/src/gnutls/lib/handshake.c

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/*
 * Copyright (C) 2000-2016 Free Software Foundation, Inc.
 * Copyright (C) 2015-2018 Red Hat, Inc.
 *
 * Author: Nikos Mavrogiannopoulos
 *
 * This file is part of GnuTLS.
 *
 * The GnuTLS is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>
 *
 */

/* Functions that relate to the TLS handshake procedure.
 */

#include "gnutls_int.h"
#include "errors.h"
#include "dh.h"
#include "debug.h"
#include "algorithms.h"
#include "cipher.h"
#include "buffers.h"
#include "mbuffers.h"
#include "kx.h"
#include "handshake.h"
#include "num.h"
#include "hash_int.h"
#include "db.h"
#include "hello_ext.h"
#include "supplemental.h"
#include "auth.h"
#include "sslv2_compat.h"
#include <auth/cert.h>
#include "constate.h"
#include <record.h>
#include <state.h>
#include <ext/pre_shared_key.h>
#include <ext/srp.h>
#include <ext/session_ticket.h>
#include <ext/status_request.h>
#include <ext/safe_renegotiation.h>
#include <auth/anon.h>    /* for gnutls_anon_server_credentials_t */
#include <auth/psk.h>   /* for gnutls_psk_server_credentials_t */
#include <random.h>
#include <dtls.h>
#include "secrets.h"
#include "tls13/early_data.h"
#include "tls13/session_ticket.h"
#include "locks.h"
#include "system/ktls.h"

static int check_if_null_comp_present(gnutls_session_t session,
              uint8_t * data, int datalen);
static int handshake_client(gnutls_session_t session);
static int handshake_server(gnutls_session_t session);

static int
read_server_hello(gnutls_session_t session, uint8_t * data, int datalen);

static int recv_handshake_final(gnutls_session_t session, int init);
static int send_handshake_final(gnutls_session_t session, int init);

/* Empties but does not free the buffer
 */
inline static void handshake_hash_buffer_reset(gnutls_session_t session)
{
  _gnutls_buffers_log("BUF[HSK]: Emptied buffer\n");

  session->internals.handshake_hash_buffer_client_hello_len = 0;
  session->internals.handshake_hash_buffer_client_kx_len = 0;
  session->internals.handshake_hash_buffer_server_finished_len = 0;
  session->internals.handshake_hash_buffer_client_finished_len = 0;
  session->internals.handshake_hash_buffer_prev_len = 0;
  session->internals.handshake_hash_buffer.length = 0;
  session->internals.full_client_hello.length = 0;
  return;
}

static int
handshake_hash_add_recvd(gnutls_session_t session,
       gnutls_handshake_description_t recv_type,
       uint8_t * header, uint16_t header_size,
       uint8_t * dataptr, uint32_t datalen);

static int
handshake_hash_add_sent(gnutls_session_t session,
      gnutls_handshake_description_t type,
      uint8_t * dataptr, uint32_t datalen);

static int
recv_hello_verify_request(gnutls_session_t session,
        uint8_t * data, int datalen);

/* Clears the handshake hash buffers and handles.
 */
void _gnutls_handshake_hash_buffers_clear(gnutls_session_t session)
{
  handshake_hash_buffer_reset(session);
  _gnutls_buffer_clear(&session->internals.handshake_hash_buffer);
  _gnutls_buffer_clear(&session->internals.full_client_hello);
}

/* Replace handshake message buffer, with the special synthetic message
 * needed by TLS1.3 when HRR is sent. */
int _gnutls13_handshake_hash_buffers_synth(gnutls_session_t session,
             const mac_entry_st * prf,
             unsigned client)
{
  int ret;
  uint8_t hdata[4 + MAX_HASH_SIZE];
  size_t length;

  if (client)
    length = session->internals.handshake_hash_buffer_prev_len;
  else
    length = session->internals.handshake_hash_buffer.length;

  /* calculate hash */
  hdata[0] = 254;
  _gnutls_write_uint24(prf->output_size, &hdata[1]);

  ret = gnutls_hash_fast((gnutls_digest_algorithm_t) prf->id,
             session->internals.handshake_hash_buffer.data,
             length, hdata + 4);
  if (ret < 0)
    return gnutls_assert_val(ret);

  handshake_hash_buffer_reset(session);

  ret =
      _gnutls_buffer_append_data(&session->internals.
               handshake_hash_buffer, hdata,
               prf->output_size + 4);
  if (ret < 0)
    return gnutls_assert_val(ret);

  _gnutls_buffers_log
      ("BUF[HSK]: Replaced handshake buffer with synth message (%d bytes)\n",
       prf->output_size + 4);

  return 0;
}

/* this will copy the required values for resuming to
 * internals, and to security_parameters.
 * this will keep as less data to security_parameters.
 */
static int tls12_resume_copy_required_vals(gnutls_session_t session,
             unsigned ticket)
{
  int ret;

  /* get the new random values */
  memcpy(session->internals.resumed_security_parameters.server_random,
         session->security_parameters.server_random, GNUTLS_RANDOM_SIZE);
  memcpy(session->internals.resumed_security_parameters.client_random,
         session->security_parameters.client_random, GNUTLS_RANDOM_SIZE);

  /* keep the ciphersuite and compression
   * That is because the client must see these in our
   * hello message.
   */
  ret = _gnutls_set_cipher_suite2(session,
          session->internals.
          resumed_security_parameters.cs);
  if (ret < 0)
    return gnutls_assert_val(ret);

  /* or write_compression_algorithm
   * they are the same
   */

  session->security_parameters.entity =
      session->internals.resumed_security_parameters.entity;

  if (session->internals.resumed_security_parameters.pversion == NULL)
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  if (_gnutls_set_current_version(session,
          session->internals.
          resumed_security_parameters.pversion->
          id) < 0)
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  session->security_parameters.client_ctype =
      session->internals.resumed_security_parameters.client_ctype;
  session->security_parameters.server_ctype =
      session->internals.resumed_security_parameters.server_ctype;

  if (!ticket) {
    memcpy(session->security_parameters.session_id,
           session->internals.
           resumed_security_parameters.session_id,
           sizeof(session->security_parameters.session_id));
    session->security_parameters.session_id_size =
        session->internals.
        resumed_security_parameters.session_id_size;
  }

  return 0;
}

void _gnutls_set_client_random(gnutls_session_t session, uint8_t * rnd)
{
  _gnutls_memory_mark_defined(session->security_parameters.client_random,
            GNUTLS_RANDOM_SIZE);
  memcpy(session->security_parameters.client_random, rnd,
         GNUTLS_RANDOM_SIZE);
}

static
int _gnutls_gen_client_random(gnutls_session_t session)
{
  int ret;

  /* no random given, we generate. */
  if (session->internals.sc_random_set != 0) {
    _gnutls_memory_mark_defined(session->
              security_parameters.client_random,
              GNUTLS_RANDOM_SIZE);
    memcpy(session->security_parameters.client_random,
           session->internals.
           resumed_security_parameters.client_random,
           GNUTLS_RANDOM_SIZE);
  } else {
    _gnutls_memory_mark_defined(session->
              security_parameters.client_random,
              GNUTLS_RANDOM_SIZE);
    ret =
        gnutls_rnd(GNUTLS_RND_NONCE,
             session->security_parameters.client_random,
             GNUTLS_RANDOM_SIZE);
    if (ret < 0) {
      _gnutls_memory_mark_undefined
          (session->security_parameters.client_random,
           GNUTLS_RANDOM_SIZE);
      return gnutls_assert_val(ret);
    }
  }

  return 0;
}

static
int _gnutls_set_server_random(gnutls_session_t session,
            const version_entry_st * vers, uint8_t * rnd)
{
  const version_entry_st *max;

  _gnutls_memory_mark_defined(session->security_parameters.server_random,
            GNUTLS_RANDOM_SIZE);
  memcpy(session->security_parameters.server_random, rnd,
         GNUTLS_RANDOM_SIZE);

  /* check whether the server random value is set according to
   * to TLS 1.3. p4.1.3 requirements */
  if (!IS_DTLS(session) && vers->id <= GNUTLS_TLS1_2
      && have_creds_for_tls13(session)) {

    max = _gnutls_version_max(session);
    if (max->id <= GNUTLS_TLS1_2)
      return 0;

    if (vers->id == GNUTLS_TLS1_2 &&
        memcmp(&session->
         security_parameters.server_random[GNUTLS_RANDOM_SIZE
                   - 8],
         "\x44\x4F\x57\x4E\x47\x52\x44\x01", 8) == 0) {

      _gnutls_audit_log(session,
            "Detected downgrade to TLS 1.2 from TLS 1.3\n");
      return
          gnutls_assert_val
          (GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
    } else if (vers->id <= GNUTLS_TLS1_1
         && memcmp(&session->security_parameters.server_random
             [GNUTLS_RANDOM_SIZE - 8],
             "\x44\x4F\x57\x4E\x47\x52\x44\x00",
             8) == 0) {

      _gnutls_audit_log(session,
            "Detected downgrade to TLS 1.1 or earlier from TLS 1.3\n");
      return
          gnutls_assert_val
          (GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
    }
  }

  return 0;
}

int _gnutls_gen_server_random(gnutls_session_t session, int version)
{
  int ret;
  const version_entry_st *max;

  if (session->internals.sc_random_set != 0) {
    _gnutls_memory_mark_defined(session->
              security_parameters.server_random,
              GNUTLS_RANDOM_SIZE);
    memcpy(session->security_parameters.server_random,
           session->internals.
           resumed_security_parameters.server_random,
           GNUTLS_RANDOM_SIZE);
    return 0;
  }

  max = _gnutls_version_max(session);
  if (max == NULL)
    return gnutls_assert_val(GNUTLS_E_NO_CIPHER_SUITES);

  _gnutls_memory_mark_defined(session->security_parameters.server_random,
            GNUTLS_RANDOM_SIZE);

  if (!IS_DTLS(session) && max->id >= GNUTLS_TLS1_3 &&
      version <= GNUTLS_TLS1_2) {
    if (version == GNUTLS_TLS1_2) {
      memcpy(&session->security_parameters.server_random
             [GNUTLS_RANDOM_SIZE - 8],
             "\x44\x4F\x57\x4E\x47\x52\x44\x01", 8);
    } else {
      memcpy(&session->security_parameters.server_random
             [GNUTLS_RANDOM_SIZE - 8],
             "\x44\x4F\x57\x4E\x47\x52\x44\x00", 8);
    }
    ret =
        gnutls_rnd(GNUTLS_RND_NONCE,
             session->security_parameters.server_random,
             GNUTLS_RANDOM_SIZE - 8);

  } else {
    ret =
        gnutls_rnd(GNUTLS_RND_NONCE,
             session->security_parameters.server_random,
             GNUTLS_RANDOM_SIZE);
  }

  if (ret < 0) {
    gnutls_assert();
    _gnutls_memory_mark_undefined(session->
                security_parameters.server_random,
                GNUTLS_RANDOM_SIZE);
    return ret;
  }

  return 0;
}

#ifdef ENABLE_SSL3
/* Calculate The SSL3 Finished message
 */
# define SSL3_CLIENT_MSG "CLNT"
# define SSL3_SERVER_MSG "SRVR"
# define SSL_MSG_LEN 4
static int
_gnutls_ssl3_finished(gnutls_session_t session, int type, uint8_t * ret,
          int sending)
{
  digest_hd_st td_md5;
  digest_hd_st td_sha;
  const char *mesg;
  int rc, len;

  if (sending)
    len = session->internals.handshake_hash_buffer.length;
  else
    len = session->internals.handshake_hash_buffer_prev_len;

  rc = _gnutls_hash_init(&td_sha, hash_to_entry(GNUTLS_DIG_SHA1));
  if (rc < 0)
    return gnutls_assert_val(rc);

  rc = _gnutls_hash_init(&td_md5, hash_to_entry(GNUTLS_DIG_MD5));
  if (rc < 0) {
    _gnutls_hash_deinit(&td_sha, NULL);
    return gnutls_assert_val(rc);
  }

  _gnutls_hash(&td_sha,
         session->internals.handshake_hash_buffer.data, len);
  _gnutls_hash(&td_md5,
         session->internals.handshake_hash_buffer.data, len);

  if (type == GNUTLS_SERVER)
    mesg = SSL3_SERVER_MSG;
  else
    mesg = SSL3_CLIENT_MSG;

  _gnutls_hash(&td_md5, mesg, SSL_MSG_LEN);
  _gnutls_hash(&td_sha, mesg, SSL_MSG_LEN);

  rc = _gnutls_mac_deinit_ssl3_handshake(&td_md5, ret,
                 session->security_parameters.
                 master_secret,
                 GNUTLS_MASTER_SIZE);
  if (rc < 0) {
    _gnutls_hash_deinit(&td_md5, NULL);
    _gnutls_hash_deinit(&td_sha, NULL);
    return gnutls_assert_val(rc);
  }

  rc = _gnutls_mac_deinit_ssl3_handshake(&td_sha, &ret[16],
                 session->security_parameters.
                 master_secret,
                 GNUTLS_MASTER_SIZE);
  if (rc < 0) {
    _gnutls_hash_deinit(&td_sha, NULL);
    return gnutls_assert_val(rc);
  }

  return 0;
}
#endif

/* Hash the handshake messages as required by TLS 1.0
 */
#define SERVER_MSG "server finished"
#define CLIENT_MSG "client finished"
#define TLS_MSG_LEN 15
static int
_gnutls_finished(gnutls_session_t session, int type, void *ret, int sending)
{
  const int siz = TLS_MSG_LEN;
  uint8_t concat[MAX_HASH_SIZE];
  size_t hash_len;
  const char *mesg;
  int rc, len, algorithm;

  if (sending)
    len = session->internals.handshake_hash_buffer.length;
  else
    len = session->internals.handshake_hash_buffer_prev_len;

  algorithm = session->security_parameters.prf->id;
  rc = _gnutls_hash_fast(algorithm,
             session->internals.handshake_hash_buffer.data,
             len, concat);
  if (rc < 0)
    return gnutls_assert_val(rc);

  hash_len = session->security_parameters.prf->output_size;

  if (type == GNUTLS_SERVER) {
    mesg = SERVER_MSG;
  } else {
    mesg = CLIENT_MSG;
  }

  _gnutls_memory_mark_defined(session->security_parameters.master_secret,
            GNUTLS_MASTER_SIZE);
  rc = _gnutls_PRF(session,
       session->security_parameters.master_secret,
       GNUTLS_MASTER_SIZE, mesg, siz, concat, hash_len,
       12, ret);
  if (rc < 0) {
    _gnutls_memory_mark_undefined(session->
                security_parameters.master_secret,
                GNUTLS_MASTER_SIZE);
  }
  return rc;
}

