s3_cbc.c revision 1.10
1/* $OpenBSD: s3_cbc.c,v 1.10 2015/07/17 07:04:40 doug 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/* ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC 105 * record in |rec| by updating |rec->length| in constant time. 106 * 107 * block_size: the block size of the cipher used to encrypt the record. 108 * returns: 109 * 0: (in non-constant time) if the record is publicly invalid. 110 * 1: if the padding was valid 111 * -1: otherwise. */ 112int 113ssl3_cbc_remove_padding(const SSL* s, SSL3_RECORD *rec, unsigned block_size, 114 unsigned mac_size) 115{ 116 unsigned padding_length, good; 117 const unsigned overhead = 1 /* padding length byte */ + mac_size; 118 119 /* These lengths are all public so we can test them in non-constant 120 * time. */ 121 if (overhead > rec->length) 122 return 0; 123 124 padding_length = rec->data[rec->length - 1]; 125 good = constant_time_ge(rec->length, padding_length + overhead); 126 /* SSLv3 requires that the padding is minimal. */ 127 good &= constant_time_ge(block_size, padding_length + 1); 128 padding_length = good & (padding_length + 1); 129 rec->length -= padding_length; 130 rec->type |= padding_length << 8; /* kludge: pass padding length */ 131 return (int)((good & 1) | (~good & -1)); 132} 133 134/* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC 135 * record in |rec| in constant time and returns 1 if the padding is valid and 136 * -1 otherwise. It also removes any explicit IV from the start of the record 137 * without leaking any timing about whether there was enough space after the 138 * padding was removed. 139 * 140 * block_size: the block size of the cipher used to encrypt the record. 141 * returns: 142 * 0: (in non-constant time) if the record is publicly invalid. 143 * 1: if the padding was valid 144 * -1: otherwise. */ 145int 146tls1_cbc_remove_padding(const SSL* s, SSL3_RECORD *rec, unsigned block_size, 147 unsigned mac_size) 148{ 149 unsigned padding_length, good, to_check, i; 150 const unsigned overhead = 1 /* padding length byte */ + mac_size; 151 152 /* Check if version requires explicit IV */ 153 if (SSL_USE_EXPLICIT_IV(s)) { 154 /* These lengths are all public so we can test them in 155 * non-constant time. 156 */ 157 if (overhead + block_size > rec->length) 158 return 0; 159 /* We can now safely skip explicit IV */ 160 rec->data += block_size; 161 rec->input += block_size; 162 rec->length -= block_size; 163 } else if (overhead > rec->length) 164 return 0; 165 166 padding_length = rec->data[rec->length - 1]; 167 168 if (EVP_CIPHER_flags(s->enc_read_ctx->cipher) & EVP_CIPH_FLAG_AEAD_CIPHER) { 169 /* padding is already verified */ 170 rec->length -= padding_length + 1; 171 return 1; 172 } 173 174 good = constant_time_ge(rec->length, overhead + padding_length); 175 /* The padding consists of a length byte at the end of the record and 176 * then that many bytes of padding, all with the same value as the 177 * length byte. Thus, with the length byte included, there are i+1 178 * bytes of padding. 179 * 180 * We can't check just |padding_length+1| bytes because that leaks 181 * decrypted information. Therefore we always have to check the maximum 182 * amount of padding possible. (Again, the length of the record is 183 * public information so we can use it.) */ 184 to_check = 255; /* maximum amount of padding. */ 185 if (to_check > rec->length - 1) 186 to_check = rec->length - 1; 187 188 for (i = 0; i < to_check; i++) { 189 unsigned char mask = constant_time_ge(padding_length, i); 190 unsigned char b = rec->data[rec->length - 1 - i]; 191 /* The final |padding_length+1| bytes should all have the value 192 * |padding_length|. Therefore the XOR should be zero. */ 193 good &= ~(mask&(padding_length ^ b)); 194 } 195 196 /* If any of the final |padding_length+1| bytes had the wrong value, 197 * one or more of the lower eight bits of |good| will be cleared. We 198 * AND the bottom 8 bits together and duplicate the result to all the 199 * bits. */ 200 good &= good >> 4; 201 good &= good >> 2; 202 good &= good >> 1; 203 good <<= sizeof(good)*8 - 1; 204 good = DUPLICATE_MSB_TO_ALL(good); 205 206 padding_length = good & (padding_length + 1); 207 rec->length -= padding_length; 208 rec->type |= padding_length<<8; /* kludge: pass padding length */ 209 210 return (int)((good & 1) | (~good & -1)); 211} 212 213/* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in 214 * constant time (independent of the concrete value of rec->length, which may 215 * vary within a 256-byte window). 