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 rec
->length
-= good
& (padding_length
+ 1);
103 return constant_time_select_int(good
, 1, -1);
107 * tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
108 * record in |rec| in constant time and returns 1 if the padding is valid and
109 * -1 otherwise. It also removes any explicit IV from the start of the record
110 * without leaking any timing about whether there was enough space after the
111 * padding was removed.
113 * block_size: the block size of the cipher used to encrypt the record.
115 * 0: (in non-constant time) if the record is publicly invalid.
116 * 1: if the padding was valid
119 int tls1_cbc_remove_padding(const SSL
*s
,
121 unsigned block_size
, unsigned mac_size
)
123 unsigned padding_length
, good
, to_check
, i
;
124 const unsigned overhead
= 1 /* padding length byte */ + mac_size
;
125 /* Check if version requires explicit IV */
126 if (SSL_USE_EXPLICIT_IV(s
)) {
128 * These lengths are all public so we can test them in non-constant
131 if (overhead
+ block_size
> rec
->length
)
133 /* We can now safely skip explicit IV */
134 rec
->data
+= block_size
;
135 rec
->input
+= block_size
;
136 rec
->length
-= block_size
;
137 rec
->orig_len
-= block_size
;
138 } else if (overhead
> rec
->length
)
141 padding_length
= rec
->data
[rec
->length
- 1];
144 * NB: if compression is in operation the first packet may not be of even
145 * length so the padding bug check cannot be performed. This bug
146 * workaround has been around since SSLeay so hopefully it is either
147 * fixed now or no buggy implementation supports compression [steve]
149 if ((s
->options
& SSL_OP_TLS_BLOCK_PADDING_BUG
) && !s
->expand
) {
150 /* First packet is even in size, so check */
151 if ((memcmp(s
->s3
->read_sequence
, "\0\0\0\0\0\0\0\0", 8) == 0) &&
152 !(padding_length
& 1)) {
153 s
->s3
->flags
|= TLS1_FLAGS_TLS_PADDING_BUG
;
155 if ((s
->s3
->flags
& TLS1_FLAGS_TLS_PADDING_BUG
) && padding_length
> 0) {
160 if (EVP_CIPHER_flags(s
->enc_read_ctx
->cipher
) & EVP_CIPH_FLAG_AEAD_CIPHER
) {
161 /* padding is already verified */
162 rec
->length
-= padding_length
+ 1;
166 good
= constant_time_ge(rec
->length
, overhead
+ padding_length
);
168 * The padding consists of a length byte at the end of the record and
169 * then that many bytes of padding, all with the same value as the length
170 * byte. Thus, with the length byte included, there are i+1 bytes of
171 * padding. We can't check just |padding_length+1| bytes because that
172 * leaks decrypted information. Therefore we always have to check the
173 * maximum amount of padding possible. (Again, the length of the record
174 * is public information so we can use it.)
176 to_check
= 255; /* maximum amount of padding. */
177 if (to_check
> rec
->length
- 1)
178 to_check
= rec
->length
- 1;
180 for (i
= 0; i
< to_check
; i
++) {
181 unsigned char mask
= constant_time_ge_8(padding_length
, i
);
182 unsigned char b
= rec
->data
[rec
->length
- 1 - i
];
184 * The final |padding_length+1| bytes should all have the value
185 * |padding_length|. Therefore the XOR should be zero.
187 good
&= ~(mask
& (padding_length
^ b
));
191 * If any of the final |padding_length+1| bytes had the wrong value, one
192 * or more of the lower eight bits of |good| will be cleared.
194 good
= constant_time_eq(0xff, good
& 0xff);
195 rec
->length
-= good
& (padding_length
+ 1);
197 return constant_time_select_int(good
, 1, -1);
201 * ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
202 * constant time (independent of the concrete value of rec->length, which may
203 * vary within a 256-byte window).
205 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to
209 * rec->orig_len >= md_size
210 * md_size <= EVP_MAX_MD_SIZE
212 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with
213 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into
214 * a single or pair of cache-lines, then the variable memory accesses don't
215 * actually affect the timing. CPUs with smaller cache-lines [if any] are
216 * not multi-core and are not considered vulnerable to cache-timing attacks.
218 #define CBC_MAC_ROTATE_IN_PLACE
220 void ssl3_cbc_copy_mac(unsigned char *out
,
221 const SSL3_RECORD
*rec
, unsigned md_size
)
223 #if defined(CBC_MAC_ROTATE_IN_PLACE)
224 unsigned char rotated_mac_buf
[64 + EVP_MAX_MD_SIZE
];
225 unsigned char *rotated_mac
;
227 unsigned char rotated_mac
[EVP_MAX_MD_SIZE
];
231 * mac_end is the index of |rec->data| just after the end of the MAC.
