2 /* ====================================================================
3 * Copyright (c) 2012 The OpenSSL Project. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in
14 * the documentation and/or other materials provided with the
17 * 3. All advertising materials mentioning features or use of this
18 * software must display the following acknowledgment:
19 * "This product includes software developed by the OpenSSL Project
20 * for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
22 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
23 * endorse or promote products derived from this software without
24 * prior written permission. For written permission, please contact
25 * openssl-core@openssl.org.
27 * 5. Products derived from this software may not be called "OpenSSL"
28 * nor may "OpenSSL" appear in their names without prior written
29 * permission of the OpenSSL Project.
31 * 6. Redistributions of any form whatsoever must retain the following
33 * "This product includes software developed by the OpenSSL Project
34 * for use in the OpenSSL Toolkit (http://www.openssl.org/)"
36 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
37 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
38 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
39 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
40 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
41 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
42 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
43 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
44 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
45 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
46 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
47 * OF THE POSSIBILITY OF SUCH DAMAGE.
48 * ====================================================================
50 * This product includes cryptographic software written by Eric Young
51 * (eay@cryptsoft.com). This product includes software written by Tim
52 * Hudson (tjh@cryptsoft.com).
56 #include "../crypto/constant_time_locl.h"
59 #include <openssl/md5.h>
60 #include <openssl/sha.h>
63 * MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's
64 * length field. (SHA-384/512 have 128-bit length.)
66 #define MAX_HASH_BIT_COUNT_BYTES 16
69 * MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support.
70 * Currently SHA-384/512 has a 128-byte block size and that's the largest
73 #define MAX_HASH_BLOCK_SIZE 128
76 * ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC
77 * record in |rec| by updating |rec->length| in constant time.
79 * block_size: the block size of the cipher used to encrypt the record.
81 * 0: (in non-constant time) if the record is publicly invalid.
82 * 1: if the padding was valid
85 int ssl3_cbc_remove_padding(const SSL *s,
87 unsigned block_size, unsigned mac_size)
89 unsigned padding_length, good;
90 const unsigned overhead = 1 /* padding length byte */ + mac_size;
93 * These lengths are all public so we can test them in non-constant time.
95 if (overhead > rec->length)
98 padding_length = rec->data[rec->length - 1];
99 good = constant_time_ge(rec->length, padding_length + overhead);
100 /* SSLv3 requires that the padding is minimal. */
101 good &= constant_time_ge(block_size, padding_length + 1);
102 padding_length = good & (padding_length + 1);
103 rec->length -= padding_length;
104 rec->type |= padding_length << 8; /* kludge: pass padding length */
105 return constant_time_select_int(good, 1, -1);
109 * tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
110 * record in |rec| in constant time and returns 1 if the padding is valid and
111 * -1 otherwise. It also removes any explicit IV from the start of the record
112 * without leaking any timing about whether there was enough space after the
113 * padding was removed.
115 * block_size: the block size of the cipher used to encrypt the record.
117 * 0: (in non-constant time) if the record is publicly invalid.
118 * 1: if the padding was valid
121 int tls1_cbc_remove_padding(const SSL *s,
123 unsigned block_size, unsigned mac_size)
125 unsigned padding_length, good, to_check, i;
126 const unsigned overhead = 1 /* padding length byte */ + mac_size;
127 /* Check if version requires explicit IV */
128 if (s->version == DTLS1_VERSION || s->version == DTLS1_BAD_VER) {
130 * These lengths are all public so we can test them in non-constant
133 if (overhead + block_size > rec->length)
135 /* We can now safely skip explicit IV */
136 rec->data += block_size;
137 rec->input += block_size;
138 rec->length -= block_size;
139 } else if (overhead > rec->length)
142 padding_length = rec->data[rec->length - 1];
145 * NB: if compression is in operation the first packet may not be of even
146 * length so the padding bug check cannot be performed. This bug
147 * workaround has been around since SSLeay so hopefully it is either
148 * fixed now or no buggy implementation supports compression [steve]
150 if ((s->options & SSL_OP_TLS_BLOCK_PADDING_BUG) && !s->expand) {
151 /* First packet is even in size, so check */
152 if ((memcmp(s->s3->read_sequence, "\0\0\0\0\0\0\0\0", 8) == 0) &&
153 !(padding_length & 1)) {
154 s->s3->flags |= TLS1_FLAGS_TLS_PADDING_BUG;
156 if ((s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) && padding_length > 0) {
161 good = constant_time_ge(rec->length, overhead + padding_length);
163 * The padding consists of a length byte at the end of the record and
164 * then that many bytes of padding, all with the same value as the length
165 * byte. Thus, with the length byte included, there are i+1 bytes of
166 * padding. We can't check just |padding_length+1| bytes because that
167 * leaks decrypted information. Therefore we always have to check the
168 * maximum amount of padding possible. (Again, the length of the record
169 * is public information so we can use it.)
