1 /* $OpenBSD: s3_cbc.c,v 1.11 2015/09/11 17:17:44 jsing Exp $ */
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).
58 #include <openssl/md5.h>
59 #include <openssl/sha.h>
61 /* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length
62 * field. (SHA-384/512 have 128-bit length.) */
63 #define MAX_HASH_BIT_COUNT_BYTES 16
65 /* MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support.
66 * Currently SHA-384/512 has a 128-byte block size and that's the largest
67 * supported by TLS.) */
68 #define MAX_HASH_BLOCK_SIZE 128
70 /* Some utility functions are needed:
72 * These macros return the given value with the MSB copied to all the other
73 * bits. They use the fact that arithmetic shift shifts-in the sign bit.
74 * However, this is not ensured by the C standard so you may need to replace
75 * them with something else on odd CPUs. */
76 #define DUPLICATE_MSB_TO_ALL(x) ((unsigned)((int)(x) >> (sizeof(int) * 8 - 1)))
77 #define DUPLICATE_MSB_TO_ALL_8(x) ((unsigned char)(DUPLICATE_MSB_TO_ALL(x)))
79 /* constant_time_lt returns 0xff if a<b and 0x00 otherwise. */
81 constant_time_lt(unsigned a
, unsigned b
)
84 return DUPLICATE_MSB_TO_ALL(a
);
87 /* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */
89 constant_time_ge(unsigned a
, unsigned b
)
92 return DUPLICATE_MSB_TO_ALL(~a
);
95 /* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */
97 constant_time_eq_8(unsigned a
, unsigned b
)
101 return DUPLICATE_MSB_TO_ALL_8(c
);
104 /* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
105 * record in |rec| in constant time and returns 1 if the padding is valid and
106 * -1 otherwise. It also removes any explicit IV from the start of the record
107 * without leaking any timing about whether there was enough space after the
108 * padding was removed.
110 * block_size: the block size of the cipher used to encrypt the record.
112 * 0: (in non-constant time) if the record is publicly invalid.
113 * 1: if the padding was valid
116 tls1_cbc_remove_padding(const SSL
* s
, SSL3_RECORD
*rec
, unsigned block_size
,
119 unsigned padding_length
, good
, to_check
, i
;
120 const unsigned overhead
= 1 /* padding length byte */ + mac_size
;
122 /* Check if version requires explicit IV */
123 if (SSL_USE_EXPLICIT_IV(s
)) {
124 /* These lengths are all public so we can test them in
127 if (overhead
+ block_size
> rec
->length
)
129 /* We can now safely skip explicit IV */
130 rec
->data
+= block_size
;
131 rec
->input
+= block_size
;
132 rec
->length
-= block_size
;
133 } else if (overhead
> rec
->length
)
136 padding_length
= rec
->data
[rec
->length
- 1];
138 if (EVP_CIPHER_flags(s
->enc_read_ctx
->cipher
) & EVP_CIPH_FLAG_AEAD_CIPHER
) {
139 /* padding is already verified */
140 rec
->length
-= padding_length
+ 1;
144 good
= constant_time_ge(rec
->length
, overhead
+ padding_length
);
145 /* The padding consists of a length byte at the end of the record and
146 * then that many bytes of padding, all with the same value as the
147 * length byte. Thus, with the length byte included, there are i+1
150 * We can't check just |padding_length+1| bytes because that leaks
151 * decrypted information. Therefore we always have to check the maximum
152 * amount of padding possible. (Again, the length of the record is
153 * public information so we can use it.) */
154 to_check
= 255; /* maximum amount of padding. */
155 if (to_check
> rec
->length
- 1)
156 to_check
= rec
->length
- 1;
158 for (i
= 0; i
< to_check
; i
++) {
159 unsigned char mask
= constant_time_ge(padding_length
, i
);
160 unsigned char b
= rec
->data
[rec
->length
- 1 - i
];
161 /* The final |padding_length+1| bytes should all have the value
162 * |padding_length|. Therefore the XOR should be zero. */
163 good
&= ~(mask
&(padding_length
^ b
));
166 /* If any of the final |padding_length+1| bytes had the wrong value,
167 * one or more of the lower eight bits of |good| will be cleared. We
168 * AND the bottom 8 bits together and duplicate the result to all the
173 good
<<= sizeof(good
)*8 - 1;
174 good
= DUPLICATE_MSB_TO_ALL(good
);
176 padding_length
= good
& (padding_length
+ 1);
177 rec
->length
-= padding_length
;
178 rec
->type
|= padding_length
<<8; /* kludge: pass padding length */
180 return (int)((good
& 1) | (~good
& -1));
183 /* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
184 * constant time (independent of the concrete value of rec->length, which may
185 * vary within a 256-byte window).