233 unsigned mac_end
= rec
->length
;
234 unsigned mac_start
= mac_end
- md_size
;
236 * scan_start contains the number of bytes that we can ignore because the
237 * MAC's position can only vary by 255 bytes.
239 unsigned scan_start
= 0;
241 unsigned div_spoiler
;
242 unsigned rotate_offset
;
244 OPENSSL_assert(rec
->orig_len
>= md_size
);
245 OPENSSL_assert(md_size
<= EVP_MAX_MD_SIZE
);
247 #if defined(CBC_MAC_ROTATE_IN_PLACE)
248 rotated_mac
= rotated_mac_buf
+ ((0 - (size_t)rotated_mac_buf
) & 63);
251 /* This information is public so it's safe to branch based on it. */
252 if (rec
->orig_len
> md_size
+ 255 + 1)
253 scan_start
= rec
->orig_len
- (md_size
+ 255 + 1);
255 * div_spoiler contains a multiple of md_size that is used to cause the
256 * modulo operation to be constant time. Without this, the time varies
257 * based on the amount of padding when running on Intel chips at least.
258 * The aim of right-shifting md_size is so that the compiler doesn't
259 * figure out that it can remove div_spoiler as that would require it to
260 * prove that md_size is always even, which I hope is beyond it.
262 div_spoiler
= md_size
>> 1;
263 div_spoiler
<<= (sizeof(div_spoiler
) - 1) * 8;
264 rotate_offset
= (div_spoiler
+ mac_start
- scan_start
) % md_size
;
266 memset(rotated_mac
, 0, md_size
);
267 for (i
= scan_start
, j
= 0; i
< rec
->orig_len
; i
++) {
268 unsigned char mac_started
= constant_time_ge_8(i
, mac_start
);
269 unsigned char mac_ended
= constant_time_ge_8(i
, mac_end
);
270 unsigned char b
= rec
->data
[i
];
271 rotated_mac
[j
++] |= b
& mac_started
& ~mac_ended
;
272 j
&= constant_time_lt(j
, md_size
);
275 /* Now rotate the MAC */
276 #if defined(CBC_MAC_ROTATE_IN_PLACE)
278 for (i
= 0; i
< md_size
; i
++) {
279 /* in case cache-line is 32 bytes, touch second line */
280 ((volatile unsigned char *)rotated_mac
)[rotate_offset
^ 32];
281 out
[j
++] = rotated_mac
[rotate_offset
++];
282 rotate_offset
&= constant_time_lt(rotate_offset
, md_size
);
285 memset(out
, 0, md_size
);
286 rotate_offset
= md_size
- rotate_offset
;
287 rotate_offset
&= constant_time_lt(rotate_offset
, md_size
);
288 for (i
= 0; i
< md_size
; i
++) {
289 for (j
= 0; j
< md_size
; j
++)
290 out
[j
] |= rotated_mac
[i
] & constant_time_eq_8(j
, rotate_offset
);
292 rotate_offset
&= constant_time_lt(rotate_offset
, md_size
);
298 * u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
299 * little-endian order. The value of p is advanced by four.
301 #define u32toLE(n, p) \
302 (*((p)++)=(unsigned char)(n), \
303 *((p)++)=(unsigned char)(n>>8), \
304 *((p)++)=(unsigned char)(n>>16), \
305 *((p)++)=(unsigned char)(n>>24))
308 * These functions serialize the state of a hash and thus perform the
309 * standard "final" operation without adding the padding and length that such
310 * a function typically does.
312 static void tls1_md5_final_raw(void *ctx
, unsigned char *md_out
)
315 u32toLE(md5
->A
, md_out
);
316 u32toLE(md5
->B
, md_out
);
317 u32toLE(md5
->C
, md_out
);
318 u32toLE(md5
->D
, md_out
);
321 static void tls1_sha1_final_raw(void *ctx
, unsigned char *md_out
)
324 l2n(sha1
->h0
, md_out
);
325 l2n(sha1
->h1
, md_out
);
326 l2n(sha1
->h2
, md_out
);
327 l2n(sha1
->h3
, md_out
);
328 l2n(sha1
->h4
, md_out
);
331 #define LARGEST_DIGEST_CTX SHA_CTX
333 #ifndef OPENSSL_NO_SHA256
334 static void tls1_sha256_final_raw(void *ctx
, unsigned char *md_out
)
336 SHA256_CTX
*sha256
= ctx
;
339 for (i
= 0; i
< 8; i
++) {
340 l2n(sha256
->h
[i
], md_out
);
344 # undef LARGEST_DIGEST_CTX
345 # define LARGEST_DIGEST_CTX SHA256_CTX
348 #ifndef OPENSSL_NO_SHA512
349 static void tls1_sha512_final_raw(void *ctx
, unsigned char *md_out
)
351 SHA512_CTX
*sha512
= ctx
;
354 for (i
= 0; i
< 8; i
++) {
355 l2n8(sha512
->h
[i
], md_out
);
359 # undef LARGEST_DIGEST_CTX
360 # define LARGEST_DIGEST_CTX SHA512_CTX
364 * ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
365 * which ssl3_cbc_digest_record supports.
