake->ecrs_state = ssl_ecrs_ske_start_processing;
    }

start_processing:
#endif
    p   = ssl->in_msg + mbedtls_ssl_hs_hdr_len(ssl);
    end = ssl->in_msg + ssl->in_hslen;
    MBEDTLS_SSL_DEBUG_BUF(3,   "server key exchange", p, end - p);

#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK) {
        if (ssl_parse_server_psk_hint(ssl, &p, end) != 0) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server key exchange message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
            return MBEDTLS_ERR_SSL_DECODE_ERROR;
        }
    } /* FALLTHROUGH */
#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */

#if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED) ||                       \
    defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK) {
        ; /* nothing more to do */
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_PSK_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
    defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_RSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK) {
        if (ssl_parse_server_dh_params(ssl, &p, end) != 0) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server key exchange message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
            return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
        }
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||     \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED) ||     \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_RSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA) {
        if (ssl_parse_server_ecdh_params(ssl, &p, end) != 0) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server key exchange message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
            return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
        }
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE) {
#if defined(MBEDTLS_USE_PSA_CRYPTO)
        /*
         * The first 3 bytes are:
         * [0] MBEDTLS_ECP_TLS_NAMED_CURVE
         * [1, 2] elliptic curve's TLS ID
         *
         * However since we only support secp256r1 for now, we check only
         * that TLS ID here
         */
        uint16_t read_tls_id = MBEDTLS_GET_UINT16_BE(p, 1);
        uint16_t exp_tls_id = mbedtls_ssl_get_tls_id_from_ecp_group_id(
            MBEDTLS_ECP_DP_SECP256R1);

        if (exp_tls_id == 0) {
            return MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
        }

        if ((*p != MBEDTLS_ECP_TLS_NAMED_CURVE) ||
            (read_tls_id != exp_tls_id)) {
            return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
        }

        p += 3;

        if ((ret = mbedtls_psa_ecjpake_read_round(
                 &ssl->handshake->psa_pake_ctx, p, end - p,
                 MBEDTLS_ECJPAKE_ROUND_TWO)) != 0) {
            psa_destroy_key(ssl->handshake->psa_pake_password);
            psa_pake_abort(&ssl->handshake->psa_pake_ctx);

            MBEDTLS_SSL_DEBUG_RET(1, "psa_pake_input round two", ret);
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
            return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
        }
#else
        ret = mbedtls_ecjpake_read_round_two(&ssl->handshake->ecjpake_ctx,
                                             p, end - p);
        if (ret != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ecjpake_read_round_two", ret);
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
            return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
        }
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
    {
        MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
        return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
    }

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED)
    if (mbedtls_ssl_ciphersuite_uses_server_signature(ciphersuite_info)) {
        size_t sig_len, hashlen;
        unsigned char hash[MBEDTLS_MD_MAX_SIZE];

        mbedtls_md_type_t md_alg = MBEDTLS_MD_NONE;
        mbedtls_pk_type_t pk_alg = MBEDTLS_PK_NONE;
        unsigned char *params = ssl->in_msg + mbedtls_ssl_hs_hdr_len(ssl);
        size_t params_len = p - params;
        void *rs_ctx = NULL;
        uint16_t sig_alg;

        mbedtls_pk_context *peer_pk;

#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
        peer_pk = &ssl->handshake->peer_pubkey;
#else /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
        if (ssl->session_negotiate->peer_cert == NULL) {
            /* Should never happen */
            MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
            return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        }
        peer_pk = &ssl->session_negotiate->peer_cert->pk;
#endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

        /*
         * Handle the digitally-signed structure
         */
        MBEDTLS_SSL_CHK_BUF_READ_PTR(p, end, 2);
        sig_alg = MBEDTLS_GET_UINT16_BE(p, 0);
        if (mbedtls_ssl_get_pk_type_and_md_alg_from_sig_alg(
                sig_alg, &pk_alg, &md_alg) != 0 &&
            !mbedtls_ssl_sig_alg_is_offered(ssl, sig_alg) &&
            !mbedtls_ssl_sig_alg_is_supported(ssl, sig_alg)) {
            MBEDTLS_SSL_DEBUG_MSG(1,
                                  ("bad server key exchange message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
            return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
        }
        p += 2;

        if (!mbedtls_pk_can_do(peer_pk, pk_alg)) {
            MBEDTLS_SSL_DEBUG_MSG(1,
                                  ("bad server key exchange message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER);
            return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
        }

        /*
         * Read signature
         */

        if (p > end - 2) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server key exchange message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
            return MBEDTLS_ERR_SSL_DECODE_ERROR;
        }
        sig_len = (p[0] << 8) | p[1];
        p += 2;

        if (p != end - sig_len) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server key exchange message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
            return MBEDTLS_ERR_SSL_DECODE_ERROR;
        }

        MBEDTLS_SSL_DEBUG_BUF(3, "signature", p, sig_len);

        /*
         * Compute the hash that has been signed
         */
        if (md_alg != MBEDTLS_MD_NONE) {
            ret = mbedtls_ssl_get_key_exchange_md_tls1_2(ssl, hash, &hashlen,
                                                         params, params_len,
                                                         md_alg);
            if (ret != 0) {
                return ret;
            }
        } else {
            MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
            return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        }

        MBEDTLS_SSL_DEBUG_BUF(3, "parameters hash", hash, hashlen);

        /*
         * Verify signature
         */
        if (!mbedtls_pk_can_do(peer_pk, pk_alg)) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad server key exchange message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE);
            return MBEDTLS_ERR_SSL_PK_TYPE_MISMATCH;
        }

