2 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
11 * RSA low level APIs are deprecated for public use, but still ok for
14 #include "internal/deprecated.h"
16 #include "internal/constant_time.h"
19 #include <openssl/bn.h>
20 #include <openssl/rsa.h>
21 #include <openssl/rand.h>
22 /* Just for the SSL_MAX_MASTER_KEY_LENGTH value */
23 #include <openssl/ssl.h>
24 #include "internal/cryptlib.h"
25 #include "crypto/rsa.h"
27 int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
28 const unsigned char *from, int flen)
33 if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
34 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_1,
35 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
39 p = (unsigned char *)to;
42 *(p++) = 1; /* Private Key BT (Block Type) */
44 /* pad out with 0xff data */
49 memcpy(p, from, (unsigned int)flen);
53 int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
54 const unsigned char *from, int flen,
58 const unsigned char *p;
64 * 00 || 01 || PS || 00 || D
65 * PS - padding string, at least 8 bytes of FF
69 if (num < RSA_PKCS1_PADDING_SIZE)
72 /* Accept inputs with and without the leading 0-byte. */
75 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
76 RSA_R_INVALID_PADDING);
82 if ((num != (flen + 1)) || (*(p++) != 0x01)) {
83 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
84 RSA_R_BLOCK_TYPE_IS_NOT_01);
88 /* scan over padding data */
89 j = flen - 1; /* one for type. */
90 for (i = 0; i < j; i++) {
91 if (*p != 0xff) { /* should decrypt to 0xff */
96 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
97 RSA_R_BAD_FIXED_HEADER_DECRYPT);
105 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
106 RSA_R_NULL_BEFORE_BLOCK_MISSING);
111 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
112 RSA_R_BAD_PAD_BYTE_COUNT);
115 i++; /* Skip over the '\0' */
118 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, RSA_R_DATA_TOO_LARGE);
121 memcpy(to, p, (unsigned int)j);
126 int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
127 const unsigned char *from, int flen)
132 if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
133 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_2,
134 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
138 p = (unsigned char *)to;
141 *(p++) = 2; /* Public Key BT (Block Type) */
143 /* pad out with non-zero random data */
146 if (RAND_bytes(p, j) <= 0)
148 for (i = 0; i < j; i++) {
151 if (RAND_bytes(p, 1) <= 0)
153 } while (*p == '\0');
159 memcpy(p, from, (unsigned int)flen);
163 int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
164 const unsigned char *from, int flen,
168 /* |em| is the encoded message, zero-padded to exactly |num| bytes */
169 unsigned char *em = NULL;
170 unsigned int good, found_zero_byte, mask;
171 int zero_index = 0, msg_index, mlen = -1;
173 if (tlen <= 0 || flen <= 0)
177 * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
181 if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
182 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
183 RSA_R_PKCS_DECODING_ERROR);
187 em = OPENSSL_malloc(num);
189 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
193 * Caller is encouraged to pass zero-padded message created with
194 * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
195 * bounds, it's impossible to have an invariant memory access pattern
196 * in case |from| was not zero-padded in advance.
198 for (from += flen, em += num, i = 0; i < num; i++) {
199 mask = ~constant_time_is_zero(flen);
202 *--em = *from & mask;
205 good = constant_time_is_zero(em[0]);
206 good &= constant_time_eq(em[1], 2);
208 /* scan over padding data */
210 for (i = 2; i < num; i++) {
211 unsigned int equals0 = constant_time_is_zero(em[i]);
213 zero_index = constant_time_select_int(~found_zero_byte & equals0,
215 found_zero_byte |= equals0;
219 * PS must be at least 8 bytes long, and it starts two bytes into |em|.
220 * If we never found a 0-byte, then |zero_index| is 0 and the check
223 good &= constant_time_ge(zero_index, 2 + 8);
226 * Skip the zero byte. This is incorrect if we never found a zero-byte
227 * but in this case we also do not copy the message out.
229 msg_index = zero_index + 1;
230 mlen = num - msg_index;
233 * For good measure, do this check in constant time as well.
235 good &= constant_time_ge(tlen, mlen);
238 * Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
239 * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
240 * Otherwise leave |to| unchanged.
241 * Copy the memory back in a way that does not reveal the size of
242 * the data being copied via a timing side channel. This requires copying
243 * parts of the buffer multiple times based on the bits set in the real
244 * length. Clear bits do a non-copy with identical access pattern.
245 * The loop below has overall complexity of O(N*log(N)).
247 tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
248 num - RSA_PKCS1_PADDING_SIZE, tlen);
249 for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
250 mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
251 for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
252 em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
254 for (i = 0; i < tlen; i++) {
255 mask = good & constant_time_lt(i, mlen);
256 to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);
259 OPENSSL_clear_free(em, num);
262 * This trick doesn't work in the FIPS provider because libcrypto manages
263 * the error stack. Instead we opt not to put an error on the stack at all
264 * in case of padding failure in the FIPS provider.