/* returns the 0 on success or a negative error code.
 */
int
_gnutls_negotiate_version(gnutls_session_t session,
        uint8_t major, uint8_t minor, unsigned allow_tls13)
{
  const version_entry_st *vers;
  const version_entry_st *aversion = nversion_to_entry(major, minor);

  /* if we do not support that version, unless that version is TLS 1.2;
   * TLS 1.2 is handled separately because it is always advertized under TLS 1.3 or later */
  if (aversion == NULL ||
      _gnutls_nversion_is_supported(session, major, minor) == 0) {

    if (aversion && aversion->id == GNUTLS_TLS1_2) {
      vers = _gnutls_version_max(session);
      if (unlikely(vers == NULL))
        return
            gnutls_assert_val
            (GNUTLS_E_NO_CIPHER_SUITES);

      if (vers->id >= GNUTLS_TLS1_2) {
        session->security_parameters.pversion =
            aversion;
        return 0;
      }
    }

    /* if we get an unknown/unsupported version, then fail if the version we
     * got is too low to be supported */
    if (!_gnutls_version_is_too_high(session, major, minor))
      return
          gnutls_assert_val
          (GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

    /* If he requested something we do not support
     * then we send him the highest we support.
     */
    vers = _gnutls_legacy_version_max(session);
    if (vers == NULL) {
      /* this check is not really needed.
       */
      gnutls_assert();
      return GNUTLS_E_UNKNOWN_CIPHER_SUITE;
    }

    session->security_parameters.pversion = vers;

    return 0;
  } else {
    session->security_parameters.pversion = aversion;

    /* we do not allow TLS1.3 negotiation using this mechanism */
    if (aversion->tls13_sem && !allow_tls13) {
      vers = _gnutls_legacy_version_max(session);
      session->security_parameters.pversion = vers;
    }

    return 0;
  }
}

/* This function returns:
 *  - zero on success
 *  - GNUTLS_E_INT_RET_0 if GNUTLS_E_AGAIN || GNUTLS_E_INTERRUPTED were returned by the callback
 *  - a negative error code on other error
 */
int
_gnutls_user_hello_func(gnutls_session_t session, uint8_t major, uint8_t minor)
{
  int ret, sret = 0;
  const version_entry_st *vers, *old_vers;
  const version_entry_st *new_max;

  if (session->internals.user_hello_func != NULL) {
    ret = session->internals.user_hello_func(session);

    if (ret == GNUTLS_E_AGAIN || ret == GNUTLS_E_INTERRUPTED) {
      gnutls_assert();
      sret = GNUTLS_E_INT_RET_0;
    } else if (ret < 0) {
      gnutls_assert();
      return ret;
    }

    /* This callback is often used to switch the priority string of the
     * server, and that includes switching version which we have already
     * negotiated; note that this doesn't apply when resuming as the version
     * negotiation is already complete. */
    if (!session->internals.resumed) {
      new_max = _gnutls_version_max(session);
      old_vers = get_version(session);

      if (!old_vers->tls13_sem
          || (new_max && !new_max->tls13_sem)) {
#if GNUTLS_TLS_VERSION_MAX != GNUTLS_TLS1_3
# error "Need to update the following logic"
#endif
        /* Here we need to renegotiate the version since the callee might
         * have disabled some TLS versions. This logic does not cope for
         * protocols later than TLS1.3 if they have the tls13_sem set */
        ret =
            _gnutls_negotiate_version(session, major,
                    minor, 0);
        if (ret < 0)
          return gnutls_assert_val(ret);

        vers = get_version(session);
        if (old_vers != vers) {
          /* at this point we need to regenerate the random value to
           * avoid the peer detecting this session as a rollback
           * attempt. */
          ret =
              _gnutls_gen_server_random(session,
                      vers->id);
          if (ret < 0)
            return gnutls_assert_val(ret);
        }
      }
    }
  }
  return sret;
}

/* Associates the right credential types for the session, and
 * performs sanity checks. */
static int set_auth_types(gnutls_session_t session)
{
  const version_entry_st *ver = get_version(session);
  gnutls_kx_algorithm_t kx;

  /* sanity check:
   * we see TLS1.3 negotiated but no key share was sent */
  if (ver->tls13_sem) {
    if (unlikely
        (!(session->internals.hsk_flags & HSK_PSK_KE_MODE_PSK)
         && !(session->
        internals.hsk_flags & HSK_KEY_SHARE_RECEIVED))) {
      return gnutls_assert_val(GNUTLS_E_MISSING_EXTENSION);
    }

    /* Under TLS1.3 this returns a KX which matches the negotiated
     * groups from the key shares; if we are resuming then the KX seen
     * here doesn't match the original session. */
    if (!session->internals.resumed)
      kx = gnutls_kx_get(session);
    else
      kx = GNUTLS_KX_UNKNOWN;
  } else {
    /* TLS1.2 or earlier, kx is associated with ciphersuite */
    kx = session->security_parameters.cs->kx_algorithm;
  }

  if (kx != GNUTLS_KX_UNKNOWN) {
    session->security_parameters.server_auth_type =
        _gnutls_map_kx_get_cred(kx, 1);
    session->security_parameters.client_auth_type =
        _gnutls_map_kx_get_cred(kx, 0);
  } else if (unlikely(!session->internals.resumed)) {
    /* Here we can only arrive if something we received
     * prevented the session from completing. */
    return gnutls_assert_val(GNUTLS_E_ILLEGAL_PARAMETER);
  }

  return 0;
}

/* Read a client hello packet.
 * A client hello must be a known version client hello
 * or version 2.0 client hello (only for compatibility
 * since SSL version 2.0 is not supported).
 */
static int
read_client_hello(gnutls_session_t session, uint8_t * data, int datalen)
{
  uint8_t session_id_len;
  int pos = 0, ret;
  uint16_t suite_size, comp_size;
  int ext_size;
  int neg_version, sret = 0;
  int len = datalen;
  uint8_t major, minor;
  uint8_t *suite_ptr, *comp_ptr, *session_id, *ext_ptr;
  const version_entry_st *vers;

  DECR_LEN(len, 2);
  _gnutls_handshake_log("HSK[%p]: Client's version: %d.%d\n",
            session, data[pos], data[pos + 1]);

  major = data[pos];
  minor = data[pos + 1];

  set_adv_version(session, major, minor);

  ret = _gnutls_negotiate_version(session, major, minor, 0);
  if (ret < 0)
    return gnutls_assert_val(ret);

  vers = get_version(session);
  if (vers == NULL)
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  neg_version = vers->id;

  pos += 2;

  /* Read client random value.
   */
  DECR_LEN(len, GNUTLS_RANDOM_SIZE);
  _gnutls_set_client_random(session, &data[pos]);

  pos += GNUTLS_RANDOM_SIZE;

  ret = _gnutls_gen_server_random(session, neg_version);
  if (ret < 0)
    return gnutls_assert_val(ret);

  session->security_parameters.timestamp = gnutls_time(NULL);

  DECR_LEN(len, 1);
  session_id_len = data[pos++];

  /* RESUME SESSION
   */
  if (session_id_len > GNUTLS_MAX_SESSION_ID_SIZE) {
    gnutls_assert();
    return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
  }
  DECR_LEN(len, session_id_len);
  session_id = &data[pos];
  pos += session_id_len;

  if (IS_DTLS(session)) {
    int cookie_size;

    DECR_LEN(len, 1);
    cookie_size = data[pos++];
    DECR_LEN(len, cookie_size);
    pos += cookie_size;
  }

  /* move forward to extensions and store other vals */
  DECR_LEN(len, 2);
  suite_size = _gnutls_read_uint16(&data[pos]);
  pos += 2;

  if (suite_size == 0 || (suite_size % 2) != 0)
    return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

  suite_ptr = &data[pos];
  DECR_LEN(len, suite_size);
  pos += suite_size;

  DECR_LEN(len, 1);
  comp_size = data[pos++];  /* the number of compression methods */

  if (comp_size == 0)
    return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

  comp_ptr = &data[pos];
  DECR_LEN(len, comp_size);
  pos += comp_size;

  ext_ptr = &data[pos];
  ext_size = len;

  /* Parse only the mandatory to read extensions for resumption
   * and version negotiation. We don't want to parse any other
   * extensions since  we don't want new extension values to override
   * the resumed ones. */
  ret =
      _gnutls_parse_hello_extensions(session,
             GNUTLS_EXT_FLAG_CLIENT_HELLO,
             GNUTLS_EXT_VERSION_NEG, ext_ptr,
             ext_size);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret =
      _gnutls_parse_hello_extensions(session,
             GNUTLS_EXT_FLAG_CLIENT_HELLO,
             GNUTLS_EXT_MANDATORY, ext_ptr,
             ext_size);
  if (ret < 0)
    return gnutls_assert_val(ret);

  vers = get_version(session);
  if (unlikely(vers == NULL))
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  if (!vers->tls13_sem) {
    ret =
        _gnutls_server_restore_session(session, session_id,
               session_id_len);

    if (session_id_len > 0)
      session->internals.resumption_requested = 1;

    if (ret == 0) { /* resumed using default TLS resumption! */
      ret =
          _gnutls_server_select_suite(session, suite_ptr,
              suite_size, 1);
      if (ret < 0)
        return gnutls_assert_val(ret);

      ret = tls12_resume_copy_required_vals(session, 0);
      if (ret < 0)
        return gnutls_assert_val(ret);

      session->internals.resumed = true;

      return _gnutls_user_hello_func(session, major, minor);
    } else {
      ret =
          _gnutls_generate_session_id
          (session->security_parameters.session_id,
           &session->security_parameters.session_id_size);
      if (ret < 0)
        return gnutls_assert_val(ret);

      session->internals.resumed = false;
    }
  } else {   /* TLS1.3 */
    /* we echo client's session ID - length was checked previously */
    assert(session_id_len <= GNUTLS_MAX_SESSION_ID_SIZE);
    if (session_id_len > 0)
      memcpy(session->security_parameters.session_id,
             session_id, session_id_len);
    session->security_parameters.session_id_size = session_id_len;
  }

  /* Parse the extensions (if any)
   *
   * Unconditionally try to parse extensions; safe renegotiation uses them in
   * sslv3 and higher, even though sslv3 doesn't officially support them.
   */
  ret =
      _gnutls_parse_hello_extensions(session,
             GNUTLS_EXT_FLAG_CLIENT_HELLO,
             GNUTLS_EXT_APPLICATION, ext_ptr,
             ext_size);
  /* len is the rest of the parsed length */
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  /* we cache this error code */
  sret = _gnutls_user_hello_func(session, major, minor);
  if (sret < 0 && sret != GNUTLS_E_INT_RET_0) {
    gnutls_assert();
    return sret;
  }

  /* Session tickets are parsed in this point */
  ret =
      _gnutls_parse_hello_extensions(session,
             GNUTLS_EXT_FLAG_CLIENT_HELLO,
             GNUTLS_EXT_TLS, ext_ptr, ext_size);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  if (session->internals.hsk_flags & HSK_EARLY_DATA_ACCEPTED) {
    const cipher_entry_st *ce;
    const mac_entry_st *me;
    record_parameters_st *params;

    ce = cipher_to_entry(session->internals.
             resumed_security_parameters.
             cs->block_algorithm);
    me = mac_to_entry(session->internals.
          resumed_security_parameters.
          cs->mac_algorithm);

    ret = _gnutls_epoch_get(session, EPOCH_NEXT, &params);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }

    params->cipher = ce;
    params->mac = me;

    ret = _tls13_read_connection_state_init(session, STAGE_EARLY);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }

    _gnutls_epoch_bump(session);
    ret = _gnutls_epoch_dup(session, EPOCH_READ_CURRENT);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }
  }

  /* resumed by session_ticket extension */
  if (!vers->tls13_sem && session->internals.resumed) {
    session->internals.resumed_security_parameters.
        max_record_recv_size =
        session->security_parameters.max_record_recv_size;
    session->internals.resumed_security_parameters.
        max_record_send_size =
        session->security_parameters.max_record_send_size;

    ret =
        _gnutls_server_select_suite(session, suite_ptr, suite_size,
            1);
    if (ret < 0)
      return gnutls_assert_val(ret);

    ret = tls12_resume_copy_required_vals(session, 1);
    if (ret < 0)
      return gnutls_assert_val(ret);

    /* to indicate to the client that the current session is resumed */
    memcpy(session->security_parameters.session_id, session_id,
           session_id_len);
    session->security_parameters.session_id_size = session_id_len;

    return 0;
  }

  /* select an appropriate cipher suite (as well as certificate)
   */
  ret = _gnutls_server_select_suite(session, suite_ptr, suite_size, 0);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  /* Only at this point we know the version we are actually going to use
   * ("supported_versions" extension is parsed, user_hello_func is called,
   * legacy version negotiation is done). */
  vers = get_version(session);
  if (unlikely(vers == NULL))
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  if (_gnutls_version_priority(session, vers->id) < 0)
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  /* check if EMS is required */
  if (!vers->tls13_sem &&
      vers->id != GNUTLS_SSL3 && vers->id != GNUTLS_DTLS0_9 &&
      session->internals.priorities->force_ext_master_secret &&
      !session->security_parameters.ext_master_secret) {
    return gnutls_assert_val(GNUTLS_E_INSUFFICIENT_SECURITY);
  }

  _gnutls_handshake_log("HSK[%p]: Selected version %s\n", session,
            vers->name);

  /* select appropriate compression method */
  ret = check_if_null_comp_present(session, comp_ptr, comp_size);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  /* call extensions that are intended to be parsed after the ciphersuite/cert
   * are known. */
  ret =
      _gnutls_parse_hello_extensions(session,
             GNUTLS_EXT_FLAG_CLIENT_HELLO,
             _GNUTLS_EXT_TLS_POST_CS, ext_ptr,
             ext_size);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  /* Calculate TLS 1.3 Early Secret */
  if (session->security_parameters.pversion->tls13_sem &&
      !(session->internals.hsk_flags & HSK_PSK_SELECTED)) {
    ret = _tls13_init_secret(session, NULL, 0);
    if (ret < 0)
      return gnutls_assert_val(ret);
  }

  ret = set_auth_types(session);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  return sret;
}

/* This is to be called after sending CHANGE CIPHER SPEC packet
 * and initializing encryption. This is the first encrypted message
 * we send.
 */
int _gnutls_send_finished(gnutls_session_t session, int again)
{
  mbuffer_st *bufel;
  uint8_t *data;
  int ret;
  size_t vdata_size = 0;
  const version_entry_st *vers;

  if (again == 0) {
    bufel = _gnutls_handshake_alloc(session, MAX_VERIFY_DATA_SIZE);
    if (bufel == NULL) {
      gnutls_assert();
      return GNUTLS_E_MEMORY_ERROR;
    }
    data = _mbuffer_get_udata_ptr(bufel);

    vers = get_version(session);
    if (unlikely(vers == NULL))
      return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