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
        if (ssl->handshake->ecrs_enabled) {
            rs_ctx = &ssl->handshake->ecrs_ctx.pk;
        }
#endif

#if defined(MBEDTLS_X509_RSASSA_PSS_SUPPORT)
        if (pk_alg == MBEDTLS_PK_RSASSA_PSS) {
            mbedtls_pk_rsassa_pss_options rsassa_pss_options;
            rsassa_pss_options.mgf1_hash_id = md_alg;
            rsassa_pss_options.expected_salt_len =
                mbedtls_md_get_size_from_type(md_alg);
            if (rsassa_pss_options.expected_salt_len == 0) {
                return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
            }

            ret = mbedtls_pk_verify_ext(pk_alg, &rsassa_pss_options,
                                        peer_pk,
                                        md_alg, hash, hashlen,
                                        p, sig_len);
        } else
#endif /* MBEDTLS_X509_RSASSA_PSS_SUPPORT */
        ret = mbedtls_pk_verify_restartable(peer_pk,
                                            md_alg, hash, hashlen, p, sig_len, rs_ctx);

        if (ret != 0) {
            int send_alert_msg = 1;
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
            send_alert_msg = (ret != MBEDTLS_ERR_ECP_IN_PROGRESS);
#endif
            if (send_alert_msg) {
                mbedtls_ssl_send_alert_message(
                    ssl,
                    MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                    MBEDTLS_SSL_ALERT_MSG_DECRYPT_ERROR);
            }
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_pk_verify", ret);
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
            if (ret == MBEDTLS_ERR_ECP_IN_PROGRESS) {
                ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
            }
#endif
            return ret;
        }

#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
        /* We don't need the peer's public key anymore. Free it,
         * so that more RAM is available for upcoming expensive
         * operations like ECDHE. */
        mbedtls_pk_free(peer_pk);
#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
    }
#endif /* MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED */

exit:
    ssl->state++;

    MBEDTLS_SSL_DEBUG_MSG(2, ("<= parse server key exchange"));

    return 0;
}

#if !defined(MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_certificate_request(mbedtls_ssl_context *ssl)
{
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;

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

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

    MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
    return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
}
#else /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_certificate_request(mbedtls_ssl_context *ssl)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char *buf;
    size_t n = 0;
    size_t cert_type_len = 0, dn_len = 0;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    size_t sig_alg_len;
#if defined(MBEDTLS_DEBUG_C)
    unsigned char *sig_alg;
    unsigned char *dn;
#endif

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

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

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

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

    ssl->state++;
    ssl->handshake->client_auth =
        (ssl->in_msg[0] == MBEDTLS_SSL_HS_CERTIFICATE_REQUEST);

    MBEDTLS_SSL_DEBUG_MSG(3, ("got %s certificate request",
                              ssl->handshake->client_auth ? "a" : "no"));

    if (ssl->handshake->client_auth == 0) {
        /* Current message is probably the ServerHelloDone */
        ssl->keep_current_message = 1;
        goto exit;
    }

    /*
     *  struct {
     *      ClientCertificateType certificate_types<1..2^8-1>;
     *      SignatureAndHashAlgorithm
     *        supported_signature_algorithms<2^16-1>; -- TLS 1.2 only
     *      DistinguishedName certificate_authorities<0..2^16-1>;
     *  } CertificateRequest;
     *
     *  Since we only support a single certificate on clients, let's just
     *  ignore all the information that's supposed to help us pick a
     *  certificate.
     *
     *  We could check that our certificate matches the request, and bail out
     *  if it doesn't, but it's simpler to just send the certificate anyway,
     *  and give the server the opportunity to decide if it should terminate
     *  the connection when it doesn't like our certificate.
     *
     *  Same goes for the hash in TLS 1.2's signature_algorithms: at this
     *  point we only have one hash available (see comments in
     *  write_certificate_verify), so let's just use what we have.
     *
     *  However, we still minimally parse the message to check it is at least
     *  superficially sane.
     */
    buf = ssl->in_msg;

    /* certificate_types */
    if (ssl->in_hslen <= mbedtls_ssl_hs_hdr_len(ssl)) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad certificate request message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }
    cert_type_len = buf[mbedtls_ssl_hs_hdr_len(ssl)];
    n = cert_type_len;

    /*
     * In the subsequent code there are two paths that read from buf:
     *     * the length of the signature algorithms field (if minor version of
     *       SSL is 3),
     *     * distinguished name length otherwise.
     * Both reach at most the index:
     *    ...hdr_len + 2 + n,
     * therefore the buffer length at this point must be greater than that
     * regardless of the actual code path.
     */
    if (ssl->in_hslen <= mbedtls_ssl_hs_hdr_len(ssl) + 2 + n) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad certificate request message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    /* supported_signature_algorithms */
    sig_alg_len = ((buf[mbedtls_ssl_hs_hdr_len(ssl) + 1 + n] <<  8)
                   | (buf[mbedtls_ssl_hs_hdr_len(ssl) + 2 + n]));

    /*
     * The furthest access in buf is in the loop few lines below:
     *     sig_alg[i + 1],
     * where:
     *     sig_alg = buf + ...hdr_len + 3 + n,
     *     max(i) = sig_alg_len - 1.
     * Therefore the furthest access is:
     *     buf[...hdr_len + 3 + n + sig_alg_len - 1 + 1],
     * which reduces to:
     *     buf[...hdr_len + 3 + n + sig_alg_len],
     * which is one less than we need the buf to be.
     */
    if (ssl->in_hslen <= mbedtls_ssl_hs_hdr_len(ssl) + 3 + n + sig_alg_len) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad certificate request message"));
        mbedtls_ssl_send_alert_message(
            ssl,
            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
            MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