171 to_check = 255; /* maximum amount of padding. */
172 if (to_check > rec->length - 1)
173 to_check = rec->length - 1;
175 for (i = 0; i < to_check; i++) {
176 unsigned char mask = constant_time_ge_8(padding_length, i);
177 unsigned char b = rec->data[rec->length - 1 - i];
179 * The final |padding_length+1| bytes should all have the value
180 * |padding_length|. Therefore the XOR should be zero.
182 good &= ~(mask & (padding_length ^ b));
186 * If any of the final |padding_length+1| bytes had the wrong value, one
187 * or more of the lower eight bits of |good| will be cleared.
189 good = constant_time_eq(0xff, good & 0xff);
190 padding_length = good & (padding_length + 1);
191 rec->length -= padding_length;
192 rec->type |= padding_length << 8; /* kludge: pass padding length */
194 return constant_time_select_int(good, 1, -1);
198 * ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
199 * constant time (independent of the concrete value of rec->length, which may
200 * vary within a 256-byte window).
202 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to
206 * rec->orig_len >= md_size
207 * md_size <= EVP_MAX_MD_SIZE
209 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with
210 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into
211 * a single or pair of cache-lines, then the variable memory accesses don't
212 * actually affect the timing. CPUs with smaller cache-lines [if any] are
213 * not multi-core and are not considered vulnerable to cache-timing attacks.
215 #define CBC_MAC_ROTATE_IN_PLACE
217 void ssl3_cbc_copy_mac(unsigned char *out,
218 const SSL3_RECORD *rec,
219 unsigned md_size, unsigned orig_len)
221 #if defined(CBC_MAC_ROTATE_IN_PLACE)
222 unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE];
223 unsigned char *rotated_mac;
225 unsigned char rotated_mac[EVP_MAX_MD_SIZE];
229 * mac_end is the index of |rec->data| just after the end of the MAC.
231 unsigned mac_end = rec->length;
232 unsigned mac_start = mac_end - md_size;
234 * scan_start contains the number of bytes that we can ignore because the
235 * MAC's position can only vary by 255 bytes.
237 unsigned scan_start = 0;
239 unsigned div_spoiler;
240 unsigned rotate_offset;
242 OPENSSL_assert(orig_len >= md_size);
243 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
245 #if defined(CBC_MAC_ROTATE_IN_PLACE)
246 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf) & 63);
249 /* This information is public so it's safe to branch based on it. */
250 if (orig_len > md_size + 255 + 1)
251 scan_start = orig_len - (md_size + 255 + 1);
253 * div_spoiler contains a multiple of md_size that is used to cause the
254 * modulo operation to be constant time. Without this, the time varies
255 * based on the amount of padding when running on Intel chips at least.
256 * The aim of right-shifting md_size is so that the compiler doesn't
257 * figure out that it can remove div_spoiler as that would require it to
258 * prove that md_size is always even, which I hope is beyond it.
