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1/* $OpenBSD: s3_cbc.c,v 1.12 2016/03/20 16:50:29 krw Exp $ */
2/* ====================================================================
3 * Copyright (c) 2012 The OpenSSL Project. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 *
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
15 * distribution.
16 *
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/)"
21 *
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.
26 *
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.
30 *
31 * 6. Redistributions of any form whatsoever must retain the following
32 * acknowledgment:
33 * "This product includes software developed by the OpenSSL Project
34 * for use in the OpenSSL Toolkit (http://www.openssl.org/)"
35 *
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 * ====================================================================
49 *
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).
53 *
54 */
55
56#include "ssl_locl.h"
57
58#include <openssl/md5.h>
59#include <openssl/sha.h>
60
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
64
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
69
70/* Some utility functions are needed:
71 *
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)))
78
79/* constant_time_lt returns 0xff if a<b and 0x00 otherwise. */
80static unsigned
81constant_time_lt(unsigned a, unsigned b)
82{
83 a -= b;
84 return DUPLICATE_MSB_TO_ALL(a);
85}
86
87/* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */
88static unsigned
89constant_time_ge(unsigned a, unsigned b)
90{
91 a -= b;
92 return DUPLICATE_MSB_TO_ALL(~a);
93}
94
95/* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */
96static unsigned char
97constant_time_eq_8(unsigned a, unsigned b)
98{
99 unsigned c = a ^ b;
100 c--;
101 return DUPLICATE_MSB_TO_ALL_8(c);
102}
103
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.
109 *
110 * block_size: the block size of the cipher used to encrypt the record.
111 * returns:
112 * 0: (in non-constant time) if the record is publicly invalid.
113 * 1: if the padding was valid
114 * -1: otherwise. */
115int
116tls1_cbc_remove_padding(const SSL* s, SSL3_RECORD *rec, unsigned block_size,
117 unsigned mac_size)
118{
119 unsigned padding_length, good, to_check, i;
120 const unsigned overhead = 1 /* padding length byte */ + mac_size;
121
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
125 * non-constant time.
126 */
127 if (overhead + block_size > rec->length)
128 return 0;
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)
134 return 0;
135
136 padding_length = rec->data[rec->length - 1];
137
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;
141 return 1;
142 }
143
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
148 * bytes of padding.
149 *
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;
157
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));
164 }
165
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
169 * bits. */
170 good &= good >> 4;
171 good &= good >> 2;
172 good &= good >> 1;
173 good <<= sizeof(good)*8 - 1;
174 good = DUPLICATE_MSB_TO_ALL(good);
175
176 padding_length = good & (padding_length + 1);
177 rec->length -= padding_length;
178 rec->type |= padding_length<<8; /* kludge: pass padding length */
179
180 return (int)((good & 1) | (~good & -1));
181}
182
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).
186 *
187 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to
188 * this function.
189 *
190 * On entry:
191 * rec->orig_len >= md_size
192 * md_size <= EVP_MAX_MD_SIZE
193 *
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.
199 */
200#define CBC_MAC_ROTATE_IN_PLACE
201
202void
203ssl3_cbc_copy_mac(unsigned char* out, const SSL3_RECORD *rec,
204 unsigned md_size, unsigned orig_len)
205{
206#if defined(CBC_MAC_ROTATE_IN_PLACE)
207 unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE];
208 unsigned char *rotated_mac;
209#else
210 unsigned char rotated_mac[EVP_MAX_MD_SIZE];
211#endif
212
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;
219 unsigned i, j;
220 unsigned div_spoiler;
221 unsigned rotate_offset;
222
223 OPENSSL_assert(orig_len >= md_size);
224 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
225
226#if defined(CBC_MAC_ROTATE_IN_PLACE)
227 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf)&63);
228#endif
229
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.