#if defined(MBEDTLS_DEBUG_C)
    sig_alg = buf + mbedtls_ssl_hs_hdr_len(ssl) + 3 + n;
    for (size_t i = 0; i < sig_alg_len; i += 2) {
        MBEDTLS_SSL_DEBUG_MSG(3,
                              ("Supported Signature Algorithm found: %02x %02x",
                               sig_alg[i], sig_alg[i + 1]));
    }
#endif

    n += 2 + sig_alg_len;

    /* certificate_authorities */
    dn_len = ((buf[mbedtls_ssl_hs_hdr_len(ssl) + 1 + n] <<  8)
              | (buf[mbedtls_ssl_hs_hdr_len(ssl) + 2 + n]));

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

#if defined(MBEDTLS_DEBUG_C)
    dn = buf + mbedtls_ssl_hs_hdr_len(ssl) + 3 + n - dn_len;
    for (size_t i = 0, dni_len = 0; i < dn_len; i += 2 + dni_len) {
        unsigned char *p = dn + i + 2;
        mbedtls_x509_name name;
        size_t asn1_len;
        char s[MBEDTLS_X509_MAX_DN_NAME_SIZE];
        memset(&name, 0, sizeof(name));
        dni_len = MBEDTLS_GET_UINT16_BE(dn + i, 0);
        if (dni_len > dn_len - i - 2 ||
            mbedtls_asn1_get_tag(&p, p + dni_len, &asn1_len,
                                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE) != 0 ||
            mbedtls_x509_get_name(&p, p + asn1_len, &name) != 0) {
            MBEDTLS_SSL_DEBUG_MSG(1, ("bad certificate request message"));
            mbedtls_ssl_send_alert_message(
                ssl,
                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
            return MBEDTLS_ERR_SSL_DECODE_ERROR;
        }
        MBEDTLS_SSL_DEBUG_MSG(3,
                              ("DN hint: %.*s",
                               mbedtls_x509_dn_gets(s, sizeof(s), &name), s));
        mbedtls_asn1_free_named_data_list_shallow(name.next);
    }
#endif

exit:
    MBEDTLS_SSL_DEBUG_MSG(2, ("<= parse certificate request"));

    return 0;
}
#endif /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */

MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_server_hello_done(mbedtls_ssl_context *ssl)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    MBEDTLS_SSL_DEBUG_MSG(2, ("=> parse server hello done"));

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

    if (ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello done message"));
        return MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE;
    }

    if (ssl->in_hslen  != mbedtls_ssl_hs_hdr_len(ssl) ||
        ssl->in_msg[0] != MBEDTLS_SSL_HS_SERVER_HELLO_DONE) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad server hello done message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    ssl->state++;

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

    MBEDTLS_SSL_DEBUG_MSG(2, ("<= parse server hello done"));

    return 0;
}

MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_client_key_exchange(mbedtls_ssl_context *ssl)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    size_t header_len;
    size_t content_len;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;

    MBEDTLS_SSL_DEBUG_MSG(2, ("=> write client key exchange"));

#if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_RSA) {
        /*
         * DHM key exchange -- send G^X mod P
         */
        content_len = mbedtls_dhm_get_len(&ssl->handshake->dhm_ctx);

        MBEDTLS_PUT_UINT16_BE(content_len, ssl->out_msg, 4);
        header_len = 6;

        ret = mbedtls_dhm_make_public(&ssl->handshake->dhm_ctx,
                                      (int) mbedtls_dhm_get_len(&ssl->handshake->dhm_ctx),
                                      &ssl->out_msg[header_len], content_len,
                                      ssl->conf->f_rng, ssl->conf->p_rng);
        if (ret != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_dhm_make_public", ret);
            return ret;
        }

        MBEDTLS_SSL_DEBUG_MPI(3, "DHM: X ", &ssl->handshake->dhm_ctx.X);
        MBEDTLS_SSL_DEBUG_MPI(3, "DHM: GX", &ssl->handshake->dhm_ctx.GX);

        if ((ret = mbedtls_dhm_calc_secret(&ssl->handshake->dhm_ctx,
                                           ssl->handshake->premaster,
                                           MBEDTLS_PREMASTER_SIZE,
                                           &ssl->handshake->pmslen,
                                           ssl->conf->f_rng, ssl->conf->p_rng)) != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_dhm_calc_secret", ret);
            return ret;
        }

        MBEDTLS_SSL_DEBUG_MPI(3, "DHM: K ", &ssl->handshake->dhm_ctx.K);
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||                     \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED) ||                   \
    defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) ||                      \
    defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_RSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_RSA ||
        ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA) {
#if defined(MBEDTLS_USE_PSA_CRYPTO)
        psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
        psa_status_t destruction_status = PSA_ERROR_CORRUPTION_DETECTED;
        psa_key_attributes_t key_attributes;

        mbedtls_ssl_handshake_params *handshake = ssl->handshake;

        header_len = 4;

        MBEDTLS_SSL_DEBUG_MSG(1, ("Perform PSA-based ECDH computation."));

        /*
         * Generate EC private key for ECDHE exchange.
         */

        /* The master secret is obtained from the shared ECDH secret by
         * applying the TLS 1.2 PRF with a specific salt and label. While
         * the PSA Crypto API encourages combining key agreement schemes
         * such as ECDH with fixed KDFs such as TLS 1.2 PRF, it does not
         * yet support the provisioning of salt + label to the KDF.
         * For the time being, we therefore need to split the computation
         * of the ECDH secret and the application of the TLS 1.2 PRF. */
        key_attributes = psa_key_attributes_init();
        psa_set_key_usage_flags(&key_attributes, PSA_KEY_USAGE_DERIVE);
        psa_set_key_algorithm(&key_attributes, PSA_ALG_ECDH);
        psa_set_key_type(&key_attributes, handshake->xxdh_psa_type);
        psa_set_key_bits(&key_attributes, handshake->xxdh_bits);

