lib/auth/rsa.c - master - githubmirror/gnutls

lib/auth/rsa.c
311 строк8 KB
Alexander Sosedkin
lib/auth/rsa: check that ciphertext matches the modulus size
29 апр 2026, 16:35
29 апр 2026, 16:3577228f2
/*
 * 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 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 RSA key exchange part of the certificate
 * authentication.
 */

#include "gnutls_int.h"
#include "auth.h"
#include "errors.h"
#include "dh.h"
#include "num.h"
#include "datum.h"
#include "auth/cert.h"
#include "pk.h"
#include "algorithms.h"
#include "global.h"
#include "debug.h"
#include "tls-sig.h"
#include "x509.h"
#include "random.h"
#include "mpi.h"
#include "abstract_int.h"
#include "auth/rsa_common.h"

int _gnutls_gen_rsa_client_kx(gnutls_session_t, gnutls_buffer_st *);
static int proc_rsa_client_kx(gnutls_session_t, uint8_t *, size_t);

const mod_auth_st rsa_auth_struct = {
	"RSA",
	_gnutls_gen_cert_server_crt,
	_gnutls_gen_cert_client_crt,
	NULL, /* gen server kx */
	_gnutls_gen_rsa_client_kx,
	_gnutls_gen_cert_client_crt_vrfy, /* gen client cert vrfy */
	_gnutls_gen_cert_server_cert_req, /* server cert request */

	_gnutls_proc_crt,
	_gnutls_proc_crt,
	NULL, /* proc server kx */
	proc_rsa_client_kx, /* proc client kx */
	_gnutls_proc_cert_client_crt_vrfy, /* proc client cert vrfy */
	_gnutls_proc_cert_cert_req /* proc server cert request */
};

static int check_key_usage_for_enc(gnutls_session_t session, unsigned key_usage)
{
	if (key_usage != 0) {
		if (!(key_usage & GNUTLS_KEY_KEY_ENCIPHERMENT) &&
		    !(key_usage & GNUTLS_KEY_KEY_AGREEMENT)) {
			gnutls_assert();
			if (session->internals.allow_key_usage_violation == 0) {
				_gnutls_audit_log(
					session,
					"Peer's certificate does not allow encryption. Key usage violation detected.\n");
				return GNUTLS_E_KEY_USAGE_VIOLATION;
			} else {
				_gnutls_audit_log(
					session,
					"Peer's certificate does not allow encryption. Key usage violation detected (ignored).\n");
			}
		}
	}
	return 0;
}

/* This function reads the RSA parameters from peer's certificate;
 *
 * IMPORTANT:
 * Currently this function gets only called on the client side
 * during generation of the client kx msg. This function
 * retrieves the RSA params from the peer's certificate. That is in
 * this case the server's certificate. As of GNUTLS version 3.6.4 it is
 * possible to negotiate different certificate types for client and
 * server. Therefore the correct cert type needs to be retrieved to be
 * used for the _gnutls_get_auth_info_pcert call. If this
 * function is to be called on the server side in the future, extra
 * checks need to be build in order to retrieve the correct
 * certificate type.
 */
int _gnutls_get_public_rsa_params(gnutls_session_t session,
				  gnutls_pk_params_st *params)
{
	int ret;
	cert_auth_info_t info;
	unsigned key_usage;
	gnutls_pcert_st peer_cert;
	gnutls_certificate_type_t cert_type;

	assert(!IS_SERVER(session));

	/* normal non export case */

	info = _gnutls_get_auth_info(session, GNUTLS_CRD_CERTIFICATE);

	if (info == NULL || info->ncerts == 0) {
		gnutls_assert();
		return GNUTLS_E_INTERNAL_ERROR;
	}
	// Get the negotiated server certificate type
	cert_type = get_certificate_type(session, GNUTLS_CTYPE_SERVER);

	ret = _gnutls_get_auth_info_pcert(&peer_cert, cert_type, info);

	if (ret < 0) {
		gnutls_assert();
		return ret;
	}

	gnutls_pubkey_get_key_usage(peer_cert.pubkey, &key_usage);

	ret = check_key_usage_for_enc(session, key_usage);
	if (ret < 0) {
		gnutls_assert();
		goto cleanup2;
	}

	gnutls_pk_params_init(params);

	ret = _gnutls_pubkey_get_mpis(peer_cert.pubkey, params);
	if (ret < 0) {
		ret = gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
		goto cleanup2;
	}

	gnutls_pcert_deinit(&peer_cert);
	return 0;

cleanup2:
	gnutls_pcert_deinit(&peer_cert);

	return ret;
}

static int proc_rsa_client_kx(gnutls_session_t session, uint8_t *data,
			      size_t _data_size)
{
	gnutls_datum_t ciphertext;
	int ret, dsize;
	ssize_t data_size = _data_size;
	volatile uint8_t ver_maj, ver_min;
	unsigned int key_bits;