216 * 217 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to 218 * this function. 219 * 220 * On entry: 221 * rec->orig_len >= md_size 222 * md_size <= EVP_MAX_MD_SIZE 223 * 224 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with 225 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into 226 * a single or pair of cache-lines, then the variable memory accesses don't 227 * actually affect the timing. CPUs with smaller cache-lines [if any] are 228 * not multi-core and are not considered vulnerable to cache-timing attacks. 229 */ 230#define CBC_MAC_ROTATE_IN_PLACE 231 232void 233ssl3_cbc_copy_mac(unsigned char* out, const SSL3_RECORD *rec, 234 unsigned md_size, unsigned orig_len) 235{ 236#if defined(CBC_MAC_ROTATE_IN_PLACE) 237 unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; 238 unsigned char *rotated_mac; 239#else 240 unsigned char rotated_mac[EVP_MAX_MD_SIZE]; 241#endif 242 243 /* mac_end is the index of |rec->data| just after the end of the MAC. */ 244 unsigned mac_end = rec->length; 245 unsigned mac_start = mac_end - md_size; 246 /* scan_start contains the number of bytes that we can ignore because 247 * the MAC's position can only vary by 255 bytes. */ 248 unsigned scan_start = 0; 249 unsigned i, j; 250 unsigned div_spoiler; 251 unsigned rotate_offset; 252 253 OPENSSL_assert(orig_len >= md_size); 254 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 255 256#if defined(CBC_MAC_ROTATE_IN_PLACE) 257 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf)&63); 258#endif 259 260 /* This information is public so it's safe to branch based on it. */ 261 if (orig_len > md_size + 255 + 1) 262 scan_start = orig_len - (md_size + 255 + 1); 263 /* div_spoiler contains a multiple of md_size that is used to cause the 264 * modulo operation to be constant time. Without this, the time varies 265 * based on the amount of padding when running on Intel chips at least. 266 * 267 * The aim of right-shifting md_size is so that the compiler doesn't 268 * figure out that it can remove div_spoiler as that would require it 269 * to prove that md_size is always even, which I hope is beyond it. */ 270 div_spoiler = md_size >> 1; 271 div_spoiler <<= (sizeof(div_spoiler) - 1) * 8; 272 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; 273 274 memset(rotated_mac, 0, md_size); 275 for (i = scan_start, j = 0; i < orig_len; i++) { 276 unsigned char mac_started = constant_time_ge(i, mac_start); 277 unsigned char mac_ended = constant_time_ge(i, mac_end); 278 unsigned char b = rec->data[i]; 279 rotated_mac[j++] |= b & mac_started & ~mac_ended; 280 j &= constant_time_lt(j, md_size); 281 } 282 283 /* Now rotate the MAC */ 284#if defined(CBC_MAC_ROTATE_IN_PLACE) 285 j = 0; 286 for (i = 0; i < md_size; i++) { 287 /* in case cache-line is 32 bytes, touch second line */ 288 ((volatile unsigned char *)rotated_mac)[rotate_offset^32]; 289 out[j++] = rotated_mac[rotate_offset++]; 290 rotate_offset &= constant_time_lt(rotate_offset, md_size); 291 } 292#else 293 memset(out, 0, md_size); 294 rotate_offset = md_size - rotate_offset; 295 rotate_offset &= constant_time_lt(rotate_offset, md_size); 296 for (i = 0; i < md_size; i++) { 297 for (j = 0; j < md_size; j++) 298 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); 299 rotate_offset++; 300 rotate_offset &= constant_time_lt(rotate_offset, md_size); 301 } 302#endif 303} 304 305/* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 306 * little-endian order. The value of p is advanced by four. */ 307#define u32toLE(n, p) \ 308 (*((p)++)=(unsigned char)(n), \ 309 *((p)++)=(unsigned char)(n>>8), \ 310 *((p)++)=(unsigned char)(n>>16), \ 311 *((p)++)=(unsigned char)(n>>24)) 312 313/* These functions serialize the state of a hash and thus perform the standard 314 * "final" operation without adding the padding and length that such a function 315 * typically does. */ 316static void 317tls1_md5_final_raw(void* ctx, unsigned char *md_out) 318{ 319 MD5_CTX *md5 = ctx; 320 u32toLE(md5->A, md_out); 321 u32toLE(md5->B, md_out); 322 u32toLE(md5->C, md_out); 323 u32toLE(md5->D, md_out); 324} 325 326static void 327tls1_sha1_final_raw(void* ctx, unsigned char *md_out) 328{ 329 SHA_CTX *sha1 = ctx; 330 l2n(sha1->h0, md_out); 331 l2n(sha1->h1, md_out); 332 l2n(sha1->h2, md_out); 333 l2n(sha1->h3, md_out); 334 l2n(sha1->h4, md_out); 335} 336#define LARGEST_DIGEST_CTX SHA_CTX 337 338static void 