        /* Generate ECDH private key. */
        status = psa_generate_key(&key_attributes,
                                  &handshake->xxdh_psa_privkey);
        if (status != PSA_SUCCESS) {
            return MBEDTLS_ERR_SSL_HW_ACCEL_FAILED;
        }

        /* Export the public part of the ECDH private key from PSA.
         * The export format is an ECPoint structure as expected by TLS,
         * but we just need to add a length byte before that. */
        unsigned char *own_pubkey = ssl->out_msg + header_len + 1;
        unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
        size_t own_pubkey_max_len = (size_t) (end - own_pubkey);
        size_t own_pubkey_len;

        status = psa_export_public_key(handshake->xxdh_psa_privkey,
                                       own_pubkey, own_pubkey_max_len,
                                       &own_pubkey_len);
        if (status != PSA_SUCCESS) {
            psa_destroy_key(handshake->xxdh_psa_privkey);
            handshake->xxdh_psa_privkey = MBEDTLS_SVC_KEY_ID_INIT;
            return MBEDTLS_ERR_SSL_HW_ACCEL_FAILED;
        }

        ssl->out_msg[header_len] = (unsigned char) own_pubkey_len;
        content_len = own_pubkey_len + 1;

        /* The ECDH secret is the premaster secret used for key derivation. */

        /* Compute ECDH shared secret. */
        status = psa_raw_key_agreement(PSA_ALG_ECDH,
                                       handshake->xxdh_psa_privkey,
                                       handshake->xxdh_psa_peerkey,
                                       handshake->xxdh_psa_peerkey_len,
                                       ssl->handshake->premaster,
                                       sizeof(ssl->handshake->premaster),
                                       &ssl->handshake->pmslen);

        destruction_status = psa_destroy_key(handshake->xxdh_psa_privkey);
        handshake->xxdh_psa_privkey = MBEDTLS_SVC_KEY_ID_INIT;

        if (status != PSA_SUCCESS || destruction_status != PSA_SUCCESS) {
            return MBEDTLS_ERR_SSL_HW_ACCEL_FAILED;
        }
#else
        /*
         * ECDH key exchange -- send client public value
         */
        header_len = 4;

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
        if (ssl->handshake->ecrs_enabled) {
            if (ssl->handshake->ecrs_state == ssl_ecrs_cke_ecdh_calc_secret) {
                goto ecdh_calc_secret;
            }

            mbedtls_ecdh_enable_restart(&ssl->handshake->ecdh_ctx);
        }
#endif

        ret = mbedtls_ecdh_make_public(&ssl->handshake->ecdh_ctx,
                                       &content_len,
                                       &ssl->out_msg[header_len], 1000,
                                       ssl->conf->f_rng, ssl->conf->p_rng);
        if (ret != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ecdh_make_public", ret);
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
            if (ret == MBEDTLS_ERR_ECP_IN_PROGRESS) {
                ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
            }
#endif
            return ret;
        }

        MBEDTLS_SSL_DEBUG_ECDH(3, &ssl->handshake->ecdh_ctx,
                               MBEDTLS_DEBUG_ECDH_Q);

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
        if (ssl->handshake->ecrs_enabled) {
            ssl->handshake->ecrs_n = content_len;
            ssl->handshake->ecrs_state = ssl_ecrs_cke_ecdh_calc_secret;
        }

ecdh_calc_secret:
        if (ssl->handshake->ecrs_enabled) {
            content_len = ssl->handshake->ecrs_n;
        }
#endif
        if ((ret = mbedtls_ecdh_calc_secret(&ssl->handshake->ecdh_ctx,
                                            &ssl->handshake->pmslen,
                                            ssl->handshake->premaster,
                                            MBEDTLS_MPI_MAX_SIZE,
                                            ssl->conf->f_rng, ssl->conf->p_rng)) != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ecdh_calc_secret", ret);
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
            if (ret == MBEDTLS_ERR_ECP_IN_PROGRESS) {
                ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
            }
#endif
            return ret;
        }

        MBEDTLS_SSL_DEBUG_ECDH(3, &ssl->handshake->ecdh_ctx,
                               MBEDTLS_DEBUG_ECDH_Z);
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED ||
          MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */
#if defined(MBEDTLS_USE_PSA_CRYPTO) &&                           \
    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK) {
        psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
        psa_status_t destruction_status = PSA_ERROR_CORRUPTION_DETECTED;
        psa_key_attributes_t key_attributes;

        mbedtls_ssl_handshake_params *handshake = ssl->handshake;

        /*
         * opaque psk_identity<0..2^16-1>;
         */
        if (mbedtls_ssl_conf_has_static_psk(ssl->conf) == 0) {
            /* We don't offer PSK suites if we don't have a PSK,
             * and we check that the server's choice is among the
             * ciphersuites we offered, so this should never happen. */
            return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        }

        /* uint16 to store content length */
        const size_t content_len_size = 2;

        header_len = 4;

        if (header_len + content_len_size + ssl->conf->psk_identity_len
            > MBEDTLS_SSL_OUT_CONTENT_LEN) {
            MBEDTLS_SSL_DEBUG_MSG(1,
                                  ("psk identity too long or SSL buffer too short"));
            return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;
        }

        unsigned char *p = ssl->out_msg + header_len;