#ifdef ENABLE_SSL3
    if (vers->id == GNUTLS_SSL3) {
      ret =
          _gnutls_ssl3_finished(session,
              session->security_parameters.
              entity, data, 1);
      _mbuffer_set_udata_size(bufel, 36);
    } else {  /* TLS 1.0+ */
#endif
      ret = _gnutls_finished(session,
                 session->
                 security_parameters.entity, data,
                 1);
      _mbuffer_set_udata_size(bufel, 12);
#ifdef ENABLE_SSL3
    }
#endif

    if (ret < 0) {
      gnutls_assert();
      return ret;
    }

    vdata_size = _mbuffer_get_udata_size(bufel);

    ret = _gnutls_ext_sr_finished(session, data, vdata_size, 0);
    if (ret < 0) {
      gnutls_assert();
      return ret;
    }

    if ((!session->internals.resumed
         && session->security_parameters.entity == GNUTLS_CLIENT)
        || (session->internals.resumed
      && session->security_parameters.entity ==
      GNUTLS_SERVER)) {
      /* if we are a client not resuming - or we are a server resuming */
      _gnutls_handshake_log
          ("HSK[%p]: recording tls-unique CB (send)\n",
           session);
      memcpy(session->internals.cb_tls_unique, data,
             vdata_size);
      session->internals.cb_tls_unique_len = vdata_size;
    }

    ret =
        _gnutls_send_handshake(session, bufel,
             GNUTLS_HANDSHAKE_FINISHED);
  } else {
    ret =
        _gnutls_send_handshake(session, NULL,
             GNUTLS_HANDSHAKE_FINISHED);
  }

  return ret;
}

/* This is to be called after sending our finished message. If everything
 * went fine we have negotiated a secure connection
 */
int _gnutls_recv_finished(gnutls_session_t session)
{
  uint8_t data[MAX_VERIFY_DATA_SIZE], *vrfy;
  gnutls_buffer_st buf;
  int data_size;
  int ret;
  int vrfy_size;
  const version_entry_st *vers = get_version(session);

  if (unlikely(vers == NULL))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  ret =
      _gnutls_recv_handshake(session, GNUTLS_HANDSHAKE_FINISHED, 0, &buf);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  vrfy = buf.data;
  vrfy_size = buf.length;

#ifdef ENABLE_SSL3
  if (vers->id == GNUTLS_SSL3)
    data_size = 36;
  else
#endif
    data_size = 12;

  if (vrfy_size != data_size) {
    gnutls_assert();
    ret = GNUTLS_E_ERROR_IN_FINISHED_PACKET;
    goto cleanup;
  }

#ifdef ENABLE_SSL3
  if (vers->id == GNUTLS_SSL3) {
    ret =
        _gnutls_ssl3_finished(session,
            (session->security_parameters.entity +
             1) % 2, data, 0);
  } else      /* TLS 1.0+ */
#endif
    ret =
        _gnutls_finished(session,
             (session->security_parameters.entity +
              1) % 2, data, 0);

  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

#if defined(FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION)
  /* When fuzzying allow to proceed without verifying the handshake
   * consistency */
  (void)vrfy;
# warning This is unsafe for production builds

#else
  if (memcmp(vrfy, data, data_size) != 0) {
    gnutls_assert();
    ret = GNUTLS_E_ERROR_IN_FINISHED_PACKET;
    goto cleanup;
  }
#endif

  ret = _gnutls_ext_sr_finished(session, data, data_size, 1);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  if ((session->internals.resumed
       && session->security_parameters.entity == GNUTLS_CLIENT)
      || (!session->internals.resumed
    && session->security_parameters.entity == GNUTLS_SERVER)) {
    /* if we are a client resuming - or we are a server not resuming */
    _gnutls_handshake_log
        ("HSK[%p]: recording tls-unique CB (recv)\n", session);
    memcpy(session->internals.cb_tls_unique, data, data_size);
    session->internals.cb_tls_unique_len = data_size;
  }

 cleanup:
  _gnutls_buffer_clear(&buf);

  return ret;
}

/* This selects the best supported ciphersuite from the given ones. Then
 * it adds the suite to the session and performs some checks.
 *
 * When @scsv_only is non-zero only the available SCSVs are parsed
 * and acted upon.
 */
int
_gnutls_server_select_suite(gnutls_session_t session, uint8_t * data,
          unsigned int datalen, unsigned scsv_only)
{
  int ret;
  unsigned int i;
  ciphersuite_list_st peer_clist;
  const gnutls_cipher_suite_entry_st *selected;
  gnutls_kx_algorithm_t kx;
  int retval;
  const version_entry_st *vers = get_version(session);

  peer_clist.size = 0;

  for (i = 0; i < datalen; i += 2) {
    /* we support the TLS renegotiation SCSV, even if we are
     * not under SSL 3.0, because openssl sends this SCSV
     * on resumption unconditionally. */
    /* TLS_RENEGO_PROTECTION_REQUEST = { 0x00, 0xff } */
    if (session->internals.priorities->sr != SR_DISABLED &&
        data[i] == GNUTLS_RENEGO_PROTECTION_REQUEST_MAJOR &&
        data[i + 1] == GNUTLS_RENEGO_PROTECTION_REQUEST_MINOR) {
      _gnutls_handshake_log
          ("HSK[%p]: Received safe renegotiation CS\n",
           session);
      retval = _gnutls_ext_sr_recv_cs(session);
      if (retval < 0) {
        gnutls_assert();
        return retval;
      }
    }

    /* TLS_FALLBACK_SCSV */
    if (data[i] == GNUTLS_FALLBACK_SCSV_MAJOR &&
        data[i + 1] == GNUTLS_FALLBACK_SCSV_MINOR) {
      const version_entry_st *max =
          _gnutls_version_max(session);

      _gnutls_handshake_log
          ("HSK[%p]: Received fallback CS\n", session);

      if (vers != max)
        return
            gnutls_assert_val
            (GNUTLS_E_INAPPROPRIATE_FALLBACK);
    } else if (!scsv_only) {
      if (peer_clist.size < MAX_CIPHERSUITE_SIZE) {
        peer_clist.entry[peer_clist.size] =
            ciphersuite_to_entry(&data[i]);
        if (peer_clist.entry[peer_clist.size] != NULL)
          peer_clist.size++;
      }
    }
  }

  if (scsv_only)
    return 0;

  ret =
      _gnutls_figure_common_ciphersuite(session, &peer_clist, &selected);
  if (ret < 0) {
    return gnutls_assert_val(ret);
  }

  _gnutls_handshake_log
      ("HSK[%p]: Selected cipher suite: %s\n", session, selected->name);

  ret = _gnutls_set_cipher_suite2(session, selected);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  if (!vers->tls13_sem) {
    /* check if the credentials (username, public key etc.) are ok
     */
    kx = selected->kx_algorithm;
    if (_gnutls_get_kx_cred(session, kx) == NULL) {
      gnutls_assert();
      return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
    }

    /* set the mod_auth_st to the appropriate struct
     * according to the KX algorithm. This is needed since all the
     * handshake functions are read from there;
     */
    session->internals.auth_struct = _gnutls_kx_auth_struct(kx);
    if (session->internals.auth_struct == NULL) {
      _gnutls_handshake_log
          ("HSK[%p]: Cannot find the appropriate handler for the KX algorithm\n",
           session);
      gnutls_assert();
      return GNUTLS_E_INTERNAL_ERROR;
    }
  }

  return 0;

}

/* This checks whether the null compression method is present.
 */
static int
check_if_null_comp_present(gnutls_session_t session,
         uint8_t * data, int datalen)
{
  int j;

  for (j = 0; j < datalen; j++) {
    if (data[j] == 0)
      return 0;
  }

  /* we were not able to find a the NULL compression
   * algorithm
   */
  gnutls_assert();
  return GNUTLS_E_UNKNOWN_COMPRESSION_ALGORITHM;

}

/* This function sends an empty handshake packet. (like hello request).
 * If the previous _gnutls_send_empty_handshake() returned
 * GNUTLS_E_AGAIN or GNUTLS_E_INTERRUPTED, then it must be called again
 * (until it returns ok), with NULL parameters.
 */
static int
_gnutls_send_empty_handshake(gnutls_session_t session,
           gnutls_handshake_description_t type, int again)
{
  mbuffer_st *bufel;

  if (again == 0) {
    bufel = _gnutls_handshake_alloc(session, 0);
    if (bufel == NULL) {
      gnutls_assert();
      return GNUTLS_E_MEMORY_ERROR;
    }
  } else
    bufel = NULL;

  return _gnutls_send_handshake(session, bufel, type);
}

int _gnutls_call_hook_func(gnutls_session_t session,
         gnutls_handshake_description_t type,
         int post, unsigned incoming,
         const uint8_t * data, unsigned data_size)
{
  gnutls_datum_t msg = { (void *)data, data_size };

  if (session->internals.h_hook != NULL) {
    if ((session->internals.h_type == type
         || session->internals.h_type == GNUTLS_HANDSHAKE_ANY)
        && (session->internals.h_post == post
      || session->internals.h_post == GNUTLS_HOOK_BOTH)) {

      /* internal API for testing: when we are expected to
       * wait for GNUTLS_HANDSHAKE_CHANGE_CIPHER_SPEC, we
       * do so, but not when doing for all messages. The
       * reason is that change cipher specs are not handshake
       * messages, and we don't support waiting for them
       * consistently (only sending is tracked, not receiving).
       */
      if (type == GNUTLS_HANDSHAKE_CHANGE_CIPHER_SPEC &&
          session->internals.h_type !=
          GNUTLS_HANDSHAKE_CHANGE_CIPHER_SPEC)
        return 0;

      return session->internals.h_hook(session, type,
               post, incoming, &msg);
    }
  }
  return 0;
}

/* Note that the "New session ticket" handshake packet behaves differently under
 * TLS 1.2 or 1.3. In 1.2 it is included in the handshake process, while in 1.3
 * it is sent asynchronously */
#define IS_ASYNC(t, v) \
  (t == GNUTLS_HANDSHAKE_HELLO_REQUEST || t == GNUTLS_HANDSHAKE_KEY_UPDATE || \
   (t == GNUTLS_HANDSHAKE_NEW_SESSION_TICKET && v->tls13_sem))

int
_gnutls_send_handshake(gnutls_session_t session, mbuffer_st * bufel,
           gnutls_handshake_description_t type)
{
  return _gnutls_send_handshake2(session, bufel, type, 0);
}

/* This function sends a handshake message of type 'type' containing the
 * data specified here. If the previous _gnutls_send_handshake() returned
 * GNUTLS_E_AGAIN or GNUTLS_E_INTERRUPTED, then it must be called again
 * (until it returns ok), with NULL parameters.
 */
int
_gnutls_send_handshake2(gnutls_session_t session, mbuffer_st * bufel,
      gnutls_handshake_description_t type,
      unsigned queue_only)
{
  int ret;
  uint8_t *data;
  uint32_t datasize, i_datasize;
  int pos = 0;
  const version_entry_st *vers = get_version(session);

  if (bufel == NULL) {
    /* we are resuming a previously interrupted
     * send.
     */
    ret = _gnutls_handshake_io_write_flush(session);
    return ret;

  }

  /* first run */
  data = _mbuffer_get_uhead_ptr(bufel);
  i_datasize = _mbuffer_get_udata_size(bufel);
  datasize = i_datasize + _mbuffer_get_uhead_size(bufel);

  data[pos++] = (uint8_t) REAL_HSK_TYPE(type);
  _gnutls_write_uint24(_mbuffer_get_udata_size(bufel), &data[pos]);
  pos += 3;

  /* Add DTLS handshake fragment headers.  The message will be
   * fragmented later by the fragmentation sub-layer. All fields must
   * be set properly for HMAC. The HMAC requires we pretend that the
   * message was sent in a single fragment. */
  if (IS_DTLS(session)) {
    _gnutls_write_uint16(session->internals.dtls.hsk_write_seq++,
             &data[pos]);
    pos += 2;

    /* Fragment offset */
    _gnutls_write_uint24(0, &data[pos]);
    pos += 3;

    /* Fragment length */
    _gnutls_write_uint24(i_datasize, &data[pos]);
    /* pos += 3; */
  }

  _gnutls_handshake_log("HSK[%p]: %s was queued [%ld bytes]\n",
            session, _gnutls_handshake2str(type),
            (long)datasize);

  /* Here we keep the handshake messages in order to hash them...
   */
  if (!IS_ASYNC(type, vers)) {
    if ((ret =
         handshake_hash_add_sent(session, type, data,
               datasize)) < 0) {
      gnutls_assert();
      _mbuffer_xfree(&bufel);
      return ret;
    }
    /* If we are sending a PSK, generate early secrets here.
     * This cannot be done in pre_shared_key.c, because it
     * relies on transcript hash of a Client Hello. */
    if (type == GNUTLS_HANDSHAKE_CLIENT_HELLO &&
        session->key.binders[0].prf != NULL) {
      ret = _gnutls_generate_early_secrets_for_psk(session);
      if (ret < 0) {
        gnutls_assert();
        _mbuffer_xfree(&bufel);
        return ret;
      }
    }
  }

  ret = _gnutls_call_hook_func(session, type, GNUTLS_HOOK_PRE, 0,
             _mbuffer_get_udata_ptr(bufel),
             _mbuffer_get_udata_size(bufel));
  if (ret < 0) {
    gnutls_assert();
    _mbuffer_xfree(&bufel);
    return ret;
  }

  session->internals.last_handshake_out = type;

  ret = _gnutls_handshake_io_cache_int(session, type, bufel);
  if (ret < 0) {
    _mbuffer_xfree(&bufel);
    gnutls_assert();
    return ret;
  }

  ret = _gnutls_call_hook_func(session, type, GNUTLS_HOOK_POST, 0,
             _mbuffer_get_udata_ptr(bufel),
             _mbuffer_get_udata_size(bufel));
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  if (queue_only)
    return 0;

  /* Decide when to cache and when to send */
  if (vers && vers->tls13_sem) {

    if (session->internals.initial_negotiation_completed) {
      /* we are under TLS1.3 in a re-authentication phase.
       * we don't attempt to cache any messages */
      goto force_send;
    }

