Added support for an old version of the DTLS protocol

[gnutls.git] / lib / gnutls_handshake.c

/*
 * Copyright (C) 2000-2012 Free Software Foundation, 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 3 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 <http://www.gnu.org/licenses/>
 *
 */

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

#include "gnutls_int.h"
#include "gnutls_errors.h"
#include "gnutls_dh.h"
#include "debug.h"
#include "algorithms.h"
#include "gnutls_compress.h"
#include "gnutls_cipher.h"
#include "gnutls_buffers.h"
#include "gnutls_mbuffers.h"
#include "gnutls_kx.h"
#include "gnutls_handshake.h"
#include "gnutls_num.h"
#include "gnutls_hash_int.h"
#include "gnutls_db.h"
#include "gnutls_extensions.h"
#include "gnutls_supplemental.h"
#include "gnutls_auth.h"
#include "gnutls_v2_compat.h"
#include <auth/cert.h>
#include "gnutls_constate.h"
#include <gnutls_record.h>
#include <gnutls_state.h>
#include <ext/srp.h>
#include <ext/session_ticket.h>
#include <ext/safe_renegotiation.h>
#include <gnutls_rsa_export.h>  /* for gnutls_get_rsa_params() */
#include <auth/anon.h>          /* for gnutls_anon_server_credentials_t */
#include <auth/psk.h>           /* for gnutls_psk_server_credentials_t */
#include <random.h>
#include <gnutls_dtls.h>

#ifdef HANDSHAKE_DEBUG
#define ERR(x, y) _gnutls_handshake_log("HSK[%p]: %s (%d)\n", session, x,y)
#else
#define ERR(x, y)
#endif

#define TRUE 1
#define FALSE 0

static int _gnutls_server_select_comp_method (gnutls_session_t session,
                                              uint8_t * data, int datalen);
static int
_gnutls_remove_unwanted_ciphersuites (gnutls_session_t session,
                                      uint8_t * cipher_suites,
                                      int cipher_suites_size,
                                      gnutls_pk_algorithm_t *pk_algos,
                                      size_t pk_algos_size);

/* Empties but does not free the buffer
 */
static inline void
_gnutls_handshake_hash_buffer_empty (gnutls_session_t session)
{

  _gnutls_buffers_log ("BUF[HSK]: Emptied buffer\n");

  session->internals.handshake_hash_buffer_prev_len = 0;
  session->internals.handshake_hash_buffer.length = 0;
  return;
}

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

static int
_gnutls_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)
{
  session->internals.handshake_hash_buffer_prev_len = 0;
  _gnutls_buffer_clear(&session->internals.handshake_hash_buffer);
}

/* this will copy the required values for resuming to
 * internals, and to security_parameters.
 * this will keep as less data to security_parameters.
 */
static void
resume_copy_required_values (gnutls_session_t session)
{
  /* 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.
   */
  memcpy (session->security_parameters.cipher_suite,
          session->internals.resumed_security_parameters.cipher_suite, 2);
  session->security_parameters.compression_method = session->internals.resumed_security_parameters.compression_method;

  _gnutls_epoch_set_cipher_suite (session, EPOCH_NEXT,
                                  session->
                                  internals.resumed_security_parameters.cipher_suite);
  _gnutls_epoch_set_compression (session, EPOCH_NEXT,
                                 session->
                                 internals.resumed_security_parameters.compression_method);

  /* or write_compression_algorithm
   * they are the same
   */

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

  _gnutls_set_current_version (session,
                               session->internals.resumed_security_parameters.
                               version);

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

  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;

}

void
_gnutls_set_server_random (gnutls_session_t session, uint8_t * rnd)
{
  memcpy (session->security_parameters.server_random, rnd,
          GNUTLS_RANDOM_SIZE);
}

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

/* 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, GNUTLS_DIG_SHA1);
  if (rc < 0)
    return gnutls_assert_val(rc);

  rc = _gnutls_hash_init (&td_md5, 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;
}

/* 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 + 16 /*MD5 */ ];
  size_t hash_len;
  const char *mesg;
  int rc, len;

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

  if (!_gnutls_version_has_selectable_prf (gnutls_protocol_get_version(session)))
    {
      rc = _gnutls_hash_fast( GNUTLS_DIG_SHA1, session->internals.handshake_hash_buffer.data, len, &concat[16]);
      if (rc < 0)
        return gnutls_assert_val(rc);

      rc = _gnutls_hash_fast( GNUTLS_DIG_MD5, session->internals.handshake_hash_buffer.data, len, concat);
      if (rc < 0)
        return gnutls_assert_val(rc);
       
      hash_len = 20 + 16;
    }
  else 
    {
      int algorithm = _gnutls_cipher_suite_get_prf(session->security_parameters.cipher_suite);

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

      hash_len = _gnutls_hash_get_algo_len (algorithm);
    }

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

  return _gnutls_PRF (session, session->security_parameters.master_secret,
                      GNUTLS_MASTER_SIZE, mesg, siz, concat, hash_len, 12, ret);
}

/* this function will produce GNUTLS_RANDOM_SIZE==32 bytes of random data
 * and put it to dst.
 */
int
_gnutls_tls_create_random (uint8_t * dst)
{
  uint32_t tim;
  int ret;

  /* Use weak random numbers for the most of the
   * buffer except for the first 4 that are the
   * system's time.
   */

  tim = gnutls_time (NULL);
  /* generate server random value */
  _gnutls_write_uint32 (tim, dst);

  ret = _gnutls_rnd (GNUTLS_RND_NONCE, &dst[4], GNUTLS_RANDOM_SIZE - 4);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  return 0;
}

/* returns the 0 on success or a negative error code.
 */
int
_gnutls_negotiate_version (gnutls_session_t session,
                           gnutls_protocol_t adv_version)
{
  int ret;

  /* if we do not support that version  */
  if (_gnutls_version_is_supported (session, adv_version) == 0)
    {
      /* If he requested something we do not support
       * then we send him the highest we support.
       */
      ret = _gnutls_version_max (session);
      if (ret == GNUTLS_VERSION_UNKNOWN)
        {
          /* this check is not really needed.
           */
          gnutls_assert ();
          return GNUTLS_E_UNKNOWN_CIPHER_SUITE;
        }
    }
  else
    {
      ret = adv_version;
    }

  _gnutls_set_current_version (session, ret);

  return ret;
}

int
_gnutls_user_hello_func (gnutls_session_t session,
                         gnutls_protocol_t adv_version)
{
  int ret;

  if (session->internals.user_hello_func != NULL)
    {
      ret = session->internals.user_hello_func (session);
      if (ret < 0)
        {
          gnutls_assert ();
          return ret;
        }
      /* Here we need to renegotiate the version since the callee might
       * have disabled some TLS versions.
       */
      ret = _gnutls_negotiate_version (session, adv_version);
      if (ret < 0)
        {
          gnutls_assert ();
          return ret;
        }
    }
  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
_gnutls_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;
  gnutls_protocol_t adv_version;
  int neg_version;
  int len = datalen;
  uint8_t rnd[GNUTLS_RANDOM_SIZE], *suite_ptr, *comp_ptr, *session_id;

  DECR_LEN (len, 2);

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

  adv_version = _gnutls_version_get (data[pos], data[pos + 1]);
  set_adv_version (session, data[pos], data[pos + 1]);
  pos += 2;

  neg_version = _gnutls_negotiate_version (session, adv_version);
  if (neg_version < 0)
    {
      gnutls_assert ();
      return neg_version;
    }

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

  _gnutls_tls_create_random (rnd);
  _gnutls_set_server_random (session, rnd);

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

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

  /* RESUME SESSION 
   */
  if (session_id_len > TLS_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;
   }

  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! */
      /* Parse only the safe renegotiation extension
       * We don't want to parse any other extensions since
       * we don't want new extension values to overwrite the
       * resumed ones.
       */