260 div_spoiler = md_size >> 1;
261 div_spoiler <<= (sizeof(div_spoiler) - 1) * 8;
262 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size;
264 memset(rotated_mac, 0, md_size);
265 for (i = scan_start, j = 0; i < orig_len; i++) {
266 unsigned char mac_started = constant_time_ge_8(i, mac_start);
267 unsigned char mac_ended = constant_time_ge_8(i, mac_end);
268 unsigned char b = rec->data[i];
269 rotated_mac[j++] |= b & mac_started & ~mac_ended;
270 j &= constant_time_lt(j, md_size);
273 /* Now rotate the MAC */
274 #if defined(CBC_MAC_ROTATE_IN_PLACE)
276 for (i = 0; i < md_size; i++) {
277 /* in case cache-line is 32 bytes, touch second line */
278 ((volatile unsigned char *)rotated_mac)[rotate_offset ^ 32];
279 out[j++] = rotated_mac[rotate_offset++];
280 rotate_offset &= constant_time_lt(rotate_offset, md_size);
283 memset(out, 0, md_size);
284 rotate_offset = md_size - rotate_offset;
285 rotate_offset &= constant_time_lt(rotate_offset, md_size);
286 for (i = 0; i < md_size; i++) {
287 for (j = 0; j < md_size; j++)
288 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset);
290 rotate_offset &= constant_time_lt(rotate_offset, md_size);
296 * u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
297 * little-endian order. The value of p is advanced by four.
299 #define u32toLE(n, p) \
300 (*((p)++)=(unsigned char)(n), \
301 *((p)++)=(unsigned char)(n>>8), \
302 *((p)++)=(unsigned char)(n>>16), \
303 *((p)++)=(unsigned char)(n>>24))
306 * These functions serialize the state of a hash and thus perform the
307 * standard "final" operation without adding the padding and length that such
308 * a function typically does.
310 static void tls1_md5_final_raw(void *ctx, unsigned char *md_out)
313 u32toLE(md5->A, md_out);
314 u32toLE(md5->B, md_out);
315 u32toLE(md5->C, md_out);
316 u32toLE(md5->D, md_out);
319 static void tls1_sha1_final_raw(void *ctx, unsigned char *md_out)
322 l2n(sha1->h0, md_out);
323 l2n(sha1->h1, md_out);
324 l2n(sha1->h2, md_out);
325 l2n(sha1->h3, md_out);
326 l2n(sha1->h4, md_out);
329 #define LARGEST_DIGEST_CTX SHA_CTX
331 #ifndef OPENSSL_NO_SHA256
332 static void tls1_sha256_final_raw(void *ctx, unsigned char *md_out)
334 SHA256_CTX *sha256 = ctx;
337 for (i = 0; i < 8; i++) {
338 l2n(sha256->h[i], md_out);
342 # undef LARGEST_DIGEST_CTX
343 # define LARGEST_DIGEST_CTX SHA256_CTX
346 #ifndef OPENSSL_NO_SHA512
347 static void tls1_sha512_final_raw(void *ctx, unsigned char *md_out)
349 SHA512_CTX *sha512 = ctx;
352 for (i = 0; i < 8; i++) {
353 l2n8(sha512->h[i], md_out);
357 # undef LARGEST_DIGEST_CTX
358 # define LARGEST_DIGEST_CTX SHA512_CTX
362 * ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
363 * which ssl3_cbc_digest_record supports.
365 char ssl3_cbc_record_digest_supported(const EVP_MD *digest)
371 switch (EVP_MD_type(digest)) {
374 #ifndef OPENSSL_NO_SHA256
378 #ifndef OPENSSL_NO_SHA512
389 * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
392 * ctx: the EVP_MD_CTX from which we take the hash function.
393 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX.
394 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
395 * md_out_size: if non-NULL, the number of output bytes is written here.
396 * header: the 13-byte, TLS record header.
397 * data: the record data itself, less any preceeding explicit IV.
398 * data_plus_mac_size: the secret, reported length of the data and MAC
399 * once the padding has been removed.
400 * data_plus_mac_plus_padding_size: the public length of the whole
401 * record, including padding.