    /* The messages which are followed by another are not sent by default
     * but are cached instead */
    switch (type) {
    case GNUTLS_HANDSHAKE_SERVER_HELLO: /* always followed by something */
    case GNUTLS_HANDSHAKE_ENCRYPTED_EXTENSIONS: /* followed by finished or cert */
    case GNUTLS_HANDSHAKE_CERTIFICATE_REQUEST:  /* followed by certificate */
    case GNUTLS_HANDSHAKE_CERTIFICATE_PKT:  /* this one is followed by cert verify */
    case GNUTLS_HANDSHAKE_COMPRESSED_CERTIFICATE_PKT: /* as above */
    case GNUTLS_HANDSHAKE_CERTIFICATE_VERIFY: /* followed by finished */
      ret = 0;  /* cache */
      break;
    default:
      /* send this and any cached messages */
      goto force_send;
    }
  } else {
    /* The messages which are followed by another are not sent by default
     * but are cached instead */
    switch (type) {
    case GNUTLS_HANDSHAKE_CERTIFICATE_PKT:  /* this one is followed by ServerHelloDone
               * or ClientKeyExchange always.
               */
    case GNUTLS_HANDSHAKE_COMPRESSED_CERTIFICATE_PKT: /* as above */
    case GNUTLS_HANDSHAKE_CERTIFICATE_STATUS:
    case GNUTLS_HANDSHAKE_SERVER_KEY_EXCHANGE:  /* as above */
    case GNUTLS_HANDSHAKE_SERVER_HELLO: /* as above */
    case GNUTLS_HANDSHAKE_CERTIFICATE_REQUEST:  /* as above */
    case GNUTLS_HANDSHAKE_NEW_SESSION_TICKET: /* followed by ChangeCipherSpec */

      /* now for client Certificate, ClientKeyExchange and
       * CertificateVerify are always followed by ChangeCipherSpec
       */
    case GNUTLS_HANDSHAKE_CERTIFICATE_VERIFY:
    case GNUTLS_HANDSHAKE_CLIENT_KEY_EXCHANGE:
      ret = 0;
      break;
    default:
      /* send this and any cached messages */
      goto force_send;
    }
  }

  return ret;

 force_send:
  return _gnutls_handshake_io_write_flush(session);
}

#define CHECK_SIZE(ll) \
  if ((session->internals.max_handshake_data_buffer_size > 0) && \
      (((ll) + session->internals.handshake_hash_buffer.length) > \
       session->internals.max_handshake_data_buffer_size)) { \
    _gnutls_debug_log("Handshake buffer length is %u (max: %u)\n", (unsigned)((ll) + session->internals.handshake_hash_buffer.length), (unsigned)session->internals.max_handshake_data_buffer_size); \
    return gnutls_assert_val(GNUTLS_E_HANDSHAKE_TOO_LARGE); \
    }

/* This function add the handshake headers and the
 * handshake data to the handshake hash buffers. Needed
 * for the finished messages calculations.
 */
static int
handshake_hash_add_recvd(gnutls_session_t session,
       gnutls_handshake_description_t recv_type,
       uint8_t * header, uint16_t header_size,
       uint8_t * dataptr, uint32_t datalen)
{
  int ret;
  const version_entry_st *vers = get_version(session);

  if (unlikely(vers == NULL))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  if ((vers->id != GNUTLS_DTLS0_9 &&
       recv_type == GNUTLS_HANDSHAKE_HELLO_VERIFY_REQUEST) ||
      IS_ASYNC(recv_type, vers))
    return 0;

  CHECK_SIZE(header_size + datalen);

  session->internals.handshake_hash_buffer_prev_len =
      session->internals.handshake_hash_buffer.length;

  if (vers->id != GNUTLS_DTLS0_9) {
    ret =
        _gnutls_buffer_append_data(&session->internals.
                 handshake_hash_buffer, header,
                 header_size);
    if (ret < 0)
      return gnutls_assert_val(ret);
  }
  if (datalen > 0) {
    ret =
        _gnutls_buffer_append_data(&session->internals.
                 handshake_hash_buffer, dataptr,
                 datalen);
    if (ret < 0)
      return gnutls_assert_val(ret);
  }

  /* save the size until client KX. That is because the TLS
   * session hash is calculated up to this message.
   */
  if (recv_type == GNUTLS_HANDSHAKE_CLIENT_HELLO)
    session->internals.handshake_hash_buffer_client_hello_len =
        session->internals.handshake_hash_buffer.length;
  if (recv_type == GNUTLS_HANDSHAKE_CLIENT_KEY_EXCHANGE)
    session->internals.handshake_hash_buffer_client_kx_len =
        session->internals.handshake_hash_buffer.length;
  if (recv_type == GNUTLS_HANDSHAKE_FINISHED
      && session->security_parameters.entity == GNUTLS_CLIENT)
    session->internals.handshake_hash_buffer_server_finished_len =
        session->internals.handshake_hash_buffer.length;
  if (recv_type == GNUTLS_HANDSHAKE_FINISHED
      && session->security_parameters.entity == GNUTLS_SERVER)
    session->internals.handshake_hash_buffer_client_finished_len =
        session->internals.handshake_hash_buffer.length;

  return 0;
}

/* This function will store the handshake message we sent.
 */
static int
handshake_hash_add_sent(gnutls_session_t session,
      gnutls_handshake_description_t type,
      uint8_t * dataptr, uint32_t datalen)
{
  int ret;
  const version_entry_st *vers = get_version(session);

  if (unlikely(vers == NULL))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  if (IS_ASYNC(type, vers))
    return 0;

  CHECK_SIZE(datalen);

  if (vers->id == GNUTLS_DTLS0_9) {
    /* Old DTLS doesn't include the header in the MAC */
    if (datalen < 12) {
      gnutls_assert();
      return GNUTLS_E_INTERNAL_ERROR;
    }
    dataptr += 12;
    datalen -= 12;

    if (datalen == 0)
      return 0;
  }

  ret =
      _gnutls_buffer_append_data(&session->internals.
               handshake_hash_buffer, dataptr, datalen);
  if (ret < 0)
    return gnutls_assert_val(ret);

  if (type == GNUTLS_HANDSHAKE_CLIENT_HELLO)
    session->internals.handshake_hash_buffer_client_hello_len =
        session->internals.handshake_hash_buffer.length;
  if (type == GNUTLS_HANDSHAKE_CLIENT_KEY_EXCHANGE)
    session->internals.handshake_hash_buffer_client_kx_len =
        session->internals.handshake_hash_buffer.length;
  if (type == GNUTLS_HANDSHAKE_FINISHED
      && session->security_parameters.entity == GNUTLS_SERVER)
    session->internals.handshake_hash_buffer_server_finished_len =
        session->internals.handshake_hash_buffer.length;
  if (type == GNUTLS_HANDSHAKE_FINISHED
      && session->security_parameters.entity == GNUTLS_CLIENT)
    session->internals.handshake_hash_buffer_client_finished_len =
        session->internals.handshake_hash_buffer.length;

  return 0;
}

/* This function will receive handshake messages of the given types,
 * and will pass the message to the right place in order to be processed.
 * E.g. for the SERVER_HELLO message (if it is expected), it will be
 * passed to _gnutls_recv_hello().
 */
int
_gnutls_recv_handshake(gnutls_session_t session,
           gnutls_handshake_description_t type,
           unsigned int optional, gnutls_buffer_st * buf)
{
  int ret, ret2;
  handshake_buffer_st hsk;

  ret = _gnutls_handshake_io_recv_int(session, type, &hsk, optional);
  if (ret < 0) {
    if (optional != 0
        && ret == GNUTLS_E_UNEXPECTED_HANDSHAKE_PACKET) {
      if (buf)
        _gnutls_buffer_init(buf);
      return 0;
    }

    return gnutls_assert_val_fatal(ret);
  }
  session->internals.last_handshake_in = hsk.htype;

  ret =
      _gnutls_call_hook_func(session, hsk.htype, GNUTLS_HOOK_PRE, 1,
           hsk.data.data, hsk.data.length);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  ret = handshake_hash_add_recvd(session, hsk.rtype,
               hsk.header, hsk.header_size,
               hsk.data.data, hsk.data.length);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

  switch (hsk.htype) {
  case GNUTLS_HANDSHAKE_CLIENT_HELLO_V2:
  case GNUTLS_HANDSHAKE_CLIENT_HELLO:
    if (!(IS_SERVER(session))) {
      ret = gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
      goto cleanup;
    }

#ifdef ENABLE_SSL2
    if (hsk.htype == GNUTLS_HANDSHAKE_CLIENT_HELLO_V2)
      ret =
          _gnutls_read_client_hello_v2(session,
               hsk.data.data,
               hsk.data.length);
    else
#endif
    {
      /* Reference the full ClientHello in case an extension needs it */
      ret = _gnutls_ext_set_full_client_hello(session, &hsk);
      if (ret < 0)
        return gnutls_assert_val(ret);

      ret = read_client_hello(session, hsk.data.data,
            hsk.data.length);
    }

    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    break;

  case GNUTLS_HANDSHAKE_SERVER_HELLO:
    if (IS_SERVER(session)) {
      ret = gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
      goto cleanup;
    }

    ret = read_server_hello(session, hsk.data.data,
          hsk.data.length);

    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    break;
  case GNUTLS_HANDSHAKE_HELLO_VERIFY_REQUEST:
    if (IS_SERVER(session)) {
      ret = gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
      goto cleanup;
    }

    ret =
        recv_hello_verify_request(session,
                hsk.data.data, hsk.data.length);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    } else {
      /* Signal our caller we have received a verification cookie
         and ClientHello needs to be sent again. */
      ret = 1;
    }

    break;
  case GNUTLS_HANDSHAKE_HELLO_RETRY_REQUEST:{
      /* hash buffer synth message is generated during hello retry parsing */
      gnutls_datum_t hrr = { hsk.data.data, hsk.data.length };

      if (IS_SERVER(session)) {
        ret =
            gnutls_assert_val
            (GNUTLS_E_UNEXPECTED_PACKET);
        goto cleanup;
      }

      ret =
          _gnutls13_recv_hello_retry_request(session,
                     &hsk.data);
      if (ret < 0) {
        gnutls_assert();
        goto cleanup;
      } else {
        /* during hello retry parsing, we reset handshake hash buffer,
         * re-add this message */
        ret =
            handshake_hash_add_recvd(session, hsk.htype,
                   hsk.header,
                   hsk.header_size,
                   hrr.data,
                   hrr.size);
        if (ret < 0) {
          gnutls_assert();
          goto cleanup;
        }

        /* Signal our caller we have received a retry request
           and ClientHello needs to be sent again. */
        ret = 1;
      }

      break;
    }
  case GNUTLS_HANDSHAKE_SERVER_HELLO_DONE:
    if (hsk.data.length == 0)
      ret = 0;
    else {
      gnutls_assert();
      ret = GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
      goto cleanup;
    }
    break;
  case GNUTLS_HANDSHAKE_CERTIFICATE_PKT:
  case GNUTLS_HANDSHAKE_COMPRESSED_CERTIFICATE_PKT:
  case GNUTLS_HANDSHAKE_CERTIFICATE_STATUS:
  case GNUTLS_HANDSHAKE_FINISHED:
  case GNUTLS_HANDSHAKE_ENCRYPTED_EXTENSIONS:
  case GNUTLS_HANDSHAKE_SERVER_KEY_EXCHANGE:
  case GNUTLS_HANDSHAKE_CLIENT_KEY_EXCHANGE:
  case GNUTLS_HANDSHAKE_CERTIFICATE_REQUEST:
  case GNUTLS_HANDSHAKE_CERTIFICATE_VERIFY:
  case GNUTLS_HANDSHAKE_SUPPLEMENTAL:
  case GNUTLS_HANDSHAKE_NEW_SESSION_TICKET:
  case GNUTLS_HANDSHAKE_END_OF_EARLY_DATA:
    ret = hsk.data.length;
    break;
  default:
    gnutls_assert();
    /* we shouldn't actually arrive here in any case .
     * unexpected messages should be caught after _gnutls_handshake_io_recv_int()
     */
    ret = GNUTLS_E_UNEXPECTED_HANDSHAKE_PACKET;
    goto cleanup;
  }

  ret2 =
      _gnutls_call_hook_func(session, hsk.htype, GNUTLS_HOOK_POST, 1,
           hsk.data.data, hsk.data.length);
  if (ret2 < 0) {
    ret = ret2;
    gnutls_assert();
    goto cleanup;
  }

  if (buf) {
    *buf = hsk.data;
    return ret;
  }

 cleanup:
  _gnutls_handshake_buffer_clear(&hsk);
  return ret;
}

/* This function checks if the given cipher suite is supported, and sets it
 * to the session;
 */
static int set_client_ciphersuite(gnutls_session_t session, uint8_t suite[2])
{
  unsigned j;
  int ret;
  const gnutls_cipher_suite_entry_st *selected = NULL;
  const version_entry_st *vers = get_version(session);
  gnutls_kx_algorithm_t kx;

  for (j = 0; j < session->internals.priorities->cs.size; j++) {
    if (suite[0] ==
        session->internals.priorities->cs.entry[j]->id[0]
        && suite[1] ==
        session->internals.priorities->cs.entry[j]->id[1]) {
      selected = session->internals.priorities->cs.entry[j];
      break;
    }
  }

  if (!selected) {
    gnutls_assert();
    _gnutls_handshake_log
        ("HSK[%p]: unsupported cipher suite %.2X.%.2X was negotiated\n",
         session, (unsigned int)suite[0], (unsigned int)suite[1]);
    return GNUTLS_E_UNKNOWN_CIPHER_SUITE;
  }

  ret = _gnutls_set_cipher_suite2(session, selected);
  if (ret < 0)
    return gnutls_assert_val(ret);

  _gnutls_handshake_log("HSK[%p]: Selected cipher suite: %s\n",
            session, selected->name);

  /* check if the credentials (username, public key etc.) are ok.
   * Actually checks if they exist.
   */
  if (!vers->tls13_sem) {
    kx = selected->kx_algorithm;

    if (!session->internals.premaster_set &&
        _gnutls_get_kx_cred(session, kx) == NULL) {
      gnutls_assert();
      return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
    }

    /* set the mod_auth_st to the appropriate struct
     * according to the KX algorithm. This is needed since all the
     * handshake functions are read from there;
     */
    session->internals.auth_struct = _gnutls_kx_auth_struct(kx);

    if (session->internals.auth_struct == NULL) {
      _gnutls_handshake_log
          ("HSK[%p]: Cannot find the appropriate handler for the KX algorithm\n",
           session);
      gnutls_assert();
      return GNUTLS_E_INTERNAL_ERROR;
    }
  } else {
    if (session->internals.hsk_flags & HSK_PSK_SELECTED) {
      if (session->key.binders[0].prf->id != selected->prf) {
        _gnutls_handshake_log
            ("HSK[%p]: PRF of ciphersuite differs with the PSK identity (cs: %s, id: %s)\n",
             session, selected->name,
             session->key.binders[0].prf->name);
        gnutls_assert();
        return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
      }
    }
  }

  return 0;
}

/* This function returns 0 if we are resuming a session or -1 otherwise.
 * This also sets the variables in the session. Used only while reading a server
 * hello. Only applicable to TLS1.2 or earlier.
 */
static int
client_check_if_resuming(gnutls_session_t session,
       uint8_t * session_id, int session_id_len)
{
  char buf[2 * GNUTLS_MAX_SESSION_ID_SIZE + 1];
  int ret;