339tls1_sha256_final_raw(void* ctx, unsigned char *md_out) 340{ 341 SHA256_CTX *sha256 = ctx; 342 unsigned i; 343 344 for (i = 0; i < 8; i++) { 345 l2n(sha256->h[i], md_out); 346 } 347} 348#undef LARGEST_DIGEST_CTX 349#define LARGEST_DIGEST_CTX SHA256_CTX 350 351static void 352tls1_sha512_final_raw(void* ctx, unsigned char *md_out) 353{ 354 SHA512_CTX *sha512 = ctx; 355 unsigned i; 356 357 for (i = 0; i < 8; i++) { 358 l2n8(sha512->h[i], md_out); 359 } 360} 361#undef LARGEST_DIGEST_CTX 362#define LARGEST_DIGEST_CTX SHA512_CTX 363 364/* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 365 * which ssl3_cbc_digest_record supports. */ 366char 367ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) 368{ 369 switch (EVP_MD_CTX_type(ctx)) { 370 case NID_md5: 371 case NID_sha1: 372 case NID_sha224: 373 case NID_sha256: 374 case NID_sha384: 375 case NID_sha512: 376 return 1; 377 default: 378 return 0; 379 } 380} 381 382/* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS 383 * record. 384 * 385 * ctx: the EVP_MD_CTX from which we take the hash function. 386 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 387 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 388 * md_out_size: if non-NULL, the number of output bytes is written here. 389 * header: the 13-byte, TLS record header. 390 * data: the record data itself, less any preceeding explicit IV. 391 * data_plus_mac_size: the secret, reported length of the data and MAC 392 * once the padding has been removed. 393 * data_plus_mac_plus_padding_size: the public length of the whole 394 * record, including padding. 395 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS. 396 * 397 * On entry: by virtue of having been through one of the remove_padding 398 * functions, above, we know that data_plus_mac_size is large enough to contain 399 * a padding byte and MAC. (If the padding was invalid, it might contain the 400 * padding too. ) */ 401int 402ssl3_cbc_digest_record(const EVP_MD_CTX *ctx, unsigned char* md_out, 403 size_t* md_out_size, const unsigned char header[13], 404 const unsigned char *data, size_t data_plus_mac_size, 405 size_t data_plus_mac_plus_padding_size, const unsigned char *mac_secret, 406 unsigned mac_secret_length, char is_sslv3) 407{ 408 union { double align; 409 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; 410 } md_state; 411 void (*md_final_raw)(void *ctx, unsigned char *md_out); 412 void (*md_transform)(void *ctx, const unsigned char *block); 413 unsigned md_size, md_block_size = 64; 414 unsigned sslv3_pad_length = 40, header_length, variance_blocks, 415 len, max_mac_bytes, num_blocks, 416 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 417 unsigned int bits; /* at most 18 bits */ 418 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 419 /* hmac_pad is the masked HMAC key. */ 420 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 421 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 422 unsigned char mac_out[EVP_MAX_MD_SIZE]; 423 unsigned i, j, md_out_size_u; 424 EVP_MD_CTX md_ctx; 425 /* mdLengthSize is the number of bytes in the length field that terminates 426 * the hash. */ 427 unsigned md_length_size = 8; 428 char length_is_big_endian = 1; 429 430 /* This is a, hopefully redundant, check that allows us to forget about 431 * many possible overflows later in this function. */ 432 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024); 433 434 switch (EVP_MD_CTX_type(ctx)) { 435 case NID_md5: 436 MD5_Init((MD5_CTX*)md_state.c); 437 md_final_raw = tls1_md5_final_raw; 438 md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform; 439 md_size = 16; 440 sslv3_pad_length = 48; 441 length_is_big_endian = 0; 442 break; 443 case NID_sha1: 444 SHA1_Init((SHA_CTX*)md_state.c); 445 md_final_raw = tls1_sha1_final_raw; 446 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform; 447 md_size = 20; 448 break; 449 case NID_sha224: 450 SHA224_Init((SHA256_CTX*)md_state.c); 451 md_final_raw = tls1_sha256_final_raw; 452 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 453 md_size = 224/8; 454 break; 455 case NID_sha256: 456 SHA256_Init((SHA256_CTX*)md_state.c); 457 md_final_raw = tls1_sha256_final_raw; 458 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 459 md_size = 32; 460 break; 461 case NID_sha384: 462 SHA384_Init((SHA512_CTX*)md_state.c); 463 md_final_raw = tls1_sha512_final_raw; 464 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 465 md_size = 384/8; 466 