1 /* ssl/s3_cbc.c */
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. */
80 static unsigned constant_time_lt(unsigned a, unsigned b)
81 {
82 a -= b;
83 return DUPLICATE_MSB_TO_ALL(a);
84 }
85
86 /* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */
87 static unsigned constant_time_ge(unsigned a, unsigned b)
88 {
89 a -= b;
90 return DUPLICATE_MSB_TO_ALL(~a);
91 }
92
93 /* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */
94 static unsigned char constant_time_eq_8(unsigned a, unsigned b)
95 {
96 unsigned c = a ^ b;
97 c--;
98 return DUPLICATE_MSB_TO_ALL_8(c);
99 }
100
101 /* ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC
102 * record in |rec| by updating |rec->length| in constant time.
103 *
104 * block_size: the block size of the cipher used to encrypt the record.
105 * returns:
106 * 0: (in non-constant time) if the record is publicly invalid.
107 * 1: if the padding was valid
108 * -1: otherwise. */
109 int ssl3_cbc_remove_padding(const SSL* s,
110 SSL3_RECORD *rec,
111 unsigned block_size,
112 unsigned mac_size)
113 {
114 unsigned padding_length, good;
115 const unsigned overhead = 1 /* padding length byte */ + mac_size;
116
117 /* These lengths are all public so we can test them in non-constant
118 * time. */
119 if (overhead > rec->length)
120 return 0;
121
122 padding_length = rec->data[rec->length-1];
123 good = constant_time_ge(rec->length, padding_length+overhead);
124 /* SSLv3 requires that the padding is minimal. */
125 good &= constant_time_ge(block_size, padding_length+1);
126 padding_length = good & (padding_length+1);
127 rec->length -= padding_length;
128 rec->type |= padding_length<<8; /* kludge: pass padding length */
129 return (int)((good & 1) | (~good & -1));
130 }
131
132 /* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
133 * record in |rec| in constant time and returns 1 if the padding is valid and
134 * -1 otherwise. It also removes any explicit IV from the start of the record
135 * without leaking any timing about whether there was enough space after the
136 * padding was removed.
137 *
138 * block_size: the block size of the cipher used to encrypt the record.
139 * returns:
140 * 0: (in non-constant time) if the record is publicly invalid.
141 * 1: if the padding was valid
142 * -1: otherwise. */
143 int tls1_cbc_remove_padding(const SSL* s,
144 SSL3_RECORD *rec,
145 unsigned block_size,
146 unsigned mac_size)
147 {
148 unsigned padding_length, good, to_check, i;
149 const unsigned overhead = 1 /* padding length byte */ + mac_size;
150 /* Check if version requires explicit IV */
151 if (s->version >= TLS1_1_VERSION || s->version == DTLS1_BAD_VER)
152 {
153 /* These lengths are all public so we can test them in
154 * non-constant time.
155 */
156 if (overhead + block_size > rec->length)
157 return 0;
158 /* We can now safely skip explicit IV */
159 rec->data += block_size;
160 rec->input += block_size;
161 rec->length -= block_size;
162 }
163 else if (overhead > rec->length)
164 return 0;
165
166 padding_length = rec->data[rec->length-1];
167
168 /* NB: if compression is in operation the first packet may not be of
169 * even length so the padding bug check cannot be performed. This bug
170 * workaround has been around since SSLeay so hopefully it is either
171 * fixed now or no buggy implementation supports compression [steve]
172 */
173 if ( (s->options&SSL_OP_TLS_BLOCK_PADDING_BUG) && !s->expand)
174 {
175 /* First packet is even in size, so check */
176 if ((memcmp(s->s3->read_sequence, "\0\0\0\0\0\0\0\0",8) == 0) &&
177 !(padding_length & 1))
178 {
179 s->s3->flags|=TLS1_FLAGS_TLS_PADDING_BUG;
180 }
181 if ((s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) &&
182 padding_length > 0)
183 {
184 padding_length--;
185 }
186 }
187
188 if (EVP_CIPHER_flags(s->enc_read_ctx->cipher)&EVP_CIPH_FLAG_AEAD_CIPHER)
189 {
190 /* padding is already verified */
191 rec->length -= padding_length + 1;
192 return 1;
193 }
194
195 good = constant_time_ge(rec->length, overhead+padding_length);
196 /* The padding consists of a length byte at the end of the record and
197 * then that many bytes of padding, all with the same value as the
198 * length byte. Thus, with the length byte included, there are i+1
199 * bytes of padding.