  _gnutls_handshake_log("HSK[%p]: SessionID length: %d\n", session,
            session_id_len);
  _gnutls_handshake_log("HSK[%p]: SessionID: %s\n", session,
            _gnutls_bin2hex(session_id, session_id_len,
                buf, sizeof(buf), NULL));

  if ((session->internals.resumption_requested != 0 ||
       session->internals.premaster_set != 0) &&
      session_id_len > 0 &&
      session->internals.resumed_security_parameters.session_id_size ==
      session_id_len
      && memcmp(session_id,
          session->internals.resumed_security_parameters.session_id,
          session_id_len) == 0) {
    /* resume session */
    memcpy(session->internals.resumed_security_parameters.
           server_random,
           session->security_parameters.server_random,
           GNUTLS_RANDOM_SIZE);
    memcpy(session->internals.resumed_security_parameters.
           client_random,
           session->security_parameters.client_random,
           GNUTLS_RANDOM_SIZE);

    ret = _gnutls_set_cipher_suite2
        (session,
         session->internals.resumed_security_parameters.cs);
    if (ret < 0) {
      gnutls_assert();
      goto no_resume;
    }

    session->internals.resumed = true;  /* we are resuming */

    return 0;
  } else {
 no_resume:
    /* keep the new session id */
    session->internals.resumed = false; /* we are not resuming */
    return -1;
  }
}

/* This function reads and parses the server hello handshake message.
 * This function also restores resumed parameters if we are resuming a
 * session.
 */
static int
read_server_hello(gnutls_session_t session, uint8_t * data, int datalen)
{
  uint8_t session_id_len = 0;
  uint8_t *session_id;
  uint8_t *cs_pos, *comp_pos, *srandom_pos;
  uint8_t major, minor;
  int pos = 0;
  int ret;
  int len = datalen;
  unsigned ext_parse_flag = 0;
  const version_entry_st *vers, *saved_vers;

  if (datalen < GNUTLS_RANDOM_SIZE + 2) {
    gnutls_assert();
    return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
  }

  _gnutls_handshake_log("HSK[%p]: Server's version: %d.%d\n",
            session, data[pos], data[pos + 1]);

  DECR_LEN(len, 2);
  major = data[pos];
  minor = data[pos + 1];

  saved_vers = get_version(session);  /* will be non-null if HRR has been received */

  vers = nversion_to_entry(major, minor);
  if (unlikely(vers == NULL))
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  if (vers->tls13_sem) /* that shouldn't have been negotiated here */
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  if (_gnutls_set_current_version(session, vers->id) < 0)
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  pos += 2;

  DECR_LEN(len, GNUTLS_RANDOM_SIZE);
  srandom_pos = &data[pos];
  pos += GNUTLS_RANDOM_SIZE;

  /* Read session ID
   */
  DECR_LEN(len, 1);
  session_id_len = data[pos++];

  if (len < session_id_len || session_id_len > GNUTLS_MAX_SESSION_ID_SIZE) {
    gnutls_assert();
    return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
  }
  DECR_LEN(len, session_id_len);
  session_id = &data[pos];
  pos += session_id_len;

  DECR_LEN(len, 2);
  cs_pos = &data[pos];
  pos += 2;

  /* move to compression
   */
  DECR_LEN(len, 1);
  comp_pos = &data[pos];
  pos++;

  /* parse extensions to figure version */
  ret =
      _gnutls_parse_hello_extensions(session,
             GNUTLS_EXT_FLAG_TLS12_SERVER_HELLO |
             GNUTLS_EXT_FLAG_TLS13_SERVER_HELLO,
             GNUTLS_EXT_VERSION_NEG, &data[pos],
             len);
  if (ret < 0)
    return gnutls_assert_val(ret);

  vers = get_version(session);
  if (unlikely(vers == NULL))
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);
  if (vers->tls13_sem) {
    if (major != 0x03 || minor != 0x03)
      return
          gnutls_assert_val
          (GNUTLS_E_UNSUPPORTED_VERSION_PACKET);
  }

  if (_gnutls_nversion_is_supported(session, vers->major, vers->minor) ==
      0)
    return gnutls_assert_val(GNUTLS_E_UNSUPPORTED_VERSION_PACKET);

  /* set server random - done after final version is selected */
  ret = _gnutls_set_server_random(session, vers, srandom_pos);
  if (ret < 0)
    return gnutls_assert_val(ret);

  /* reset keys and binders if we are not using TLS 1.3 */
  if (!vers->tls13_sem) {
    gnutls_memset(&session->key.proto.tls13, 0,
            sizeof(session->key.proto.tls13));
    reset_binders(session);
  }

  /* check if we are resuming and set the appropriate
   * values;
   */
  if (!vers->tls13_sem &&
      client_check_if_resuming(session, session_id,
             session_id_len) == 0) {
    ret =
        _gnutls_parse_hello_extensions(session,
               GNUTLS_EXT_FLAG_TLS12_SERVER_HELLO,
               GNUTLS_EXT_MANDATORY,
               &data[pos], len);
    if (ret < 0)
      return gnutls_assert_val(ret);

    return 0;
  } else {
    session->security_parameters.session_id_size = session_id_len;
    if (session_id_len > 0)
      memcpy(session->security_parameters.session_id,
             session_id, session_id_len);
  }

  /* Check if the given cipher suite is supported and copy
   * it to the session.
   */
  ret = set_client_ciphersuite(session, cs_pos);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  if (session->internals.hsk_flags & HSK_HRR_RECEIVED) {
    /* check if ciphersuite matches */
    if (memcmp(cs_pos, session->internals.hrr_cs, 2) != 0)
      return
          gnutls_assert_val
          (GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);

    /* check if HRR version matches this version */
    if (vers != saved_vers)
      return
          gnutls_assert_val
          (GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
  }

  if (*comp_pos != 0)
    return gnutls_assert_val(GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);

  if (vers->tls13_sem)
    ext_parse_flag |= GNUTLS_EXT_FLAG_TLS13_SERVER_HELLO;
  else
    ext_parse_flag |= GNUTLS_EXT_FLAG_TLS12_SERVER_HELLO;

  /* Parse extensions in order.
   */
  ret =
      _gnutls_parse_hello_extensions(session,
             ext_parse_flag,
             GNUTLS_EXT_MANDATORY,
             &data[pos], len);
  if (ret < 0)
    return gnutls_assert_val(ret);

  if (!vers->tls13_sem) {
    /* check if EtM is required */
    if (session->internals.priorities->force_etm &&
        !session->security_parameters.etm) {
      const cipher_entry_st *cipher =
          cipher_to_entry(session->security_parameters.
              cs->block_algorithm);
      if (_gnutls_cipher_type(cipher) == CIPHER_BLOCK)
        return
            gnutls_assert_val
            (GNUTLS_E_UNWANTED_ALGORITHM);
    }

    /* check if EMS is required */
    if (vers->id != GNUTLS_SSL3 && vers->id != GNUTLS_DTLS0_9 &&
        session->internals.priorities->force_ext_master_secret &&
        !session->security_parameters.ext_master_secret) {
      return
          gnutls_assert_val(GNUTLS_E_INSUFFICIENT_SECURITY);
    }
  }

  ret =
      _gnutls_parse_hello_extensions(session,
             ext_parse_flag,
             GNUTLS_EXT_APPLICATION,
             &data[pos], len);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret =
      _gnutls_parse_hello_extensions(session,
             ext_parse_flag,
             GNUTLS_EXT_TLS, &data[pos], len);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret =
      _gnutls_parse_hello_extensions(session,
             ext_parse_flag,
             _GNUTLS_EXT_TLS_POST_CS,
             &data[pos], len);
  if (ret < 0)
    return gnutls_assert_val(ret);

  /* Calculate TLS 1.3 Early Secret */
  if (vers->tls13_sem &&
      !(session->internals.hsk_flags & HSK_PSK_SELECTED)) {
    ret = _tls13_init_secret(session, NULL, 0);
    if (ret < 0)
      return gnutls_assert_val(ret);
  }

  ret = set_auth_types(session);
  if (ret < 0)
    return gnutls_assert_val(ret);

  session->internals.hsk_flags |= HSK_SERVER_HELLO_RECEIVED;

  return 0;
}

/* This function copies the appropriate compression methods, to a locally allocated buffer
 * Needed in hello messages. Returns the new data length.
 */
static int append_null_comp(gnutls_session_t session, gnutls_buffer_st * cdata)
{
  uint8_t compression_methods[2] = { 0x01, 0x00 };
  size_t init_length = cdata->length;
  int ret;

  ret = _gnutls_buffer_append_data(cdata, compression_methods, 2);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret = cdata->length - init_length;

  return ret;
}

/* This function sends the client hello handshake message.
 */
static int send_client_hello(gnutls_session_t session, int again)
{
  mbuffer_st *bufel = NULL;
  int type;
  int ret = 0;
  const version_entry_st *hver, *min_ver, *max_ver;
  uint8_t tver[2];
  gnutls_buffer_st extdata;
  bool rehandshake = false;
  bool resuming = false;
  unsigned add_sr_scsv = 0;
  uint8_t *session_id =
      session->internals.resumed_security_parameters.session_id;
  uint8_t session_id_len =
      session->internals.resumed_security_parameters.session_id_size;

  if (again == 0) {
    /* note that rehandshake is different than resuming
     */
    if (session->internals.initial_negotiation_completed)
      rehandshake = true;

    ret = _gnutls_buffer_init_handshake_mbuffer(&extdata);
    if (ret < 0)
      return gnutls_assert_val(ret);

    /* if we are resuming a session then we set the
     * version number to the previously established.
     */
    if (session->internals.resumption_requested == 0 &&
        session->internals.premaster_set == 0) {
      if (rehandshake) /* already negotiated version thus version_max == negotiated version */
        hver = get_version(session);
      else  /* new handshake. just get the max */
        hver = _gnutls_legacy_version_max(session);
    } else {
      /* we are resuming a session */
      resuming = true;

      hver =
          session->internals.resumed_security_parameters.
          pversion;

      if (hver && hver->tls13_sem)
        hver = _gnutls_legacy_version_max(session);
    }

    if (hver == NULL) {
      gnutls_assert();
      if (session->internals.flags & INT_FLAG_NO_TLS13)
        ret = GNUTLS_E_INSUFFICIENT_CREDENTIALS;
      else
        ret = GNUTLS_E_NO_PRIORITIES_WERE_SET;
      goto cleanup;
    }

    if (unlikely(session->internals.default_hello_version[0] != 0)) {
      tver[0] = session->internals.default_hello_version[0];
      tver[1] = session->internals.default_hello_version[1];
    } else {
      tver[0] = hver->major;
      tver[1] = hver->minor;
    }
    ret = _gnutls_buffer_append_data(&extdata, tver, 2);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }
    _gnutls_handshake_log("HSK[%p]: Adv. version: %u.%u\n", session,
              (unsigned)tver[0], (unsigned)tver[1]);

    min_ver = _gnutls_version_lowest(session);
    max_ver = _gnutls_version_max(session);
    if (min_ver == NULL || max_ver == NULL) {
      gnutls_assert();
      ret = GNUTLS_E_NO_PRIORITIES_WERE_SET;
      goto cleanup;
    }

    /* if we are replying to an HRR the version is already negotiated */
    if (!(session->internals.hsk_flags & HSK_HRR_RECEIVED)
        || !get_version(session)) {
      /* Set the version we advertized as maximum
       * (RSA uses it). */
      set_adv_version(session, hver->major, hver->minor);
      if (_gnutls_set_current_version(session, hver->id) < 0) {
        ret =
            gnutls_assert_val
            (GNUTLS_E_UNSUPPORTED_VERSION_PACKET);
        goto cleanup;
      }
    }

    if (session->internals.priorities->min_record_version != 0) {
      /* Advertise the lowest supported (SSL 3.0) record packet
       * version in record packets during the handshake.
       * That is to avoid confusing implementations
       * that do not support TLS 1.2 and don't know
       * how 3,3 version of record packets look like.
       */
      set_default_version(session, min_ver);
    } else {
      set_default_version(session, hver);
    }

    /* In order to know when this session was initiated.
     */
    session->security_parameters.timestamp = gnutls_time(NULL);

    /* Generate random data
     */
    if (!(session->internals.hsk_flags & HSK_HRR_RECEIVED) &&
        !(IS_DTLS(session)
          && session->internals.dtls.hsk_hello_verify_requests !=
          0)) {
      ret = _gnutls_gen_client_random(session);
      if (ret < 0) {
        gnutls_assert();
        goto cleanup;
      }

    }

    ret = _gnutls_buffer_append_data(&extdata,
             session->
             security_parameters.client_random,
             GNUTLS_RANDOM_SIZE);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

#ifdef TLS13_APPENDIX_D4
    if (max_ver->tls13_sem &&
        session->internals.priorities->tls13_compat_mode &&
        !resuming) {
      if (!(session->internals.hsk_flags & HSK_HRR_RECEIVED)) {
        /* Under TLS1.3 we generate a random session ID to make
         * the TLS1.3 session look like a resumed TLS1.2 session */
        ret =
            _gnutls_generate_session_id
            (session->security_parameters.session_id,
             &session->security_parameters.
             session_id_size);
        if (ret < 0) {
          gnutls_assert();
          goto cleanup;
        }
      }
      session_id = session->security_parameters.session_id;
      session_id_len =
          session->security_parameters.session_id_size;
    }
#endif

    /* Copy the Session ID - if any
     */
    ret = _gnutls_buffer_append_data_prefix(&extdata, 8,
              session_id,
              session_id_len);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    /* Copy the DTLS cookie
     */
    if (IS_DTLS(session)) {
      ret = _gnutls_buffer_append_data_prefix(&extdata, 8,
                session->internals.
                dtls.dcookie.
                data,
                session->internals.
                dtls.dcookie.
                size);
      if (ret < 0) {
        gnutls_assert();
        goto cleanup;
      }
      _gnutls_free_datum(&session->internals.dtls.dcookie);
    }

    /* Copy the ciphersuites.
     */
#ifdef ENABLE_SSL3
    /* If using SSLv3 Send TLS_RENEGO_PROTECTION_REQUEST SCSV for MITM
     * prevention on initial negotiation (but not renegotiation; that's
     * handled with the RI extension below).
     */
    if (!session->internals.initial_negotiation_completed &&
        session->security_parameters.entity == GNUTLS_CLIENT &&
        (hver->id == GNUTLS_SSL3 &&
         session->internals.priorities->no_extensions != 0)) {
      add_sr_scsv = 1;
    }
#endif
    ret =
        _gnutls_get_client_ciphersuites(session, &extdata, min_ver,
                add_sr_scsv);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    /* Copy the compression methods.
     */
    ret = append_null_comp(session, &extdata);
    if (ret < 0) {
      gnutls_assert();
      goto cleanup;
    }