md_block_size = 128; 467 md_length_size = 16; 468 break; 469 case NID_sha512: 470 SHA512_Init((SHA512_CTX*)md_state.c); 471 md_final_raw = tls1_sha512_final_raw; 472 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 473 md_size = 64; 474 md_block_size = 128; 475 md_length_size = 16; 476 break; 477 default: 478 /* ssl3_cbc_record_digest_supported should have been 479 * called first to check that the hash function is 480 * supported. */ 481 OPENSSL_assert(0); 482 if (md_out_size) 483 *md_out_size = 0; 484 return 0; 485 } 486 487 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 488 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 489 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 490 491 header_length = 13; 492 if (is_sslv3) { 493 header_length = mac_secret_length + sslv3_pad_length + 494 8 /* sequence number */ + 495 1 /* record type */ + 496 2 /* record length */; 497 } 498 499 /* variance_blocks is the number of blocks of the hash that we have to 500 * calculate in constant time because they could be altered by the 501 * padding value. 502 * 503 * In SSLv3, the padding must be minimal so the end of the plaintext 504 * varies by, at most, 15+20 = 35 bytes. (We conservatively assume that 505 * the MAC size varies from 0..20 bytes.) In case the 9 bytes of hash 506 * termination (0x80 + 64-bit length) don't fit in the final block, we 507 * say that the final two blocks can vary based on the padding. 508 * 509 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 510 * required to be minimal. Therefore we say that the final six blocks 511 * can vary based on the padding. 512 * 513 * Later in the function, if the message is short and there obviously 514 * cannot be this many blocks then variance_blocks can be reduced. */ 515 variance_blocks = is_sslv3 ? 2 : 6; 516 /* From now on we're dealing with the MAC, which conceptually has 13 517 * bytes of `header' before the start of the data (TLS) or 71/75 bytes 518 * (SSLv3) */ 519 len = data_plus_mac_plus_padding_size + header_length; 520 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including 521 * |header|, assuming that there's no padding. */ 522 max_mac_bytes = len - md_size - 1; 523 /* num_blocks is the maximum number of hash blocks. */ 524 num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size; 525 /* In order to calculate the MAC in constant time we have to handle 526 * the final blocks specially because the padding value could cause the 527 * end to appear somewhere in the final |variance_blocks| blocks and we 528 * can't leak where. However, |num_starting_blocks| worth of data can 529 * be hashed right away because no padding value can affect whether 530 * they are plaintext. */ 531 num_starting_blocks = 0; 532 /* k is the starting byte offset into the conceptual header||data where 533 * we start processing. */ 534 k = 0; 535 /* mac_end_offset is the index just past the end of the data to be 536 * MACed. */ 537 mac_end_offset = data_plus_mac_size + header_length - md_size; 538 /* c is the index of the 0x80 byte in the final hash block that 539 * contains application data. */ 540 c = mac_end_offset % md_block_size; 541 /* index_a is the hash block number that contains the 0x80 terminating 542 * value. */ 543 index_a = mac_end_offset / md_block_size; 544 /* index_b is the hash block number that contains the 64-bit hash 545 * length, in bits. */ 546 index_b = (mac_end_offset + md_length_size) / md_block_size; 547 /* bits is the hash-length in bits. It includes the additional hash 548 * block for the masked HMAC key, or whole of |header| in the case of 549 * SSLv3. */ 550 551 /* For SSLv3, if we're going to have any starting blocks then we need 552 * at least two because the header is larger than a single block. */ 553 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) { 554 num_starting_blocks = num_blocks - variance_blocks; 555 k = md_block_size*num_starting_blocks; 556 } 557 558 bits = 8*mac_end_offset; 559 if (!is_sslv3) { 560 /* Compute the initial HMAC block. For SSLv3, the padding and 561 * secret bytes are included in |header| because they take more 562 * than a single block. */ 563 bits += 8*md_block_size; 564 memset(hmac_pad, 0, md_block_size); 565 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad)); 566 memcpy(hmac_pad, mac_secret, mac_secret_length); 567 for (i = 0; i < md_block_size; i++) 568 hmac_pad[i] ^= 0x36; 569 570 md_transform(md_state.c, hmac_pad); 571 } 572 573 if (length_is_big_endian) { 574 memset(length_bytes, 0, md_length_size - 4); 575 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); 576 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); 577 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); 578 length_bytes[md_length_size - 1] = (unsigned char)bits; 579 } else { 580 memset(length_bytes, 0, md_length_size); 581 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); 582 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); 583 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); 584 length_bytes[md_length_size - 8] = (unsigned char)bits; 585 } 586 587 if (k > 0) { 588 if (is_sslv3) { 589 /* The SSLv3 header is larger than a single block. 590 * overhang is the number of bytes beyond a single 591 * block that the header consumes: either 7 bytes 592 * (SHA1) or 11 bytes (MD5). */ 593 unsigned overhang = header_length - md_block_size; 594 md_transform(md_state.c, header); 595 memcpy(first_block, header + md_block_size, overhang); 596 memcpy(first_block + overhang, data, md_block_size - overhang); 597 md_transform(md_state.c, first_block); 598 for (i = 1; i < k/md_block_size - 1; i++) 599 md_transform(md_state.c, data + md_block_size*i - overhang); 600 } else { 601 /* k is a multiple of md_block_size. */ 602 memcpy(first_block, header, 13); 603 memcpy(first_block + 13, data, md_block_size - 13); 604 md_transform(md_state.c, first_block); 605 for (i = 1; i < k/md_block_size; i++) 606 md_transform(md_state.c, data + md_block_size*i - 13); 607 } 608 } 609 610 memset(mac_out, 0, sizeof(mac_out)); 611 612 /* We now process the final hash blocks. For each block, we construct 613 * it in constant time. If the |i==index_a| then we'll include the 0x80 614 * bytes and zero pad etc. For each block we selectively copy it, in 615 * constant time, to |mac_out|. */ 616 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks; i++) { 617 unsigned char block[MAX_HASH_BLOCK_SIZE]; 618 unsigned char is_block_a = constant_time_eq_8(i, index_a); 619 unsigned char is_block_b = constant_time_eq_8(i, index_b); 620 for (j = 0; j < md_block_size; j++) { 621 unsigned char b = 0, is_past_c, is_past_cp1; 622 if (k < header_length) 623 b = header[k]; 624 else if (k < data_plus_mac_plus_padding_size + header_length) 625 b = data[k - header_length]; 626 k++; 627 628 is_past_c = is_block_a & constant_time_ge(j, c); 629 is_past_cp1 = is_block_a & constant_time_ge(j, c + 1); 630 /* If this is the block containing the end of the 631 * application data, and we are at the offset for the 632 * 0x80 value, then overwrite b with 0x80. */ 633 b = (b&~is_past_c) | (0x80&is_past_c); 634 /* If this the the block containing the end of the 635 * application data and we're past the 0x80 value then 636 * just write zero. */ 637 b = b&~is_past_cp1; 638 /* If this is index_b (the final block), but not 639 * index_a (the end of the data), then the 64-bit 640 * length didn't fit into index_a and we're having to 641 * add an extra block of zeros. */ 642 b &= ~is_block_b | is_block_a; 643 644 /* The final bytes of one of the blocks contains the 645 * length. */ 646 if (j >= md_block_size - md_length_size) { 647 /* If this is index_b, write a length byte. */ 648 b = (b&~is_block_b) | (is_block_b&length_bytes[j - (md_block_size - md_length_size)]); 649 } 650 block[j] = b; 651 } 652 653 md_transform(md_state.c, block); 654 md_final_raw(md_state.c, block); 655 /* If this is index_b, copy the hash value to |mac_out|. */ 656 for (j = 0; j < md_size; j++) 657 mac_out[j] |= block[j]&is_block_b; 658 } 659 660 EVP_MD_CTX_init(&md_ctx); 661 if (!EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */)) { 662 EVP_MD_CTX_cleanup(&md_ctx); 663 return 0; 664 } 665 if (is_sslv3) { 666 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */ 667 memset(hmac_pad, 0x5c, sslv3_pad_length); 668 669 EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length); 670 EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length); 671 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 672 } else { 673 /* Complete the HMAC in the standard manner. */ 674 for (i = 0; i < md_block_size; i++) 675 hmac_pad[i] ^= 0x6a; 676 677 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 678 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 679 } 680 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 681 if (md_out_size) 682 *md_out_size = md_out_size_u; 683 EVP_MD_CTX_cleanup(&md_ctx); 684 685 return 1; 686} 687