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

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

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

      ret = _gnutls_parse_extensions (session, GNUTLS_EXT_MANDATORY,
                                      &data[pos], len);
      if (ret < 0)
        {
          gnutls_assert ();
          return ret;
        }

      resume_copy_required_values (session);
      session->internals.resumed = RESUME_TRUE;

      return _gnutls_user_hello_func (session, adv_version);
    }
  else
    {
      _gnutls_generate_session_id (session->security_parameters.session_id,
                                   &session->
                                   security_parameters.session_id_size);

      session->internals.resumed = RESUME_FALSE;
    }

  /* Remember ciphersuites for later
   */
  DECR_LEN (len, 2);
  suite_size = _gnutls_read_uint16 (&data[pos]);
  pos += 2;

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

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

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

  /* 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_extensions (session, GNUTLS_EXT_APPLICATION,
                                  &data[pos], len);
  /* len is the rest of the parsed length */
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  ret = _gnutls_user_hello_func (session, adv_version);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  ret = _gnutls_parse_extensions (session, GNUTLS_EXT_MANDATORY,
                                  &data[pos], len);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  ret = _gnutls_parse_extensions (session, GNUTLS_EXT_TLS, &data[pos], len);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  /* resumed by session_ticket extension */
  if (session->internals.resumed != RESUME_FALSE)
    {
      /* to indicate the client that the current session is resumed */
      memcpy (session->internals.resumed_security_parameters.session_id,
              session_id, session_id_len);
      session->internals.resumed_security_parameters.session_id_size =
        session_id_len;

      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;

      resume_copy_required_values (session);

      return _gnutls_user_hello_func (session, adv_version);
    }

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

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

  return 0;
}

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

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

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

      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 == RESUME_FALSE
           && session->security_parameters.entity == GNUTLS_CLIENT)
          || (session->internals.resumed != RESUME_FALSE
              && 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 
 */
static 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;

  ret =
    _gnutls_recv_handshake (session, GNUTLS_HANDSHAKE_FINISHED, 
                            0, &buf);
  if (ret < 0)
    {
      ERR ("recv finished int", ret);
      gnutls_assert ();
      return ret;
    }

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

  if (gnutls_protocol_get_version (session) == GNUTLS_SSL3)
    {
      data_size = 36;
    }
  else
    {
      data_size = 12;
    }

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

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

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

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

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

  if ((session->internals.resumed != RESUME_FALSE
       && session->security_parameters.entity == GNUTLS_CLIENT)
      || (session->internals.resumed == RESUME_FALSE
          && 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;
    }


  session->internals.initial_negotiation_completed = 1;

cleanup:
  _gnutls_buffer_clear(&buf);

  return ret;
}

/* returns PK_RSA if the given cipher suite list only supports,
 * RSA algorithms, PK_DSA if DSS, and PK_ANY for both or PK_NONE for none.
 */
static int
server_find_pk_algos_in_ciphersuites (const uint8_t *
                                              data, unsigned int datalen,
                                              gnutls_pk_algorithm_t * algos,
                                              size_t* algos_size)
{
  unsigned int j;
  gnutls_kx_algorithm_t kx;
  unsigned int max = *algos_size;

  if (datalen % 2 != 0)
    {
      gnutls_assert ();
      return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
    }

  *algos_size = 0;
  for (j = 0; j < datalen; j += 2)
    {
      kx = _gnutls_cipher_suite_get_kx_algo (&data[j]);
      if (_gnutls_map_kx_get_cred (kx, 1) == GNUTLS_CRD_CERTIFICATE)
        {
          algos[(*algos_size)++] = _gnutls_map_pk_get_pk (kx);
          
          if ((*algos_size) >= max)
            return 0;
        }
    }

  return 0;
}

/* This selects the best supported ciphersuite from the given ones. Then
 * it adds the suite to the session and performs some checks.
 */
int
_gnutls_server_select_suite (gnutls_session_t session, uint8_t * data,
                             unsigned int datalen)
{
  int ret;
  unsigned int i, j, cipher_suites_size;
  size_t pk_algos_size;
  uint8_t cipher_suites[MAX_CIPHERSUITE_SIZE];
  int retval, err;
  gnutls_pk_algorithm_t pk_algos[MAX_ALGOS];        /* will hold the pk algorithms
                                         * supported by the peer.
                                         */

  /* First, check for safe renegotiation SCSV.
   */
  if (session->internals.priorities.sr != SR_DISABLED)
    {
      unsigned int offset;

      for (offset = 0; offset < datalen; offset += 2)
        {
          /* TLS_RENEGO_PROTECTION_REQUEST = { 0x00, 0xff } */
          if (data[offset] == GNUTLS_RENEGO_PROTECTION_REQUEST_MAJOR &&
              data[offset + 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;
                }
              break;
            }
        }
    }

  pk_algos_size = MAX_ALGOS;
  ret = server_find_pk_algos_in_ciphersuites (data, datalen, pk_algos, &pk_algos_size);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret = _gnutls_supported_ciphersuites (session, cipher_suites, sizeof(cipher_suites));
  if (ret < 0)
    return gnutls_assert_val(ret);
    
  cipher_suites_size = ret;

  /* Here we remove any ciphersuite that does not conform
   * the certificate requested, or to the
   * authentication requested (e.g. SRP).
   */
  ret = _gnutls_remove_unwanted_ciphersuites (session, cipher_suites, cipher_suites_size, pk_algos, pk_algos_size);
  if (ret <= 0)
    {
      gnutls_assert ();
      if (ret < 0)
        return ret;
      else
        return GNUTLS_E_UNKNOWN_CIPHER_SUITE;
    }
    
  cipher_suites_size = ret;

  /* Data length should be zero mod 2 since
   * every ciphersuite is 2 bytes. (this check is needed
   * see below).
   */
  if (datalen % 2 != 0)
    {
      gnutls_assert ();
      return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
    }

  memset (session->security_parameters.cipher_suite, 0, 2);

  retval = GNUTLS_E_UNKNOWN_CIPHER_SUITE;

  _gnutls_handshake_log ("HSK[%p]: Requested cipher suites[size: %d]: \n", session, (int)datalen);

  if (session->internals.priorities.server_precedence == 0)
    {
      for (j = 0; j < datalen; j += 2)
        {
          _gnutls_handshake_log ("\t0x%.2x, 0x%.2x %s\n", data[j], data[j+1], _gnutls_cipher_suite_get_name (&data[j]));
          for (i = 0; i < cipher_suites_size; i+=2)
            {
              if (memcmp (&cipher_suites[i], &data[j], 2) == 0)
                {
                  _gnutls_handshake_log
                    ("HSK[%p]: Selected cipher suite: %s\n", session,
                    _gnutls_cipher_suite_get_name (&data[j]));
                  memcpy (session->security_parameters.cipher_suite,
                      &cipher_suites[i], 2);
                  _gnutls_epoch_set_cipher_suite (session, EPOCH_NEXT,
                                                  session->
                                                  security_parameters.cipher_suite);


                  retval = 0;
                  goto finish;
                }
            }
        }
    }
  else /* server selects */
    {
      for (i = 0; i < cipher_suites_size; i+=2)
        {
          for (j = 0; j < datalen; j += 2)
            {
              if (memcmp (&cipher_suites[i], &data[j], 2) == 0)
                {
                  _gnutls_handshake_log
                    ("HSK[%p]: Selected cipher suite: %s\n", session,
                    _gnutls_cipher_suite_get_name (&data[j]));
                  memcpy (session->security_parameters.cipher_suite,
                      &cipher_suites[i], 2);
                  _gnutls_epoch_set_cipher_suite (session, EPOCH_NEXT,
                                                  session->
                                                  security_parameters.cipher_suite);


                  retval = 0;
                  goto finish;
                }
            }
        }
    }
finish:

  if (retval != 0)
    {
      gnutls_assert ();
      return retval;
    }

  /* check if the credentials (username, public key etc.) are ok
   */
  if (_gnutls_get_kx_cred
      (session,
       _gnutls_cipher_suite_get_kx_algo (session->
                                         security_parameters.cipher_suite),
       &err) == NULL && err != 0)
    {
      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 (_gnutls_cipher_suite_get_kx_algo
                            (session->
                             security_parameters.cipher_suite));
  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 selects the best supported compression method from the ones provided 
 */
static int
_gnutls_server_select_comp_method (gnutls_session_t session,
                                   uint8_t * data, int datalen)
{
  int x, i, j;
  uint8_t comps[MAX_ALGOS];

  x = _gnutls_supported_compression_methods (session, comps, MAX_ALGOS);
  if (x < 0)
    {
      gnutls_assert ();
      return x;
    }

  if (session->internals.priorities.server_precedence == 0)
    {
      for (j = 0; j < datalen; j++)
        {
          for (i = 0; i < x; i++)
            {
              if (comps[i] == data[j])
                {
                  gnutls_compression_method_t method =
                    _gnutls_compression_get_id (comps[i]);

