1 /* $OpenBSD: s3_cbc.c,v 1.16 2017/01/23 08:08:06 beck 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. */ 80 static unsigned 81 constant_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. */ 88 static unsigned 89 constant_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. */ 96 static unsigned char 97 constant_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. */ 115 int 116 tls1_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 201 202 void 203 ssl3_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. */ 286 static void 287 tls1_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 } 295 296 static void 297 tls1_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 } 306 307 static void 308 tls1_sha256_final_raw(void* ctx, unsigned char *md_out) 309 { 310 SHA256_CTX *sha256 = ctx; 311 unsigned i; 312 313 for (i = 0; i < 8; i++) { 314 l2n(sha256->h[i], md_out); 315 } 316 } 317 318 static void 319 tls1_sha512_final_raw(void* ctx, unsigned char *md_out) 320 { 321 SHA512_CTX *sha512 = ctx; 322 unsigned i; 323 324 for (i = 0; i < 8; i++) { 325 l2n8(sha512->h[i], md_out); 326 } 327 } 328 329 /* Largest hash context ever used by the functions above. */ 330 #define LARGEST_DIGEST_CTX SHA512_CTX 331 332 /* Type giving the alignment needed by the above */ 333 #define LARGEST_DIGEST_CTX_ALIGNMENT SHA_LONG64 334 335 /* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 336 * which ssl3_cbc_digest_record supports. */ 337 char 338 ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) 339 { 340 switch (EVP_MD_CTX_type(ctx)) { 341 case NID_md5: 342 case NID_sha1: 343 case NID_sha224: 344 case NID_sha256: 345 case NID_sha384: 346 case NID_sha512: 347 return 1; 348 default: 349 return 0; 350 } 351 } 352 353 /* ssl3_cbc_digest_record computes the MAC of a decrypted, padded TLS 354 * record. 355 * 356 * ctx: the EVP_MD_CTX from which we take the hash function. 357 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 358 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 359 * md_out_size: if non-NULL, the number of output bytes is written here. 360 * header: the 13-byte, TLS record header. 361 * data: the record data itself, less any preceeding explicit IV. 362 * data_plus_mac_size: the secret, reported length of the data and MAC 363 * once the padding has been removed. 364 * data_plus_mac_plus_padding_size: the public length of the whole 365 * record, including padding. 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. ) 371 */ 372 int 373 ssl3_cbc_digest_record(const EVP_MD_CTX *ctx, unsigned char* md_out, 374 size_t* md_out_size, const unsigned char header[13], 375 const unsigned char *data, size_t data_plus_mac_size, 376 size_t data_plus_mac_plus_padding_size, const unsigned char *mac_secret, 377 unsigned mac_secret_length) 378 { 379 union { 380 /* 381 * Alignment here is to allow this to be cast as SHA512_CTX 382 * without losing alignment required by the 64-bit SHA_LONG64 383 * integer it contains. 384 */ 385 LARGEST_DIGEST_CTX_ALIGNMENT align; 386 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; 387 } md_state; 388 void (*md_final_raw)(void *ctx, unsigned char *md_out); 389 void (*md_transform)(void *ctx, const unsigned char *block); 390 unsigned md_size, md_block_size = 64; 391 unsigned header_length, variance_blocks, 392 len, max_mac_bytes, num_blocks, 393 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 394 unsigned int bits; /* at most 18 bits */ 395 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 396 /* hmac_pad is the masked HMAC key. */ 397 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 398 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 399 unsigned char mac_out[EVP_MAX_MD_SIZE]; 400 unsigned i, j, md_out_size_u; 401 EVP_MD_CTX md_ctx; 402 /* mdLengthSize is the number of bytes in the length field that terminates 403 * the hash. */ 404 unsigned md_length_size = 8; 405 char length_is_big_endian = 1; 406 407 /* This is a, hopefully redundant, check that allows