200 *
201 * We can't check just |padding_length+1| bytes because that leaks
202 * decrypted information. Therefore we always have to check the maximum
203 * amount of padding possible. (Again, the length of the record is
204 * public information so we can use it.) */
205 to_check = 255; /* maximum amount of padding. */
206 if (to_check > rec->length-1)
207 to_check = rec->length-1;
208
209 for (i = 0; i < to_check; i++)
210 {
211 unsigned char mask = constant_time_ge(padding_length, i);
212 unsigned char b = rec->data[rec->length-1-i];
213 /* The final |padding_length+1| bytes should all have the value
214 * |padding_length|. Therefore the XOR should be zero. */
215 good &= ~(mask&(padding_length ^ b));
216 }
217
218 /* If any of the final |padding_length+1| bytes had the wrong value,
219 * one or more of the lower eight bits of |good| will be cleared. We
220 * AND the bottom 8 bits together and duplicate the result to all the
221 * bits. */
222 good &= good >> 4;
223 good &= good >> 2;
224 good &= good >> 1;
225 good <<= sizeof(good)*8-1;
226 good = DUPLICATE_MSB_TO_ALL(good);
227
228 padding_length = good & (padding_length+1);
229 rec->length -= padding_length;
230 rec->type |= padding_length<<8; /* kludge: pass padding length */
231
232 return (int)((good & 1) | (~good & -1));
233 }
234
235 /* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
236 * constant time (independent of the concrete value of rec->length, which may
237 * vary within a 256-byte window).
238 *
239 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to
240 * this function.
241 *
242 * On entry:
243 * rec->orig_len >= md_size
244 * md_size <= EVP_MAX_MD_SIZE
245 *
246 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with
247 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into
248 * a single or pair of cache-lines, then the variable memory accesses don't
249 * actually affect the timing. CPUs with smaller cache-lines [if any] are
250 * not multi-core and are not considered vulnerable to cache-timing attacks.
251 */
252 #define CBC_MAC_ROTATE_IN_PLACE
253
254 void ssl3_cbc_copy_mac(unsigned char* out,
255 const SSL3_RECORD *rec,
256 unsigned md_size,unsigned orig_len)
257 {
258 #if defined(CBC_MAC_ROTATE_IN_PLACE)
259 unsigned char rotated_mac_buf[64+EVP_MAX_MD_SIZE];
260 unsigned char *rotated_mac;
261 #else
262 unsigned char rotated_mac[EVP_MAX_MD_SIZE];
263 #endif
264
265 /* mac_end is the index of |rec->data| just after the end of the MAC. */
266 unsigned mac_end = rec->length;
267 unsigned mac_start = mac_end - md_size;
268 /* scan_start contains the number of bytes that we can ignore because
269 * the MAC's position can only vary by 255 bytes. */
270 unsigned scan_start = 0;
271 unsigned i, j;
272 unsigned div_spoiler;
273 unsigned rotate_offset;
274
275 OPENSSL_assert(orig_len >= md_size);
276 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
277
278 #if defined(CBC_MAC_ROTATE_IN_PLACE)
279 rotated_mac = rotated_mac_buf + ((0-(size_t)rotated_mac_buf)&63);
280 #endif
281
282 /* This information is public so it's safe to branch based on it. */
283 if (orig_len > md_size + 255 + 1)
284 scan_start = orig_len - (md_size + 255 + 1);
285 /* div_spoiler contains a multiple of md_size that is used to cause the
286 * modulo operation to be constant time. Without this, the time varies
287 * based on the amount of padding when running on Intel chips at least.