                  _gnutls_epoch_set_compression (session, EPOCH_NEXT, method);
                  session->security_parameters.compression_method = method;

                  _gnutls_handshake_log
                    ("HSK[%p]: Selected Compression Method: %s\n", session,
                    gnutls_compression_get_name (method));
                  return 0;
                }
            }
        }
    }
  else
    {
      for (i = 0; i < x; i++)
        {
          for (j = 0; j < datalen; j++)
            {
              if (comps[i] == data[j])
                {
                  gnutls_compression_method_t method =
                    _gnutls_compression_get_id (comps[i]);

                  _gnutls_epoch_set_compression (session, EPOCH_NEXT, method);
                  session->security_parameters.compression_method = method;

                  _gnutls_handshake_log
                    ("HSK[%p]: Selected Compression Method: %s\n", session,
                    gnutls_compression_get_name (method));
                  return 0;
                }
            }
        }
    }

  /* we were not able to find a compatible 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, 0);
      if (bufel == NULL)
        {
          gnutls_assert ();
          return GNUTLS_E_MEMORY_ERROR;
        }
    }
  else
    bufel = NULL;

  return _gnutls_send_handshake (session, bufel, type);
}




/* 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_handshake (gnutls_session_t session, mbuffer_st * bufel,
                        gnutls_handshake_description_t type)
{
  int ret;
  uint8_t *data;
  uint32_t datasize, i_datasize;
  int pos = 0;

  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) 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 (type != GNUTLS_HANDSHAKE_HELLO_REQUEST)
    if ((ret =
         _gnutls_handshake_hash_add_sent (session, type, data, datasize)) < 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;
    }

  switch (type)
    {
    case GNUTLS_HANDSHAKE_CERTIFICATE_PKT:     /* this one is followed by ServerHelloDone
                                                 * or ClientKeyExchange always.
                                                 */
    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 cached messages */
      ret = _gnutls_handshake_io_write_flush (session);
      break;
    }

  return ret;
}

#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)) \
    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
_gnutls_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;

  if ((gnutls_protocol_get_version (session) != GNUTLS_DTLS0_9 &&
       recv_type == GNUTLS_HANDSHAKE_HELLO_VERIFY_REQUEST) ||
      recv_type == GNUTLS_HANDSHAKE_HELLO_REQUEST)
    return 0;

  CHECK_SIZE(header_size + datalen);

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

  if (gnutls_protocol_get_version (session) != 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);
    }

  return 0;
}

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

  /* We don't check for GNUTLS_HANDSHAKE_HELLO_VERIFY_REQUEST because it
   * is not sent via that channel.
   */
  if (type != GNUTLS_HANDSHAKE_HELLO_REQUEST)
    {
      CHECK_SIZE(datalen);

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

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

      return 0;
    }

  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;
  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);
    }

  ret = _gnutls_handshake_hash_add_recvd (session, hsk.htype,
                                              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:
    case GNUTLS_HANDSHAKE_SERVER_HELLO:
      if (hsk.htype == GNUTLS_HANDSHAKE_CLIENT_HELLO_V2)
        ret = _gnutls_read_client_hello_v2 (session, hsk.data.data, hsk.data.length);
      else
        ret = _gnutls_recv_hello (session, hsk.data.data, hsk.data.length);

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

      goto cleanup; /* caller doesn't need dataptr */

      break;
    case GNUTLS_HANDSHAKE_HELLO_VERIFY_REQUEST:
      ret = _gnutls_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;
        
      goto cleanup; /* caller doesn't need dataptr */

      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_FINISHED:
    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:
      ret = hsk.data.length;
      break;
    default:
      gnutls_assert ();
      /* we shouldn't actually arrive here in any case .
       * unexpected messages should be catched after _gnutls_handshake_io_recv_int()
       */
      ret = GNUTLS_E_UNEXPECTED_HANDSHAKE_PACKET;
      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
_gnutls_client_set_ciphersuite (gnutls_session_t session, uint8_t suite[2])
{
  uint8_t z;
  uint8_t cipher_suites[MAX_CIPHERSUITE_SIZE];
  int cipher_suite_size;
  int i, err;

  z = 1;
  cipher_suite_size = _gnutls_supported_ciphersuites (session, cipher_suites, sizeof(cipher_suites));
  if (cipher_suite_size < 0)
    {
      gnutls_assert ();
      return cipher_suite_size;
    }

  for (i = 0; i < cipher_suite_size; i+=2)
    {
      if (memcmp (&cipher_suites[i], suite, 2) == 0)
        {
          z = 0;
          break;
        }
    }

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

  memcpy (session->security_parameters.cipher_suite, suite, 2);
  _gnutls_epoch_set_cipher_suite (session, EPOCH_NEXT,
                                  session->
                                  security_parameters.cipher_suite);

  _gnutls_handshake_log ("HSK[%p]: Selected cipher suite: %s\n", session,
                         _gnutls_cipher_suite_get_name
                         (session->
                          security_parameters.cipher_suite));


  /* check if the credentials (username, public key etc.) are ok.
   * Actually checks if they exist.
   */
  if (!session->internals.premaster_set &&
      _gnutls_get_kx_cred
      (session,
       _gnutls_cipher_suite_get_kx_algo
       (session->security_parameters.cipher_suite), &err) == NULL
      && err != 0)
    {
      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 (_gnutls_cipher_suite_get_kx_algo
                            (session->
                             security_parameters.cipher_suite));

  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 function sets the given comp method to the session.
 */
static int
_gnutls_client_set_comp_method (gnutls_session_t session, uint8_t comp_method)
{
  int comp_methods_num;
  uint8_t compression_methods[MAX_ALGOS];
  int id = _gnutls_compression_get_id(comp_method);
  int i;

  _gnutls_handshake_log ("HSK[%p]: Selected compression method: %s (%d)\n", session,
                         gnutls_compression_get_name(id), (int)comp_method);

  comp_methods_num = _gnutls_supported_compression_methods (session,
                                                            compression_methods, MAX_ALGOS);
  if (comp_methods_num < 0)
    {
      gnutls_assert ();
      return comp_methods_num;
    }

  for (i = 0; i < comp_methods_num; i++)
    {
      if (compression_methods[i] == comp_method)
        {
          comp_methods_num = 0;
          break;
        }
    }

  if (comp_methods_num != 0)
    {
      gnutls_assert ();
      return GNUTLS_E_UNKNOWN_COMPRESSION_ALGORITHM;
    }

  session->security_parameters.compression_method = id;
  _gnutls_epoch_set_compression (session, EPOCH_NEXT, id);

  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.
 */
static int
_gnutls_client_check_if_resuming (gnutls_session_t session,
                                  uint8_t * session_id, int session_id_len)
{
  char buf[2 * TLS_MAX_SESSION_ID_SIZE + 1];

  _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_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);

      _gnutls_epoch_set_cipher_suite
        (session, EPOCH_NEXT,
         session->internals.
         resumed_security_parameters.cipher_suite);
      _gnutls_epoch_set_compression (session, EPOCH_NEXT,
                                     session->
                                     internals.resumed_security_parameters.compression_method);