        *p++ = MBEDTLS_BYTE_1(ssl->conf->psk_identity_len);
        *p++ = MBEDTLS_BYTE_0(ssl->conf->psk_identity_len);
        header_len += content_len_size;

        memcpy(p, ssl->conf->psk_identity,
               ssl->conf->psk_identity_len);
        p += ssl->conf->psk_identity_len;

        header_len += ssl->conf->psk_identity_len;

        MBEDTLS_SSL_DEBUG_MSG(1, ("Perform PSA-based ECDH computation."));

        /*
         * Generate EC private key for ECDHE exchange.
         */

        /* The master secret is obtained from the shared ECDH secret by
         * applying the TLS 1.2 PRF with a specific salt and label. While
         * the PSA Crypto API encourages combining key agreement schemes
         * such as ECDH with fixed KDFs such as TLS 1.2 PRF, it does not
         * yet support the provisioning of salt + label to the KDF.
         * For the time being, we therefore need to split the computation
         * of the ECDH secret and the application of the TLS 1.2 PRF. */
        key_attributes = psa_key_attributes_init();
        psa_set_key_usage_flags(&key_attributes, PSA_KEY_USAGE_DERIVE);
        psa_set_key_algorithm(&key_attributes, PSA_ALG_ECDH);
        psa_set_key_type(&key_attributes, handshake->xxdh_psa_type);
        psa_set_key_bits(&key_attributes, handshake->xxdh_bits);

        /* Generate ECDH private key. */
        status = psa_generate_key(&key_attributes,
                                  &handshake->xxdh_psa_privkey);
        if (status != PSA_SUCCESS) {
            return PSA_TO_MBEDTLS_ERR(status);
        }

        /* Export the public part of the ECDH private key from PSA.
         * The export format is an ECPoint structure as expected by TLS,
         * but we just need to add a length byte before that. */
        unsigned char *own_pubkey = p + 1;
        unsigned char *end = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN;
        size_t own_pubkey_max_len = (size_t) (end - own_pubkey);
        size_t own_pubkey_len = 0;

        status = psa_export_public_key(handshake->xxdh_psa_privkey,
                                       own_pubkey, own_pubkey_max_len,
                                       &own_pubkey_len);
        if (status != PSA_SUCCESS) {
            psa_destroy_key(handshake->xxdh_psa_privkey);
            handshake->xxdh_psa_privkey = MBEDTLS_SVC_KEY_ID_INIT;
            return PSA_TO_MBEDTLS_ERR(status);
        }

        *p = (unsigned char) own_pubkey_len;
        content_len = own_pubkey_len + 1;

        /* As RFC 5489 section 2, the premaster secret is formed as follows:
         * - a uint16 containing the length (in octets) of the ECDH computation
         * - the octet string produced by the ECDH computation
         * - a uint16 containing the length (in octets) of the PSK
         * - the PSK itself
         */
        unsigned char *pms = ssl->handshake->premaster;
        const unsigned char * const pms_end = pms +
                                              sizeof(ssl->handshake->premaster);
        /* uint16 to store length (in octets) of the ECDH computation */
        const size_t zlen_size = 2;
        size_t zlen = 0;

        /* Perform ECDH computation after the uint16 reserved for the length */
        status = psa_raw_key_agreement(PSA_ALG_ECDH,
                                       handshake->xxdh_psa_privkey,
                                       handshake->xxdh_psa_peerkey,
                                       handshake->xxdh_psa_peerkey_len,
                                       pms + zlen_size,
                                       pms_end - (pms + zlen_size),
                                       &zlen);

        destruction_status = psa_destroy_key(handshake->xxdh_psa_privkey);
        handshake->xxdh_psa_privkey = MBEDTLS_SVC_KEY_ID_INIT;

        if (status != PSA_SUCCESS) {
            return PSA_TO_MBEDTLS_ERR(status);
        } else if (destruction_status != PSA_SUCCESS) {
            return PSA_TO_MBEDTLS_ERR(destruction_status);
        }

        /* Write the ECDH computation length before the ECDH computation */
        MBEDTLS_PUT_UINT16_BE(zlen, pms, 0);
        pms += zlen_size + zlen;
    } else
#endif /* MBEDTLS_USE_PSA_CRYPTO &&
          MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
    if (mbedtls_ssl_ciphersuite_uses_psk(ciphersuite_info)) {
        /*
         * opaque psk_identity<0..2^16-1>;
         */
        if (mbedtls_ssl_conf_has_static_psk(ssl->conf) == 0) {
            /* We don't offer PSK suites if we don't have a PSK,
             * and we check that the server's choice is among the
             * ciphersuites we offered, so this should never happen. */
            return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        }

        header_len = 4;
        content_len = ssl->conf->psk_identity_len;

        if (header_len + 2 + content_len > MBEDTLS_SSL_OUT_CONTENT_LEN) {
            MBEDTLS_SSL_DEBUG_MSG(1,
                                  ("psk identity too long or SSL buffer too short"));
            return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;
        }

        ssl->out_msg[header_len++] = MBEDTLS_BYTE_1(content_len);
        ssl->out_msg[header_len++] = MBEDTLS_BYTE_0(content_len);

        memcpy(ssl->out_msg + header_len,
               ssl->conf->psk_identity,
               ssl->conf->psk_identity_len);
        header_len += ssl->conf->psk_identity_len;