288 *
289 * The aim of right-shifting md_size is so that the compiler doesn't
290 * figure out that it can remove div_spoiler as that would require it
291 * to prove that md_size is always even, which I hope is beyond it. */
292 div_spoiler = md_size >> 1;
293 div_spoiler <<= (sizeof(div_spoiler)-1)*8;
294 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size;
295
296 memset(rotated_mac, 0, md_size);
297 for (i = scan_start, j = 0; i < orig_len; i++)
298 {
299 unsigned char mac_started = constant_time_ge(i, mac_start);
300 unsigned char mac_ended = constant_time_ge(i, mac_end);
301 unsigned char b = rec->data[i];
302 rotated_mac[j++] |= b & mac_started & ~mac_ended;
303 j &= constant_time_lt(j,md_size);
304 }
305
306 /* Now rotate the MAC */
307 #if defined(CBC_MAC_ROTATE_IN_PLACE)
308 j = 0;
309 for (i = 0; i < md_size; i++)
310 {
311 /* in case cache-line is 32 bytes, touch second line */
312 ((volatile unsigned char *)rotated_mac)[rotate_offset^32];
313 out[j++] = rotated_mac[rotate_offset++];
314 rotate_offset &= constant_time_lt(rotate_offset,md_size);
315 }
316 #else
317 memset(out, 0, md_size);
318 rotate_offset = md_size - rotate_offset;
319 rotate_offset &= constant_time_lt(rotate_offset,md_size);
320 for (i = 0; i < md_size; i++)
321 {
322 for (j = 0; j < md_size; j++)
323 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset);
324 rotate_offset++;
325 rotate_offset &= constant_time_lt(rotate_offset,md_size);
326 }
327 #endif
328 }
329
330 /* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
331 * little-endian order. The value of p is advanced by four. */
332 #define u32toLE(n, p) \
333 (*((p)++)=(unsigned char)(n), \
334 *((p)++)=(unsigned char)(n>>8), \
335 *((p)++)=(unsigned char)(n>>16), \
336 *((p)++)=(unsigned char)(n>>24))
337
338 /* These functions serialize the state of a hash and thus perform the standard
339 * "final" operation without adding the padding and length that such a function
340 * typically does. */
341 static void tls1_md5_final_raw(void* ctx, unsigned char *md_out)
342 {
343 MD5_CTX *md5 = ctx;
344 u32toLE(md5->A, md_out);
345 u32toLE(md5->B, md_out);
346 u32toLE(md5->C, md_out);
347 u32toLE(md5->D, md_out);
348 }
349
350 static void tls1_sha1_final_raw(void* ctx, unsigned char *md_out)
351 {
352 SHA_CTX *sha1 = ctx;
353 l2n(sha1->h0, md_out);
354 l2n(sha1->h1, md_out);
355 l2n(sha1->h2, md_out);
356 l2n(sha1->h3, md_out);
357 l2n(sha1->h4, md_out);
358 }
359 #define LARGEST_DIGEST_CTX SHA_CTX
360
361 #ifndef OPENSSL_NO_SHA256
362 static void tls1_sha256_final_raw(void* ctx, unsigned char *md_out)
363 {
364 SHA256_CTX *sha256 = ctx;
365 unsigned i;
366
367 for (i = 0; i < 8; i++)
368 {
369 l2n(sha256->h[i], md_out);
370 }
371 }
372 #undef LARGEST_DIGEST_CTX
373 #define LARGEST_DIGEST_CTX SHA256_CTX
374 #endif
375
376 #ifndef OPENSSL_NO_SHA512
377 static void tls1_sha512_final_raw(void* ctx, unsigned char *md_out)
378 {
379 SHA512_CTX *sha512 = ctx;
380 unsigned i;
381
382 for (i = 0; i < 8; i++)
383 {
384 l2n8(sha512->h[i], md_out);
385 }
386 }
387 #undef LARGEST_DIGEST_CTX
388 #define LARGEST_DIGEST_CTX SHA512_CTX
389 #endif
390
391 /* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
392 * which ssl3_cbc_digest_record supports. */
393 char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx)
394 {
395 #ifdef OPENSSL_FIPS
396 if (FIPS_mode())
397 return 0;
398 #endif
399 switch (EVP_MD_CTX_type(ctx))
400 {
401 case NID_md5:
402 case NID_sha1:
403 #ifndef OPENSSL_NO_SHA256
404 case NID_sha224:
405 case NID_sha256:
406 #endif
407 #ifndef OPENSSL_NO_SHA512
408 case NID_sha384:
409 case NID_sha512:
410 #endif
411 return 1;
412 default:
413 return 0;
414 }
415 }
416
417 /* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
418 * record.