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

      return 0;
    }
  else
    {
      /* keep the new session id */
      session->internals.resumed = RESUME_FALSE;        /* we are not resuming */
      session->security_parameters.session_id_size = session_id_len;
      memcpy (session->security_parameters.session_id,
              session_id, session_id_len);

      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
_gnutls_read_server_hello (gnutls_session_t session,
                           uint8_t * data, int datalen)
{
  uint8_t session_id_len = 0;
  int pos = 0;
  int ret = 0;
  gnutls_protocol_t version;
  int len = datalen;

  if (datalen < 38)
    {
      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);
  version = _gnutls_version_get (data[pos], data[pos + 1]);
  if (_gnutls_version_is_supported (session, version) == 0)
    {
      gnutls_assert ();
      return GNUTLS_E_UNSUPPORTED_VERSION_PACKET;
    }
  else
    {
      _gnutls_set_current_version (session, version);
    }

  pos += 2;

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


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

  if (len < session_id_len)
    {
      gnutls_assert ();
      return GNUTLS_E_UNSUPPORTED_VERSION_PACKET;
    }
  DECR_LEN (len, session_id_len);

  /* check if we are resuming and set the appropriate
   * values;
   */
  if (_gnutls_client_check_if_resuming
      (session, &data[pos], session_id_len) == 0)
    {
      pos += session_id_len + 2 + 1;
      DECR_LEN (len, 2 + 1);

      ret = _gnutls_parse_extensions (session, GNUTLS_EXT_MANDATORY,
                                      &data[pos], len);
      if (ret < 0)
        {
          gnutls_assert ();
          return ret;
        }
      return 0;
    }

  pos += session_id_len;

  /* Check if the given cipher suite is supported and copy
   * it to the session.
   */

  DECR_LEN (len, 2);
  ret = _gnutls_client_set_ciphersuite (session, &data[pos]);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }
  pos += 2;

  /* move to compression 
   */
  DECR_LEN (len, 1);

  ret = _gnutls_client_set_comp_method (session, data[pos++]);
  if (ret < 0)
    {
      gnutls_assert ();
      return GNUTLS_E_UNKNOWN_COMPRESSION_ALGORITHM;
    }

  /* Parse extensions.
   */
  ret = _gnutls_parse_extensions (session, GNUTLS_EXT_ANY, &data[pos], len);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  return ret;
}


/* This function copies the appropriate ciphersuites to a locally allocated buffer
 * Needed in client hello messages. Returns the new data length. If add_scsv is
 * true, add the special safe renegotiation CS.
 */
static int
_gnutls_copy_ciphersuites (gnutls_session_t session,
                           gnutls_buffer_st * cdata, 
                           int add_scsv)
{
  int ret;
  uint8_t cipher_suites[MAX_CIPHERSUITE_SIZE+2];
  int cipher_suites_size;
  size_t init_length = cdata->length;

  ret = _gnutls_supported_ciphersuites (session, cipher_suites, sizeof(cipher_suites)-2);
  if (ret < 0)
    return gnutls_assert_val(ret);

  /* Here we remove any ciphersuite that does not conform
   * the certificate requested, or to the
   * authentication requested (eg SRP).
   */
  ret =
    _gnutls_remove_unwanted_ciphersuites (session, cipher_suites, ret, NULL, 0);
  if (ret < 0)
    return gnutls_assert_val(ret);

  /* If no cipher suites were enabled.
   */
  if (ret == 0)
    return gnutls_assert_val(GNUTLS_E_INSUFFICIENT_CREDENTIALS);

  cipher_suites_size = ret;
  if (add_scsv)
    {
      cipher_suites[cipher_suites_size] = 0x00;
      cipher_suites[cipher_suites_size+1] = 0xff;
      cipher_suites_size += 2;

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

  ret = _gnutls_buffer_append_data_prefix(cdata, 16, cipher_suites, cipher_suites_size);
  if (ret < 0)
    return gnutls_assert_val(ret);

  ret = cdata->length - init_length;

  return ret;
}


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

  ret = _gnutls_supported_compression_methods (session, compression_methods, MAX_ALGOS);
  if (ret < 0)
    return gnutls_assert_val(ret);

  comp_num = ret;

  /* put the number of compression methods */
  ret = _gnutls_buffer_append_prefix(cdata, 8, comp_num);
  if (ret < 0)
    return gnutls_assert_val(ret);

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

  ret = cdata->length - init_length;

  return ret;
}

/* This should be sufficient by now. It should hold all the extensions
 * plus the headers in a hello message.
 */
#define MAX_EXT_DATA_LENGTH 32*1024

/* This function sends the client hello handshake message.
 */
static int
_gnutls_send_client_hello (gnutls_session_t session, int again)
{
  mbuffer_st *bufel = NULL;
  uint8_t *data = NULL;
  int pos = 0, type;
  int datalen = 0, ret = 0;
  uint8_t rnd[GNUTLS_RANDOM_SIZE];
  gnutls_protocol_t hver;
  gnutls_buffer_st extdata;
  int rehandshake = 0;
  uint8_t session_id_len =
    session->internals.resumed_security_parameters.session_id_size;
  uint8_t cookie_len;

  _gnutls_buffer_init(&extdata);

  /* note that rehandshake is different than resuming
   */
  if (session->security_parameters.session_id_size)
    rehandshake = 1;

  if (again == 0)
    {
      if(IS_DTLS(session))
        {
          cookie_len = session->internals.dtls.cookie_len + 1;
        }
      else
        {
          cookie_len = 0;
        }

      datalen = 2 + (session_id_len + 1) + GNUTLS_RANDOM_SIZE + cookie_len;
      /* 2 for version, (4 for unix time + 28 for random bytes==GNUTLS_RANDOM_SIZE) 
       */

      bufel = _gnutls_handshake_alloc (session, datalen, datalen+MAX_EXT_DATA_LENGTH);
      if (bufel == NULL)
        {
          gnutls_assert ();
          return GNUTLS_E_MEMORY_ERROR;
        }
      data = _mbuffer_get_udata_ptr (bufel);

      /* if we are resuming a session then we set the
       * version number to the previously established.
       */
      if (session_id_len == 0)
        {
          if (rehandshake)      /* already negotiated version thus version_max == negotiated version */
            hver = session->security_parameters.version;
          else                  /* new handshake. just get the max */
            hver = _gnutls_version_max (session);
        }
      else
        {
          /* we are resuming a session */
          hver = session->internals.resumed_security_parameters.version;
        }

      if (hver == GNUTLS_VERSION_UNKNOWN || hver == 0)
        {
          gnutls_assert ();
          gnutls_free (bufel);
          return GNUTLS_E_INTERNAL_ERROR;
        }

      data[pos++] = _gnutls_version_get_major (hver);
      data[pos++] = _gnutls_version_get_minor (hver);

      /* Set the version we advertized as maximum 
       * (RSA uses it).
       */
      _gnutls_set_adv_version (session, hver);
      _gnutls_set_current_version (session, hver);

      if (session->internals.priorities.ssl3_record_version != 0)
        {
          /* Advertize the 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.
           */
          if (!IS_DTLS(session))
            _gnutls_record_set_default_version (session, 3, 0);
          else if (gnutls_protocol_get_version (session) == GNUTLS_DTLS0_9)
            _gnutls_record_set_default_version (session, 1, 0);
          else
            _gnutls_record_set_default_version (session, 254, 255);
        }

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

      /* Generate random data 
       */
      if (!IS_DTLS (session)
        || session->internals.dtls.hsk_hello_verify_requests == 0)
        {
          _gnutls_tls_create_random (rnd);
          _gnutls_set_client_random (session, rnd);

          memcpy (&data[pos], rnd, GNUTLS_RANDOM_SIZE);
        }
      else
        memcpy (&data[pos], session->security_parameters.client_random, GNUTLS_RANDOM_SIZE);

      pos += GNUTLS_RANDOM_SIZE;