402 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS.
404 * On entry: by virtue of having been through one of the remove_padding
405 * functions, above, we know that data_plus_mac_size is large enough to contain
406 * a padding byte and MAC. (If the padding was invalid, it might contain the
409 void ssl3_cbc_digest_record(const EVP_MD *digest,
410 unsigned char *md_out,
412 const unsigned char header[13],
413 const unsigned char *data,
414 size_t data_plus_mac_size,
415 size_t data_plus_mac_plus_padding_size,
416 const unsigned char *mac_secret,
417 unsigned mac_secret_length, char is_sslv3)
421 unsigned char c[sizeof(LARGEST_DIGEST_CTX)];
423 void (*md_final_raw) (void *ctx, unsigned char *md_out);
424 void (*md_transform) (void *ctx, const unsigned char *block);
425 unsigned md_size, md_block_size = 64;
426 unsigned sslv3_pad_length = 40, header_length, variance_blocks,
427 len, max_mac_bytes, num_blocks,
428 num_starting_blocks, k, mac_end_offset, c, index_a, index_b;
429 unsigned int bits; /* at most 18 bits */
430 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES];
431 /* hmac_pad is the masked HMAC key. */
432 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE];
433 unsigned char first_block[MAX_HASH_BLOCK_SIZE];
434 unsigned char mac_out[EVP_MAX_MD_SIZE];
435 unsigned i, j, md_out_size_u;
438 * mdLengthSize is the number of bytes in the length field that
439 * terminates * the hash.
441 unsigned md_length_size = 8;
442 char length_is_big_endian = 1;
445 * This is a, hopefully redundant, check that allows us to forget about
446 * many possible overflows later in this function.
448 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024 * 1024);
450 switch (EVP_MD_type(digest)) {
452 MD5_Init((MD5_CTX *)md_state.c);
453 md_final_raw = tls1_md5_final_raw;
455 (void (*)(void *ctx, const unsigned char *block))MD5_Transform;
457 sslv3_pad_length = 48;
458 length_is_big_endian = 0;
461 SHA1_Init((SHA_CTX *)md_state.c);
462 md_final_raw = tls1_sha1_final_raw;
464 (void (*)(void *ctx, const unsigned char *block))SHA1_Transform;
467 #ifndef OPENSSL_NO_SHA256
469 SHA224_Init((SHA256_CTX *)md_state.c);
470 md_final_raw = tls1_sha256_final_raw;
472 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
476 SHA256_Init((SHA256_CTX *)md_state.c);
477 md_final_raw = tls1_sha256_final_raw;
479 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform;
483 #ifndef OPENSSL_NO_SHA512
485 SHA384_Init((SHA512_CTX *)md_state.c);
486 md_final_raw = tls1_sha512_final_raw;
488 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform;
494 SHA512_Init((SHA512_CTX *)md_state.c);
495 md_final_raw = tls1_sha512_final_raw;
497 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform;
505 * ssl3_cbc_record_digest_supported should have been called first to
506 * check that the hash function is supported.
514 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES);
515 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE);
516 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
520 header_length = mac_secret_length + sslv3_pad_length + 8 /* sequence
522 1 /* record type */ +
523 2 /* record length */ ;
527 * variance_blocks is the number of blocks of the hash that we have to
528 * calculate in constant time because they could be altered by the
529 * padding value. In SSLv3, the padding must be minimal so the end of
530 * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively
531 * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes
532 * of hash termination (0x80 + 64-bit length) don't fit in the final
533 * block, we say that the final two blocks can vary based on the padding.
534 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
535 * required to be minimal. Therefore we say that the final six blocks can
536 * vary based on the padding. Later in the function, if the message is
537 * short and there obviously cannot be this many blocks then
538 * variance_blocks can be reduced.
540 variance_blocks = is_sslv3 ? 2 : 6;
542 * From now on we're dealing with the MAC, which conceptually has 13
543 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
546 len = data_plus_mac_plus_padding_size + header_length;
548 * max_mac_bytes contains the maximum bytes of bytes in the MAC,
549 * including * |header|, assuming that there's no padding.
