/*

 * Copyright (C) 2011-2012 Free Software Foundation, Inc.

 * Copyright (C) 2017 Red Hat, Inc.

 *

 * Author: Nikos Mavrogiannopoulos

 *

 * This file is part of GnuTLS.

 *

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

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

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

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

 *

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

 * WITHOUT ANY WARRANTY; without even the implied warranty of

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

 * Lesser General Public License for more details.

 *

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

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

 *

 */

/* This file contains the code for the Supported Groups extension (rfc7919).

 * This extension was previously named Supported Elliptic Curves under TLS 1.2.

 */

#include "ext/supported_groups.h"

#include "str.h"

#include "num.h"

#include "auth/psk.h"

#include "auth/cert.h"

#include "auth/anon.h"

#include "algorithms.h"

#include <gnutls/gnutls.h>

static int _gnutls_supported_groups_recv_params(gnutls_session_t session,

            const uint8_t *data,

            size_t data_size);

static int _gnutls_supported_groups_send_params(gnutls_session_t session,

            gnutls_buffer_st *extdata);

const hello_ext_entry_st ext_mod_supported_groups = {

  .name = "Supported Groups",

  .tls_id = 10,

  .gid = GNUTLS_EXTENSION_SUPPORTED_GROUPS,

  .client_parse_point = GNUTLS_EXT_TLS,

  .server_parse_point = GNUTLS_EXT_TLS,

  .validity = GNUTLS_EXT_FLAG_TLS | GNUTLS_EXT_FLAG_DTLS |

        GNUTLS_EXT_FLAG_CLIENT_HELLO | GNUTLS_EXT_FLAG_EE |

        GNUTLS_EXT_FLAG_TLS12_SERVER_HELLO,

  .recv_func = _gnutls_supported_groups_recv_params,

  .send_func = _gnutls_supported_groups_send_params,

  .pack_func = NULL,

  .unpack_func = NULL,

  .deinit_func = NULL,

  .cannot_be_overriden = 1

};

static unsigned get_min_dh(gnutls_session_t session)

{

  gnutls_certificate_credentials_t cert_cred;

  gnutls_psk_server_credentials_t psk_cred;

  gnutls_anon_server_credentials_t anon_cred;

  unsigned level = 0;

  cert_cred = (gnutls_certificate_credentials_t)_gnutls_get_cred(

    session, GNUTLS_CRD_CERTIFICATE);

  psk_cred = (gnutls_psk_server_credentials_t)_gnutls_get_cred(

    session, GNUTLS_CRD_PSK);

  anon_cred = (gnutls_anon_server_credentials_t)_gnutls_get_cred(

    session, GNUTLS_CRD_ANON);

  if (cert_cred) {

    level = cert_cred->dh_sec_param;

  } else if (psk_cred) {

    level = psk_cred->dh_sec_param;

  } else if (anon_cred) {

    level = anon_cred->dh_sec_param;

  }

  if (level)

    return gnutls_sec_param_to_pk_bits(GNUTLS_PK_DH, level);

  return 0;

}

/*

 * In case of a server: if a SUPPORTED_GROUPS extension type is received then it stores

 * into the session security parameters the new value. The server may use gnutls_session_certificate_type_get(),

 * to access it.

 *

 * In case of a client: If supported_eccs have been specified then we send the extension.

 *

 */

static int _gnutls_supported_groups_recv_params(gnutls_session_t session,

            const uint8_t *data,

            size_t data_size)

{

  int i;

  uint16_t len;

  const uint8_t *p = data;

  const gnutls_group_entry_st *group = NULL;

  unsigned have_ffdhe = 0;

  unsigned tls_id;

  unsigned min_dh;

  unsigned j;

  int serv_ec_idx, serv_dh_idx,

    serv_hybrid_idx; /* index in server's priority listing */

  int cli_ec_pos, cli_dh_pos,

    cli_hybrid_pos; /* position in listing sent by client */

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

    /* A client shouldn't receive this extension in TLS1.2. It is

     * possible to read that message under TLS1.3 as an encrypted

     * extension. */

    return 0;

  } else { /* SERVER SIDE - we must check if the sent supported ecc type is the right one

         */

    if (data_size < 2)

      return gnutls_assert_val(

        GNUTLS_E_RECEIVED_ILLEGAL_EXTENSION);

    DECR_LEN(data_size, 2);

    len = _gnutls_read_uint16(p);

    p += 2;

    if (len % 2 != 0)

      return gnutls_assert_val(

        GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

    DECR_LEN(data_size, len);

    /* we figure what is the minimum DH allowed for this session, if any */

    min_dh = get_min_dh(session);

    serv_ec_idx = serv_dh_idx = serv_hybrid_idx = -1;

    cli_ec_pos = cli_dh_pos = cli_hybrid_pos = -1;

    /* This extension is being processed prior to a ciphersuite being selected,

     * so we cannot rely on ciphersuite information. */

    for (i = 0; i < len; i += 2) {

      if (have_ffdhe == 0 && p[i] == 0x01)

        have_ffdhe = 1;

      tls_id = _gnutls_read_uint16(&p[i]);

      group = _gnutls_tls_id_to_group(tls_id);