      /* Copy the Session ID 
       */
      data[pos++] = session_id_len;

      if (session_id_len > 0)
        {
          memcpy (&data[pos],
                  session->internals.resumed_security_parameters.session_id,
                  session_id_len);
          pos += session_id_len;
        }

      /* Copy the DTLS cookie
       */
      if (IS_DTLS(session))
        {
          data[pos++] = session->internals.dtls.cookie_len;
          memcpy(&data[pos], &session->internals.dtls.cookie, session->internals.dtls.cookie_len);
          pos += session->internals.dtls.cookie_len;
        }

      /* Copy the ciphersuites.
       *
       * 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 &&
          (gnutls_protocol_get_version (session) == GNUTLS_SSL3 || 
          session->internals.priorities.no_extensions != 0))
        {
          ret =
            _gnutls_copy_ciphersuites (session, &extdata, TRUE);
          _gnutls_extension_list_add (session,
                                      GNUTLS_EXTENSION_SAFE_RENEGOTIATION);
        }
      else
        ret = _gnutls_copy_ciphersuites (session, &extdata, FALSE);

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

      /* Copy the compression methods.
       */
      ret = _gnutls_copy_comp_methods (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
            {
              if (session->internals.initial_negotiation_completed != 0)
                type = GNUTLS_EXT_MANDATORY;
              else
                type = GNUTLS_EXT_NONE;
            }

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

        }

      ret = _mbuffer_append_data (bufel, extdata.data, extdata.length);
      if (ret < 0)
        {
          gnutls_assert ();
          goto cleanup;
        }
    }

  _gnutls_buffer_clear(&extdata);

  return
    _gnutls_send_handshake (session, bufel, GNUTLS_HANDSHAKE_CLIENT_HELLO);

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

static int
_gnutls_send_server_hello (gnutls_session_t session, int again)
{
  mbuffer_st *bufel = NULL;
  uint8_t *data = NULL;
  gnutls_buffer_st extdata;
  int pos = 0;
  int datalen, ret = 0;
  uint8_t comp;
  uint8_t session_id_len = session->security_parameters.session_id_size;
  char buf[2 * TLS_MAX_SESSION_ID_SIZE + 1];

  datalen = 0;

  _gnutls_buffer_init(&extdata);

  if (again == 0)
    {
      datalen = 2 + session_id_len + 1 + GNUTLS_RANDOM_SIZE + 3;
      ret =
        _gnutls_gen_extensions (session, &extdata, GNUTLS_EXT_ANY);
      if (ret < 0)
        {
          gnutls_assert ();
          goto fail;
        }

      bufel = _gnutls_handshake_alloc (session, datalen + extdata.length, datalen + extdata.length);
      if (bufel == NULL)
        {
          gnutls_assert ();
          ret = GNUTLS_E_MEMORY_ERROR;
          goto fail;
        }
      data = _mbuffer_get_udata_ptr (bufel);

      data[pos++] =
        _gnutls_version_get_major (session->security_parameters.version);
      data[pos++] =
        _gnutls_version_get_minor (session->security_parameters.version);

      memcpy (&data[pos],
              session->security_parameters.server_random, GNUTLS_RANDOM_SIZE);
      pos += GNUTLS_RANDOM_SIZE;

      data[pos++] = session_id_len;
      if (session_id_len > 0)
        {
          memcpy (&data[pos], session->security_parameters.session_id,
                  session_id_len);
        }
      pos += session_id_len;

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

      memcpy (&data[pos],
              session->security_parameters.cipher_suite, 2);
      pos += 2;

      comp = _gnutls_compression_get_num ( session->security_parameters.compression_method);
      data[pos++] = comp;

      if (extdata.length > 0)
        {
          datalen += extdata.length;
          memcpy (&data[pos], extdata.data, extdata.length);
        }
    }

  ret =
    _gnutls_send_handshake (session, bufel, GNUTLS_HANDSHAKE_SERVER_HELLO);

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

int
_gnutls_send_hello (gnutls_session_t session, int again)
{
  int ret;

  if (session->security_parameters.entity == GNUTLS_CLIENT)
    {
      ret = _gnutls_send_client_hello (session, again);

    }
  else
    {                           /* SERVER */
      ret = _gnutls_send_server_hello (session, again);
    }

  return ret;
}

/* RECEIVE A HELLO MESSAGE. This should be called from gnutls_recv_handshake_int only if a
 * hello message is expected. It uses the security_parameters.cipher_suite
 * and internals.compression_method.
 */
int
_gnutls_recv_hello (gnutls_session_t session, uint8_t * data, int datalen)
{
  int ret;

  if (session->security_parameters.entity == GNUTLS_CLIENT)
    {
      ret = _gnutls_read_server_hello (session, data, datalen);
      if (ret < 0)
        {
          gnutls_assert ();
          return ret;
        }
    }
  else
    {                           /* Server side reading a client hello */

      ret = _gnutls_read_client_hello (session, data, datalen);
      if (ret < 0)
        {
          gnutls_assert ();
          return ret;
        }
    }

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

  return 0;
}

static int
_gnutls_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;

  if (!IS_DTLS (session)
      || session->security_parameters.entity == GNUTLS_SERVER)
    {
      gnutls_assert ();
      return GNUTLS_E_INTERNAL_ERROR;
    }

  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;
    }

  /* TODO: determine if we need to do anything with the server version field */
  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);

  session->internals.dtls.cookie_len = cookie_len;
  memcpy (session->internals.dtls.cookie, &data[pos], cookie_len);

  pos += cookie_len;

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

  /* reset handshake hash buffers */
  _gnutls_handshake_hash_buffer_empty (session);

  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 structure.
 *
 * This function will renegotiate security parameters with the
 * client.  This should only be called in case of a server.
 *
 * This message informs the peer that we want to renegotiate
 * parameters (perform a handshake).
 *
 * If this function succeeds (returns 0), you must call the
 * gnutls_handshake() function in order to negotiate the new
 * parameters.
 *
 * Since TLS is full duplex some application data might have been
 * sent during peer's processing of this message. In that case
 * one should call gnutls_record_recv() until GNUTLS_E_REHANDSHAKE
 * is returned to clear any pending data. Care must be taken if
 * rehandshake is mandatory to terminate if it does not start after
 * some threshold.
 *
 * If the client does not wish to renegotiate parameters he will
 * should with an alert message, thus the return code will be
 * %GNUTLS_E_WARNING_ALERT_RECEIVED and the alert will be
 * %GNUTLS_A_NO_RENEGOTIATION.  A client may also choose to ignore
 * this message.
 *
 * Returns: %GNUTLS_E_SUCCESS on success, otherwise a negative error code.
 **/
int
gnutls_rehandshake (gnutls_session_t session)
{
  int ret;

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

  _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;
}

inline static int
_gnutls_abort_handshake (gnutls_session_t session, int ret)
{
  if (((ret == GNUTLS_E_WARNING_ALERT_RECEIVED) &&
       (gnutls_alert_get (session) == GNUTLS_A_NO_RENEGOTIATION))
      || ret == GNUTLS_E_GOT_APPLICATION_DATA)
    return 0;

  /* this doesn't matter */
  return GNUTLS_E_INTERNAL_ERROR;
}



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

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

  if (again)
    ret =
      _gnutls_send_handshake (session, NULL, GNUTLS_HANDSHAKE_SUPPLEMENTAL);
  else
    {
      gnutls_buffer_st buf;
      _gnutls_buffer_init (&buf);

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

      bufel = _gnutls_handshake_alloc(session, buf.length, buf.length);
      if (bufel == NULL)
        {
          gnutls_assert ();
          return GNUTLS_E_MEMORY_ERROR;
        }

