/*

 * Copyright (C) 2017 Free Software Foundation, Inc.

 *

 * Author: Ander Juaristi

 *

 * This file is part of GnuTLS.

 *

 * The GnuTLS is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public License

 * as published by the Free Software Foundation; either version 2.1 of

 * the License, or (at your option) any later version.

 *

 * This library is distributed in the hope that it will be useful, but

 * WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with this program.  If not, see <https://www.gnu.org/licenses/>

 *

 */

#include "gnutls_int.h"

#include "ext/psk_ke_modes.h"

#include "ext/pre_shared_key.h"

#include <assert.h>

#define PSK_KE 0

#define PSK_DHE_KE 1

static int psk_ke_modes_send_params(gnutls_session_t session,

            gnutls_buffer_t extdata)

{

  int ret;

  const version_entry_st *vers;

  uint8_t data[2];

  unsigned pos, i;

  unsigned have_dhpsk = 0;

  unsigned have_psk = 0;

  /* Server doesn't send psk_key_exchange_modes */

  if (session->security_parameters.entity == GNUTLS_SERVER)

    return 0;

  /* If session ticket is disabled and no PSK key exchange is

   * enabled, don't send the extension */

  if ((session->internals.flags & GNUTLS_NO_TICKETS) &&

      !session->internals.priorities->have_psk)

    return 0;

  vers = _gnutls_version_max(session);

  if (!vers || !vers->tls13_sem)

    return 0;

  /* We send the list prioritized according to our preferences as a convention

   * (used throughout the protocol), even if the protocol doesn't mandate that

   * for this particular message. That way we can keep the TLS 1.2 semantics/

   * prioritization when negotiating PSK or DHE-PSK. Receiving servers would

   * very likely respect our prioritization if they parse the message serially. */

  pos = 0;

  for (i = 0; i < session->internals.priorities->_kx.num_priorities;

       i++) {

    if (session->internals.priorities->_kx.priorities[i] ==

          GNUTLS_KX_PSK &&

        !have_psk) {

      assert(pos <= 1);

      data[pos++] = PSK_KE;

      session->internals.hsk_flags |= HSK_PSK_KE_MODE_PSK;

      have_psk = 1;

    } else if ((session->internals.priorities->_kx.priorities[i] ==

            GNUTLS_KX_DHE_PSK ||

          session->internals.priorities->_kx.priorities[i] ==

            GNUTLS_KX_ECDHE_PSK) &&

         !have_dhpsk) {

      assert(pos <= 1);

      data[pos++] = PSK_DHE_KE;

      session->internals.hsk_flags |= HSK_PSK_KE_MODE_DHE_PSK;

      have_dhpsk = 1;

    }

    if (have_psk && have_dhpsk)

      break;

  }

  /* For session resumption we need to send at least one */

  if (pos == 0) {

    if (session->internals.flags & GNUTLS_NO_TICKETS)

      return 0;

    data[pos++] = PSK_DHE_KE;

    data[pos++] = PSK_KE;

    session->internals.hsk_flags |= HSK_PSK_KE_MODE_DHE_PSK;

    session->internals.hsk_flags |= HSK_PSK_KE_MODE_PSK;

  }

  ret = _gnutls_buffer_append_data_prefix(extdata, 8, data, pos);

  if (ret < 0)

    return gnutls_assert_val(ret);

  session->internals.hsk_flags |= HSK_PSK_KE_MODES_SENT;

  return 0;

}

#define MAX_POS INT_MAX

/*

 * Since we only support ECDHE-authenticated PSKs, the server

 * just verifies that a "psk_key_exchange_modes" extension was received,

 * and that it contains the value one.

 */

static int psk_ke_modes_recv_params(gnutls_session_t session,

            const unsigned char *data, size_t len)

{

  uint8_t ke_modes_len;

  const version_entry_st *vers = get_version(session);

  gnutls_psk_server_credentials_t cred;

  int dhpsk_pos = MAX_POS;

  int psk_pos = MAX_POS;

  int cli_psk_pos = MAX_POS;

  int cli_dhpsk_pos = MAX_POS;

  unsigned i;

  /* Client doesn't receive psk_key_exchange_modes */

  if (session->security_parameters.entity == GNUTLS_CLIENT)

    return gnutls_assert_val(GNUTLS_E_RECEIVED_ILLEGAL_EXTENSION);