us to forget about 408 * many possible overflows later in this function. */ 409 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024); 410 411 switch (EVP_MD_CTX_type(ctx)) { 412 case NID_md5: 413 MD5_Init((MD5_CTX*)md_state.c); 414 md_final_raw = tls1_md5_final_raw; 415 md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform; 416 md_size = 16; 417 length_is_big_endian = 0; 418 break; 419 case NID_sha1: 420 SHA1_Init((SHA_CTX*)md_state.c); 421 md_final_raw = tls1_sha1_final_raw; 422 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform; 423 md_size = 20; 424 break; 425 case NID_sha224: 426 SHA224_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 = 224/8; 430 break; 431 case NID_sha256: 432 SHA256_Init((SHA256_CTX*)md_state.c); 433 md_final_raw = tls1_sha256_final_raw; 434 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 435 md_size = 32; 436 break; 437 case NID_sha384: 438 SHA384_Init((SHA512_CTX*)md_state.c); 439 md_final_raw = tls1_sha512_final_raw; 440 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 441 md_size = 384/8; 442 md_block_size = 128; 443 md_length_size = 16; 444 break; 445 case NID_sha512: 446 SHA512_Init((SHA512_CTX*)md_state.c); 447 md_final_raw = tls1_sha512_final_raw; 448 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 449 md_size = 64; 450 md_block_size = 128; 451 md_length_size = 16; 452 break; 453 default: 454 /* ssl3_cbc_record_digest_supported should have been 455 * called first to check that the hash function is 456 * supported. */ 457 OPENSSL_assert(0); 458 if (md_out_size) 459 *md_out_size = 0; 460 return 0; 461 } 462 463 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 464 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 465 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 466 467 header_length = 13; 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 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 474 * required to be minimal. Therefore we say that the final six blocks 475 * can vary based on the padding. 476 * 477 * Later in the function, if the message is short and there obviously 478 * cannot be this many blocks then variance_blocks can be reduced. */ 479 variance_blocks = 6; 480 /* From now on we're dealing with the MAC, which conceptually has 13 481 * bytes of `header' before the start of the data (TLS) */ 482 len = data_plus_mac_plus_padding_size + header_length; 483 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including 484 * |header|, assuming that there's no padding. */ 485 max_mac_bytes = len - md_size - 1; 486 /* num_blocks is the maximum number of hash blocks. */ 487 num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size; 488 /* In order to calculate the MAC in constant time we have to handle 489 * the final blocks specially because the padding value could cause the 490 * end to appear somewhere in the final |variance_blocks| blocks and we 491 * can't leak where. However, |num_starting_blocks| worth of data can 492 * be hashed right away because no padding value can affect whether 493 * they are plaintext. */ 494 num_starting_blocks = 0; 495 /* k is the starting byte offset into the conceptual header||data where 496 * we start processing. */ 497 k = 0; 498 /* mac_end_offset is the index just past the end of the data to be 499 * MACed. */ 500 mac_end_offset = data_plus_mac_size + header_length - md_size; 501 /* c is the index of the 0x80 byte in the final hash block that 502 * contains application data. */ 503 c = mac_end_offset % md_block_size; 504 /* index_a is the hash block number that contains the 0x80 terminating 505 * value. */ 506 index_a = mac_end_offset / md_block_size; 507 /* index_b is the hash block number that contains the 64-bit hash 508 * length, in bits. */ 509 index_b = (mac_end_offset + md_length_size) / md_block_size; 510 /* bits is the hash-length in bits. It includes the additional hash 511 * block for the masked HMAC key. */ 512 513 if (num_blocks > variance_blocks) { 514 num_starting_blocks = num_blocks - variance_blocks; 515 k = md_block_size*num_starting_blocks; 516 } 517 518 bits = 8*mac_end_offset; 519 /* Compute the initial HMAC block. */ 520 bits += 8*md_block_size; 521 memset(hmac_pad, 0, md_block_size); 522 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad)); 523 memcpy(hmac_pad, mac_secret, mac_secret_length); 524 for (i = 0; i < md_block_size; i++) 525 hmac_pad[i] ^= 0x36; 526 527 md_transform(md_state.c, hmac_pad); 528 529 if (length_is_big_endian) { 530 memset(length_bytes, 0, md_length_size - 4); 531 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); 532 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); 533 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); 534 length_bytes[md_length_size - 1] = (unsigned char)bits; 535 } else { 536 memset(length_bytes, 0, md_length_size); 537 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); 538 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); 539 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); 540 length_bytes[md_length_size - 8] = (unsigned char)bits; 541 } 542 543 if (k > 0) { 544 /* k is a multiple of md_block_size. */ 545 memcpy(first_block, header, 13); 546 memcpy(first_block + 13, data, md_block_size - 13); 547 md_transform(md_state.c, first_block); 548 for (i = 1; i < k/md_block_size; i++) 549 md_transform(md_state.c, data + md_block_size*i - 13); 550 } 551 552 memset(mac_out, 0, sizeof(mac_out)); 553 554 /* We now process the final hash blocks. For each block, we construct 555 * it in constant time. If the |i==index_a| then we'll include the 0x80 556 * bytes and zero pad etc. For each block we selectively copy it, in 557 * constant time, to |mac_out|. */ 558 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks; i++) { 559 unsigned char block[MAX_HASH_BLOCK_SIZE]; 560 unsigned char is_block_a = constant_time_eq_8(i, index_a); 561 unsigned char is_block_b = constant_time_eq_8(i, index_b); 562 for (j = 0; j < md_block_size; j++) { 563 unsigned char b = 0, is_past_c, is_past_cp1; 564 if (k < header_length) 565 b = header[k]; 566 else if (k < data_plus_mac_plus_padding_size + header_length) 567 b = data[k - header_length]; 568 k++; 569 570 is_past_c = is_block_a & constant_time_ge(j, c); 571 is_past_cp1 = is_block_a & constant_time_ge(j, c + 1); 572 /* If this is the block containing the end of the 573 * application data, and we are at the offset for the 574 * 0x80 value, then overwrite b with 0x80. */ 575 b = (b&~is_past_c) | (0x80&is_past_c); 576 /* If this is the block containing the end of the 577 * application data and we're past the 0x80 value then 578 * just write zero. */ 579 b = b&~is_past_cp1; 580 /* If this is index_b (the final block), but not 581 * index_a (the end of the data), then the 64-bit 582 * length didn't fit into index_a and we're having to 583 * add an extra block of zeros. */ 584 b &= ~is_block_b | is_block_a; 585 586 /* The final bytes of one of the blocks contains the 587 * length. */ 588 if (j >= md_block_size - md_length_size) { 589 /* If this is index_b, write a length byte. */ 590 b = (b&~is_block_b) | (is_block_b&length_bytes[j - (md_block_size - md_length_size)]); 591 } 592 block[j] = b; 593 } 594 595 md_transform(md_state.c, block); 596 md_final_raw(md_state.c, block); 597 /* If this is index_b, copy the hash value to |mac_out|. */ 598 for (j = 0; j < md_size; j++) 599 mac_out[j] |= block[j]&is_block_b; 600 } 601 602 EVP_MD_CTX_init(&md_ctx); 603 if (!EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */)) { 604 EVP_MD_CTX_cleanup(&md_ctx); 605 return 0; 606 } 607 608 /* Complete the HMAC in the standard manner. */ 609 for (i = 0; i < md_block_size; i++) 610 hmac_pad[i] ^= 0x6a; 611 612 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 613 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 614 615 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 616 if (md_out_size) 617 *md_out_size = md_out_size_u; 618 EVP_MD_CTX_cleanup(&md_ctx); 619 620 return 1; 621 } 622