      _mbuffer_set_udata (bufel, buf.data, buf.length);
      _gnutls_buffer_clear (&buf);

      ret = _gnutls_send_handshake (session, bufel,
                                    GNUTLS_HANDSHAKE_SUPPLEMENTAL);
    }

  return ret;
}

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 structure.
 *
 * This function does the handshake of the TLS/SSL protocol, and
 * initializes the TLS connection.
 *
 * This function will fail if any problem is encountered, and will
 * return a negative error code. In case of a client, if the client
 * has asked to resume a session, but the server couldn't, then a
 * full handshake will be performed.
 *
 * The non-fatal errors such as %GNUTLS_E_AGAIN and
 * %GNUTLS_E_INTERRUPTED interrupt the handshake procedure, which
 * should be resumed later.  Call this function again, until it
 * returns 0; cf.  gnutls_record_get_direction() and
 * gnutls_error_is_fatal().
 *
 * If this function is called by a server after a rehandshake request
 * then %GNUTLS_E_GOT_APPLICATION_DATA or
 * %GNUTLS_E_WARNING_ALERT_RECEIVED may be returned.  Note that these
 * are non fatal errors, only in the specific case of a rehandshake.
 * Their meaning is that the client rejected the rehandshake request or
 * in the case of %GNUTLS_E_GOT_APPLICATION_DATA it might also mean that
 * some data were pending.
 *
 * Returns: %GNUTLS_E_SUCCESS on success, otherwise a negative error code.
 **/
int
gnutls_handshake (gnutls_session_t session)
{
  int ret;
  record_parameters_st *params;
  
  /* sanity check. Verify that there are priorities setup.
   */
  if (session->internals.priorities.protocol.algorithms == 0)
    return gnutls_assert_val(GNUTLS_E_NO_PRIORITIES_WERE_SET);

  ret = _gnutls_epoch_get (session, session->security_parameters.epoch_next,
                           &params);
  if (ret < 0)
    {
      /* We assume the epoch is not allocated if _gnutls_epoch_get fails. */
      ret =
        _gnutls_epoch_alloc (session, session->security_parameters.epoch_next,
                             NULL);
      if (ret < 0)
        return gnutls_assert_val(ret);
    }

  if (session->security_parameters.entity == GNUTLS_CLIENT)
    {
      do
        {
          ret = _gnutls_handshake_client (session);
        } while (ret == 1);
    }
  else
    {
      ret = _gnutls_handshake_server (session);
    }
  if (ret < 0)
    {
      /* In the case of a rehandshake abort
       * we should reset the handshake's internal state.
       */
      if (_gnutls_abort_handshake (session, ret) == 0)
        STATE = STATE0;

      return ret;
    }

  ret = _gnutls_handshake_common (session);

  if (ret < 0)
    {
      if (_gnutls_abort_handshake (session, ret) == 0)
        STATE = STATE0;

      return ret;
    }

  STATE = STATE0;

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

  _gnutls_handshake_internal_state_clear (session);

  session->security_parameters.epoch_next++;

  return 0;
}


#define IMED_RET( str, ret, allow_alert) do { \
        if (ret < 0) { \
                /* EAGAIN and INTERRUPTED are always non-fatal */ \
                if (ret == GNUTLS_E_AGAIN || ret == GNUTLS_E_INTERRUPTED) \
                        return ret; \
                /* a warning alert might interrupt handshake */ \
                if (allow_alert != 0 && ret==GNUTLS_E_WARNING_ALERT_RECEIVED) return ret; \
                gnutls_assert(); \
                ERR( str, ret); \
                _gnutls_handshake_hash_buffers_clear(session); \
                return ret; \
        } } while (0)



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

#ifdef HANDSHAKE_DEBUG
  char buf[64];

  if (session->internals.resumed_security_parameters.session_id_size > 0)
    _gnutls_handshake_log ("HSK[%p]: Ask to resume: %s\n", session,
                           _gnutls_bin2hex (session->
                                            internals.resumed_security_parameters.session_id,
                                            session->
                                            internals.resumed_security_parameters.session_id_size,
                                            buf, sizeof (buf), NULL));
#endif

  switch (STATE)
    {
    case STATE0:
    case STATE1:
      ret = _gnutls_send_hello (session, AGAIN (STATE1));
      STATE = STATE1;
      IMED_RET ("send hello", ret, 1);

    case STATE11:
      if (IS_DTLS (session))
        {
          ret =
            _gnutls_recv_handshake (session, 
                  GNUTLS_HANDSHAKE_HELLO_VERIFY_REQUEST,
                  1, NULL);
          STATE = STATE11;
          IMED_RET ("recv hello verify", ret, 1);

          if (ret == 1)
            {
              STATE = STATE0;
              return 1;
            }
        }
    case STATE2:
      /* receive the server hello */
      ret =
        _gnutls_recv_handshake (session,
                                GNUTLS_HANDSHAKE_SERVER_HELLO,
                                0, NULL);
      STATE = STATE2;
      IMED_RET ("recv hello", ret, 1);

    case STATE70:
      if (session->security_parameters.do_recv_supplemental)
        {
          ret = _gnutls_recv_supplemental (session);
          STATE = STATE70;
          IMED_RET ("recv supplemental", ret, 1);
        }

    case STATE3:
      /* RECV CERTIFICATE */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret = _gnutls_recv_server_certificate (session);
      STATE = STATE3;
      IMED_RET ("recv server certificate", ret, 1);

    case STATE4:
      /* receive the server key exchange */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret = _gnutls_recv_server_kx_message (session);
      STATE = STATE4;
      IMED_RET ("recv server kx message", ret, 1);

    case STATE5:
      /* receive the server certificate request - if any 
       */

      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret = _gnutls_recv_server_crt_request (session);
      STATE = STATE5;
      IMED_RET ("recv server certificate request message", ret, 1);

    case STATE6:
      /* receive the server hello done */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret =
          _gnutls_recv_handshake (session,
                                  GNUTLS_HANDSHAKE_SERVER_HELLO_DONE,
                                  0, NULL);
      STATE = STATE6;
      IMED_RET ("recv server hello done", ret, 1);
    case STATE71:
      if (session->security_parameters.do_send_supplemental)
        {
          ret = _gnutls_send_supplemental (session, AGAIN (STATE71));
          STATE = STATE71;
          IMED_RET ("send supplemental", ret, 0);
        }

    case STATE7:
      /* send our certificate - if any and if requested
       */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret = _gnutls_send_client_certificate (session, AGAIN (STATE7));
      STATE = STATE7;
      IMED_RET ("send client certificate", ret, 0);

    case STATE8:
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret = _gnutls_send_client_kx_message (session, AGAIN (STATE8));
      STATE = STATE8;
      IMED_RET ("send client kx", ret, 0);

    case STATE9:
      /* send client certificate verify */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret =
          _gnutls_send_client_certificate_verify (session, AGAIN (STATE9));
      STATE = STATE9;
      IMED_RET ("send client certificate verify", ret, 1);

      STATE = STATE0;
    default:
      break;
    }


  return 0;
}



/* This function is to be called if the handshake was successfully 
 * completed. This sends a Change Cipher Spec packet to the peer.
 */
static ssize_t
send_change_cipher_spec (gnutls_session_t session, int again)
{
  uint8_t* data;
  mbuffer_st * bufel;
  int ret;
  
  if (again == 0)
    {
      bufel = _gnutls_handshake_alloc (session, 1, 1);
      if (bufel == NULL)
        return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);

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

      ret = _gnutls_handshake_io_cache_int (session, GNUTLS_HANDSHAKE_CHANGE_CIPHER_SPEC, bufel);
      if (ret < 0)
        {
          _mbuffer_xfree(&bufel);
          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
_gnutls_send_handshake_final (gnutls_session_t session, int init)
{
  int ret = 0;

  /* Send the CHANGE CIPHER SPEC PACKET */

  switch (STATE)
    {
    case STATE0:
    case STATE20:
      ret = send_change_cipher_spec (session, AGAIN (STATE20));
      STATE = STATE0;

      if (ret < 0)
        {
          ERR ("send ChangeCipherSpec", ret);
          gnutls_assert ();
          return ret;
        }
      /* Initialize the connection session (start encryption) - in case of client 
       */
      if (init == TRUE)
        {
          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;
        }

    case STATE21:
      /* send the finished message */
      ret = _gnutls_send_finished (session, AGAIN (STATE21));
      STATE = STATE21;
      if (ret < 0)
        {
          ERR ("send Finished", ret);
          gnutls_assert ();
          return ret;
        }