551 max_mac_bytes = len - md_size - 1;
552 /* num_blocks is the maximum number of hash blocks. */
554 (max_mac_bytes + 1 + md_length_size + md_block_size -
557 * In order to calculate the MAC in constant time we have to handle the
558 * final blocks specially because the padding value could cause the end
559 * to appear somewhere in the final |variance_blocks| blocks and we can't
560 * leak where. However, |num_starting_blocks| worth of data can be hashed
561 * right away because no padding value can affect whether they are
564 num_starting_blocks = 0;
566 * k is the starting byte offset into the conceptual header||data where
567 * we start processing.
571 * mac_end_offset is the index just past the end of the data to be MACed.
573 mac_end_offset = data_plus_mac_size + header_length - md_size;
575 * c is the index of the 0x80 byte in the final hash block that contains
578 c = mac_end_offset % md_block_size;
580 * index_a is the hash block number that contains the 0x80 terminating
583 index_a = mac_end_offset / md_block_size;
585 * index_b is the hash block number that contains the 64-bit hash length,
588 index_b = (mac_end_offset + md_length_size) / md_block_size;
590 * bits is the hash-length in bits. It includes the additional hash block
591 * for the masked HMAC key, or whole of |header| in the case of SSLv3.
595 * For SSLv3, if we're going to have any starting blocks then we need at
596 * least two because the header is larger than a single block.
598 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) {
599 num_starting_blocks = num_blocks - variance_blocks;
600 k = md_block_size * num_starting_blocks;
603 bits = 8 * mac_end_offset;
606 * Compute the initial HMAC block. For SSLv3, the padding and secret
607 * bytes are included in |header| because they take more than a
610 bits += 8 * md_block_size;
611 memset(hmac_pad, 0, md_block_size);
612 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad));
613 memcpy(hmac_pad, mac_secret, mac_secret_length);
614 for (i = 0; i < md_block_size; i++)
617 md_transform(md_state.c, hmac_pad);
620 if (length_is_big_endian) {
621 memset(length_bytes, 0, md_length_size - 4);
622 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24);
623 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16);
624 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8);
625 length_bytes[md_length_size - 1] = (unsigned char)bits;
627 memset(length_bytes, 0, md_length_size);
628 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24);
629 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16);
630 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8);
631 length_bytes[md_length_size - 8] = (unsigned char)bits;
637 * The SSLv3 header is larger than a single block. overhang is
638 * the number of bytes beyond a single block that the header
639 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5).
641 unsigned overhang = header_length - md_block_size;
642 md_transform(md_state.c, header);
643 memcpy(first_block, header + md_block_size, overhang);
644 memcpy(first_block + overhang, data, md_block_size - overhang);
645 md_transform(md_state.c, first_block);
646 for (i = 1; i < k / md_block_size - 1; i++)
647 md_transform(md_state.c, data + md_block_size * i - overhang);
649 /* k is a multiple of md_block_size. */
650 memcpy(first_block, header, 13);
651 memcpy(first_block + 13, data, md_block_size - 13);
652 md_transform(md_state.c, first_block);
653 for (i = 1; i < k / md_block_size; i++)
654 md_transform(md_state.c, data + md_block_size * i - 13);
658 memset(mac_out, 0, sizeof(mac_out));
661 * We now process the final hash blocks. For each block, we construct it
662 * in constant time. If the |i==index_a| then we'll include the 0x80
663 * bytes and zero pad etc. For each block we selectively copy it, in
664 * constant time, to |mac_out|.