187 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to
191 * rec->orig_len >= md_size
192 * md_size <= EVP_MAX_MD_SIZE
194 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with
195 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into
196 * a single or pair of cache-lines, then the variable memory accesses don't
197 * actually affect the timing. CPUs with smaller cache-lines [if any] are
198 * not multi-core and are not considered vulnerable to cache-timing attacks.
200 #define CBC_MAC_ROTATE_IN_PLACE
203 ssl3_cbc_copy_mac(unsigned char* out
, const SSL3_RECORD
*rec
,
204 unsigned md_size
, unsigned orig_len
)
206 #if defined(CBC_MAC_ROTATE_IN_PLACE)
207 unsigned char rotated_mac_buf
[64 + EVP_MAX_MD_SIZE
];
208 unsigned char *rotated_mac
;
210 unsigned char rotated_mac
[EVP_MAX_MD_SIZE
];
213 /* mac_end is the index of |rec->data| just after the end of the MAC. */
214 unsigned mac_end
= rec
->length
;
215 unsigned mac_start
= mac_end
- md_size
;
216 /* scan_start contains the number of bytes that we can ignore because
217 * the MAC's position can only vary by 255 bytes. */
218 unsigned scan_start
= 0;
220 unsigned div_spoiler
;
221 unsigned rotate_offset
;
223 OPENSSL_assert(orig_len
>= md_size
);
224 OPENSSL_assert(md_size
<= EVP_MAX_MD_SIZE
);
226 #if defined(CBC_MAC_ROTATE_IN_PLACE)
227 rotated_mac
= rotated_mac_buf
+ ((0 - (size_t)rotated_mac_buf
)&63);
230 /* This information is public so it's safe to branch based on it. */
231 if (orig_len
> md_size
+ 255 + 1)
232 scan_start
= orig_len
- (md_size
+ 255 + 1);
233 /* div_spoiler contains a multiple of md_size that is used to cause the
234 * modulo operation to be constant time. Without this, the time varies
235 * based on the amount of padding when running on Intel chips at least.
237 * The aim of right-shifting md_size is so that the compiler doesn't
238 * figure out that it can remove div_spoiler as that would require it
239 * to prove that md_size is always even, which I hope is beyond it. */
240 div_spoiler
= md_size
>> 1;
241 div_spoiler
<<= (sizeof(div_spoiler
) - 1) * 8;
242 rotate_offset
= (div_spoiler
+ mac_start
- scan_start
) % md_size
;
244 memset(rotated_mac
, 0, md_size
);
245 for (i
= scan_start
, j
= 0; i
< orig_len
; i
++) {
246 unsigned char mac_started
= constant_time_ge(i
, mac_start
);
247 unsigned char mac_ended
= constant_time_ge(i
, mac_end
);
248 unsigned char b
= rec
->data
[i
];
249 rotated_mac
[j
++] |= b
& mac_started
& ~mac_ended
;
250 j
&= constant_time_lt(j
, md_size
);
253 /* Now rotate the MAC */
254 #if defined(CBC_MAC_ROTATE_IN_PLACE)
256 for (i
= 0; i
< md_size
; i
++) {
257 /* in case cache-line is 32 bytes, touch second line */
258 ((volatile unsigned char *)rotated_mac
)[rotate_offset
^32];
259 out