    /* Generate and copy TLS extensions.
     */
    if (session->internals.priorities->no_extensions == 0) {
      if (_gnutls_version_has_extensions(hver)) {
        type = GNUTLS_EXT_ANY;
      } else {
        type = GNUTLS_EXT_MANDATORY;
      }

      ret =
          _gnutls_gen_hello_extensions(session, &extdata,
               GNUTLS_EXT_FLAG_CLIENT_HELLO,
               type);
      if (ret < 0) {
        gnutls_assert();
        goto cleanup;
      }
    }

    bufel = _gnutls_buffer_to_mbuffer(&extdata);
  }

  ret = _gnutls_send_handshake(session, bufel,
             GNUTLS_HANDSHAKE_CLIENT_HELLO);

  if (session->internals.hsk_flags & HSK_EARLY_DATA_IN_FLIGHT) {
    const cipher_entry_st *ce;
    const mac_entry_st *me;
    record_parameters_st *params;

    ce = cipher_to_entry(session->internals.
             resumed_security_parameters.
             cs->block_algorithm);
    me = mac_to_entry(session->internals.
          resumed_security_parameters.
          cs->mac_algorithm);

    ret = _gnutls_epoch_get(session, EPOCH_NEXT, &params);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }

    params->cipher = ce;
    params->mac = me;

    ret = _tls13_write_connection_state_init(session, STAGE_EARLY);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }

    _gnutls_epoch_bump(session);
    ret = _gnutls_epoch_dup(session, EPOCH_WRITE_CURRENT);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }

    ret = _gnutls13_send_early_data(session);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }
  }

  return ret;

 cleanup:
  _gnutls_buffer_clear(&extdata);
  return ret;
}

int _gnutls_send_server_hello(gnutls_session_t session, int again)
{
  mbuffer_st *bufel = NULL;
  gnutls_buffer_st buf;
  int ret;
  uint8_t session_id_len = session->security_parameters.session_id_size;
  char tmpbuf[2 * GNUTLS_MAX_SESSION_ID_SIZE + 1];
  const version_entry_st *vers;
  uint8_t vbytes[2];
  unsigned extflag = 0;
  gnutls_ext_parse_type_t etype;

  _gnutls_buffer_init(&buf);

  if (again == 0) {
    vers = get_version(session);
    if (unlikely
        (vers == NULL || session->security_parameters.cs == NULL))
      return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

    if (vers->tls13_sem) {
      vbytes[0] = 0x03; /* TLS1.2 */
      vbytes[1] = 0x03;
      extflag |= GNUTLS_EXT_FLAG_TLS13_SERVER_HELLO;
    } else {
      vbytes[0] = vers->major;
      vbytes[1] = vers->minor;
      extflag |= GNUTLS_EXT_FLAG_TLS12_SERVER_HELLO;
    }

    ret = _gnutls_buffer_init_handshake_mbuffer(&buf);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    ret = _gnutls_buffer_append_data(&buf, vbytes, 2);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    ret = _gnutls_buffer_append_data(&buf,
             session->
             security_parameters.server_random,
             GNUTLS_RANDOM_SIZE);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    ret = _gnutls_buffer_append_data_prefix(&buf, 8,
              session->security_parameters.session_id,
              session_id_len);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    _gnutls_handshake_log("HSK[%p]: SessionID: %s\n", session,
              _gnutls_bin2hex
              (session->security_parameters.session_id,
               session_id_len, tmpbuf, sizeof(tmpbuf),
               NULL));

    ret = _gnutls_buffer_append_data(&buf,
             session->
             security_parameters.cs->id, 2);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    /* compression */
    ret = _gnutls_buffer_append_prefix(&buf, 8, 0);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    if (!vers->tls13_sem && session->internals.resumed)
      etype = GNUTLS_EXT_MANDATORY;
    else
      etype = GNUTLS_EXT_ANY;
    ret =
        _gnutls_gen_hello_extensions(session, &buf, extflag, etype);
    if (ret < 0) {
      gnutls_assert();
      goto fail;
    }

    if (vers->tls13_sem) {
      /* Under TLS1.3, the session ID is used for different purposes than
       * the TLS1.0 session ID. Ensure that there is an internally set
       * value which the server will see on the original and resumed sessions */
      ret =
          _gnutls_generate_session_id
          (session->security_parameters.session_id,
           &session->security_parameters.session_id_size);
      if (ret < 0) {
        gnutls_assert();
        goto fail;
      }
    }

    bufel = _gnutls_buffer_to_mbuffer(&buf);
  }

  ret =
      _gnutls_send_handshake(session, bufel,
           GNUTLS_HANDSHAKE_SERVER_HELLO);

 fail:
  _gnutls_buffer_clear(&buf);
  return ret;
}

static int
recv_hello_verify_request(gnutls_session_t session, uint8_t * data, int datalen)
{
  ssize_t len = datalen;
  size_t pos = 0;
  uint8_t cookie_len;
  unsigned int nb_verifs;
  int ret;

  if (!IS_DTLS(session)) {
    gnutls_assert();
    return GNUTLS_E_UNEXPECTED_PACKET;
  }

  nb_verifs = ++session->internals.dtls.hsk_hello_verify_requests;
  if (nb_verifs >= MAX_HANDSHAKE_HELLO_VERIFY_REQUESTS) {
    /* The server is either buggy, malicious or changing cookie
       secrets _way_ too fast. */
    gnutls_assert();
    return GNUTLS_E_UNEXPECTED_PACKET;
  }

  DECR_LEN(len, 2);
  pos += 2;

  DECR_LEN(len, 1);
  cookie_len = data[pos];
  pos++;

  if (cookie_len > DTLS_MAX_COOKIE_SIZE) {
    gnutls_assert();
    return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
  }

  DECR_LEN(len, cookie_len);

  gnutls_free(session->internals.dtls.dcookie.data);
  ret =
      _gnutls_set_datum(&session->internals.dtls.dcookie, &data[pos],
            cookie_len);
  if (ret < 0)
    return gnutls_assert_val(ret);

  if (len != 0) {
    gnutls_assert();
    return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
  }

  /* reset handshake hash buffers */
  handshake_hash_buffer_reset(session);
  /* reset extensions used in previous hello */
  session->internals.used_exts = 0;

  return 0;
}

/* The packets in gnutls_handshake (it's more broad than original TLS handshake)
 *
 *     Client                Server
 *
 *     ClientHello      -------->
 *          <--------  ServerHello
 *
 *                Certificate*
 *                ServerKeyExchange*
 *          <--------   CertificateRequest*
 *
 *          <--------      ServerHelloDone
 *     Certificate*
 *     ClientKeyExchange
 *     CertificateVerify*
 *     [ChangeCipherSpec]
 *     Finished        -------->
 *            NewSessionTicket
 *                [ChangeCipherSpec]
 *          <--------      Finished
 *
 * (*): means optional packet.
 */

/* Handshake when resumming session:
 *      Client            Server
 *
 *      ClientHello      -------->
 *                  ServerHello
 *                 [ChangeCipherSpec]
 *           <--------       Finished
 *     [ChangeCipherSpec]
 *     Finished         -------->
 *
 */

/**
 * gnutls_rehandshake:
 * @session: is a #gnutls_session_t type.
 *
 * This function can only be called in server side, and
 * instructs a TLS 1.2 or earlier client to renegotiate
 * parameters (perform a handshake), by sending a
 * hello request message.
 *
 * If this function succeeds, the calling application
 * should call gnutls_record_recv() until %GNUTLS_E_REHANDSHAKE
 * is returned to clear any pending data. If the %GNUTLS_E_REHANDSHAKE
 * error code is not seen, then the handshake request was
 * not followed by the peer (the TLS protocol does not require
 * the client to do, and such compliance should be handled
 * by the application protocol).
 *
 * Once the %GNUTLS_E_REHANDSHAKE error code is seen, the
 * calling application should proceed to calling
 * gnutls_handshake() to negotiate the new
 * parameters.
 *
 * If the client does not wish to renegotiate parameters he
 * may reply with an alert message, and in that case the return code seen
 * by subsequent gnutls_record_recv() will be
 * %GNUTLS_E_WARNING_ALERT_RECEIVED with the specific alert being
 * %GNUTLS_A_NO_RENEGOTIATION.  A client may also choose to ignore
 * this request.
 *
 * Under TLS 1.3 this function is equivalent to gnutls_session_key_update()
 * with the %GNUTLS_KU_PEER flag. In that case subsequent calls to
 * gnutls_record_recv() will not return %GNUTLS_E_REHANDSHAKE, and
 * calls to gnutls_handshake() in server side are a no-op.
 *
 * This function always fails with %GNUTLS_E_INVALID_REQUEST when
 * called in client side.
 *
 * Returns: %GNUTLS_E_SUCCESS on success, otherwise a negative error code.
 **/
int gnutls_rehandshake(gnutls_session_t session)
{
  int ret;
  const version_entry_st *vers = get_version(session);

  /* only server sends that handshake packet */
  if (session->security_parameters.entity == GNUTLS_CLIENT)
    return GNUTLS_E_INVALID_REQUEST;

  if (vers->tls13_sem) {
    return gnutls_session_key_update(session, GNUTLS_KU_PEER);
  }

  _dtls_async_timer_delete(session);

  ret =
      _gnutls_send_empty_handshake(session,
           GNUTLS_HANDSHAKE_HELLO_REQUEST,
           AGAIN(STATE50));
  STATE = STATE50;

  if (ret < 0) {
    gnutls_assert();
    return ret;
  }
  STATE = STATE0;

  return 0;
}

/* This function checks whether the error code should be treated fatal
 * or not, and also does the necessary state transition.  In
 * particular, in the case of a rehandshake abort it resets the
 * handshake's internal state.
 */
inline static int _gnutls_abort_handshake(gnutls_session_t session, int ret)
{
  switch (ret) {
  case GNUTLS_E_WARNING_ALERT_RECEIVED:
    if (gnutls_alert_get(session) == GNUTLS_A_NO_RENEGOTIATION) {
      /* The server always toleretes a "no_renegotiation" alert. */
      if (session->security_parameters.entity ==
          GNUTLS_SERVER) {
        STATE = STATE0;
        return ret;
      }

      /* The client should tolerete a "no_renegotiation" alert only if:
       * - the initial handshake has completed, or
       * - a Server Hello is not yet received
       */
      if (session->internals.initial_negotiation_completed ||
          !(session->
            internals.hsk_flags & HSK_SERVER_HELLO_RECEIVED))
      {
        STATE = STATE0;
        return ret;
      }

      return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET);
    }
    return ret;
  case GNUTLS_E_GOT_APPLICATION_DATA:
    STATE = STATE0;
    return ret;
  default:
    return ret;
  }
}

static int _gnutls_send_supplemental(gnutls_session_t session, int again)
{
  mbuffer_st *bufel = NULL;
  int ret = 0;

  _gnutls_debug_log("EXT[%p]: Sending supplemental data\n", session);

  if (!again) {
    gnutls_buffer_st buf;
    ret = _gnutls_buffer_init_handshake_mbuffer(&buf);
    if (ret < 0)
      return gnutls_assert_val(ret);

    ret = _gnutls_gen_supplemental(session, &buf);
    if (ret < 0) {
      gnutls_assert();
      _gnutls_buffer_clear(&buf);
      return ret;
    }

    bufel = _gnutls_buffer_to_mbuffer(&buf);
  }

  return _gnutls_send_handshake(session, bufel,
              GNUTLS_HANDSHAKE_SUPPLEMENTAL);
}

static int _gnutls_recv_supplemental(gnutls_session_t session)
{
  gnutls_buffer_st buf;
  int ret;

  _gnutls_debug_log("EXT[%p]: Expecting supplemental data\n", session);

  ret =
      _gnutls_recv_handshake(session, GNUTLS_HANDSHAKE_SUPPLEMENTAL,
           1, &buf);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  ret = _gnutls_parse_supplemental(session, buf.data, buf.length);
  if (ret < 0) {
    gnutls_assert();
    goto cleanup;
  }

 cleanup:
  _gnutls_buffer_clear(&buf);

  return ret;
}

/**
 * gnutls_handshake:
 * @session: is a #gnutls_session_t type.
 *
 * This function performs the handshake of the TLS/SSL protocol, and
 * initializes the TLS session parameters.
 *
 * The non-fatal errors expected by this function are:
 * %GNUTLS_E_INTERRUPTED, %GNUTLS_E_AGAIN,
 * %GNUTLS_E_WARNING_ALERT_RECEIVED. When this function is called
 * for re-handshake under TLS 1.2 or earlier, the non-fatal error code
 * %GNUTLS_E_GOT_APPLICATION_DATA may also be returned.
 *
 * The former two interrupt the handshake procedure due to the transport
 * layer being interrupted, and the latter because of a "warning" alert that
 * was sent by the peer (it is always a good idea to check any
 * received alerts). On these non-fatal errors call this function again,
 * until it returns 0; cf.  gnutls_record_get_direction() and
 * gnutls_error_is_fatal(). In DTLS sessions the non-fatal error
 * %GNUTLS_E_LARGE_PACKET is also possible, and indicates that
 * the MTU should be adjusted.
 *
 * When this function is called by a server after a rehandshake request
 * under TLS 1.2 or earlier the %GNUTLS_E_GOT_APPLICATION_DATA error code indicates
 * that some data were pending prior to peer initiating the handshake.
 * Under TLS 1.3 this function when called after a successful handshake, is a no-op
 * and always succeeds in server side; in client side this function is
 * equivalent to gnutls_session_key_update() with %GNUTLS_KU_PEER flag.
 *
 * This function handles both full and abbreviated TLS handshakes (resumption).
 * For abbreviated handshakes, in client side, the gnutls_session_set_data()
 * should be called prior to this function to set parameters from a previous session.
 * In server side, resumption is handled by either setting a DB back-end, or setting
 * up keys for session tickets.
 *
 * Returns: %GNUTLS_E_SUCCESS on a successful handshake, otherwise a negative error code.
 **/
int gnutls_handshake(gnutls_session_t session)
{
  const version_entry_st *vers = get_version(session);
  int ret;

  if (unlikely(session->internals.initial_negotiation_completed)) {
    if (vers->tls13_sem) {
      if (session->security_parameters.entity ==
          GNUTLS_CLIENT) {
        return gnutls_session_key_update(session,
                 GNUTLS_KU_PEER);
      } else {
        /* This is a no-op for a server under TLS 1.3, as
         * a server has already called gnutls_rehandshake()
         * which performed a key update.
         */
        return 0;
      }
    }
  }

  if (STATE == STATE0) {
    unsigned int tmo_ms;
    struct timespec *end;
    struct timespec *start;

