1/* ==================================================================== 2 * Copyright (c) 2012 The OpenSSL Project. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in 13 * the documentation and/or other materials provided with the 14 * distribution. 15 * 16 * 3. All advertising materials mentioning features or use of this 17 * software must display the following acknowledgment: 18 * "This product includes software developed by the OpenSSL Project 19 * for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 20 * 21 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 22 * endorse or promote products derived from this software without 23 * prior written permission. For written permission, please contact 24 * openssl-core@openssl.org. 25 * 26 * 5. Products derived from this software may not be called "OpenSSL" 27 * nor may "OpenSSL" appear in their names without prior written 28 * permission of the OpenSSL Project. 29 * 30 * 6. Redistributions of any form whatsoever must retain the following 31 * acknowledgment: 32 * "This product includes software developed by the OpenSSL Project 33 * for use in the OpenSSL Toolkit (http://www.openssl.org/)" 34 * 35 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 36 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 37 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 38 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 39 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 40 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 41 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 42 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 43 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 44 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 45 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 46 * OF THE POSSIBILITY OF SUCH DAMAGE. 47 * ==================================================================== 48 * 49 * This product includes cryptographic software written by Eric Young 50 * (eay@cryptsoft.com). This product includes software written by Tim 51 * Hudson (tjh@cryptsoft.com). */ 52 53#include <assert.h> 54 55#include <openssl/obj.h> 56#include <openssl/sha.h> 57 58#include "ssl_locl.h" 59 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 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. */ 87static 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. */ 94static 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. */ 109int 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. */ 143int 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 (SSL_USE_EXPLICIT_IV(s)) 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 good = constant_time_ge(rec->length, overhead+padding_length); 169 /* The padding consists of a length byte at the end of the record and 170 * then that many bytes of padding, all with the same value as the 171 * length byte. Thus, with the length byte included, there are i+1 172 * bytes of padding. 173 * 174 * We can't check just |padding_length+1| bytes because that leaks 175 * decrypted information. Therefore we always have to check the maximum 176 * amount of padding possible. (Again, the length of the record is 177 * public information so we can use it.) */ 178 to_check = 256; /* maximum amount of padding, inc length byte. */ 179 if (to_check > rec->length) 180 to_check = rec->length; 181 182 for (i = 0; i < to_check; i++) 183 { 184 unsigned char mask = constant_time_ge(padding_length, i); 185 unsigned char b = rec->data[rec->length-1-i]; 186 /* The final |padding_length+1| bytes should all have the value 187 * |padding_length|. Therefore the XOR should be zero. */ 188 good &= ~(mask&(padding_length ^ b)); 189 } 190 191 /* If any of the final |padding_length+1| bytes had the wrong value, 192 * one or more of the lower eight bits of |good| will be cleared. We 193 * AND the bottom 8 bits together and duplicate the result to all the 194 * bits. */ 195 good &= good >> 4; 196 good &= good >> 2; 197 good &= good >> 1; 198 good <<= sizeof(good)*8-1; 199 good = DUPLICATE_MSB_TO_ALL(good); 200 201 padding_length = good & (padding_length+1); 202 rec->length -= padding_length; 203 rec->type |= padding_length<<8; /* kludge: pass padding length */ 204 205 return (int)((good & 1) | (~good & -1)); 206 } 207 208/* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in 209 * constant time (independent of the concrete value of rec->length, which may 210 * vary within a 256-byte window). 