367 char ssl3_cbc_record_digest_supported(const EVP_MD_CTX
*ctx
)
371 switch (EVP_MD_CTX_type(ctx
)) {
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 preceding 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_CTX
*ctx
,
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;
446 * This is a, hopefully redundant, check that allows us to forget about
447 * many possible overflows later in this function.
449 OPENSSL_assert(data_plus_mac_plus_padding_size
< 1024 * 1024);
451 switch (EVP_MD_CTX_type(ctx
)) {
453 MD5_Init((MD5_CTX
*)md_state
.c
);
454 md_final_raw
= tls1_md5_final_raw
;
456 (void (*)(void *ctx
, const unsigned char *block
))MD5_Transform
;
458 sslv3_pad_length
= 48;
459 length_is_big_endian
= 0;
462 SHA1_Init((SHA_CTX
*)md_state
.c
);
463 md_final_raw
= tls1_sha1_final_raw
;
465 (void (*)(void *ctx
, const unsigned char *block
))SHA1_Transform
;
468 #ifndef OPENSSL_NO_SHA256
470 SHA224_Init((SHA256_CTX
*)md_state
.c
);
471 md_final_raw
= tls1_sha256_final_raw
;
473 (void (*)(void *ctx
, const unsigned char *block
))SHA256_Transform
;
477 SHA256_Init((SHA256_CTX
*)md_state
.c
);
478 md_final_raw
= tls1_sha256_final_raw
;
480 (void (*)(void *ctx
, const unsigned char *block
))SHA256_Transform
;
484 #ifndef OPENSSL_NO_SHA512
486 SHA384_Init((SHA512_CTX
*)md_state
.c
);
487 md_final_raw
= tls1_sha512_final_raw
;
489 (void (*)(void *ctx
, const unsigned char *block
))SHA512_Transform
;
495 SHA512_Init((SHA512_CTX
*)md_state
.c
);
496 md_final_raw
= tls1_sha512_final_raw
;
498 (void (*)(void *ctx
, const unsigned char *block
))SHA512_Transform
;
506 * ssl3_cbc_record_digest_supported should have been called first to
507 * check that the hash function is supported.
515 OPENSSL_assert(md_length_size
<= MAX_HASH_BIT_COUNT_BYTES
);
516 OPENSSL_assert(md_block_size
<= MAX_HASH_BLOCK_SIZE
);
517 OPENSSL_assert(md_size
<= EVP_MAX_MD_SIZE
);
521 header_length
= mac_secret_length
+ sslv3_pad_length
+ 8 /* sequence
523 1 /* record type */ +
524 2 /* record length */ ;
528 * variance_blocks is the number of blocks of the hash that we have to
529 * calculate in constant time because they could be altered by the
530 * padding value. In SSLv3, the padding must be minimal so the end of
531 * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively
532 * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes
533 * of hash termination (0x80 + 64-bit length) don't fit in the final
534 * block, we say that the final two blocks can vary based on the padding.
535 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
536 * required to be minimal. Therefore we say that the final six blocks can
537 * vary based on the padding. Later in the function, if the message is
538 * short and there obviously cannot be this many blocks then
539 * variance_blocks can be reduced.
541 variance_blocks
= is_sslv3
? 2 : 6;
543 * From now on we're dealing with the MAC, which conceptually has 13
544 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
547 len
= data_plus_mac_plus_padding_size
+ header_length
;
549 * max_mac_bytes contains the maximum bytes of bytes in the MAC,
550 * including * |header|, assuming that there's no padding.
552 max_mac_bytes
= len
- md_size
- 1;
553 /* num_blocks is the maximum number of hash blocks. */
555 (max_mac_bytes
+ 1 + md_length_size
+ md_block_size
-
558 * In order to calculate the MAC in constant time we have to handle the
559 * final blocks specially because the padding value could cause the end
560 * to appear somewhere in the final |variance_blocks| blocks and we can't
561 * leak where. However, |num_starting_blocks| worth of data can be hashed
562 * right away because no padding value can affect whether they are
565 num_starting_blocks
= 0;
567 * k is the starting byte offset into the conceptual header||data where
568 * we start processing.