  /* we set hsk_flags to HSK_PSK_KE_MODE_INVALID on failure to ensure that

   * when we parse the pre-shared key extension we detect PSK_KE_MODES as

   * received. */

  if (!vers || !vers->tls13_sem) {

    session->internals.hsk_flags |= HSK_PSK_KE_MODE_INVALID;

    return gnutls_assert_val(0);

  }

  cred = (gnutls_psk_server_credentials_t)_gnutls_get_cred(

    session, GNUTLS_CRD_PSK);

  if (cred == NULL && (session->internals.flags & GNUTLS_NO_TICKETS)) {

    session->internals.hsk_flags |= HSK_PSK_KE_MODE_INVALID;

    return gnutls_assert_val(0);

  }

  DECR_LEN(len, 1);

  ke_modes_len = *(data++);

  for (i = 0; i < session->internals.priorities->_kx.num_priorities;

       i++) {

    if (session->internals.priorities->_kx.priorities[i] ==

          GNUTLS_KX_PSK &&

        psk_pos == MAX_POS) {

      psk_pos = i;

    } else if ((session->internals.priorities->_kx.priorities[i] ==

            GNUTLS_KX_DHE_PSK ||

          session->internals.priorities->_kx.priorities[i] ==

            GNUTLS_KX_ECDHE_PSK) &&

         dhpsk_pos == MAX_POS) {

      dhpsk_pos = i;

    }

    if (dhpsk_pos != MAX_POS && psk_pos != MAX_POS)

      break;

  }

  if (psk_pos == MAX_POS && dhpsk_pos == MAX_POS) {

    if (!(session->internals.flags & GNUTLS_NO_TICKETS))

      dhpsk_pos = 0;

    else if (session->internals.priorities->groups.size == 0)

      return gnutls_assert_val(0);

  }

  for (i = 0; i < ke_modes_len; i++) {

    DECR_LEN(len, 1);

    if (data[i] == PSK_DHE_KE)

      cli_dhpsk_pos = i;

    else if (data[i] == PSK_KE)

      cli_psk_pos = i;

    _gnutls_handshake_log("EXT[%p]: PSK KE mode %.2x received\n",

              session, (unsigned)data[i]);

    if (cli_psk_pos != MAX_POS && cli_dhpsk_pos != MAX_POS)

      break;

  }

  if (session->internals.priorities->server_precedence) {

    if (dhpsk_pos != MAX_POS && cli_dhpsk_pos != MAX_POS &&

        (dhpsk_pos < psk_pos || cli_psk_pos == MAX_POS))

      session->internals.hsk_flags |= HSK_PSK_KE_MODE_DHE_PSK;

    else if (psk_pos != MAX_POS && cli_psk_pos != MAX_POS &&

       (psk_pos < dhpsk_pos || cli_dhpsk_pos == MAX_POS))

      session->internals.hsk_flags |= HSK_PSK_KE_MODE_PSK;

  } else {

    if (dhpsk_pos != MAX_POS && cli_dhpsk_pos != MAX_POS &&

        (cli_dhpsk_pos < cli_psk_pos || psk_pos == MAX_POS))

      session->internals.hsk_flags |= HSK_PSK_KE_MODE_DHE_PSK;

    else if (psk_pos != MAX_POS && cli_psk_pos != MAX_POS &&

       (cli_psk_pos < cli_dhpsk_pos || dhpsk_pos == MAX_POS))

      session->internals.hsk_flags |= HSK_PSK_KE_MODE_PSK;

  }

  if ((session->internals.hsk_flags & HSK_PSK_KE_MODE_PSK) ||

      (session->internals.hsk_flags & HSK_PSK_KE_MODE_DHE_PSK)) {

    return 0;

  } else {

    session->internals.hsk_flags |= HSK_PSK_KE_MODE_INVALID;

    return gnutls_assert_val(0);

  }

}

const hello_ext_entry_st ext_mod_psk_ke_modes = {

  .name = "PSK Key Exchange Modes",

  .tls_id = 45,

  .gid = GNUTLS_EXTENSION_PSK_KE_MODES,

  .client_parse_point = GNUTLS_EXT_TLS,

  .server_parse_point = GNUTLS_EXT_TLS,

  .validity = GNUTLS_EXT_FLAG_TLS | GNUTLS_EXT_FLAG_CLIENT_HELLO |

        GNUTLS_EXT_FLAG_TLS13_SERVER_HELLO,

  .send_func = psk_ke_modes_send_params,

  .recv_func = psk_ke_modes_recv_params

};