      _gnutls_handshake_log(

        "EXT[%p]: Received group %s (0x%x)\n", session,

        group ? group->name : "unknown", tls_id);

      if (group == NULL)

        continue;

      if (min_dh > 0 && group->prime &&

          group->prime->size * 8 < min_dh)

        continue;

      /* we simulate _gnutls_session_supports_group, but we prioritize if

       * %SERVER_PRECEDENCE is given */

      for (j = 0;

           j < session->internals.priorities->groups.size;

           j++) {

        if (session->internals.priorities->groups

              .entry[j]

              ->id == group->id) {

          if (session->internals.priorities

                ->server_precedence) {

            if (group->pk == GNUTLS_PK_DH) {

              if (serv_dh_idx != -1 &&

                  (int)j >

                    serv_dh_idx)

                break;

              serv_dh_idx = j;

              cli_dh_pos = i;

            } else if (IS_EC(group->pk)) {

              if (serv_ec_idx != -1 &&

                  (int)j >

                    serv_ec_idx)

                break;

              serv_ec_idx = j;

              cli_ec_pos = i;

            } else if (IS_GROUP_HYBRID(

                   group)) {

              if (serv_hybrid_idx !=

                    -1 &&

                  (int)j >

                    serv_hybrid_idx)

                break;

              serv_hybrid_idx = j;

              cli_hybrid_pos = i;

            }

          } else {

            if (group->pk == GNUTLS_PK_DH) {

              if (cli_dh_pos != -1)

                break;

              cli_dh_pos = i;

              serv_dh_idx = j;

            } else if (IS_EC(group->pk)) {

              if (cli_ec_pos != -1)

                break;

              cli_ec_pos = i;

              serv_ec_idx = j;

            } else if (IS_GROUP_HYBRID(

                   group)) {

              if (cli_hybrid_pos !=

                  -1)

                break;

              cli_hybrid_pos = i;

              serv_hybrid_idx = j;

            }

          }

          break;

        }

      }

    }

    /* serv_{dh,ec,hybrid}_idx contain the index of the groups we want to use.

     */

    if (serv_dh_idx != -1) {

      session->internals.cand_dh_group =

        session->internals.priorities->groups

          .entry[serv_dh_idx];

      session->internals.cand_group =

        session->internals.cand_dh_group;

    }

    if (serv_ec_idx != -1) {

      session->internals.cand_ec_group =

        session->internals.priorities->groups

          .entry[serv_ec_idx];

      if (session->internals.cand_group == NULL ||

          (session->internals.priorities->server_precedence &&

           serv_ec_idx < serv_dh_idx) ||

          (!session->internals.priorities->server_precedence &&

           cli_ec_pos < cli_dh_pos)) {

        session->internals.cand_group =

          session->internals.cand_ec_group;

      }

    }

    /* PQC hybrid key exchange groups can only be used in

     * TLS 1.3, where no distinction between ECDH and DH

     * in the group definitions, and thus only cand_group

     * is set here.

     */

    if (serv_hybrid_idx != -1) {

      if (session->internals.cand_group == NULL ||

          (session->internals.priorities->server_precedence &&

           serv_hybrid_idx < MIN(serv_ec_idx, serv_dh_idx)) ||

          (!session->internals.priorities->server_precedence &&

           cli_hybrid_pos < MIN(cli_ec_pos, cli_dh_pos))) {

        session->internals.cand_group =

          session->internals.priorities->groups

            .entry[serv_hybrid_idx];

      }

    }

    if (session->internals.cand_group)

      _gnutls_handshake_log(

        "EXT[%p]: Selected group %s\n", session,

        session->internals.cand_group->name);

    if (have_ffdhe)

      session->internals.hsk_flags |= HSK_HAVE_FFDHE;

  }

  return 0;

}

/* returns data_size or a negative number on failure

 */

static int _gnutls_supported_groups_send_params(gnutls_session_t session,

            gnutls_buffer_st *extdata)

{

  unsigned len, i;

  int ret;

  uint16_t p;

  /* this extension is only being sent on client side */

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

    len = session->internals.priorities->groups.size;

    if (len > 0) {

      ret = _gnutls_buffer_append_prefix(extdata, 16,

                 len * 2);

      if (ret < 0)

        return gnutls_assert_val(ret);

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

        p = session->internals.priorities->groups

              .entry[i]

              ->tls_id;

        _gnutls_handshake_log(

          "EXT[%p]: Sent group %s (0x%x)\n",

          session,

          session->internals.priorities->groups

            .entry[i]

            ->name,

          (unsigned)p);

        ret = _gnutls_buffer_append_prefix(extdata, 16,

                   p);

        if (ret < 0)

          return gnutls_assert_val(ret);

      }

      return (len + 1) * 2;

    }

  }

  return 0;

}

/* Returns 0 if the given ECC curve is allowed in the current

 * session. A negative error value is returned otherwise.

 */

bool _gnutls_session_supports_group(gnutls_session_t session,

            unsigned int group)

{

  unsigned i;

  for (i = 0; i < session->internals.priorities->groups.size; i++) {

    if (session->internals.priorities->groups.entry[i]->id == group)

      return true;

  }

  return false;

}