211 * 212 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to 213 * this function. 214 * 215 * On entry: 216 * rec->orig_len >= md_size 217 * md_size <= EVP_MAX_MD_SIZE 218 * 219 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with 220 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into 221 * a single or pair of cache-lines, then the variable memory accesses don't 222 * actually affect the timing. CPUs with smaller cache-lines [if any] are 223 * not multi-core and are not considered vulnerable to cache-timing attacks. 224 */ 225#define CBC_MAC_ROTATE_IN_PLACE 226 227void ssl3_cbc_copy_mac(unsigned char* out, 228 const SSL3_RECORD *rec, 229 unsigned md_size,unsigned orig_len) 230 { 231#if defined(CBC_MAC_ROTATE_IN_PLACE) 232 unsigned char rotated_mac_buf[64+EVP_MAX_MD_SIZE]; 233 unsigned char *rotated_mac; 234#else 235 unsigned char rotated_mac[EVP_MAX_MD_SIZE]; 236#endif 237 238 /* mac_end is the index of |rec->data| just after the end of the MAC. */ 239 unsigned mac_end = rec->length; 240 unsigned mac_start = mac_end - md_size; 241 /* scan_start contains the number of bytes that we can ignore because 242 * the MAC's position can only vary by 255 bytes. */ 243 unsigned scan_start = 0; 244 unsigned i, j; 245 unsigned div_spoiler; 246 unsigned rotate_offset; 247 248 assert(orig_len >= md_size); 249 assert(md_size <= EVP_MAX_MD_SIZE); 250 251#if defined(CBC_MAC_ROTATE_IN_PLACE) 252 rotated_mac = rotated_mac_buf + ((0-(size_t)rotated_mac_buf)&63); 253#endif 254 255 /* This information is public so it's safe to branch based on it. */ 256 if (orig_len > md_size + 255 + 1) 257 scan_start = orig_len - (md_size + 255 + 1); 258 /* div_spoiler contains a multiple of md_size that is used to cause the 259 * modulo operation to be constant time. Without this, the time varies 260 * based on the amount of padding when running on Intel chips at least. 261 * 262 * The aim of right-shifting md_size is so that the compiler doesn't 263 * figure out that it can remove div_spoiler as that would require it 264 * to prove that md_size is always even, which I hope is beyond it. */ 265 div_spoiler = md_size >> 1; 266 div_spoiler <<= (sizeof(div_spoiler)-1)*8; 267 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; 268 269 memset(rotated_mac, 0, md_size); 270 for (i = scan_start, j = 0; i < orig_len; i++) 271 { 272 unsigned char mac_started = constant_time_ge(i, mac_start); 273 unsigned char mac_ended = constant_time_ge(i, mac_end); 274 unsigned char b = rec->data[i]; 275 rotated_mac[j++] |= b & mac_started & ~mac_ended; 276 j &= constant_time_lt(j,md_size); 277 } 278 279 /* Now rotate the MAC */ 280#if defined(CBC_MAC_ROTATE_IN_PLACE) 281 j = 0; 282 for (i = 0; i < md_size; i++) 283 { 284 /* in case cache-line is 32 bytes, touch second line */ 285 ((volatile unsigned char *)rotated_mac)[rotate_offset^32]; 286 out[j++] = rotated_mac[rotate_offset++]; 287 rotate_offset &= constant_time_lt(rotate_offset,md_size); 288 } 289#else 290 memset(out, 0, md_size); 291 rotate_offset = md_size - rotate_offset; 292 rotate_offset &= constant_time_lt(rotate_offset,md_size); 293 for (i = 0; i < md_size; i++) 294 { 295 for (j = 0; j < md_size; j++) 296 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); 297 rotate_offset++; 298 rotate_offset &= constant_time_lt(rotate_offset,md_size); 299 } 300#endif 301 } 302 303/* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 304 * little-endian order. The value of p is advanced by four. */ 305#define u32toLE(n, p) \ 306 (*((p)++)=(unsigned char)(n), \ 307 *((p)++)=(unsigned char)(n>>8), \ 308 *((p)++)=(unsigned char)(n>>16), \ 309 *((p)++)=(unsigned char)(n>>24)) 310 311/* These functions serialize the state of a hash and thus perform the