      STATE = STATE0;
    default:
      break;
    }

  return 0;
}

/* This function receives the final handshake packets 
 * And executes the appropriate function to initialize the
 * read session.
 */
static int
_gnutls_recv_handshake_final (gnutls_session_t session, int init)
{
  int ret = 0;
  uint8_t ch;
  unsigned int ccs_len = 1;

  switch (STATE)
    {
    case STATE0:
    case STATE30:
      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);
        }

      if (gnutls_protocol_get_version (session) == GNUTLS_DTLS0_9)
        ccs_len = 3;

      ret = _gnutls_recv_int (session, GNUTLS_CHANGE_CIPHER_SPEC, -1, &ch, ccs_len, NULL);
      if (ret <= 0)
        {
          ERR ("recv ChangeCipherSpec", ret);
          gnutls_assert ();
          return (ret < 0) ? ret : GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
        }

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

      /* Initialize the connection session (start encryption) - in case of server */
      if (init == TRUE)
        {
          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;
        }

    case STATE31:
      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)
        {
          ERR ("recv finished", ret);
          gnutls_assert ();
          return ret;
        }
      STATE = STATE0;
    default:
      break;
    }


  return 0;
}

/*
 * _gnutls_handshake_server
 * This function does the server stuff of the handshake protocol.
 */
int
_gnutls_handshake_server (gnutls_session_t session)
{
  int ret = 0;

  switch (STATE)
    {
    case STATE0:
    case STATE1:
      ret =
        _gnutls_recv_handshake (session,
                                GNUTLS_HANDSHAKE_CLIENT_HELLO,
                                0, NULL);
      STATE = STATE1;
      IMED_RET ("recv hello", ret, 1);

    case STATE2:
      ret = _gnutls_send_hello (session, AGAIN (STATE2));
      STATE = STATE2;
      IMED_RET ("send hello", ret, 1);

    case STATE70:
      if (session->security_parameters.do_send_supplemental)
        {
          ret = _gnutls_send_supplemental (session, AGAIN (STATE70));
          STATE = STATE70;
          IMED_RET ("send supplemental data", ret, 0);
        }

      /* SEND CERTIFICATE + KEYEXCHANGE + CERTIFICATE_REQUEST */
    case STATE3:
      /* NOTE: these should not be send if we are resuming */

      if (session->internals.resumed == RESUME_FALSE)
        ret = _gnutls_send_server_certificate (session, AGAIN (STATE3));
      STATE = STATE3;
      IMED_RET ("send server certificate", ret, 0);

    case STATE4:
      /* send server key exchange (A) */
      if (session->internals.resumed == RESUME_FALSE)
        ret = _gnutls_send_server_kx_message (session, AGAIN (STATE4));
      STATE = STATE4;
      IMED_RET ("send server kx", ret, 0);

    case STATE5:
      /* Send certificate request - if requested to */
      if (session->internals.resumed == RESUME_FALSE)
        ret =
          _gnutls_send_server_crt_request (session, AGAIN (STATE5));
      STATE = STATE5;
      IMED_RET ("send server cert request", ret, 0);

    case STATE6:
      /* send the server hello done */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret =
          _gnutls_send_empty_handshake (session,
                                        GNUTLS_HANDSHAKE_SERVER_HELLO_DONE,
                                        AGAIN (STATE6));
      STATE = STATE6;
      IMED_RET ("send server hello done", ret, 1);

    case STATE71:
      if (session->security_parameters.do_recv_supplemental)
        {
          ret = _gnutls_recv_supplemental (session);
          STATE = STATE71;
          IMED_RET ("recv client supplemental", ret, 1);
        }

      /* RECV CERTIFICATE + KEYEXCHANGE + CERTIFICATE_VERIFY */
    case STATE7:
      /* receive the client certificate message */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret = _gnutls_recv_client_certificate (session);
      STATE = STATE7;
      IMED_RET ("recv client certificate", ret, 1);

    case STATE8:
      /* receive the client key exchange message */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret = _gnutls_recv_client_kx_message (session);
      STATE = STATE8;
      IMED_RET ("recv client kx", ret, 1);

    case STATE9:
      /* receive the client certificate verify message */
      if (session->internals.resumed == RESUME_FALSE)   /* if we are not resuming */
        ret = _gnutls_recv_client_certificate_verify_message (session);
      STATE = STATE9;
      IMED_RET ("recv client certificate verify", ret, 1);

      STATE = STATE0;           /* finished thus clear session */
    default:
      break;
    }

  return 0;
}

int
_gnutls_handshake_common (gnutls_session_t session)
{
  int ret = 0;

  /* send and recv the change cipher spec and finished messages */
  if ((session->internals.resumed != RESUME_FALSE
       && session->security_parameters.entity == GNUTLS_CLIENT)
      || (session->internals.resumed == RESUME_FALSE
          && session->security_parameters.entity == GNUTLS_SERVER))
    {
      /* if we are a client resuming - or we are a server not resuming */
      ret = _gnutls_recv_handshake_final (session, TRUE);
      IMED_RET ("recv handshake final", ret, 1);

      switch (STATE)
        {
        case STATE0:
        case STATE40:
          ret = _gnutls_send_new_session_ticket (session, AGAIN (STATE40));
          STATE = STATE40;
          IMED_RET ("send handshake new session ticket", ret, 0);
          STATE = STATE0;
        default:
          break;
        }

      ret = _gnutls_send_handshake_final (session, FALSE);
      IMED_RET ("send handshake final", ret, 1);

      /* only store if we are not resuming a session and we didn't previously send a ticket 
       */
      if (session->security_parameters.entity == GNUTLS_SERVER && session->internals.ticket_sent == 0)
        {
          /* in order to support session resuming */
          _gnutls_server_register_current_session (session);
        }
    }
  else
    {                           /* if we are a client not resuming - or we are a server resuming */

      ret = _gnutls_send_handshake_final (session, TRUE);
      IMED_RET ("send handshake final 2", ret, 1);

      switch (STATE)
        {
        case STATE0:
        case STATE41:
          ret = _gnutls_recv_new_session_ticket (session);
          STATE = STATE41;
          IMED_RET ("recv handshake new session ticket", ret, 1);
          STATE = STATE0;
        default:
          break;
        }

      ret = _gnutls_recv_handshake_final (session, FALSE);
      IMED_RET ("recv handshake final 2", ret, 1);

    }


  /* clear handshake buffer */
  _gnutls_handshake_hash_buffers_clear (session);
  return ret;

}

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

  *len = TLS_MAX_SESSION_ID_SIZE;

  ret = _gnutls_rnd (GNUTLS_RND_NONCE, session_id, *len);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  return 0;
}

int
_gnutls_recv_hello_request (gnutls_session_t session, void *data,
                            uint32_t data_size)
{
  uint8_t type;

  if (session->security_parameters.entity == GNUTLS_SERVER)
    {
      gnutls_assert ();
      return GNUTLS_E_UNEXPECTED_PACKET;
    }
  if (data_size < 1)
    {
      gnutls_assert ();
      return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
    }
  type = ((uint8_t *) data)[0];
  if (type == GNUTLS_HANDSHAKE_HELLO_REQUEST)
    {
      if (IS_DTLS(session))
        session->internals.dtls.hsk_read_seq++;
      return GNUTLS_E_REHANDSHAKE;
    }
  else
    {
      gnutls_assert ();
      return GNUTLS_E_UNEXPECTED_PACKET;
    }
}