266 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
267 err_clear_last_constant_time(1 & good);
270 return constant_time_select_int(good, mlen, -1);
274 * rsa_padding_check_PKCS1_type_2_TLS() checks and removes the PKCS1 type 2
275 * padding from a decrypted RSA message in a TLS signature. The result is stored
276 * in the buffer pointed to by |to| which should be |tlen| bytes long. |tlen|
277 * must be at least SSL_MAX_MASTER_KEY_LENGTH. The original decrypted message
278 * should be stored in |from| which must be |flen| bytes in length and padded
279 * such that |flen == RSA_size()|. The TLS protocol version that the client
280 * originally requested should be passed in |client_version|. Some buggy clients
281 * can exist which use the negotiated version instead of the originally
282 * requested protocol version. If it is necessary to work around this bug then
283 * the negotiated protocol version can be passed in |alt_version|, otherwise 0
286 * If the passed message is publicly invalid or some other error that can be
287 * treated in non-constant time occurs then -1 is returned. On success the
288 * length of the decrypted data is returned. This will always be
289 * SSL_MAX_MASTER_KEY_LENGTH. If an error occurs that should be treated in
290 * constant time then this function will appear to return successfully, but the
291 * decrypted data will be randomly generated (as per
292 * https://tools.ietf.org/html/rfc5246#section-7.4.7.1).
294 int rsa_padding_check_PKCS1_type_2_TLS(unsigned char *to, size_t tlen,
295 const unsigned char *from, size_t flen,
296 int client_version, int alt_version)
298 unsigned int i, good, version_good;
299 unsigned char rand_premaster_secret[SSL_MAX_MASTER_KEY_LENGTH];
302 * If these checks fail then either the message in publicly invalid, or
303 * we've been called incorrectly. We can fail immediately.
305 if (flen < RSA_PKCS1_PADDING_SIZE + SSL_MAX_MASTER_KEY_LENGTH
306 || tlen < SSL_MAX_MASTER_KEY_LENGTH) {
307 ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
312 * Generate a random premaster secret to use in the event that we fail
315 if (RAND_priv_bytes(rand_premaster_secret,
316 sizeof(rand_premaster_secret)) <= 0) {
317 ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
321 good = constant_time_is_zero(from[0]);
322 good &= constant_time_eq(from[1], 2);
324 /* Check we have the expected padding data */
325 for (i = 2; i < flen - SSL_MAX_MASTER_KEY_LENGTH - 1; i++)
326 good &= ~constant_time_is_zero_8(from[i]);
327 good &= constant_time_is_zero_8(from[flen - SSL_MAX_MASTER_KEY_LENGTH - 1]);
331 * If the version in the decrypted pre-master secret is correct then
332 * version_good will be 0xff, otherwise it'll be zero. The
333 * Klima-Pokorny-Rosa extension of Bleichenbacher's attack
334 * (http://eprint.iacr.org/2003/052/) exploits the version number
335 * check as a "bad version oracle". Thus version checks are done in
336 * constant time and are treated like any other decryption error.
339 constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],
340 (client_version >> 8) & 0xff);
342 constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],
343 client_version & 0xff);
346 * The premaster secret must contain the same version number as the
347 * ClientHello to detect version rollback attacks (strangely, the
348 * protocol does not offer such protection for DH ciphersuites).
349 * However, buggy clients exist that send the negotiated protocol
350 * version instead if the server does not support the requested
351 * protocol version. If SSL_OP_TLS_ROLLBACK_BUG is set then we tolerate
352 * such clients. In that case alt_version will be non-zero and set to
353 * the negotiated version.
355 if (alt_version > 0) {
356 unsigned int workaround_good;
359 constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],
360 (alt_version >> 8) & 0xff);
362 constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],
364 version_good |= workaround_good;
367 good &= version_good;
371 * Now copy the result over to the to buffer if good, or random data if
374 for (i = 0; i < SSL_MAX_MASTER_KEY_LENGTH; i++) {
376 constant_time_select_8(good,
377 from[flen - SSL_MAX_MASTER_KEY_LENGTH + i],
378 rand_premaster_secret[i]);
382 * We must not leak whether a decryption failure occurs because of
383 * Bleichenbacher's attack on PKCS #1 v1.5 RSA padding (see RFC 2246,
384 * section 7.4.7.1). The code follows that advice of the TLS RFC and
385 * generates a random premaster secret for the case that the decrypt
386 * fails. See https://tools.ietf.org/html/rfc5246#section-7.4.7.1
387 * So, whether we actually succeeded or not, return success.
390 return SSL_MAX_MASTER_KEY_LENGTH;