standard 312 * "final" operation without adding the padding and length that such a function 313 * typically does. */ 314static void tls1_sha1_final_raw(void* ctx, unsigned char *md_out) 315 { 316 SHA_CTX *sha1 = ctx; 317 l2n(sha1->h0, md_out); 318 l2n(sha1->h1, md_out); 319 l2n(sha1->h2, md_out); 320 l2n(sha1->h3, md_out); 321 l2n(sha1->h4, md_out); 322 } 323#define LARGEST_DIGEST_CTX SHA_CTX 324 325static void tls1_sha256_final_raw(void* ctx, unsigned char *md_out) 326 { 327 SHA256_CTX *sha256 = ctx; 328 unsigned i; 329 330 for (i = 0; i < 8; i++) 331 { 332 l2n(sha256->h[i], md_out); 333 } 334 } 335#undef LARGEST_DIGEST_CTX 336#define LARGEST_DIGEST_CTX SHA256_CTX 337 338static void tls1_sha512_final_raw(void* ctx, unsigned char *md_out) 339 { 340 SHA512_CTX *sha512 = ctx; 341 unsigned i; 342 343 for (i = 0; i < 8; i++) 344 { 345 l2n8(sha512->h[i], md_out); 346 } 347 } 348#undef LARGEST_DIGEST_CTX 349#define LARGEST_DIGEST_CTX SHA512_CTX 350 351/* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 352 * which ssl3_cbc_digest_record supports. */ 353char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) 354 { 355 switch (EVP_MD_CTX_type(ctx)) 356 { 357 case NID_sha1: 358 case NID_sha256: 359 case NID_sha384: 360 return 1; 361 default: 362 return 0; 363 } 364 } 365 366/* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS 367 * record. 368 * 369 * ctx: the EVP_MD_CTX from which we take the hash function. 370 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 371 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 372 * md_out_size: if non-NULL, the number of output bytes is written here. 373 * header: the 13-byte, TLS record header. 374 * data: the record data itself, less any preceeding explicit IV. 375 * data_plus_mac_size: the secret, reported length of the data and MAC 376 * once the padding has been removed. 377 * data_plus_mac_plus_padding_size: the public length of the whole 378 * record, including padding. 379 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS. 380 * 381 * On entry: by virtue of having been through one of the remove_padding 382 * functions, above, we know that data_plus_mac_size is large enough to contain 383 * a padding byte and MAC. (If the padding was invalid, it might contain the 384 * padding too. ) */ 385void ssl3_cbc_digest_record( 386 const EVP_MD_CTX *ctx, 387 unsigned char* md_out, 388 size_t* md_out_size, 389 const unsigned char header[13], 390 const unsigned char *data, 391 size_t data_plus_mac_size, 392 size_t data_plus_mac_plus_padding_size, 393 const unsigned char *mac_secret, 394 unsigned mac_secret_length, 395 char is_sslv3) 396 { 397 union { double align; 398 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; } md_state; 399 void (*md_final_raw)(void *ctx, unsigned char *md_out); 400 void (*md_transform)(void *ctx, const unsigned char *block); 401 unsigned md_size, md_block_size = 64; 402 unsigned sslv3_pad_length = 40, header_length, variance_blocks, 403 len, max_mac_bytes, num_blocks, 404 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 405 unsigned int bits; /* at most 18 bits */ 406 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 407 /* hmac_pad is the masked HMAC key. */ 408 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 409 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 410 unsigned char mac_out[EVP_MAX_MD_SIZE]; 411 unsigned i, j, md_out_size_u; 412 EVP_MD_CTX md_ctx; 413 /* mdLengthSize is the number of bytes in the length field that terminates 414 * the hash. */ 415 unsigned md_length_size = 8; 416 417 /* This is a, hopefully redundant, check that allows us to forget about 418 * many possible overflows later in this function. */ 419 assert(data_plus_mac_plus_padding_size < 1024*1024); 420 421 switch (EVP_MD_CTX_type(ctx)) 422 { 423 case NID_sha1: 424 SHA1_Init((SHA_CTX*)md_state.c); 425 md_final_raw = tls1_sha1_final_raw; 426 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform; 427 md_size = 20; 428 break; 429 case NID_sha256: 430 SHA256_Init((SHA256_CTX*)md_state.c); 431 md_final_raw = tls1_sha256_final_raw; 432 