419 *
420 * ctx: the EVP_MD_CTX from which we take the hash function.
421 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX.
422 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
423 * md_out_size: if non-NULL, the number of output bytes is written here.
424 * header: the 13-byte, TLS record header.
425 * data: the record data itself, less any preceeding explicit IV.
426 * data_plus_mac_size: the secret, reported length of the data and MAC
427 * once the padding has been removed.
428 * data_plus_mac_plus_padding_size: the public length of the whole
429 * record, including padding.
430 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS.
431 *
432 * On entry: by virtue of having been through one of the remove_padding
433 * functions, above, we know that data_plus_mac_size is large enough to contain
434 * a padding byte and MAC. (If the padding was invalid, it might contain the
435 * padding too. ) */
436 void ssl3_cbc_digest_record(
437 const EVP_MD_CTX *ctx,
438 unsigned char* md_out,
439 size_t* md_out_size,
440 const unsigned char header[13],
441 const unsigned char *data,
442 size_t data_plus_mac_size,
443 size_t data_plus_mac_plus_padding_size,
444 const unsigned char *mac_secret,
445 unsigned mac_secret_length,
446 char is_sslv3)
447 {
448 union { double align;
449 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; } md_state;
450 void (*md_final_raw)(void *ctx, unsigned char *md_out);
451 void (*md_transform)(void *ctx, const unsigned char *block);
452 unsigned md_size, md_block_size = 64;
453 unsigned sslv3_pad_length = 40, header_length, variance_blocks,
454 len, max_mac_bytes, num_blocks,
455 num_starting_blocks, k, mac_end_offset, c, index_a, index_b;
456 unsigned int bits; /* at most 18 bits */
457 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES];
458 /* hmac_pad is the masked HMAC key. */
459 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE];
460 unsigned char first_block[MAX_HASH_BLOCK_SIZE];
461 unsigned char mac_out[EVP_MAX_MD_SIZE];
462 unsigned i, j, md_out_size_u;
463 EVP_MD_CTX md_ctx;
464 /* mdLengthSize is the number of bytes in the length field that terminates
465 * the hash. */
466 unsigned md_length_size = 8;
467 char length_is_big_endian = 1;
468
469 /* This is a, hopefully redundant, check that allows us to forget about
470 * many possible overflows later in this function. */
471 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024);
472
473 switch (EVP_MD_CTX_type(ctx))
474 {
475 case NID_md5:
476 MD5_Init((MD5_CTX*)md_state.c);
477 md_final_raw = tls1_md5_final_raw;
478 md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform;
479 md_size = 16;
480 sslv3_pad_length = 48;
481 length_is_big_endian = 0;
482 break;
483 case NID_sha1:
484 SHA1_Init((SHA_CTX*)md_state.c);
485 md_final_raw = tls1_sha1_final_raw;
486 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform;
487 md_size = 20;
488 break;
489 #ifndef OPENSSL_NO_SHA256
490 case NID_sha224:
491 SHA224_Init((SHA256_CTX*)md_state.c);
492 md_final_raw = tls1_sha256_final_raw;
493 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform;
494 md_size = 224/8;
495 break;
496 case NID_sha256:
497 SHA256_Init((SHA256_CTX*)md_state.c);
498 md_final_raw = tls1_sha256_final_raw;
499 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform;
500 md_size = 32;
501 break;
502 #endif
503 #ifndef OPENSSL_NO_SHA512
504 case NID_sha384:
505 SHA384_Init((SHA512_CTX*)md_state.c);
506 md_final_raw = tls1_sha512_final_raw;
507 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform;