666 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks;
668 unsigned char block[MAX_HASH_BLOCK_SIZE];
669 unsigned char is_block_a = constant_time_eq_8(i, index_a);
670 unsigned char is_block_b = constant_time_eq_8(i, index_b);
671 for (j = 0; j < md_block_size; j++) {
672 unsigned char b = 0, is_past_c, is_past_cp1;
673 if (k < header_length)
675 else if (k < data_plus_mac_plus_padding_size + header_length)
676 b = data[k - header_length];
679 is_past_c = is_block_a & constant_time_ge_8(j, c);
680 is_past_cp1 = is_block_a & constant_time_ge_8(j, c + 1);
682 * If this is the block containing the end of the application
683 * data, and we are at the offset for the 0x80 value, then
684 * overwrite b with 0x80.
686 b = constant_time_select_8(is_past_c, 0x80, b);
688 * If this the the block containing the end of the application
689 * data and we're past the 0x80 value then just write zero.
691 b = b & ~is_past_cp1;
693 * If this is index_b (the final block), but not index_a (the end
694 * of the data), then the 64-bit length didn't fit into index_a
695 * and we're having to add an extra block of zeros.
697 b &= ~is_block_b | is_block_a;
700 * The final bytes of one of the blocks contains the length.
702 if (j >= md_block_size - md_length_size) {
703 /* If this is index_b, write a length byte. */
704 b = constant_time_select_8(is_block_b,
707 md_length_size)], b);
712 md_transform(md_state.c, block);
713 md_final_raw(md_state.c, block);
714 /* If this is index_b, copy the hash value to |mac_out|. */
715 for (j = 0; j < md_size; j++)
716 mac_out[j] |= block[j] & is_block_b;
719 EVP_MD_CTX_init(&md_ctx);
720 EVP_DigestInit_ex(&md_ctx, digest, NULL /* engine */ );
722 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
723 memset(hmac_pad, 0x5c, sslv3_pad_length);
725 EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length);
726 EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length);
727 EVP_DigestUpdate(&md_ctx, mac_out, md_size);
729 /* Complete the HMAC in the standard manner. */
730 for (i = 0; i < md_block_size; i++)
733 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size);
734 EVP_DigestUpdate(&md_ctx, mac_out, md_size);
736 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
738 *md_out_size = md_out_size_u;
739 EVP_MD_CTX_cleanup(&md_ctx);
745 * Due to the need to use EVP in FIPS mode we can't reimplement digests but
746 * we can ensure the number of blocks processed is equal for all cases by
747 * digesting additional data.
750 void tls_fips_digest_extra(const EVP_CIPHER_CTX *cipher_ctx,
751 const EVP_MD *hash, HMAC_CTX *hctx,
752 const unsigned char *data, size_t data_len,
755 size_t block_size, digest_pad, blocks_data, blocks_orig;
756 if (EVP_CIPHER_CTX_mode(cipher_ctx) != EVP_CIPH_CBC_MODE)
758 block_size = EVP_MD_block_size(hash);
760 * We are in FIPS mode if we get this far so we know we have only SHA*
761 * digests and TLS to deal with. Minimum digest padding length is 17 for
762 * SHA384/SHA512 and 9 otherwise. Additional header is 13 bytes. To get
763 * the number of digest blocks processed round up the amount of data plus
764 * padding to the nearest block length. Block length is 128 for
765 * SHA384/SHA512 and 64 otherwise. So we have: blocks = (payload_len +
766 * digest_pad + 13 + block_size - 1)/block_size equivalently: blocks =
767 * (payload_len + digest_pad + 12)/block_size + 1 HMAC adds a constant
768 * overhead. We're ultimately only interested in differences so this
769 * becomes blocks = (payload_len + 29)/128 for SHA384/SHA512 and blocks =
770 * (payload_len + 21)/64 otherwise.
772 digest_pad = block_size == 64 ? 21 : 29;
773 blocks_orig = (orig_len + digest_pad) / block_size;
774 blocks_data = (data_len + digest_pad) / block_size;
776 * MAC enough blocks to make up the difference between the original and
777 * actual lengths plus one extra block to ensure this is never a no op.
778 * The "data" pointer should always have enough space to perform this
779 * operation as it is large enough for a maximum length TLS buffer.
781 HMAC_Update(hctx, data, (blocks_orig - blocks_data + 1) * block_size);