#if defined(MBEDTLS_KEY_EXCHANGE_PSK_ENABLED)
        if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_PSK) {
            content_len = 0;
        } else
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
        if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA_PSK) {
            if ((ret = ssl_write_encrypted_pms(ssl, header_len,
                                               &content_len, 2)) != 0) {
                return ret;
            }
        } else
#endif
#if defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
        if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_DHE_PSK) {
            /*
             * ClientDiffieHellmanPublic public (DHM send G^X mod P)
             */
            content_len = mbedtls_dhm_get_len(&ssl->handshake->dhm_ctx);

            if (header_len + 2 + content_len >
                MBEDTLS_SSL_OUT_CONTENT_LEN) {
                MBEDTLS_SSL_DEBUG_MSG(1,
                                      ("psk identity or DHM size too long or SSL buffer too short"));
                return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;
            }

            ssl->out_msg[header_len++] = MBEDTLS_BYTE_1(content_len);
            ssl->out_msg[header_len++] = MBEDTLS_BYTE_0(content_len);

            ret = mbedtls_dhm_make_public(&ssl->handshake->dhm_ctx,
                                          (int) mbedtls_dhm_get_len(&ssl->handshake->dhm_ctx),
                                          &ssl->out_msg[header_len], content_len,
                                          ssl->conf->f_rng, ssl->conf->p_rng);
            if (ret != 0) {
                MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_dhm_make_public", ret);
                return ret;
            }

#if defined(MBEDTLS_USE_PSA_CRYPTO)
            unsigned char *pms = ssl->handshake->premaster;
            unsigned char *pms_end = pms + sizeof(ssl->handshake->premaster);
            size_t pms_len;

            /* Write length only when we know the actual value */
            if ((ret = mbedtls_dhm_calc_secret(&ssl->handshake->dhm_ctx,
                                               pms + 2, pms_end - (pms + 2), &pms_len,
                                               ssl->conf->f_rng, ssl->conf->p_rng)) != 0) {
                MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_dhm_calc_secret", ret);
                return ret;
            }
            MBEDTLS_PUT_UINT16_BE(pms_len, pms, 0);
            pms += 2 + pms_len;

            MBEDTLS_SSL_DEBUG_MPI(3, "DHM: K ", &ssl->handshake->dhm_ctx.K);
#endif
        } else
#endif /* MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED */
#if !defined(MBEDTLS_USE_PSA_CRYPTO) &&                             \
        defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED)
        if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECDHE_PSK) {
            /*
             * ClientECDiffieHellmanPublic public;
             */
            ret = mbedtls_ecdh_make_public(&ssl->handshake->ecdh_ctx,
                                           &content_len,
                                           &ssl->out_msg[header_len],
                                           MBEDTLS_SSL_OUT_CONTENT_LEN - header_len,
                                           ssl->conf->f_rng, ssl->conf->p_rng);
            if (ret != 0) {
                MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ecdh_make_public", ret);
                return ret;
            }

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

#if !defined(MBEDTLS_USE_PSA_CRYPTO)
        if ((ret = mbedtls_ssl_psk_derive_premaster(ssl,
                                                    ciphersuite_info->key_exchange)) != 0) {
            MBEDTLS_SSL_DEBUG_RET(1,
                                  "mbedtls_ssl_psk_derive_premaster", ret);
            return ret;
        }
#endif /* !MBEDTLS_USE_PSA_CRYPTO */
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_RSA) {
        header_len = 4;
        if ((ret = ssl_write_encrypted_pms(ssl, header_len,
                                           &content_len, 0)) != 0) {
            return ret;
        }
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_RSA_ENABLED */
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    if (ciphersuite_info->key_exchange == MBEDTLS_KEY_EXCHANGE_ECJPAKE) {
        header_len = 4;

#if defined(MBEDTLS_USE_PSA_CRYPTO)
        unsigned char *out_p = ssl->out_msg + header_len;
        unsigned char *end_p = ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN -
                               header_len;
        ret = mbedtls_psa_ecjpake_write_round(&ssl->handshake->psa_pake_ctx,
                                              out_p, end_p - out_p, &content_len,
                                              MBEDTLS_ECJPAKE_ROUND_TWO);
        if (ret != 0) {
            psa_destroy_key(ssl->handshake->psa_pake_password);
            psa_pake_abort(&ssl->handshake->psa_pake_ctx);
            MBEDTLS_SSL_DEBUG_RET(1, "psa_pake_output", ret);
            return ret;
        }
#else
        ret = mbedtls_ecjpake_write_round_two(&ssl->handshake->ecjpake_ctx,
                                              ssl->out_msg + header_len,
                                              MBEDTLS_SSL_OUT_CONTENT_LEN - header_len,
                                              &content_len,
                                              ssl->conf->f_rng, ssl->conf->p_rng);
        if (ret != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ecjpake_write_round_two", ret);
            return ret;
        }

        ret = mbedtls_ecjpake_derive_secret(&ssl->handshake->ecjpake_ctx,
                                            ssl->handshake->premaster, 32, &ssl->handshake->pmslen,
                                            ssl->conf->f_rng, ssl->conf->p_rng);
        if (ret != 0) {
            MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_ecjpake_derive_secret", ret);
            return ret;
        }
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    } else
#endif /* MBEDTLS_KEY_EXCHANGE_RSA_ENABLED */
    {
        ((void) ciphersuite_info);
        MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
        return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
    }

    ssl->out_msglen  = header_len + content_len;
    ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
    ssl->out_msg[0]  = MBEDTLS_SSL_HS_CLIENT_KEY_EXCHANGE;

    ssl->state++;

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

    MBEDTLS_SSL_DEBUG_MSG(2, ("<= write client key exchange"));

    return 0;
}

#if !defined(MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_certificate_verify(mbedtls_ssl_context *ssl)
{
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