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 433 md_size = 32; 434 break; 435 case NID_sha384: 436 SHA384_Init((SHA512_CTX*)md_state.c); 437 md_final_raw = tls1_sha512_final_raw; 438 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 439 md_size = 384/8; 440 md_block_size = 128; 441 md_length_size = 16; 442 break; 443 default: 444 /* ssl3_cbc_record_digest_supported should have been 445 * called first to check that the hash function is 446 * supported. */ 447 assert(0); 448 if (md_out_size) 449 *md_out_size = -1; 450 return; 451 } 452 453 assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 454 assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 455 assert(md_size <= EVP_MAX_MD_SIZE); 456 457 header_length = 13; 458 if (is_sslv3) 459 { 460 header_length = 461 mac_secret_length + 462 sslv3_pad_length + 463 8 /* sequence number */ + 464 1 /* record type */ + 465 2 /* record length */; 466 } 467 468 /* variance_blocks is the number of blocks of the hash that we have to 469 * calculate in constant time because they could be altered by the 470 * padding value. 471 * 472 * In SSLv3, the padding must be minimal so the end of the plaintext 473 * varies by, at most, 15+20 = 35 bytes. (We conservatively assume that 474 * the MAC size varies from 0..20 bytes.) In case the 9 bytes of hash 475 * termination (0x80 + 64-bit length) don't fit in the final block, we 476 * say that the final two blocks can vary based on the padding. 477 * 478 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 479 * required to be minimal. Therefore we say that the final six blocks 480 * can vary based on the padding. 481 * 482 * Later in the function, if the message is short and there obviously 483 * cannot be this many blocks then variance_blocks can be reduced. */ 484 variance_blocks = is_sslv3 ? 2 : 6; 485 /* From now on we're dealing with the MAC, which conceptually has 13 486 * bytes of `header' before the start of the data (TLS) or 71/75 bytes 487 * (SSLv3) */ 488 len = data_plus_mac_plus_padding_size + header_length; 489 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including 490 * |header|, assuming that there's no padding. */ 491 max_mac_bytes = len - md_size - 1; 492 /* num_blocks is the maximum number of hash blocks. */ 493 num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size; 494 /* In order to calculate the MAC in constant time we have to handle 495 * the final blocks specially because the padding value could cause the 496 * end to appear somewhere in the final |variance_blocks| blocks and we 497 * can't leak where. However, |num_starting_blocks| worth of data can 498 * be hashed right away because no padding value can affect whether 499 * they are plaintext. */ 500 num_starting_blocks = 0; 501 /* k is the starting byte offset into the conceptual header||data where 502 * we start processing. */ 503 k = 0; 504 /* mac_end_offset is the index just past the end of the data to be 505 * MACed. */ 506 mac_end_offset = data_plus_mac_size + header_length - md_size; 507 /* c is the index of the 0x80 byte in the final hash block that 508 * contains application data. */ 509 c = mac_end_offset % md_block_size; 510 /* index_a is the hash block number that contains the 0x80 terminating 511 * value. */ 512 index_a = mac_end_offset / md_block_size; 513 /* index_b is the hash block number that contains the 64-bit hash 514 * length, in bits. */ 515 index_b = (mac_end_offset + md_length_size) / md_block_size; 516 /* bits is the hash-length in bits. It includes the additional hash 517 * block for the masked HMAC key, or whole of |header| in the case of 518 * SSLv3. */ 519 520 /* For SSLv3, if we're going to have any starting blocks then we need 521 * at least two because the header is larger than a single block. */ 522 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) 523 { 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 { 531 /* Compute the initial HMAC block. For SSLv3, the padding and 532 * secret bytes are included in |header| because they take more 533 * than a single block. */ 534 bits += 8*md_block_size; 535 memset(hmac_pad, 0, md_block_size); 536 assert(mac_secret_length <= sizeof(hmac_pad)); 537 memcpy(hmac_pad, mac_secret, mac_secret_length); 538 for (i = 0; i < md_block_size; i++) 539 hmac_pad[i] ^= 0x36; 540 541 md_transform(md_state.c, hmac_pad); 542 } 543 544 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; 549 550 if (k > 0) 551 { 552 if (is_sslv3) 553 { 554 /* The SSLv3 header is larger than a single block. 