[j
++] = rotated_mac
[rotate_offset
++];
260 rotate_offset
&= constant_time_lt(rotate_offset
, md_size
);
263 memset(out
, 0, md_size
);
264 rotate_offset
= md_size
- rotate_offset
;
265 rotate_offset
&= constant_time_lt(rotate_offset
, md_size
);
266 for (i
= 0; i
< md_size
; i
++) {
267 for (j
= 0; j
< md_size
; j
++)
268 out
[j
] |= rotated_mac
[i
] & constant_time_eq_8(j
, rotate_offset
);
270 rotate_offset
&= constant_time_lt(rotate_offset
, md_size
);
275 /* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
276 * little-endian order. The value of p is advanced by four. */
277 #define u32toLE(n, p) \
278 (*((p)++)=(unsigned char)(n), \
279 *((p)++)=(unsigned char)(n>>8), \
280 *((p)++)=(unsigned char)(n>>16), \
281 *((p)++)=(unsigned char)(n>>24))
283 /* These functions serialize the state of a hash and thus perform the standard
284 * "final" operation without adding the padding and length that such a function
287 tls1_md5_final_raw(void* ctx
, unsigned char *md_out
)
290 u32toLE(md5
->A
, md_out
);
291 u32toLE(md5
->B
, md_out
);
292 u32toLE(md5
->C
, md_out
);
293 u32toLE(md5
->D
, md_out
);
297 tls1_sha1_final_raw(void* ctx
, unsigned char *md_out
)
300 l2n(sha1
->h0
, md_out
);
301 l2n(sha1
->h1
, md_out
);
302 l2n(sha1
->h2
, md_out
);
303 l2n(sha1
->h3
, md_out
);
304 l2n(sha1
->h4
, md_out
);
306 #define LARGEST_DIGEST_CTX SHA_CTX
309 tls1_sha256_final_raw(void* ctx
, unsigned char *md_out
)
311 SHA256_CTX
*sha256
= ctx
;
314 for (i
= 0; i
< 8; i
++) {
315 l2n(sha256
->h
[i
], md_out
);
318 #undef LARGEST_DIGEST_CTX
319 #define LARGEST_DIGEST_CTX SHA256_CTX
322 tls1_sha512_final_raw(void* ctx
, unsigned char *md_out
)
324 SHA512_CTX
*sha512
= ctx
;
327 for (i
= 0; i
< 8; i
++) {
328 l2n8(sha512
->h
[i
], md_out
);
331 #undef LARGEST_DIGEST_CTX
332 #define LARGEST_DIGEST_CTX SHA512_CTX
334 /* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
335 * which ssl3_cbc_digest_record supports. */
337 ssl3_cbc_record_digest_supported(const EVP_MD_CTX
*ctx
)
339 switch (EVP_MD_CTX_type(ctx
)) {
352 /* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
355 * ctx: the EVP_MD_CTX from which we take the hash function.
356 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX.
357 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
358 * md_out_size: if non-NULL, the number of output bytes is written here.
359 * header: the 13-byte, TLS record header.
360 * data: the record data itself, less any preceeding explicit IV.
361 * data_plus_mac_size: the secret, reported length of the data and MAC
362 * once the padding has been removed.
363 * data_plus_mac_plus_padding_size: the public length of the whole
364 * record, including padding.
365 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS.