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

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

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

    MBEDTLS_SSL_DEBUG_MSG(1, ("should never happen"));
    return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
}
#else /* !MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_write_certificate_verify(mbedtls_ssl_context *ssl)
{
    int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
    const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
        ssl->handshake->ciphersuite_info;
    size_t n = 0, offset = 0;
    unsigned char hash[48];
    unsigned char *hash_start = hash;
    mbedtls_md_type_t md_alg = MBEDTLS_MD_NONE;
    size_t hashlen;
    void *rs_ctx = NULL;
#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
    size_t out_buf_len = ssl->out_buf_len - (ssl->out_msg - ssl->out_buf);
#else
    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN - (ssl->out_msg - ssl->out_buf);
#endif

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

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if (ssl->handshake->ecrs_enabled &&
        ssl->handshake->ecrs_state == ssl_ecrs_crt_vrfy_sign) {
        goto sign;
    }
#endif

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

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

    if (ssl->handshake->client_auth == 0 ||
        mbedtls_ssl_own_cert(ssl) == NULL) {
        MBEDTLS_SSL_DEBUG_MSG(2, ("<= skip write certificate verify"));
        ssl->state++;
        return 0;
    }

    if (mbedtls_ssl_own_key(ssl) == NULL) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("got no private key for certificate"));
        return MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED;
    }

    /*
     * Make a signature of the handshake digests
     */
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if (ssl->handshake->ecrs_enabled) {
        ssl->handshake->ecrs_state = ssl_ecrs_crt_vrfy_sign;
    }

sign:
#endif

    ret = ssl->handshake->calc_verify(ssl, hash, &hashlen);
    if (0 != ret) {
        MBEDTLS_SSL_DEBUG_RET(1, ("calc_verify"), ret);
        return ret;
    }

    /*
     * digitally-signed struct {
     *     opaque handshake_messages[handshake_messages_length];
     * };
     *
     * Taking shortcut here. We assume that the server always allows the
     * PRF Hash function and has sent it in the allowed signature
     * algorithms list received in the Certificate Request message.
     *
     * Until we encounter a server that does not, we will take this
     * shortcut.
     *
     * Reason: Otherwise we should have running hashes for SHA512 and
     *         SHA224 in order to satisfy 'weird' needs from the server
     *         side.
     */
    if (ssl->handshake->ciphersuite_info->mac == MBEDTLS_MD_SHA384) {
        md_alg = MBEDTLS_MD_SHA384;
        ssl->out_msg[4] = MBEDTLS_SSL_HASH_SHA384;
    } else {
        md_alg = MBEDTLS_MD_SHA256;
        ssl->out_msg[4] = MBEDTLS_SSL_HASH_SHA256;
    }
    ssl->out_msg[5] = mbedtls_ssl_sig_from_pk(mbedtls_ssl_own_key(ssl));

    /* Info from md_alg will be used instead */
    hashlen = 0;
    offset = 2;

#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
    if (ssl->handshake->ecrs_enabled) {
        rs_ctx = &ssl->handshake->ecrs_ctx.pk;
    }
#endif

    if ((ret = mbedtls_pk_sign_restartable(mbedtls_ssl_own_key(ssl),
                                           md_alg, hash_start, hashlen,
                                           ssl->out_msg + 6 + offset,
                                           out_buf_len - 6 - offset,
                                           &n,
                                           ssl->conf->f_rng, ssl->conf->p_rng, rs_ctx)) != 0) {
        MBEDTLS_SSL_DEBUG_RET(1, "mbedtls_pk_sign", ret);
#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
        if (ret == MBEDTLS_ERR_ECP_IN_PROGRESS) {
            ret = MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS;
        }
#endif
        return ret;
    }

    MBEDTLS_PUT_UINT16_BE(n, ssl->out_msg, offset + 4);

    ssl->out_msglen  = 6 + n + offset;
    ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
    ssl->out_msg[0]  = MBEDTLS_SSL_HS_CERTIFICATE_VERIFY;

    ssl->state++;

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

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

    return ret;
}
#endif /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */

#if defined(MBEDTLS_SSL_SESSION_TICKETS)
MBEDTLS_CHECK_RETURN_CRITICAL
static int ssl_parse_new_session_ticket(mbedtls_ssl_context *ssl)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    uint32_t lifetime;
    size_t ticket_len;
    unsigned char *ticket;
    const unsigned char *msg;

    MBEDTLS_SSL_DEBUG_MSG(2, ("=> parse new session ticket"));

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

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

    /*
     * struct {
     *     uint32 ticket_lifetime_hint;
     *     opaque ticket<0..2^16-1>;
     * } NewSessionTicket;
     *
     * 0  .  3   ticket_lifetime_hint
     * 4  .  5   ticket_len (n)
     * 6  .  5+n ticket content
     */
    if (ssl->in_msg[0] != MBEDTLS_SSL_HS_NEW_SESSION_TICKET ||
        ssl->in_hslen < 6 + mbedtls_ssl_hs_hdr_len(ssl)) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad new session ticket message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    msg = ssl->in_msg + mbedtls_ssl_hs_hdr_len(ssl);

    lifetime = (((uint32_t) msg[0]) << 24) | (msg[1] << 16) |
               (msg[2] << 8) | (msg[3]);

    ticket_len = (msg[4] << 8) | (msg[5]);

    if (ticket_len + 6 + mbedtls_ssl_hs_hdr_len(ssl) != ssl->in_hslen) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("bad new session ticket message"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR);
        return MBEDTLS_ERR_SSL_DECODE_ERROR;
    }

    MBEDTLS_SSL_DEBUG_MSG(3, ("ticket length: %" MBEDTLS_PRINTF_SIZET, ticket_len));

    /* We're not waiting for a NewSessionTicket message any more */
    ssl->handshake->new_session_ticket = 0;
    ssl->state = MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC;