508 md_size = 384/8;
509 md_block_size = 128;
510 md_length_size = 16;
511 break;
512 case NID_sha512:
513 SHA512_Init((SHA512_CTX*)md_state.c);
514 md_final_raw = tls1_sha512_final_raw;
515 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform;
516 md_size = 64;
517 md_block_size = 128;
518 md_length_size = 16;
519 break;
520 #endif
521 default:
522 /* ssl3_cbc_record_digest_supported should have been
523 * called first to check that the hash function is
524 * supported. */
525 OPENSSL_assert(0);
526 if (md_out_size)
527 *md_out_size = -1;
528 return;
529 }
530
531 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES);
532 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE);
533 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
534
535 header_length = 13;
536 if (is_sslv3)
537 {
538 header_length =
539 mac_secret_length +
540 sslv3_pad_length +
541 8 /* sequence number */ +
542 1 /* record type */ +
543 2 /* record length */;
544 }
545
546 /* variance_blocks is the number of blocks of the hash that we have to
547 * calculate in constant time because they could be altered by the
548 * padding value.
549 *
550 * In SSLv3, the padding must be minimal so the end of the plaintext
551 * varies by, at most, 15+20 = 35 bytes. (We conservatively assume that
552 * the MAC size varies from 0..20 bytes.) In case the 9 bytes of hash
553 * termination (0x80 + 64-bit length) don't fit in the final block, we
554 * say that the final two blocks can vary based on the padding.
555 *
556 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
557 * required to be minimal. Therefore we say that the final six blocks
558 * can vary based on the padding.
559 *
560 * Later in the function, if the message is short and there obviously
561 * cannot be this many blocks then variance_blocks can be reduced. */
562 variance_blocks = is_sslv3 ? 2 : 6;
563 /* From now on we're dealing with the MAC, which conceptually has 13
564 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
565 * (SSLv3) */
566 len = data_plus_mac_plus_padding_size + header_length;
567 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including
568 * |header|, assuming that there's no padding. */
569 max_mac_bytes = len - md_size - 1;
570 /* num_blocks is the maximum number of hash blocks. */
571 num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size;
572 /* In order to calculate the MAC in constant time we have to handle
573 * the final blocks specially because the padding value could cause the
574 * end to appear somewhere in the final |variance_blocks| blocks and we
575 * can't leak where. However, |num_starting_blocks| worth of data can
576 * be hashed right away because no padding value can affect whether
577 * they are plaintext. */
578 num_starting_blocks = 0;
579 /* k is the starting byte offset into the conceptual header||data where
580 * we start processing. */
581 k = 0;
582 /* mac_end_offset is the index just past the end of the data to be
583 * MACed. */
584 mac_end_offset = data_plus_mac_size + header_length - md_size;
585 /* c is the index of the 0x80 byte in the final hash block that
586 * contains application data. */
587 c = mac_end_offset % md_block_size;
588 /* index_a is the hash block number that contains the 0x80 terminating
589 * value. */
590 index_a = mac_end_offset / md_block_size;
591 /* index_b is the hash block number that contains the 64-bit hash
592 * length, in bits. */
593 index_b = (mac_end_offset + md_length_size) / md_block_size;
