/*

 * 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,

	.parse_type = 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; /* index in server's priority listing */

	int cli_ec_pos, cli_dh_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 = -1;

		cli_ec_pos = cli_dh_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 (serv_ec_idx != -1 && (int)j > serv_ec_idx)

								break;

							serv_ec_idx = j;

							cli_ec_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 (cli_ec_pos != -1)

								break;

							cli_ec_pos = i;

							serv_ec_idx = j;

						}

					}

					break;

				}

			}

		}

		/* serv_dh/ec_pos 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;

			}

		}

		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.

 */

int

_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 0;

	}

	return GNUTLS_E_ECC_UNSUPPORTED_CURVE;

}