    /*
     * Zero-length ticket means the server changed his mind and doesn't want
     * to send a ticket after all, so just forget it
     */
    if (ticket_len == 0) {
        return 0;
    }

    if (ssl->session != NULL && ssl->session->ticket != NULL) {
        mbedtls_zeroize_and_free(ssl->session->ticket,
                                 ssl->session->ticket_len);
        ssl->session->ticket = NULL;
        ssl->session->ticket_len = 0;
    }

    mbedtls_zeroize_and_free(ssl->session_negotiate->ticket,
                             ssl->session_negotiate->ticket_len);
    ssl->session_negotiate->ticket = NULL;
    ssl->session_negotiate->ticket_len = 0;

    if ((ticket = mbedtls_calloc(1, ticket_len)) == NULL) {
        MBEDTLS_SSL_DEBUG_MSG(1, ("ticket alloc failed"));
        mbedtls_ssl_send_alert_message(ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                                       MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR);
        return MBEDTLS_ERR_SSL_ALLOC_FAILED;
    }

    memcpy(ticket, msg + 6, ticket_len);

    ssl->session_negotiate->ticket = ticket;
    ssl->session_negotiate->ticket_len = ticket_len;
    ssl->session_negotiate->ticket_lifetime = lifetime;

    /*
     * RFC 5077 section 3.4:
     * "If the client receives a session ticket from the server, then it
     * discards any Session ID that was sent in the ServerHello."
     */
    MBEDTLS_SSL_DEBUG_MSG(3, ("ticket in use, discarding session id"));
    ssl->session_negotiate->id_len = 0;

    MBEDTLS_SSL_DEBUG_MSG(2, ("<= parse new session ticket"));

    return 0;
}
#endif /* MBEDTLS_SSL_SESSION_TICKETS */

/*
 * SSL handshake -- client side -- single step
 */
int mbedtls_ssl_handshake_client_step(mbedtls_ssl_context *ssl)
{
    int ret = 0;

    /* Change state now, so that it is right in mbedtls_ssl_read_record(), used
     * by DTLS for dropping out-of-sequence ChangeCipherSpec records */
#if defined(MBEDTLS_SSL_SESSION_TICKETS)
    if (ssl->state == MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC &&
        ssl->handshake->new_session_ticket != 0) {
        ssl->state = MBEDTLS_SSL_NEW_SESSION_TICKET;
    }
#endif

    switch (ssl->state) {
        case MBEDTLS_SSL_HELLO_REQUEST:
            ssl->state = MBEDTLS_SSL_CLIENT_HELLO;
            break;

        /*
         *  ==>   ClientHello
         */
        case MBEDTLS_SSL_CLIENT_HELLO:
            ret = mbedtls_ssl_write_client_hello(ssl);
            break;

        /*
         *  <==   ServerHello
         *        Certificate
         *      ( ServerKeyExchange  )
         *      ( CertificateRequest )
         *        ServerHelloDone
         */
        case MBEDTLS_SSL_SERVER_HELLO:
            ret = ssl_parse_server_hello(ssl);
            break;

        case MBEDTLS_SSL_SERVER_CERTIFICATE:
            ret = mbedtls_ssl_parse_certificate(ssl);
            break;

        case MBEDTLS_SSL_SERVER_KEY_EXCHANGE:
            ret = ssl_parse_server_key_exchange(ssl);
            break;

        case MBEDTLS_SSL_CERTIFICATE_REQUEST:
            ret = ssl_parse_certificate_request(ssl);
            break;

        case MBEDTLS_SSL_SERVER_HELLO_DONE:
            ret = ssl_parse_server_hello_done(ssl);
            break;

        /*
         *  ==> ( Certificate/Alert  )
         *        ClientKeyExchange
         *      ( CertificateVerify  )
         *        ChangeCipherSpec
         *        Finished
         */
        case MBEDTLS_SSL_CLIENT_CERTIFICATE:
            ret = mbedtls_ssl_write_certificate(ssl);
            break;

        case MBEDTLS_SSL_CLIENT_KEY_EXCHANGE:
            ret = ssl_write_client_key_exchange(ssl);
            break;

        case MBEDTLS_SSL_CERTIFICATE_VERIFY:
            ret = ssl_write_certificate_verify(ssl);
            break;

        case MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC:
            ret = mbedtls_ssl_write_change_cipher_spec(ssl);
            break;

        case MBEDTLS_SSL_CLIENT_FINISHED:
            ret = mbedtls_ssl_write_finished(ssl);
            break;

            /*
             *  <==   ( NewSessionTicket )
             *        ChangeCipherSpec
             *        Finished
             */
#if defined(MBEDTLS_SSL_SESSION_TICKETS)
        case MBEDTLS_SSL_NEW_SESSION_TICKET:
            ret = ssl_parse_new_session_ticket(ssl);
            break;
#endif

        case MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC:
            ret = mbedtls_ssl_parse_change_cipher_spec(ssl);
            break;

        case MBEDTLS_SSL_SERVER_FINISHED:
            ret = mbedtls_ssl_parse_finished(ssl);
            break;

        case MBEDTLS_SSL_FLUSH_BUFFERS:
            MBEDTLS_SSL_DEBUG_MSG(2, ("handshake: done"));
            ssl->state = MBEDTLS_SSL_HANDSHAKE_WRAPUP;
            break;

        case MBEDTLS_SSL_HANDSHAKE_WRAPUP:
            mbedtls_ssl_handshake_wrapup(ssl);
            break;

        default:
            MBEDTLS_SSL_DEBUG_MSG(1, ("invalid state %d", ssl->state));
            return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
    }

    return ret;
}

#endif /* MBEDTLS_SSL_CLI_C && MBEDTLS_SSL_PROTO_TLS1_2 */