594 /* bits is the hash-length in bits. It includes the additional hash
595 * block for the masked HMAC key, or whole of |header| in the case of
596 * SSLv3. */
597
598 /* For SSLv3, if we're going to have any starting blocks then we need
599 * at least two because the header is larger than a single block. */
600 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0))
601 {
602 num_starting_blocks = num_blocks - variance_blocks;
603 k = md_block_size*num_starting_blocks;
604 }
605
606 bits = 8*mac_end_offset;
607 if (!is_sslv3)
608 {
609 /* Compute the initial HMAC block. For SSLv3, the padding and
610 * secret bytes are included in |header| because they take more
611 * than a single block. */
612 bits += 8*md_block_size;
613 memset(hmac_pad, 0, md_block_size);
614 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad));
615 memcpy(hmac_pad, mac_secret, mac_secret_length);
616 for (i = 0; i < md_block_size; i++)
617 hmac_pad[i] ^= 0x36;
618
619 md_transform(md_state.c, hmac_pad);
620 }
621
622 if (length_is_big_endian)
623 {
624 memset(length_bytes,0,md_length_size-4);
625 length_bytes[md_length_size-4] = (unsigned char)(bits>>24);
626 length_bytes[md_length_size-3] = (unsigned char)(bits>>16);
627 length_bytes[md_length_size-2] = (unsigned char)(bits>>8);
628 length_bytes[md_length_size-1] = (unsigned char)bits;
629 }
630 else
631 {
632 memset(length_bytes,0,md_length_size);
633 length_bytes[md_length_size-5] = (unsigned char)(bits>>24);
634 length_bytes[md_length_size-6] = (unsigned char)(bits>>16);
635 length_bytes[md_length_size-7] = (unsigned char)(bits>>8);
636 length_bytes[md_length_size-8] = (unsigned char)bits;
637 }
638
639 if (k > 0)
640 {
641 if (is_sslv3)
642 {
643 /* The SSLv3 header is larger than a single block.
644 * overhang is the number of bytes beyond a single
645 * block that the header consumes: either 7 bytes
646 * (SHA1) or 11 bytes (MD5). */
647 unsigned overhang = header_length-md_block_size;
648 md_transform(md_state.c, header);
649 memcpy(first_block, header + md_block_size, overhang);
650 memcpy(first_block + overhang, data, md_block_size-overhang);
651 md_transform(md_state.c, first_block);
652 for (i = 1; i < k/md_block_size - 1; i++)
653 md_transform(md_state.c, data + md_block_size*i - overhang);
654 }
655 else
656 {
657 /* k is a multiple of md_block_size. */
658 memcpy(first_block, header, 13);
659 memcpy(first_block+13, data, md_block_size-13);
660 md_transform(md_state.c, first_block);
661 for (i = 1; i < k/md_block_size; i++)
662 md_transform(md_state.c, data + md_block_size*i - 13);
663 }
664 }
665
666 memset(mac_out, 0, sizeof(mac_out));
667
668 /* We now process the final hash blocks. For each block, we construct
669 * it in constant time. If the |i==index_a| then we'll include the 0x80
670 * bytes and zero pad etc. For each block we selectively copy it, in
671 * constant time, to |mac_out|. */
672 for (i = num_starting_blocks; i <= num_starting_blocks+variance_blocks; i++)
673 {
674 unsigned char block[MAX_HASH_BLOCK_SIZE];
675 unsigned char is_block_a = constant_time_eq_8(i, index_a);
676 unsigned char is_block_b = constant_time_eq_8(i, index_b);
677 for (j = 0; j < md_block_size; j++)
678 {
679 unsigned char b = 0, is_past_c, is_past_cp1;
680 if (k < header_length)
681 b = header[k];
682 else if (k < data_plus_mac_plus_padding_size + header_length)
683 b = data[k-header_length];
684 k++;
685
686 is_past_c = is_block_a & constant_time_ge(j, c);
687 is_past_cp1 = is_block_a & constant_time_ge(j, c+1);
688 /* If this is the block containing the end of the
