path: root/lib/prf.c

/*
 * Copyright (C) 2002-2015 Free Software Foundation, Inc.
 * Copyright (C) 2014-2015 Nikos Mavrogiannopoulos
 * Copyright (C) 2016-2017 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 <http://www.gnu.org/licenses/>
 *
 */

/* Functions for the TLS PRF handling.
 */

#include "gnutls_int.h"
#include "errors.h"
#include <num.h>
#include <state.h>
#include <algorithms.h>

/* The PRF function expands a given secret 
 * needed by the TLS specification. ret must have a least total_bytes
 * available.
 */
int
_gnutls_PRF(gnutls_session_t session,
	    const uint8_t * secret, unsigned int secret_size,
	    const char *label, int label_size, const uint8_t * seed,
	    int seed_size, int total_bytes, void *ret)
{
	return _gnutls_prf_raw(session->security_parameters.prf_mac,
			       secret_size, secret,
			       label_size, label,
			       seed_size, seed,
			       total_bytes, ret);
}

/**
 * gnutls_prf_raw:
 * @session: is a #gnutls_session_t type.
 * @label_size: length of the @label variable.
 * @label: label used in PRF computation, typically a short string.
 * @seed_size: length of the @seed variable.
 * @seed: optional extra data to seed the PRF with.
 * @outsize: size of pre-allocated output buffer to hold the output.
 * @out: pre-allocated buffer to hold the generated data.
 *
 * Apply the TLS Pseudo-Random-Function (PRF) on the master secret
 * and the provided data.
 *
 * The @label variable usually contains a string denoting the purpose
 * for the generated data.  The @seed usually contains data such as the
 * client and server random, perhaps together with some additional
 * data that is added to guarantee uniqueness of the output for a
 * particular purpose.
 *
 * Because the output is not guaranteed to be unique for a particular
 * session unless @seed includes the client random and server random
 * fields (the PRF would output the same data on another connection
 * resumed from the first one), it is not recommended to use this
 * function directly.  The gnutls_prf() function seeds the PRF with the
 * client and server random fields directly, and is recommended if you
 * want to generate pseudo random data unique for each session.
 *
 * Returns: %GNUTLS_E_SUCCESS on success, or an error code.
 **/
int
gnutls_prf_raw(gnutls_session_t session,
	       size_t label_size,
	       const char *label,
	       size_t seed_size, const char *seed, size_t outsize,
	       char *out)
{
	int ret;

	ret = _gnutls_PRF(session,
			  session->security_parameters.master_secret,
			  GNUTLS_MASTER_SIZE,
			  label,
			  label_size, (uint8_t *) seed, seed_size, outsize,
			  out);

	return ret;
}

/**
 * gnutls_prf_rfc5705:
 * @session: is a #gnutls_session_t type.
 * @label_size: length of the @label variable.
 * @label: label used in PRF computation, typically a short string.
 * @context_size: length of the @extra variable.
 * @context: optional extra data to seed the PRF with.
 * @outsize: size of pre-allocated output buffer to hold the output.
 * @out: pre-allocated buffer to hold the generated data.
 *
 * Applies the TLS Pseudo-Random-Function (PRF) on the master secret
 * and the provided data, seeded with the client and server random fields,
 * as specified in RFC5705.
 *
 * The @label variable usually contains a string denoting the purpose
 * for the generated data.  The @server_random_first indicates whether
 * the client random field or the server random field should be first
 * in the seed.  Non-zero indicates that the server random field is first,
 * 0 that the client random field is first.
 *
 * The @context variable can be used to add more data to the seed, after
 * the random variables.  It can be used to make sure the
 * generated output is strongly connected to some additional data
 * (e.g., a string used in user authentication). 
 *
 * The output is placed in @out, which must be pre-allocated.
 *
 * Note that, to provide the RFC5705 context, the @context variable
 * must be non-null.
 *
 * Returns: %GNUTLS_E_SUCCESS on success, or an error code.
 *
 * Since: 3.4.4
 **/
int
gnutls_prf_rfc5705(gnutls_session_t session,
		   size_t label_size, const char *label,
		   size_t context_size, const char *context,
		   size_t outsize, char *out)
{
	char *pctx = NULL;
	int ret;

	if (context != NULL && context_size > 65535)  {
		gnutls_assert();
		return GNUTLS_E_INVALID_REQUEST;
	}

	if (context != NULL) {
		pctx = gnutls_malloc(context_size+2);
		if (!pctx) {
			gnutls_assert();
			return GNUTLS_E_MEMORY_ERROR;
		}

		memcpy(pctx+2, context, context_size);
		_gnutls_write_uint16(context_size, (void*)pctx);
		context_size += 2;
	}

	ret = gnutls_prf(session, label_size, label, 0,
			 context_size, pctx, outsize, out);

	gnutls_free(pctx);
	return ret;
}

/**
 * gnutls_prf:
 * @session: is a #gnutls_session_t type.
 * @label_size: length of the @label variable.
 * @label: label used in PRF computation, typically a short string.
 * @server_random_first: non-zero if server random field should be first in seed
 * @extra_size: length of the @extra variable.
 * @extra: optional extra data to seed the PRF with.
 * @outsize: size of pre-allocated output buffer to hold the output.
 * @out: pre-allocated buffer to hold the generated data.
 *
 * Applies the TLS Pseudo-Random-Function (PRF) on the master secret
 * and the provided data, seeded with the client and server random fields.
 * For the key expansion specified in RFC5705 see gnutls_prf_rfc5705().
 *
 * The @label variable usually contains a string denoting the purpose
 * for the generated data.  The @server_random_first indicates whether
 * the client random field or the server random field should be first
 * in the seed.  Non-zero indicates that the server random field is first,
 * 0 that the client random field is first.
 *
 * The @extra variable can be used to add more data to the seed, after
 * the random variables.  It can be used to make sure the
 * generated output is strongly connected to some additional data
 * (e.g., a string used in user authentication).
 *
 * The output is placed in @out, which must be pre-allocated.
 *
 * Note: This function produces identical output with gnutls_prf_rfc5705()
 * when @server_random_first is set to 0 and @extra is %NULL.
 *
 * Returns: %GNUTLS_E_SUCCESS on success, or an error code.
 **/
int
gnutls_prf(gnutls_session_t session,
	   size_t label_size,
	   const char *label,
	   int server_random_first,
	   size_t extra_size, const char *extra,
	   size_t outsize, char *out)
{
	int ret;
	uint8_t *seed;
	size_t seedsize = 2 * GNUTLS_RANDOM_SIZE + extra_size;

	seed = gnutls_malloc(seedsize);
	if (!seed) {
		gnutls_assert();
		return GNUTLS_E_MEMORY_ERROR;
	}

	memcpy(seed, server_random_first ?
	       session->security_parameters.server_random :
	       session->security_parameters.client_random,
	       GNUTLS_RANDOM_SIZE);
	memcpy(seed + GNUTLS_RANDOM_SIZE,
	       server_random_first ? session->security_parameters.
	       client_random : session->security_parameters.server_random,
	       GNUTLS_RANDOM_SIZE);

	if (extra && extra_size) {
		memcpy(seed + 2 * GNUTLS_RANDOM_SIZE, extra, extra_size);
	}

	ret =
	    _gnutls_PRF(session,
			session->security_parameters.master_secret,
			GNUTLS_MASTER_SIZE, label, label_size, seed,
			seedsize, outsize, out);

	gnutls_free(seed);

	return ret;
}