367 * On entry: by virtue of having been through one of the remove_padding
368 * functions, above, we know that data_plus_mac_size is large enough to contain
369 * a padding byte and MAC. (If the padding was invalid, it might contain the
372 ssl3_cbc_digest_record(const EVP_MD_CTX
*ctx
, unsigned char* md_out
,
373 size_t* md_out_size
, const unsigned char header
[13],
374 const unsigned char *data
, size_t data_plus_mac_size
,
375 size_t data_plus_mac_plus_padding_size
, const unsigned char *mac_secret
,
376 unsigned mac_secret_length
, char is_sslv3
)
378 union { double align
;
379 unsigned char c
[sizeof(LARGEST_DIGEST_CTX
)];
381 void (*md_final_raw
)(void *ctx
, unsigned char *md_out
);
382 void (*md_transform
)(void *ctx
, const unsigned char *block
);
383 unsigned md_size
, md_block_size
= 64;
384 unsigned sslv3_pad_length
= 40, header_length
, variance_blocks
,
385 len
, max_mac_bytes
, num_blocks
,
386 num_starting_blocks
, k
, mac_end_offset
, c
, index_a
, index_b
;
387 unsigned int bits
; /* at most 18 bits */
388 unsigned char length_bytes
[MAX_HASH_BIT_COUNT_BYTES
];
389 /* hmac_pad is the masked HMAC key. */
390 unsigned char hmac_pad
[MAX_HASH_BLOCK_SIZE
];
391 unsigned char first_block
[MAX_HASH_BLOCK_SIZE
];
392 unsigned char mac_out
[EVP_MAX_MD_SIZE
];
393 unsigned i
, j
, md_out_size_u
;
395 /* mdLengthSize is the number of bytes in the length field that terminates
397 unsigned md_length_size
= 8;
398 char length_is_big_endian
= 1;
400 /* This is a, hopefully redundant, check that allows us to forget about
401 * many possible overflows later in this function. */
402 OPENSSL_assert(data_plus_mac_plus_padding_size
< 1024*1024);
404 switch (EVP_MD_CTX_type(ctx
)) {
406 MD5_Init((MD5_CTX
*)md_state
.c
);
407 md_final_raw
= tls1_md5_final_raw
;
408 md_transform
= (void(*)(void *ctx
, const unsigned char *block
)) MD5_Transform
;
410 sslv3_pad_length
= 48;
411 length_is_big_endian
= 0;
414 SHA1_Init((SHA_CTX
*)md_state
.c
);
415 md_final_raw
= tls1_sha1_final_raw
;
416 md_transform
= (void(*)(void *ctx
, const unsigned char *block
)) SHA1_Transform
;
420 SHA224_Init((SHA256_CTX
*)md_state
.c
);
421 md_final_raw
= tls1_sha256_final_raw
;
422 md_transform
= (void(*)(void *ctx
, const unsigned char *block
)) SHA256_Transform
;
426 SHA256_Init((SHA256_CTX
*)md_state
.c
);
427 md_final_raw
= tls1_sha256_final_raw
;
428 md_transform
= (void(*)(void *ctx
, const unsigned char *block
)) SHA256_Transform
;
432 SHA384_Init((SHA512_CTX
*)md_state
.c
);
433 md_final_raw
= tls1_sha512_final_raw
;
434 md_transform
= (void(*)(void *ctx
, const unsigned char *block
)) SHA512_Transform
;
440 SHA512_Init((SHA512_CTX
*)md_state
.c
);
441 md_final_raw
= tls1_sha512_final_raw
;
442 md_transform
= (void(*)(void *ctx
, const unsigned char *block
)) SHA512_Transform
;
448 /* ssl3_cbc_record_digest_supported should have been
449 * called first to check that the hash function is
457 OPENSSL_assert(md_length_size
<= MAX_HASH_BIT_COUNT_BYTES
);
458 OPENSSL_assert(md_block_size
<= MAX_HASH_BLOCK_SIZE
);
459 OPENSSL_assert(md_size
<= EVP_MAX_MD_SIZE
);
463 header_length
= mac_secret_length
+ sslv3_pad_length
+
464 8 /* sequence number */ +
465 1 /* record type */ +
466 2 /* record length */;
469 /* variance_blocks is the number of blocks of the hash that we have to
470 * calculate in constant time because they could be altered by the
473 * In SSLv3, the padding must be minimal so the end of the plaintext
474 * varies by, at most, 15+20 = 35 bytes. (We conservatively assume that
475 * the MAC size varies from 0..20 bytes.) In case the 9 bytes of hash
476 * termination (0x80 + 64-bit length) don't fit in the final block, we
477 * say that the final two blocks can vary based on the padding.
479 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
480 * required to be minimal. Therefore we say that the final six blocks
481 * can vary based on the padding.