689 * application data, and we are at the offset for the
690 * 0x80 value, then overwrite b with 0x80. */
691 b = (b&~is_past_c) | (0x80&is_past_c);
692 /* If this the the block containing the end of the
693 * application data and we're past the 0x80 value then
694 * just write zero. */
695 b = b&~is_past_cp1;
696 /* If this is index_b (the final block), but not
697 * index_a (the end of the data), then the 64-bit
698 * length didn't fit into index_a and we're having to
699 * add an extra block of zeros. */
700 b &= ~is_block_b | is_block_a;
701
702 /* The final bytes of one of the blocks contains the
703 * length. */
704 if (j >= md_block_size - md_length_size)
705 {
706 /* If this is index_b, write a length byte. */
707 b = (b&~is_block_b) | (is_block_b&length_bytes[j-(md_block_size-md_length_size)]);
708 }
709 block[j] = b;
710 }
711
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;
717 }
718
719 EVP_MD_CTX_init(&md_ctx);
720 EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */);
721 if (is_sslv3)
722 {
723 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
724 memset(hmac_pad, 0x5c, sslv3_pad_length);
725
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);
729 }
730 else
731 {
732 /* Complete the HMAC in the standard manner. */
733 for (i = 0; i < md_block_size; i++)
734 hmac_pad[i] ^= 0x6a;
735
736 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size);
737 EVP_DigestUpdate(&md_ctx, mac_out, md_size);
738 }
739 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
740 if (md_out_size)
741 *md_out_size = md_out_size_u;
742 EVP_MD_CTX_cleanup(&md_ctx);
743 }
744
745 #ifdef OPENSSL_FIPS
746
747 /* Due to the need to use EVP in FIPS mode we can't reimplement digests but
748 * we can ensure the number of blocks processed is equal for all cases
749 * by digesting additional data.
750 */
751
752 void tls_fips_digest_extra(
753 const EVP_CIPHER_CTX *cipher_ctx, EVP_MD_CTX *mac_ctx,
754 const unsigned char *data, size_t data_len, size_t orig_len)
755 {
756 size_t block_size, digest_pad, blocks_data, blocks_orig;
757 if (EVP_CIPHER_CTX_mode(cipher_ctx) != EVP_CIPH_CBC_MODE)
758 return;
759 block_size = EVP_MD_CTX_block_size(mac_ctx);
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.
762 * Minimum digest padding length is 17 for SHA384/SHA512 and 9
763 * otherwise.
764 * Additional header is 13 bytes. To get the number of digest blocks
765 * processed round up the amount of data plus padding to the nearest
766 * block length. Block length is 128 for SHA384/SHA512 and 64 otherwise.
767 * So we have:
768 * blocks = (payload_len + digest_pad + 13 + block_size - 1)/block_size
769 * equivalently:
770 * blocks = (payload_len + digest_pad + 12)/block_size + 1
771 * HMAC adds a constant overhead.
772 * We're ultimately only interested in differences so this becomes
773 * blocks = (payload_len + 29)/128
774 * for SHA384/SHA512 and
775 * blocks = (payload_len + 21)/64
776 * otherwise.
777 */
778 digest_pad = block_size == 64 ? 21 : 29;
779 blocks_orig = (orig_len + digest_pad)/block_size;
780 blocks_data = (data_len + digest_pad)/block_size;
781 /* MAC enough blocks to make up the difference between the original
782 * and actual lengths plus one extra block to ensure this is never a
783 * no op. The "data" pointer should always have enough space to
784 * perform this operation as it is large enough for a maximum
785 * length TLS buffer.
786 */
787 EVP_DigestSignUpdate(mac_ctx, data,
788 (blocks_orig - blocks_data + 1) * block_size);
789 }
790 #endif