572 * mac_end_offset is the index just past the end of the data to be MACed.
574 mac_end_offset
= data_plus_mac_size
+ header_length
- md_size
;
576 * c is the index of the 0x80 byte in the final hash block that contains
579 c
= mac_end_offset
% md_block_size
;
581 * index_a is the hash block number that contains the 0x80 terminating
584 index_a
= mac_end_offset
/ md_block_size
;
586 * index_b is the hash block number that contains the 64-bit hash length,
589 index_b
= (mac_end_offset
+ md_length_size
) / md_block_size
;
591 * bits is the hash-length in bits. It includes the additional hash block
592 * for the masked HMAC key, or whole of |header| in the case of SSLv3.
596 * For SSLv3, if we're going to have any starting blocks then we need at
597 * least two because the header is larger than a single block.
599 if (num_blocks
> variance_blocks
+ (is_sslv3
? 1 : 0)) {
600 num_starting_blocks
= num_blocks
- variance_blocks
;
601 k
= md_block_size
* num_starting_blocks
;
604 bits
= 8 * mac_end_offset
;
607 * Compute the initial HMAC block. For SSLv3, the padding and secret
608 * bytes are included in |header| because they take more than a
611 bits
+= 8 * md_block_size
;
612 memset(hmac_pad
, 0, md_block_size
);
613 OPENSSL_assert(mac_secret_length
<= sizeof(hmac_pad
));
614 memcpy(hmac_pad
, mac_secret
, mac_secret_length
);
615 for (i
= 0; i
< md_block_size
; i
++)
618 md_transform(md_state
.c
, hmac_pad
);
621 if (length_is_big_endian
) {
622 memset(length_bytes
, 0, md_length_size
- 4);
623 length_bytes
[md_length_size
- 4] = (unsigned char)(bits
>> 24);
624 length_bytes
[md_length_size
- 3] = (unsigned char)(bits
>> 16);
625 length_bytes
[md_length_size
- 2] = (unsigned char)(bits
>> 8);
626 length_bytes
[md_length_size
- 1] = (unsigned char)bits
;
628 memset(length_bytes
, 0, md_length_size
);
629 length_bytes
[md_length_size
- 5] = (unsigned char)(bits
>> 24);
630 length_bytes
[md_length_size
- 6] = (unsigned char)(bits
>> 16);
631 length_bytes
[md_length_size
- 7] = (unsigned char)(bits
>> 8);
632 length_bytes
[md_length_size
- 8] = (unsigned char)bits
;
638 * The SSLv3 header is larger than a single block. overhang is
639 * the number of bytes beyond a single block that the header
640 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5).
642 unsigned overhang
= header_length
- md_block_size
;
643 md_transform(md_state
.c
, header
);
644 memcpy(first_block
, header
+ md_block_size
, overhang
);
645 memcpy(first_block
+ overhang
, data
, md_block_size
- overhang
);
646 md_transform(md_state
.c
, first_block
);
647 for (i
= 1; i
< k
/ md_block_size
- 1; i
++)
648 md_transform(md_state
.c
, data
+ md_block_size
* i
- overhang
);
650 /* k is a multiple of md_block_size. */
651 memcpy(first_block
, header
, 13);
652 memcpy(first_block
+ 13, data
, md_block_size
- 13);
653 md_transform(md_state
.c
, first_block
);
654 for (i
= 1; i
< k
/ md_block_size
; i
++)
655 md_transform(md_state
.c
, data
+ md_block_size
* i
- 13);
659 memset(mac_out
, 0, sizeof(mac_out
));
662 * We now process the final hash blocks. For each block, we construct it
663 * in constant time. If the |i==index_a| then we'll include the 0x80
664 * bytes and zero pad etc. For each block we selectively copy it, in
665 * constant time, to |mac_out|.
667 for (i
= num_starting_blocks
; i
<= num_starting_blocks
+ variance_blocks
;
669 unsigned char block
[MAX_HASH_BLOCK_SIZE
];
670 unsigned char is_block_a
= constant_time_eq_8(i
, index_a
);
671 unsigned char is_block_b
= constant_time_eq_8(i
, index_b
);
672 for (j
= 0; j
< md_block_size
; j
++) {
673 unsigned char b
= 0, is_past_c
, is_past_cp1
;
674 if (k
< header_length
)
676 else if (k
< data_plus_mac_plus_padding_size
+ header_length
)
677 b
= data
[k
- header_length
];
680 is_past_c
= is_block_a
& constant_time_ge_8(j
, c
);
681 is_past_cp1
= is_block_a
& constant_time_ge_8(j
, c
+ 1);
683 * If this is the block containing the end of the application
684 * data, and we are at the offset for the 0x80 value, then
685 * overwrite b with 0x80.