483 * Later in the function, if the message is short and there obviously
484 * cannot be this many blocks then variance_blocks can be reduced. */
485 variance_blocks
= is_sslv3
? 2 : 6;
486 /* From now on we're dealing with the MAC, which conceptually has 13
487 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
489 len
= data_plus_mac_plus_padding_size
+ header_length
;
490 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including
491 * |header|, assuming that there's no padding. */
492 max_mac_bytes
= len
- md_size
- 1;
493 /* num_blocks is the maximum number of hash blocks. */
494 num_blocks
= (max_mac_bytes
+ 1 + md_length_size
+ md_block_size
- 1) / md_block_size
;
495 /* In order to calculate the MAC in constant time we have to handle
496 * the final blocks specially because the padding value could cause the
497 * end to appear somewhere in the final |variance_blocks| blocks and we
498 * can't leak where. However, |num_starting_blocks| worth of data can
499 * be hashed right away because no padding value can affect whether
500 * they are plaintext. */
501 num_starting_blocks
= 0;
502 /* k is the starting byte offset into the conceptual header||data where
503 * we start processing. */
505 /* mac_end_offset is the index just past the end of the data to be
507 mac_end_offset
= data_plus_mac_size
+ header_length
- md_size
;
508 /* c is the index of the 0x80 byte in the final hash block that
509 * contains application data. */
510 c
= mac_end_offset
% md_block_size
;
511 /* index_a is the hash block number that contains the 0x80 terminating
513 index_a
= mac_end_offset
/ md_block_size
;
514 /* index_b is the hash block number that contains the 64-bit hash
515 * length, in bits. */
516 index_b
= (mac_end_offset
+ md_length_size
) / md_block_size
;
517 /* bits is the hash-length in bits. It includes the additional hash
518 * block for the masked HMAC key, or whole of |header| in the case of
521 /* For SSLv3, if we're going to have any starting blocks then we need
522 * at least two because the header is larger than a single block. */
523 if (num_blocks
> variance_blocks
+ (is_sslv3
? 1 : 0)) {
524 num_starting_blocks
= num_blocks
- variance_blocks
;
525 k
= md_block_size
*num_starting_blocks
;
528 bits
= 8*mac_end_offset
;
530 /* Compute the initial HMAC block. For SSLv3, the padding and
531 * secret bytes are included in |header| because they take more
532 * than a single block. */
533 bits
+= 8*md_block_size
;
534 memset(hmac_pad
, 0, md_block_size
);
535 OPENSSL_assert(mac_secret_length
<= sizeof(hmac_pad
));
536 memcpy(hmac_pad
, mac_secret
, mac_secret_length
);
537 for (i
= 0; i
< md_block_size
; i
++)
540 md_transform(md_state
.c
, hmac_pad
);
543 if (length_is_big_endian
) {
544 memset(length_bytes
, 0, md_length_size
- 4);
545 length_bytes
[md_length_size
- 4] = (unsigned char)(bits
>> 24);
546 length_bytes
[md_length_size
- 3] = (unsigned char)(bits
>> 16);
547 length_bytes
[md_length_size
- 2] = (unsigned char)(bits
>> 8);
548 length_bytes
[md_length_size
- 1] = (unsigned char)bits
;
550 memset(length_bytes
, 0, md_length_size
);
551 length_bytes
[md_length_size
- 5] = (unsigned char)(bits
>> 24);
552 length_bytes
[md_length_size
- 6] = (unsigned char)(bits
>> 16);
553 length_bytes
[md_length_size
- 7] = (unsigned char)(bits
>> 8);
554 length_bytes
[md_length_size
- 8] = (unsigned char)bits
;
559 /* The SSLv3 header is larger than a single block.