/* Returns 1 if the given KX has not the corresponding parameters
 * (DH or RSA) set up. Otherwise returns 0.
 */
inline static int
check_server_params (gnutls_session_t session,
                     gnutls_kx_algorithm_t kx,
                     gnutls_kx_algorithm_t * alg, int alg_size)
{
  int cred_type;
  gnutls_dh_params_t dh_params = NULL;
  gnutls_rsa_params_t rsa_params = NULL;
  int j;

  cred_type = _gnutls_map_kx_get_cred (kx, 1);

  /* Read the Diffie-Hellman parameters, if any.
   */
  if (cred_type == GNUTLS_CRD_CERTIFICATE)
    {
      int delete;
      gnutls_certificate_credentials_t x509_cred =
        (gnutls_certificate_credentials_t) _gnutls_get_cred (session->key,
                                                             cred_type, NULL);

      if (x509_cred != NULL)
        {
          dh_params =
            _gnutls_get_dh_params (x509_cred->dh_params,
                                   x509_cred->params_func, session);
          rsa_params =
            _gnutls_certificate_get_rsa_params (x509_cred->rsa_params,
                                                x509_cred->params_func,
                                                session);
        }

      /* Check also if the certificate supports the
       * KX method.
       */
      delete = 1;
      for (j = 0; j < alg_size; j++)
        {
          if (alg[j] == kx)
            {
              delete = 0;
              break;
            }
        }

      if (delete == 1)
        return 1;

#ifdef ENABLE_ANON
    }
  else if (cred_type == GNUTLS_CRD_ANON)
    {
      gnutls_anon_server_credentials_t anon_cred =
        (gnutls_anon_server_credentials_t) _gnutls_get_cred (session->key,
                                                             cred_type, NULL);

      if (anon_cred != NULL)
        {
          dh_params =
            _gnutls_get_dh_params (anon_cred->dh_params,
                                   anon_cred->params_func, session);
        }
#endif
#ifdef ENABLE_PSK
    }
  else if (cred_type == GNUTLS_CRD_PSK)
    {
      gnutls_psk_server_credentials_t psk_cred =
        (gnutls_psk_server_credentials_t) _gnutls_get_cred (session->key,
                                                            cred_type, NULL);

      if (psk_cred != NULL)
        {
          dh_params =
            _gnutls_get_dh_params (psk_cred->dh_params, psk_cred->params_func,
                                   session);
        }
#endif
    }
  else
    return 0;                   /* no need for params */


  /* If the key exchange method needs RSA or DH params,
   * but they are not set then remove it.
   */
  if (_gnutls_kx_needs_rsa_params (kx) != 0)
    {
      /* needs rsa params. */
      if (_gnutls_rsa_params_to_mpi (rsa_params) == NULL)
        {
          gnutls_assert ();
          return 1;
        }
    }

  if (_gnutls_kx_needs_dh_params (kx) != 0)
    {
      /* needs DH params. */
      if (_gnutls_dh_params_to_mpi (dh_params) == NULL)
        {
          gnutls_assert ();
          return 1;
        }
    }

  return 0;
}

/* This function will remove algorithms that are not supported by
 * the requested authentication method. We remove an algorithm if
 * we have a certificate with keyUsage bits set.
 *
 * This does a more high level check than  gnutls_supported_ciphersuites(),
 * by checking certificates etc.
 */
static int
_gnutls_remove_unwanted_ciphersuites (gnutls_session_t session,
                                      uint8_t * cipher_suites,
                                      int cipher_suites_size,
                                      gnutls_pk_algorithm_t *pk_algos,
                                      size_t pk_algos_size)
{

  int ret = 0;
  int i, new_suites_size;
  gnutls_certificate_credentials_t cert_cred;
  gnutls_kx_algorithm_t kx;
  int server = session->security_parameters.entity == GNUTLS_SERVER ? 1 : 0;
  gnutls_kx_algorithm_t alg[MAX_ALGOS];
  int alg_size = MAX_ALGOS;

  /* if we should use a specific certificate, 
   * we should remove all algorithms that are not supported
   * by that certificate and are on the same authentication
   * method (CERTIFICATE).
   */

  cert_cred =
    (gnutls_certificate_credentials_t) _gnutls_get_cred (session->key,
                                                         GNUTLS_CRD_CERTIFICATE,
                                                         NULL);

  /* If there are certificate credentials, find an appropriate certificate
   * or disable them;
   */
  if (session->security_parameters.entity == GNUTLS_SERVER
      && cert_cred != NULL && pk_algos_size > 0)
    {
      ret = _gnutls_server_select_cert (session, pk_algos, pk_algos_size);
      if (ret < 0)
        {
          gnutls_assert ();
          _gnutls_debug_log ("Could not find an appropriate certificate: %s\n",
                             gnutls_strerror (ret));
        }
    }

  /* get all the key exchange algorithms that are 
   * supported by the X509 certificate parameters.
   */
  if ((ret =
       _gnutls_selected_cert_supported_kx (session, alg, &alg_size)) < 0)
    {
      gnutls_assert ();
      return ret;
    }

  new_suites_size = 0;

  /* now removes ciphersuites based on the KX algorithm
   */
  for (i = 0; i < cipher_suites_size; i+=2)
    {
      int delete = 0;

      /* finds the key exchange algorithm in
       * the ciphersuite
       */
      kx = _gnutls_cipher_suite_get_kx_algo (&cipher_suites[i]);

      /* if it is defined but had no credentials 
       */
      if (!session->internals.premaster_set &&
          _gnutls_get_kx_cred (session, kx, NULL) == NULL)
        {
          delete = 1;
        }
      else
        {
          delete = 0;

          if (server)
            delete = check_server_params (session, kx, alg, alg_size);
        }
       
      /* If we have not agreed to a common curve with the peer don't bother
       * negotiating ECDH.
       */
      if (server != 0 && _gnutls_kx_is_ecc(kx))
        {
          if (_gnutls_session_ecc_curve_get(session) == GNUTLS_ECC_CURVE_INVALID)
            {
              delete = 1;
            }
        }

      /* These two SRP kx's are marked to require a CRD_CERTIFICATE,
         (see cred_mappings in gnutls_algorithms.c), but it also
         requires a SRP credential.  Don't use SRP kx unless we have a
         SRP credential too.  */
      if (kx == GNUTLS_KX_SRP_RSA || kx == GNUTLS_KX_SRP_DSS)
        {
          if (!_gnutls_get_cred (session->key, GNUTLS_CRD_SRP, NULL))
            {
              delete = 1;
            }
        }

      if (delete == 0)
        {

          _gnutls_handshake_log ("HSK[%p]: Keeping ciphersuite: %s (%.2X.%.2X)\n",
                                 session,
                                 _gnutls_cipher_suite_get_name (&cipher_suites[i]),
                                 cipher_suites[i], cipher_suites[i+1]);

          if (i != new_suites_size)
            memmove( &cipher_suites[new_suites_size], &cipher_suites[i], 2);
          new_suites_size+=2;
        }
      else
        {
          _gnutls_handshake_log ("HSK[%p]: Removing ciphersuite: %s\n",
                                 session,
                                 _gnutls_cipher_suite_get_name (&cipher_suites[i]));

        }
    }

  ret = new_suites_size;

  return ret;

}

/**
 * gnutls_handshake_set_max_packet_length:
 * @session: is a #gnutls_session_t structure.
 * @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
 * 48kb 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.
 **/
void
gnutls_handshake_set_max_packet_length (gnutls_session_t session, size_t max)
{
  session->internals.max_handshake_data_buffer_size = max;
}

void
_gnutls_set_adv_version (gnutls_session_t session, gnutls_protocol_t ver)
{
  set_adv_version (session, _gnutls_version_get_major (ver),
                   _gnutls_version_get_minor (ver));
}

gnutls_protocol_t
_gnutls_get_adv_version (gnutls_session_t session)
{
  return _gnutls_version_get (_gnutls_get_adv_version_major (session),
                              _gnutls_get_adv_version_minor (session));
}

/**
 * gnutls_handshake_get_last_in:
 * @session: is a #gnutls_session_t structure.
 *
 * 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 structure.
 *
 * 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;
}