236 *
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;
243
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);
251 }
252
253 /* Now rotate the MAC */
254#if defined(CBC_MAC_ROTATE_IN_PLACE)
255 j = 0;
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);
261 }
262#else
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);
269 rotate_offset++;
270 rotate_offset &= constant_time_lt(rotate_offset, md_size);
271 }
272#endif
273}
274
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))
282
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
285 * typically does. */
286static void
287tls1_md5_final_raw(void* ctx, unsigned char *md_out)
288{
289 MD5_CTX *md5 = ctx;
290 u32toLE(md5->A, md_out);
291 u32toLE(md5->B, md_out);
292 u32toLE(md5->C, md_out);
293 u32toLE(md5->D, md_out);
294}
295
296static void
297tls1_sha1_final_raw(void* ctx, unsigned char *md_out)
298{
299 SHA_CTX *sha1 = ctx;
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);
305}
306#define LARGEST_DIGEST_CTX SHA_CTX
307
308static void
309tls1_sha256_final_raw(void* ctx, unsigned char *md_out)
310{
311 SHA256_CTX *sha256 = ctx;
312 unsigned i;
313
314 for (i = 0; i < 8; i++) {
315 l2n(sha256->h[i], md_out);
316 }
317}
318#undef LARGEST_DIGEST_CTX
319#define LARGEST_DIGEST_CTX SHA256_CTX
320
321static void
322tls1_sha512_final_raw(void* ctx, unsigned char *md_out)
323{
324 SHA512_CTX *sha512 = ctx;
325 unsigned i;
326
327 for (i = 0; i < 8; i++) {
328 l2n8(sha512->h[i], md_out);
329 }
330}
331#undef LARGEST_DIGEST_CTX
332#define LARGEST_DIGEST_CTX SHA512_CTX
333
334/* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
335 * which ssl3_cbc_digest_record supports. */
336char
337ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx)
338{
339 switch (EVP_MD_CTX_type(ctx)) {
340 case NID_md5:
341 case NID_sha1:
342 case NID_sha224:
343 case NID_sha256:
344 case NID_sha384:
345 case NID_sha512:
346 return 1;
347 default:
348 return 0;
349 }
350}
351
352/* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
353 * record.
354 *
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.
366 *
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
370 * padding too. ) */
371int
372ssl3_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)
377{
378 union { double align;
379 unsigned char c[sizeof(LARGEST_DIGEST_CTX)];
380 } md_state;
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;
394 EVP_MD_CTX md_ctx;
395 /* mdLengthSize is the number of bytes in the length field that terminates
396 * the hash. */
397 unsigned md_length_size = 8;
398 char length_is_big_endian = 1;
399
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);
403
404 switch (EVP_MD_CTX_type(ctx)) {
405 case NID_md5:
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;
409 md_size = 16;
410 sslv3_pad_length = 48;
411 length_is_big_endian = 0;
412 break;
413 case NID_sha1:
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;
417 md_size = 20;
418 break;
419 case NID_sha224:
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;
423 md_size = 224/8;
424 break;
425 case NID_sha256:
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;
429 md_size = 32;
430 break;
431 case NID_sha384:
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;
435 md_size = 384/8;
436 md_block_size = 128;
437 md_length_size = 16;
438 break;
439 case NID_sha512:
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;
443 md_size = 64;
444 md_block_size = 128;
445 md_length_size = 16;
446 break;
447 default:
448 /* ssl3_cbc_record_digest_supported should have been
449 * called first to check that the hash function is
450 * supported. */
451 OPENSSL_assert(0);
452 if (md_out_size)
453 *md_out_size = 0;
454 return 0;
455 }
456
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);
460
461 header_length = 13;
462 if (is_sslv3) {
463 header_length = mac_secret_length + sslv3_pad_length +
464 8 /* sequence number */ +
465 1 /* record type */ +
466 2 /* record length */;
467 }
468
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
471 * padding value.
472 *
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.
478 *
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.
482 *
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
488 * (SSLv3) */
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. */
504 k = 0;
505 /* mac_end_offset is the index just past the end of the data to be
506 * MACed. */
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
512 * value. */
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
519 * SSLv3. */
520
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;
526 }
527
528 bits = 8*mac_end_offset;
529 if (!is_sslv3) {
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++)
538 hmac_pad[i] ^= 0x36;
539
540 md_transform(md_state.c, hmac_pad);
541 }
542
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;
549 } else {
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;
555 }
556
557 if (k > 0) {
558 if (is_sslv3) {
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);
570 } else {
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);
577 }
578 }
579
580 memset(mac_out, 0, sizeof(mac_out));
581
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)
593 b = header[k];
594 else if (k < data_plus_mac_plus_padding_size + header_length)
595 b = data[k - header_length];
596 k++;
597
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. */
607 b = b&~is_past_cp1;
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;
613
614 /* The final bytes of one of the blocks contains the
615 * length. */
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)]);
619 }
620 block[j] = b;
621 }
622
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;
628 }
629
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);
633 return 0;
634 }
635 if (is_sslv3) {
636 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
637 memset(hmac_pad, 0x5c, sslv3_pad_length);
638
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);
642 } else {
643 /* Complete the HMAC in the standard manner. */
644 for (i = 0; i < md_block_size; i++)
645 hmac_pad[i] ^= 0x6a;
646
647 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size);
648 EVP_DigestUpdate(&md_ctx, mac_out, md_size);
649 }
650 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
651 if (md_out_size)
652 *md_out_size = md_out_size_u;
653 EVP_MD_CTX_cleanup(&md_ctx);
654
655 return 1;
656}
generated by cgit v1.2.3-55-g6feb (git 2.39.1) at 2025-05-09 19:45:02 +0000