    /* first call */
    if (session->internals.priorities == NULL ||
        session->internals.priorities->cs.size == 0)
      return
          gnutls_assert_val(GNUTLS_E_NO_PRIORITIES_WERE_SET);

    ret = _gnutls_epoch_setup_next(session, 0, NULL);
    if (ret < 0)
      return gnutls_assert_val(ret);

    session->internals.used_exts = 0;
    session->internals.hsk_flags = 0;
    session->internals.handshake_in_progress = 1;
    session->internals.vc_status = -1;
    gnutls_gettime(&session->internals.handshake_start_time);

    tmo_ms = session->internals.handshake_timeout_ms;
    end = &session->internals.handshake_abs_timeout;
    start = &session->internals.handshake_start_time;

    if (tmo_ms && end->tv_sec == 0 && end->tv_nsec == 0) {
      end->tv_sec =
          start->tv_sec + (start->tv_nsec +
               tmo_ms * 1000000LL) / 1000000000LL;
      end->tv_nsec =
          (start->tv_nsec +
           tmo_ms * 1000000LL) % 1000000000LL;
    }

#ifdef ENABLE_KTLS
    if (_gnutls_config_is_ktls_enabled()) {
      if ((session->internals.pull_func &&
           session->internals.pull_func != system_read) ||
          session->internals.push_func) {
        _gnutls_audit_log(session,
              "Not enabling KTLS with "
              "custom pull/push function\n");
      } else {
        _gnutls_ktls_enable(session);
      }
    }
#endif
  }

  if (session->internals.recv_state == RECV_STATE_FALSE_START) {
    session_invalidate(session);
    return gnutls_assert_val(GNUTLS_E_HANDSHAKE_DURING_FALSE_START);
  }

  if (session->security_parameters.entity == GNUTLS_CLIENT) {
    do {
      ret = handshake_client(session);
    } while (ret == 1);
  } else {
    ret = handshake_server(session);
  }

  if (ret < 0) {
    return _gnutls_abort_handshake(session, ret);
  }

  /* clear handshake buffer */
  if (session->internals.recv_state != RECV_STATE_FALSE_START &&
      session->internals.recv_state != RECV_STATE_EARLY_START) {

    _gnutls_handshake_hash_buffers_clear(session);

    if (IS_DTLS(session) == 0) {
      _gnutls_handshake_io_buffer_clear(session);
    } else {
      _dtls_async_timer_init(session);
    }

    _gnutls_handshake_internal_state_clear(session);

    _gnutls_buffer_clear(&session->internals.record_presend_buffer);

    _gnutls_epoch_bump(session);
  }

  /* Give an estimation of the round-trip under TLS1.3, used by gnutls_session_get_data2() */
  if (!IS_SERVER(session) && vers->tls13_sem) {
    struct timespec handshake_finish_time;
    gnutls_gettime(&handshake_finish_time);

    if (!(session->internals.hsk_flags & HSK_HRR_RECEIVED)) {
      session->internals.ertt =
          timespec_sub_ms(&handshake_finish_time,
              &session->
              internals.handshake_start_time) / 2;
    } else {
      session->internals.ertt =
          timespec_sub_ms(&handshake_finish_time,
              &session->
              internals.handshake_start_time) / 4;
    }
  }

#ifdef ENABLE_KTLS
  if (IS_KTLS_ENABLED(session, GNUTLS_KTLS_DUPLEX)) {
    ret = _gnutls_ktls_set_keys(session, GNUTLS_KTLS_DUPLEX);
    if (ret < 0) {
      /* no need to invalidate the session as keys were not set */
      session->internals.ktls_enabled = 0;
      _gnutls_audit_log(session,
            "disabling KTLS: failed to set keys\n");
    }
  }
#endif

  return 0;
}

/**
 * gnutls_handshake_set_timeout:
 * @session: is a #gnutls_session_t type.
 * @ms: is a timeout value in milliseconds
 *
 * This function sets the timeout for the TLS handshake process
 * to the provided value. Use an @ms value of zero to disable
 * timeout, or %GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT for a reasonable
 * default value. For the DTLS protocol, the more detailed
 * gnutls_dtls_set_timeouts() is provided.
 *
 * This function requires to set a pull timeout callback. See
 * gnutls_transport_set_pull_timeout_function().
 *
 * Since: 3.1.0
 **/
void gnutls_handshake_set_timeout(gnutls_session_t session, unsigned int ms)
{
  if (ms == GNUTLS_INDEFINITE_TIMEOUT) {
    session->internals.handshake_timeout_ms = 0;
    return;
  }

  if (ms == GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT)
    ms = DEFAULT_HANDSHAKE_TIMEOUT_MS;

  if (IS_DTLS(session)) {
    gnutls_dtls_set_timeouts(session, DTLS_RETRANS_TIMEOUT, ms);
    return;
  }

  session->internals.handshake_timeout_ms = ms;
}

/* Runs the certificate verification callback.
 * side is the side that we verify the certificate
 * from (either GNUTLS_CLIENT or GNUTLS_SERVER).
 */
int _gnutls_run_verify_callback(gnutls_session_t session, unsigned int side)
{
  gnutls_certificate_credentials_t cred;
  int ret, type;

  if (session->internals.hsk_flags & HSK_PSK_SELECTED)
    return 0;

  cred =
      (gnutls_certificate_credentials_t) _gnutls_get_cred(session,
                GNUTLS_CRD_CERTIFICATE);

  if (side == GNUTLS_CLIENT)
    type = gnutls_auth_server_get_type(session);
  else
    type = gnutls_auth_client_get_type(session);

  if (type != GNUTLS_CRD_CERTIFICATE)
    return 0;

  /* verify whether the certificate of the peer remained the same
   * as with any previous handshakes */
  if (cred != NULL) {
    ret = _gnutls_check_if_cert_hash_is_same(session, cred);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }
  }

  if (cred != NULL &&
      (cred->verify_callback != NULL
       || session->internals.verify_callback != NULL)
      && (session->security_parameters.entity == GNUTLS_CLIENT
    || session->internals.send_cert_req != GNUTLS_CERT_IGNORE)) {
    if (session->internals.verify_callback)
      ret = session->internals.verify_callback(session);
    else
      ret = cred->verify_callback(session);
    if (ret < -1)
      return gnutls_assert_val(ret);
    else if (ret != 0)
      return gnutls_assert_val(GNUTLS_E_CERTIFICATE_ERROR);
  }

  return 0;
}

static bool can_send_false_start(gnutls_session_t session)
{
  const version_entry_st *vers;

  vers = get_version(session);
  if (unlikely(vers == NULL || !vers->false_start))
    return 0;

  if (session->internals.selected_cert_list != NULL)
    return 0;

  if (!_gnutls_kx_allows_false_start(session))
    return 0;

  return 1;
}

/*
 * handshake_client
 * This function performs the client side of the handshake of the TLS/SSL protocol.
 */
static int handshake_client(gnutls_session_t session)
{
  int ret = 0;
  const version_entry_st *ver;

 reset:
  if (STATE >= STATE99)
    return _gnutls13_handshake_client(session);

  switch (STATE) {
  case STATE0:
  case STATE1:
    ret = send_client_hello(session, AGAIN(STATE1));
    STATE = STATE1;
    IMED_RET("send hello", ret, 1);
    FALLTHROUGH;
  case STATE2:
    if (IS_DTLS(session)) {
      ret =
          _gnutls_recv_handshake(session,
               GNUTLS_HANDSHAKE_HELLO_VERIFY_REQUEST,
               1, NULL);
      STATE = STATE2;
      IMED_RET("recv hello verify", ret, 1);

      if (ret == 1) {
        STATE = STATE0;
        return 1;
      }
    } else {
      ret =
          _gnutls_recv_handshake(session,
               GNUTLS_HANDSHAKE_HELLO_RETRY_REQUEST,
               1, NULL);
      STATE = STATE2;
      IMED_RET("recv hello retry", ret, 1);

      if (ret == 1) {
        STATE = STATE0;
        return 1;
      }
    }
    FALLTHROUGH;
  case STATE3:
    /* receive the server hello */
    ret =
        _gnutls_recv_handshake(session,
             GNUTLS_HANDSHAKE_SERVER_HELLO,
             0, NULL);
    STATE = STATE3;
    IMED_RET("recv hello", ret, 1);
    FALLTHROUGH;
  case STATE4:
    ver = get_version(session);
    if (ver->tls13_sem) { /* TLS 1.3 state machine */
      STATE = STATE99;
      goto reset;
    }

    ret = _gnutls_ext_sr_verify(session);
    STATE = STATE4;
    IMED_RET_FATAL("recv hello", ret, 0);
    FALLTHROUGH;
  case STATE5:
    if (session->security_parameters.do_recv_supplemental) {
      ret = _gnutls_recv_supplemental(session);
      STATE = STATE5;
      IMED_RET("recv supplemental", ret, 1);
    }
    FALLTHROUGH;
  case STATE6:
    /* RECV CERTIFICATE */
    if (!session->internals.resumed) /* if we are not resuming */
      ret = _gnutls_recv_server_certificate(session);
    STATE = STATE6;
    IMED_RET("recv server certificate", ret, 1);
    FALLTHROUGH;
  case STATE7:
#ifdef ENABLE_OCSP
    /* RECV CERTIFICATE STATUS */
    if (!session->internals.resumed) /* if we are not resuming */
      ret = _gnutls_recv_server_certificate_status(session);
    STATE = STATE7;
    IMED_RET("recv server certificate", ret, 1);
#endif
    FALLTHROUGH;
  case STATE8:
    ret = _gnutls_run_verify_callback(session, GNUTLS_CLIENT);
    STATE = STATE8;
    if (ret < 0)
      return gnutls_assert_val(ret);

    FALLTHROUGH;
  case STATE9:
    /* receive the server key exchange */
    if (!session->internals.resumed) /* if we are not resuming */
      ret = _gnutls_recv_server_kx_message(session);
    STATE = STATE9;
    IMED_RET("recv server kx message", ret, 1);
    FALLTHROUGH;
  case STATE10:
    /* receive the server certificate request - if any
     */

    if (!session->internals.resumed) /* if we are not resuming */
      ret = _gnutls_recv_server_crt_request(session);
    STATE = STATE10;
    IMED_RET("recv server certificate request message", ret, 1);
    FALLTHROUGH;
  case STATE11:
    /* receive the server hello done */
    if (!session->internals.resumed) /* if we are not resuming */
      ret =
          _gnutls_recv_handshake(session,
               GNUTLS_HANDSHAKE_SERVER_HELLO_DONE,
               0, NULL);
    STATE = STATE11;
    IMED_RET("recv server hello done", ret, 1);
    FALLTHROUGH;
  case STATE12:
    if (session->security_parameters.do_send_supplemental) {
      ret =
          _gnutls_send_supplemental(session, AGAIN(STATE12));
      STATE = STATE12;
      IMED_RET("send supplemental", ret, 0);
    }
    FALLTHROUGH;
  case STATE13:
    /* send our certificate - if any and if requested
     */
    if (!session->internals.resumed) /* if we are not resuming */
      ret =
          _gnutls_send_client_certificate(session,
                  AGAIN(STATE13));
    STATE = STATE13;
    IMED_RET("send client certificate", ret, 0);
    FALLTHROUGH;
  case STATE14:
    if (!session->internals.resumed) /* if we are not resuming */
      ret =
          _gnutls_send_client_kx_message(session,
                 AGAIN(STATE14));
    STATE = STATE14;
    IMED_RET("send client kx", ret, 0);
    FALLTHROUGH;
  case STATE15:
    /* send client certificate verify */
    if (!session->internals.resumed) /* if we are not resuming */
      ret =
          _gnutls_send_client_certificate_verify(session,
                   AGAIN
                   (STATE15));
    STATE = STATE15;
    IMED_RET("send client certificate verify", ret, 1);
    FALLTHROUGH;
  case STATE16:
    STATE = STATE16;
    if (!session->internals.resumed) {
      ret = send_handshake_final(session, true);
      IMED_RET("send handshake final 2", ret, 1);
    } else {
      ret = _gnutls_recv_new_session_ticket(session);
      IMED_RET("recv handshake new session ticket", ret, 1);
    }
    FALLTHROUGH;
  case STATE17:
    STATE = STATE17;
    if (!session->internals.resumed
        && (session->internals.flags & GNUTLS_ENABLE_FALSE_START)
        && can_send_false_start(session)) {
      session->internals.hsk_flags |= HSK_FALSE_START_USED;
      session->internals.recv_state = RECV_STATE_FALSE_START;
      /* complete this phase of the handshake. We
       * should be called again by gnutls_record_recv()
       */
      STATE = STATE18;
      gnutls_assert();

      return 0;
    }
    FALLTHROUGH;
  case STATE18:
    STATE = STATE18;

    if (!session->internals.resumed) {
      ret = _gnutls_recv_new_session_ticket(session);
      IMED_RET("recv handshake new session ticket", ret, 1);
    } else {
      ret = recv_handshake_final(session, true);
      IMED_RET("recv handshake final", ret, 1);
    }
    FALLTHROUGH;
  case STATE19:
    STATE = STATE19;
    if (!session->internals.resumed) {
      ret = recv_handshake_final(session, false);
      IMED_RET("recv handshake final 2", ret, 1);
    } else {
      ret = send_handshake_final(session, false);
      IMED_RET("send handshake final", ret, 1);
    }

    STATE = STATE0;
    FALLTHROUGH;
  default:
    break;
  }

  /* explicitly reset any false start flags */
  gnutls_mutex_lock(&session->internals.post_negotiation_lock);
  session->internals.initial_negotiation_completed = 1;
  session->internals.recv_state = RECV_STATE_0;
  gnutls_mutex_unlock(&session->internals.post_negotiation_lock);

  return 0;
}

/* This function is to be called if the handshake was successfully
 * completed. This sends a Change Cipher Spec packet to the peer.
 */
ssize_t _gnutls_send_change_cipher_spec(gnutls_session_t session, int again)
{
  uint8_t *data;
  mbuffer_st *bufel;
  int ret;
  const version_entry_st *vers;

  if (again == 0) {
    bufel = _gnutls_handshake_alloc(session, 3);  /* max for DTLS0.9 */
    if (bufel == NULL)
      return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);

    vers = get_version(session);
    if (unlikely(vers == NULL))
      return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

    if (vers->id == GNUTLS_DTLS0_9)
      _mbuffer_set_uhead_size(bufel, 3);
    else
      _mbuffer_set_uhead_size(bufel, 1);
    _mbuffer_set_udata_size(bufel, 0);

    data = _mbuffer_get_uhead_ptr(bufel);

    data[0] = 1;
    if (vers->id == GNUTLS_DTLS0_9) {
      _gnutls_write_uint16(session->internals.dtls.
               hsk_write_seq, &data[1]);
      session->internals.dtls.hsk_write_seq++;
    }

    ret =
        _gnutls_call_hook_func(session,
             GNUTLS_HANDSHAKE_CHANGE_CIPHER_SPEC,
             GNUTLS_HOOK_PRE, 0, data, 1);
    if (ret < 0) {
      _mbuffer_xfree(&bufel);
      return gnutls_assert_val(ret);
    }

    ret =
        _gnutls_handshake_io_cache_int(session,
               GNUTLS_HANDSHAKE_CHANGE_CIPHER_SPEC,
               bufel);
    if (ret < 0) {
      _mbuffer_xfree(&bufel);
      return gnutls_assert_val(ret);
    }

    ret =
        _gnutls_call_hook_func(session,
             GNUTLS_HANDSHAKE_CHANGE_CIPHER_SPEC,
             GNUTLS_HOOK_POST, 0, data, 1);
    if (ret < 0) {
      return gnutls_assert_val(ret);
    }