555 * overhang is the number of bytes beyond a single 556 * block that the header consumes: 7 bytes (SHA1). */ 557 unsigned overhang = header_length-md_block_size; 558 md_transform(md_state.c, header); 559 memcpy(first_block, header + md_block_size, overhang); 560 memcpy(first_block + overhang, data, md_block_size-overhang); 561 md_transform(md_state.c, first_block); 562 for (i = 1; i < k/md_block_size - 1; i++) 563 md_transform(md_state.c, data + md_block_size*i - overhang); 564 } 565 else 566 { 567 /* k is a multiple of md_block_size. */ 568 memcpy(first_block, header, 13); 569 memcpy(first_block+13, data, md_block_size-13); 570 md_transform(md_state.c, first_block); 571 for (i = 1; i < k/md_block_size; i++) 572 md_transform(md_state.c, data + md_block_size*i - 13); 573 } 574 } 575 576 memset(mac_out, 0, sizeof(mac_out)); 577 578 /* We now process the final hash blocks. For each block, we construct 579 * it in constant time. If the |i==index_a| then we'll include the 0x80 580 * bytes and zero pad etc. For each block we selectively copy it, in 581 * constant time, to |mac_out|. */ 582 for (i = num_starting_blocks; i <= num_starting_blocks+variance_blocks; i++) 583 { 584 unsigned char block[MAX_HASH_BLOCK_SIZE]; 585 unsigned char is_block_a = constant_time_eq_8(i, index_a); 586 unsigned char is_block_b = constant_time_eq_8(i, index_b); 587 for (j = 0; j < md_block_size; j++) 588 { 589 unsigned char b = 0, is_past_c, is_past_cp1; 590 if (k < header_length) 591 b = header[k]; 592 else if (k < data_plus_mac_plus_padding_size + header_length) 593 b = data[k-header_length]; 594 k++; 595 596 is_past_c = is_block_a & constant_time_ge(j, c); 597 is_past_cp1 = is_block_a & constant_time_ge(j, c+1); 598 /* If this is the block containing the end of the 599 * application data, and we are at the offset for the 600 * 0x80 value, then overwrite b with 0x80. */ 601 b = (b&~is_past_c) | (0x80&is_past_c); 602 /* If this the the block containing the end of the 603 * application data and we're past the 0x80 value then 604 * just write zero. */ 605 b = b&~is_past_cp1; 606 /* If this is index_b (the final block), but not 607 * index_a (the end of the data), then the 64-bit 608 * length didn't fit into index_a and we're having to 609 * add an extra block of zeros. */ 610 b &= ~is_block_b | is_block_a; 611 612 /* The final bytes of one of the blocks contains the 613 * length. */ 614 if (j >= md_block_size - md_length_size) 615 { 616 /* If this is index_b, write a length byte. */ 617 b = (b&~is_block_b) | (is_block_b&length_bytes[j-(md_block_size-md_length_size)]); 618 } 619 block[j] = b; 620 } 621 622 md_transform(md_state.c, block); 623 md_final_raw(md_state.c, block); 624 /* If this is index_b, copy the hash value to |mac_out|. */ 625 for (j = 0; j < md_size; j++) 626 mac_out[j] |= block[j]&is_block_b; 627 } 628 629 EVP_MD_CTX_init(&md_ctx); 630 EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */); 631 if (is_sslv3) 632 { 633 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */ 634 memset(hmac_pad, 0x5c, sslv3_pad_length); 635 636 EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length); 637 EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length); 638 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 639 } 640 else 641 { 642 /* Complete the HMAC in the standard manner. */ 643 for (i = 0; i < md_block_size; i++) 644 hmac_pad[i] ^= 0x6a; 645 646 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 647 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 648 } 649 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 650 if (md_out_size) 651 *md_out_size = md_out_size_u; 652 EVP_MD_CTX_cleanup(&md_ctx); 653 } 654