#ifdef ENABLE_SSL3
	if (get_num_version(session) == GNUTLS_SSL3) {
		/* SSL 3.0 
		 */
		ciphertext.data = data;
		ciphertext.size = data_size;
	} else
#endif
	{
		/* TLS 1.0+
		 */
		DECR_LEN(data_size, 2);
		ciphertext.data = &data[2];
		dsize = _gnutls_read_uint16(data);

		if (dsize != data_size) {
			gnutls_assert();
			return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
		}
		ciphertext.size = dsize;
	}
	gnutls_privkey_get_pk_algorithm(session->internals.selected_key,
					&key_bits);
	if (ciphertext.size != (key_bits + 7) / 8)
		return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

	ver_maj = _gnutls_get_adv_version_major(session);
	ver_min = _gnutls_get_adv_version_minor(session);

	session->key.key.data = gnutls_malloc(GNUTLS_MASTER_SIZE);
	if (session->key.key.data == NULL) {
		gnutls_assert();
		return GNUTLS_E_MEMORY_ERROR;
	}
	session->key.key.size = GNUTLS_MASTER_SIZE;

	/* Fallback value when decryption fails. Needs to be unpredictable. */
	ret = gnutls_rnd(GNUTLS_RND_NONCE, session->key.key.data,
			 GNUTLS_MASTER_SIZE);
	if (ret < 0) {
		gnutls_free(session->key.key.data);
		session->key.key.size = 0;
		gnutls_assert();
		return ret;
	}

	gnutls_privkey_decrypt_data2(session->internals.selected_key, 0,
				     &ciphertext, session->key.key.data,
				     session->key.key.size);
	/* After this point, any conditional on failure that cause differences
	 * in execution may create a timing or cache access pattern side
	 * channel that can be used as an oracle, so tread carefully */

	/* Error handling logic:
	 * In case decryption fails then don't inform the peer. Just use the
	 * random key previously generated. (in order to avoid attack against
	 * pkcs-1 formatting).
	 *
	 * If we get version mismatches no error is returned either. We
	 * proceed normally. This is to defend against the attack described
	 * in the paper "Attacking RSA-based sessions in SSL/TLS" by
	 * Vlastimil Klima, Ondej Pokorny and Tomas Rosa.
	 */

	/* This is here to avoid the version check attack
	 * discussed above.
	 */
	session->key.key.data[0] = ver_maj;
	session->key.key.data[1] = ver_min;

	return 0;
}

/* return RSA(random) using the peers public key 
 */
int _gnutls_gen_rsa_client_kx(gnutls_session_t session, gnutls_buffer_st *data)
{
	cert_auth_info_t auth = session->key.auth_info;
	gnutls_datum_t sdata; /* data to send */
	gnutls_pk_params_st params;
	int ret;

	if (auth == NULL) {
		/* this shouldn't have happened. The proc_certificate
		 * function should have detected that.
		 */
		gnutls_assert();
		return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
	}

	session->key.key.size = GNUTLS_MASTER_SIZE;
	session->key.key.data = gnutls_malloc(session->key.key.size);

	if (session->key.key.data == NULL) {
		gnutls_assert();
		return GNUTLS_E_MEMORY_ERROR;
	}

	ret = gnutls_rnd(GNUTLS_RND_RANDOM, session->key.key.data,
			 session->key.key.size);
	if (ret < 0) {
		gnutls_assert();
		return ret;
	}

	if (session->internals.rsa_pms_version[0] == 0) {
		session->key.key.data[0] =
			_gnutls_get_adv_version_major(session);
		session->key.key.data[1] =
			_gnutls_get_adv_version_minor(session);
	} else { /* use the version provided */
		session->key.key.data[0] =
			session->internals.rsa_pms_version[0];
		session->key.key.data[1] =
			session->internals.rsa_pms_version[1];
	}

	/* move RSA parameters to key (session).
	 */
	if ((ret = _gnutls_get_public_rsa_params(session, &params)) < 0) {
		gnutls_assert();
		return ret;
	}

	ret = _gnutls_pk_encrypt(GNUTLS_PK_RSA, &sdata, &session->key.key,
				 &params, &params.spki);

	gnutls_pk_params_release(&params);

	if (ret < 0)
		return gnutls_assert_val(ret);

#ifdef ENABLE_SSL3
	if (get_num_version(session) == GNUTLS_SSL3) {
		/* SSL 3.0 */
		ret = _gnutls_buffer_append_data(data, sdata.data, sdata.size);

		_gnutls_free_datum(&sdata);
		return ret;
	} else
#endif
	{ /* TLS 1.x */
		ret = _gnutls_buffer_append_data_prefix(data, 16, sdata.data,
							sdata.size);

		_gnutls_free_datum(&sdata);
		return ret;
	}
}