687 b
= constant_time_select_8(is_past_c
, 0x80, b
);
689 * If this the the block containing the end of the application
690 * data and we're past the 0x80 value then just write zero.
692 b
= b
& ~is_past_cp1
;
694 * If this is index_b (the final block), but not index_a (the end
695 * of the data), then the 64-bit length didn't fit into index_a
696 * and we're having to add an extra block of zeros.
698 b
&= ~is_block_b
| is_block_a
;
701 * The final bytes of one of the blocks contains the length.
703 if (j
>= md_block_size
- md_length_size
) {
704 /* If this is index_b, write a length byte. */
705 b
= constant_time_select_8(is_block_b
,
708 md_length_size
)], b
);
713 md_transform(md_state
.c
, block
);
714 md_final_raw(md_state
.c
, block
);
715 /* If this is index_b, copy the hash value to |mac_out|. */
716 for (j
= 0; j
< md_size
; j
++)
717 mac_out
[j
] |= block
[j
] & is_block_b
;
720 EVP_MD_CTX_init(&md_ctx
);
721 EVP_DigestInit_ex(&md_ctx
, ctx
->digest
, NULL
/* engine */ );
723 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
724 memset(hmac_pad
, 0x5c, sslv3_pad_length
);
726 EVP_DigestUpdate(&md_ctx
, mac_secret
, mac_secret_length
);
727 EVP_DigestUpdate(&md_ctx
, hmac_pad
, sslv3_pad_length
);
728 EVP_DigestUpdate(&md_ctx
, mac_out
, md_size
);
730 /* Complete the HMAC in the standard manner. */
731 for (i
= 0; i
< md_block_size
; i
++)
734 EVP_DigestUpdate(&md_ctx
, hmac_pad
, md_block_size
);
735 EVP_DigestUpdate(&md_ctx
, mac_out
, md_size
);
737 ret
= EVP_DigestFinal(&md_ctx
, md_out
, &md_out_size_u
);
738 if (ret
&& md_out_size
)
739 *md_out_size
= md_out_size_u
;
740 EVP_MD_CTX_cleanup(&md_ctx
);
744 * Due to the need to use EVP in FIPS mode we can't reimplement digests but
745 * we can ensure the number of blocks processed is equal for all cases by
746 * digesting additional data.
749 void tls_fips_digest_extra(const EVP_CIPHER_CTX
*cipher_ctx
,
750 EVP_MD_CTX
*mac_ctx
, const unsigned char *data
,
751 size_t data_len
, size_t orig_len
)
753 size_t block_size
, digest_pad
, blocks_data
, blocks_orig
;
754 if (EVP_CIPHER_CTX_mode(cipher_ctx
) != EVP_CIPH_CBC_MODE
)
756 block_size
= EVP_MD_CTX_block_size(mac_ctx
);
758 * We are in FIPS mode if we get this far so we know we have only SHA*
759 * digests and TLS to deal with.
760 * Minimum digest padding length is 17 for SHA384/SHA512 and 9
762 * Additional header is 13 bytes. To get the number of digest blocks
763 * processed round up the amount of data plus padding to the nearest
764 * block length. Block length is 128 for SHA384/SHA512 and 64 otherwise.
766 * blocks = (payload_len + digest_pad + 13 + block_size - 1)/block_size
768 * blocks = (payload_len + digest_pad + 12)/block_size + 1
769 * HMAC adds a constant overhead.
770 * We're ultimately only interested in differences so this becomes
771 * blocks = (payload_len + 29)/128
772 * for SHA384/SHA512 and
773 * blocks = (payload_len + 21)/64
776 digest_pad
= block_size
== 64 ? 21 : 29;
777 blocks_orig
= (orig_len
+ digest_pad
) / block_size
;
778 blocks_data
= (data_len
+ digest_pad
) / block_size
;
780 * MAC enough blocks to make up the difference between the original and
781 * actual lengths plus one extra block to ensure this is never a no op.
782 * The "data" pointer should always have enough space to perform this
783 * operation as it is large enough for a maximum length TLS buffer.
785 EVP_DigestSignUpdate(mac_ctx
, data
,
786 (blocks_orig
- blocks_data
+ 1) * block_size
);