560 * overhang is the number of bytes beyond a single
561 * block that the header consumes: either 7 bytes
562 * (SHA1) or 11 bytes (MD5). */
563 unsigned overhang
= header_length
- md_block_size
;
564 md_transform(md_state
.c
, header
);
565 memcpy(first_block
, header
+ md_block_size
, overhang
);
566 memcpy(first_block
+ overhang
, data
, md_block_size
- overhang
);
567 md_transform(md_state
.c
, first_block
);
568 for (i
= 1; i
< k
/md_block_size
- 1; i
++)
569 md_transform(md_state
.c
, data
+ md_block_size
*i
- overhang
);
571 /* k is a multiple of md_block_size. */
572 memcpy(first_block
, header
, 13);
573 memcpy(first_block
+ 13, data
, md_block_size
- 13);
574 md_transform(md_state
.c
, first_block
);
575 for (i
= 1; i
< k
/md_block_size
; i
++)
576 md_transform(md_state
.c
, data
+ md_block_size
*i
- 13);
580 memset(mac_out
, 0, sizeof(mac_out
));
582 /* We now process the final hash blocks. For each block, we construct
583 * it in constant time. If the |i==index_a| then we'll include the 0x80
584 * bytes and zero pad etc. For each block we selectively copy it, in
585 * constant time, to |mac_out|. */
586 for (i
= num_starting_blocks
; i
<= num_starting_blocks
+ variance_blocks
; i
++) {
587 unsigned char block
[MAX_HASH_BLOCK_SIZE
];
588 unsigned char is_block_a
= constant_time_eq_8(i
, index_a
);
589 unsigned char is_block_b
= constant_time_eq_8(i
, index_b
);
590 for (j
= 0; j
< md_block_size
; j
++) {
591 unsigned char b
= 0, is_past_c
, is_past_cp1
;
592 if (k
< header_length
)
594 else if (k
< data_plus_mac_plus_padding_size
+ header_length
)
595 b
= data
[k
- header_length
];
598 is_past_c
= is_block_a
& constant_time_ge(j
, c
);
599 is_past_cp1
= is_block_a
& constant_time_ge(j
, c
+ 1);
600 /* If this is the block containing the end of the
601 * application data, and we are at the offset for the
602 * 0x80 value, then overwrite b with 0x80. */
603 b
= (b
&~is_past_c
) | (0x80&is_past_c
);
604 /* If this is the block containing the end of the
605 * application data and we're past the 0x80 value then
606 * just write zero. */
608 /* If this is index_b (the final block), but not
609 * index_a (the end of the data), then the 64-bit
610 * length didn't fit into index_a and we're having to
611 * add an extra block of zeros. */
612 b
&= ~is_block_b
| is_block_a
;
614 /* The final bytes of one of the blocks contains the
616 if (j
>= md_block_size
- md_length_size
) {
617 /* If this is index_b, write a length byte. */
618 b
= (b
&~is_block_b
) | (is_block_b
&length_bytes
[j
- (md_block_size
- md_length_size
)]);
623 md_transform(md_state
.c
, block
);
624 md_final_raw(md_state
.c
, block
);
625 /* If this is index_b, copy the hash value to |mac_out|. */
626 for (j
= 0; j
< md_size
; j
++)
627 mac_out
[j
] |= block
[j
]&is_block_b
;
630 EVP_MD_CTX_init(&md_ctx
);
631 if (!EVP_DigestInit_ex(&md_ctx
, ctx
->digest
, NULL
/* engine */)) {
632 EVP_MD_CTX_cleanup(&md_ctx
);
636 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
637 memset(hmac_pad
, 0x5c, sslv3_pad_length
);
639 EVP_DigestUpdate(&md_ctx
, mac_secret
, mac_secret_length
);
640 EVP_DigestUpdate(&md_ctx
, hmac_pad
, sslv3_pad_length
);
641 EVP_DigestUpdate(&md_ctx
, mac_out
, md_size
);
643 /* Complete the HMAC in the standard manner. */
644 for (i
= 0; i
< md_block_size
; i
++)
647 EVP_DigestUpdate(&md_ctx
, hmac_pad
, md_block_size
);
648 EVP_DigestUpdate(&md_ctx
, mac_out
, md_size
);
650 EVP_DigestFinal(&md_ctx
, md_out
, &md_out_size_u
);
652 *md_out_size
= md_out_size_u
;
653 EVP_MD_CTX_cleanup(&md_ctx
);