    /* under TLS 1.3, CCS may be immediately followed by
     * receiving ClientHello thus cannot be cached */
    if (vers->tls13_sem) {
      ret = _gnutls_handshake_io_write_flush(session);
      if (ret < 0)
        return gnutls_assert_val(ret);
    }

    _gnutls_handshake_log("REC[%p]: Sent ChangeCipherSpec\n",
              session);
  }

  return 0;
}

/* This function sends the final handshake packets and initializes connection
 */
static int send_handshake_final(gnutls_session_t session, int init)
{
  int ret = 0;

  /* Send the CHANGE CIPHER SPEC PACKET */

  switch (FINAL_STATE) {
  case STATE0:
  case STATE1:
    ret = _gnutls_send_change_cipher_spec(session, FAGAIN(STATE1));
    FINAL_STATE = STATE0;

    if (ret < 0) {
      gnutls_assert();
      return ret;
    }
    /* Initialize the connection session (start encryption) - in case of client
     */
    if (init) {
      ret = _gnutls_connection_state_init(session);
      if (ret < 0) {
        gnutls_assert();
        return ret;
      }
    }

    ret = _gnutls_write_connection_state_init(session);
    if (ret < 0) {
      gnutls_assert();
      return ret;
    }

    FALLTHROUGH;
  case STATE2:
    /* send the finished message */
    ret = _gnutls_send_finished(session, FAGAIN(STATE2));
    FINAL_STATE = STATE2;
    if (ret < 0) {
      gnutls_assert();
      return ret;
    }

    FINAL_STATE = STATE0;
    FALLTHROUGH;
  default:
    break;
  }

  return 0;
}

/* This function receives the final handshake packets
 * And executes the appropriate function to initialize the
 * read session.
 */
static int recv_handshake_final(gnutls_session_t session, int init)
{
  int ret = 0;
  uint8_t ccs[3];
  unsigned int ccs_len = 1;
  unsigned int tleft;
  const version_entry_st *vers;

  ret = handshake_remaining_time(session);
  if (ret < 0)
    return gnutls_assert_val(ret);
  tleft = ret;

  switch (FINAL_STATE) {
  case STATE0:
  case STATE30:
    FINAL_STATE = STATE30;

    /* This is the last flight and peer cannot be sure
     * we have received it unless we notify him. So we
     * wait for a message and retransmit if needed. */
    if (IS_DTLS(session) && !_dtls_is_async(session) &&
        (gnutls_record_check_pending(session) +
         record_check_unprocessed(session)) == 0) {
      ret = _dtls_wait_and_retransmit(session);
      if (ret < 0)
        return gnutls_assert_val(ret);
    }

    vers = get_version(session);
    if (unlikely(vers == NULL))
      return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

    if (vers->id == GNUTLS_DTLS0_9)
      ccs_len = 3;

    ret =
        _gnutls_recv_int(session, GNUTLS_CHANGE_CIPHER_SPEC,
             ccs, ccs_len, NULL, tleft);
    if (ret <= 0) {
      gnutls_assert();
      return (ret < 0) ? ret : GNUTLS_E_UNEXPECTED_PACKET;
    }

    if (vers->id == GNUTLS_DTLS0_9)
      session->internals.dtls.hsk_read_seq++;

    /* Initialize the connection session (start encryption) - in case of server */
    if (init) {
      ret = _gnutls_connection_state_init(session);
      if (ret < 0) {
        gnutls_assert();
        return ret;
      }
    }

    ret = _gnutls_read_connection_state_init(session);
    if (ret < 0) {
      gnutls_assert();
      return ret;
    }
    FALLTHROUGH;
  case STATE31:
    FINAL_STATE = STATE31;

    if (IS_DTLS(session) && !_dtls_is_async(session) &&
        (gnutls_record_check_pending(session) +
         record_check_unprocessed(session)) == 0) {
      ret = _dtls_wait_and_retransmit(session);
      if (ret < 0)
        return gnutls_assert_val(ret);
    }

    ret = _gnutls_recv_finished(session);
    if (ret < 0) {
      gnutls_assert();
      return ret;
    }
    FINAL_STATE = STATE0;
    FALLTHROUGH;
  default:
    break;
  }

  return 0;
}

/*
 * handshake_server
 * This function does the server stuff of the handshake protocol.
 */
static int handshake_server(gnutls_session_t session)
{
  int ret = 0;
  const version_entry_st *ver;

 reset:

  if (STATE >= STATE90)
    return _gnutls13_handshake_server(session);

  switch (STATE) {
  case STATE0:
  case STATE1:
    ret =
        _gnutls_recv_handshake(session,
             GNUTLS_HANDSHAKE_CLIENT_HELLO,
             0, NULL);
    if (ret == GNUTLS_E_INT_RET_0) {
      /* this is triggered by post_client_hello, and instructs the
       * handshake to proceed but be put on hold */
      ret = GNUTLS_E_INTERRUPTED;
      STATE = STATE2;  /* hello already parsed -> move on */
    } else {
      STATE = STATE1;
    }

    if (ret == GNUTLS_E_NO_COMMON_KEY_SHARE) {
      STATE = STATE90;
      session->internals.hsk_flags |= HSK_HRR_SENT;
      goto reset;
    }

    IMED_RET("recv hello", ret, 1);
    FALLTHROUGH;
  case STATE2:

    ret = _gnutls_ext_sr_verify(session);
    STATE = STATE2;
    IMED_RET_FATAL("recv hello", ret, 0);
    FALLTHROUGH;
  case STATE3:
    ret = _gnutls_send_server_hello(session, AGAIN(STATE3));
    STATE = STATE3;
    IMED_RET("send hello", ret, 1);

    ver = get_version(session);
    if (ver->tls13_sem) { /* TLS 1.3 state machine */
      STATE = STATE99;
      goto reset;
    }

    FALLTHROUGH;
  case STATE4:
    if (session->security_parameters.do_send_supplemental) {
      ret = _gnutls_send_supplemental(session, AGAIN(STATE4));
      STATE = STATE4;
      IMED_RET("send supplemental data", ret, 0);
    }
    /* SEND CERTIFICATE + KEYEXCHANGE + CERTIFICATE_REQUEST */
    FALLTHROUGH;
  case STATE5:
    /* NOTE: these should not be send if we are resuming */

    if (!session->internals.resumed)
      ret =
          _gnutls_send_server_certificate(session,
                  AGAIN(STATE5));
    STATE = STATE5;
    IMED_RET("send server certificate", ret, 0);
    FALLTHROUGH;
  case STATE6:
#ifdef ENABLE_OCSP
    if (!session->internals.resumed)
      ret =
          _gnutls_send_server_certificate_status(session,
                   AGAIN
                   (STATE6));
    STATE = STATE6;
    IMED_RET("send server certificate status", ret, 0);
#endif
    FALLTHROUGH;
  case STATE7:
    /* send server key exchange (A) */
    if (!session->internals.resumed)
      ret =
          _gnutls_send_server_kx_message(session,
                 AGAIN(STATE7));
    STATE = STATE7;
    IMED_RET("send server kx", ret, 0);
    FALLTHROUGH;
  case STATE8:
    /* Send certificate request - if requested to */
    if (!session->internals.resumed)
      ret =
          _gnutls_send_server_crt_request(session,
                  AGAIN(STATE8));
    STATE = STATE8;
    IMED_RET("send server cert request", ret, 0);
    FALLTHROUGH;
  case STATE9:
    /* send the server hello done */
    if (!session->internals.resumed) /* if we are not resuming */
      ret =
          _gnutls_send_empty_handshake(session,
               GNUTLS_HANDSHAKE_SERVER_HELLO_DONE,
               AGAIN(STATE9));
    STATE = STATE9;
    IMED_RET("send server hello done", ret, 1);
    FALLTHROUGH;
  case STATE10:
    if (session->security_parameters.do_recv_supplemental) {
      ret = _gnutls_recv_supplemental(session);
      STATE = STATE10;
      IMED_RET("recv client supplemental", ret, 1);
    }
    /* RECV CERTIFICATE + KEYEXCHANGE + CERTIFICATE_VERIFY */
    FALLTHROUGH;
  case STATE11:
    /* receive the client certificate message */
    if (!session->internals.resumed) /* if we are not resuming */
      ret = _gnutls_recv_client_certificate(session);
    STATE = STATE11;
    IMED_RET("recv client certificate", ret, 1);
    FALLTHROUGH;
  case STATE12:
    ret = _gnutls_run_verify_callback(session, GNUTLS_SERVER);
    STATE = STATE12;
    if (ret < 0)
      return gnutls_assert_val(ret);
    FALLTHROUGH;
  case STATE13:
    /* receive the client key exchange message */
    if (!session->internals.resumed) /* if we are not resuming */
      ret = _gnutls_recv_client_kx_message(session);
    STATE = STATE13;
    IMED_RET("recv client kx", ret, 1);
    FALLTHROUGH;
  case STATE14:
    /* receive the client certificate verify message */
    if (!session->internals.resumed) /* if we are not resuming */
      ret =
          _gnutls_recv_client_certificate_verify_message
          (session);
    STATE = STATE14;
    IMED_RET("recv client certificate verify", ret, 1);
    FALLTHROUGH;
  case STATE15:
    STATE = STATE15;
    if (!session->internals.resumed) { /* if we are not resuming */
      ret = recv_handshake_final(session, true);
      IMED_RET("recv handshake final", ret, 1);
    } else {
      ret = send_handshake_final(session, true);
      IMED_RET("send handshake final 2", ret, 1);
    }
    FALLTHROUGH;
  case STATE16:
    ret = _gnutls_send_new_session_ticket(session, AGAIN(STATE16));
    STATE = STATE16;
    IMED_RET("send handshake new session ticket", ret, 0);
    FALLTHROUGH;
  case STATE17:
    STATE = STATE17;
    if (!session->internals.resumed) { /* if we are not resuming */
      ret = send_handshake_final(session, false);
      IMED_RET("send handshake final", ret, 1);

      if (session->security_parameters.entity ==
          GNUTLS_SERVER
          && !(session->
         internals.hsk_flags & HSK_TLS12_TICKET_SENT)) {
        /* if no ticket, save session data */
        _gnutls_server_register_current_session
            (session);
      }
    } else {
      ret = recv_handshake_final(session, false);
      IMED_RET("recv handshake final 2", ret, 1);
    }

    STATE = STATE0;
    FALLTHROUGH;
  default:
    break;
  }

  /* no lock of post_negotiation_lock is required here as this is not run
   * after handshake */
  session->internals.initial_negotiation_completed = 1;

  return _gnutls_check_id_for_change(session);
}

int _gnutls_generate_session_id(uint8_t * session_id, uint8_t * len)
{
  int ret;

  *len = GNUTLS_DEF_SESSION_ID_SIZE;

  ret =
      gnutls_rnd(GNUTLS_RND_NONCE, session_id,
           GNUTLS_DEF_SESSION_ID_SIZE);
  if (ret < 0) {
    gnutls_assert();
    return ret;
  }

  return 0;
}

/**
 * gnutls_handshake_set_max_packet_length:
 * @session: is a #gnutls_session_t type.
 * @max: is the maximum number.
 *
 * This function will set the maximum size of all handshake messages.
 * Handshakes over this size are rejected with
 * %GNUTLS_E_HANDSHAKE_TOO_LARGE error code.  The default value is
 * 128kb which is typically large enough.  Set this to 0 if you do not
 * want to set an upper limit.
 *
 * The reason for restricting the handshake message sizes are to
 * limit Denial of Service attacks.
 *
 * Note that the maximum handshake size was increased to 128kb
 * from 48kb in GnuTLS 3.5.5.
 **/
void
gnutls_handshake_set_max_packet_length(gnutls_session_t session, size_t max)
{
  session->internals.max_handshake_data_buffer_size = max;
}

/**
 * gnutls_handshake_get_last_in:
 * @session: is a #gnutls_session_t type.
 *
 * This function is only useful to check where the last performed
 * handshake failed.  If the previous handshake succeed or was not
 * performed at all then no meaningful value will be returned.
 *
 * Check %gnutls_handshake_description_t in gnutls.h for the
 * available handshake descriptions.
 *
 * Returns: the last handshake message type received, a
 * %gnutls_handshake_description_t.
 **/
gnutls_handshake_description_t
gnutls_handshake_get_last_in(gnutls_session_t session)
{
  return session->internals.last_handshake_in;
}

/**
 * gnutls_handshake_get_last_out:
 * @session: is a #gnutls_session_t type.
 *
 * This function is only useful to check where the last performed
 * handshake failed.  If the previous handshake succeed or was not
 * performed at all then no meaningful value will be returned.
 *
 * Check %gnutls_handshake_description_t in gnutls.h for the
 * available handshake descriptions.
 *
 * Returns: the last handshake message type sent, a
 * %gnutls_handshake_description_t.
 **/
gnutls_handshake_description_t
gnutls_handshake_get_last_out(gnutls_session_t session)
{
  return session->internals.last_handshake_out;
}

/* This returns the session hash as in draft-ietf-tls-session-hash-02.
 */
int _gnutls_handshake_get_session_hash(gnutls_session_t session,
               gnutls_datum_t * shash)
{
  const version_entry_st *ver = get_version(session);
  int ret;
  uint8_t concat[2 * MAX_HASH_SIZE];

  if (unlikely(ver == NULL))
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

  if (session->internals.handshake_hash_buffer_client_kx_len == 0 ||
      (session->internals.handshake_hash_buffer.length <
       session->internals.handshake_hash_buffer_client_kx_len)) {
    return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
  }

  ret = _gnutls_hash_fast((gnutls_digest_algorithm_t)
        session->security_parameters.prf->id,
        session->internals.handshake_hash_buffer.data,
        session->
        internals.handshake_hash_buffer_client_kx_len,
        concat);
  if (ret < 0)
    return gnutls_assert_val(ret);

  return _gnutls_set_datum(shash, concat,
         session->security_parameters.prf->output_size);
}

Coverage Report

Created: 2023-03-26 07:33