s3_cbc.c revision 296465
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 "../crypto/constant_time_locl.h" 57#include "ssl_locl.h" 58 59#include <openssl/md5.h> 60#include <openssl/sha.h> 61 62/* 63 * MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's 64 * length field. (SHA-384/512 have 128-bit length.) 65 */ 66#define MAX_HASH_BIT_COUNT_BYTES 16 67 68/* 69 * MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support. 70 * Currently SHA-384/512 has a 128-byte block size and that's the largest 71 * supported by TLS.) 72 */ 73#define MAX_HASH_BLOCK_SIZE 128 74 75/*- 76 * ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC 77 * record in |rec| by updating |rec->length| in constant time. 78 * 79 * block_size: the block size of the cipher used to encrypt the record. 80 * returns: 81 * 0: (in non-constant time) if the record is publicly invalid. 82 * 1: if the padding was valid 83 * -1: otherwise. 84 */ 85int ssl3_cbc_remove_padding(const SSL *s, 86 SSL3_RECORD *rec, 87 unsigned block_size, unsigned mac_size) 88{ 89 unsigned padding_length, good; 90 const unsigned overhead = 1 /* padding length byte */ + mac_size; 91 92 /* 93 * These lengths are all public so we can test them in non-constant time. 94 */ 95 if (overhead > rec->length) 96 return 0; 97 98 padding_length = rec->data[rec->length - 1]; 99 good = constant_time_ge(rec->length, padding_length + overhead); 100 /* SSLv3 requires that the padding is minimal. */ 101 good &= constant_time_ge(block_size, padding_length + 1); 102 padding_length = good & (padding_length + 1); 103 rec->length -= padding_length; 104 rec->type |= padding_length << 8; /* kludge: pass padding length */ 105 return constant_time_select_int(good, 1, -1); 106} 107 108/*- 109 * tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC 110 * record in |rec| in constant time and returns 1 if the padding is valid and 111 * -1 otherwise. It also removes any explicit IV from the start of the record 112 * without leaking any timing about whether there was enough space after the 113 * padding was removed. 114 * 115 * block_size: the block size of the cipher used to encrypt the record. 116 * returns: 117 * 0: (in non-constant time) if the record is publicly invalid. 118 * 1: if the padding was valid 119 * -1: otherwise. 120 */ 121int tls1_cbc_remove_padding(const SSL *s, 122 SSL3_RECORD *rec, 123 unsigned block_size, unsigned mac_size) 124{ 125 unsigned padding_length, good, to_check, i; 126 const unsigned overhead = 1 /* padding length byte */ + mac_size; 127 /* Check if version requires explicit IV */ 128 if (s->version == DTLS1_VERSION || s->version == DTLS1_BAD_VER) { 129 /* 130 * These lengths are all public so we can test them in non-constant 131 * time. 132 */ 133 if (overhead + block_size > rec->length) 134 return 0; 135 /* We can now safely skip explicit IV */ 136 rec->data += block_size; 137 rec->input += block_size; 138 rec->length -= block_size; 139 } else if (overhead > rec->length) 140 return 0; 141 142 padding_length = rec->data[rec->length - 1]; 143 144 /* 145 * NB: if compression is in operation the first packet may not be of even 146 * length so the padding bug check cannot be performed. This bug 147 * workaround has been around since SSLeay so hopefully it is either 148 * fixed now or no buggy implementation supports compression [steve] 149 */ 150 if ((s->options & SSL_OP_TLS_BLOCK_PADDING_BUG) && !s->expand) { 151 /* First packet is even in size, so check */ 152 if ((memcmp(s->s3->read_sequence, "\0\0\0\0\0\0\0\0", 8) == 0) && 153 !(padding_length & 1)) { 154 s->s3->flags |= TLS1_FLAGS_TLS_PADDING_BUG; 155 } 156 if ((s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) && padding_length > 0) { 157 padding_length--; 158 } 159 } 160 161 good = constant_time_ge(rec->length, overhead + padding_length); 162 /* 163 * The padding consists of a length byte at the end of the record and 164 * then that many bytes of padding, all with the same value as the length 165 * byte. Thus, with the length byte included, there are i+1 bytes of 166 * padding. We can't check just |padding_length+1| bytes because that 167 * leaks decrypted information. Therefore we always have to check the 168 * maximum amount of padding possible. (Again, the length of the record 169 * is public information so we can use it.) 170 */ 171 to_check = 255; /* maximum amount of padding. */ 172 if (to_check > rec->length - 1) 173 to_check = rec->length - 1; 174 175 for (i = 0; i < to_check; i++) { 176 unsigned char mask = constant_time_ge_8(padding_length, i); 177 unsigned char b = rec->data[rec->length - 1 - i]; 178 /* 179 * The final |padding_length+1| bytes should all have the value 180 * |padding_length|. Therefore the XOR should be zero. 181 */ 182 good &= ~(mask & (padding_length ^ b)); 183 } 184 185 /* 186 * If any of the final |padding_length+1| bytes had the wrong value, one 187 * or more of the lower eight bits of |good| will be cleared. 188 */ 189 good = constant_time_eq(0xff, good & 0xff); 190 padding_length = good & (padding_length + 1); 191 rec->length -= padding_length; 192 rec->type |= padding_length << 8; /* kludge: pass padding length */ 193 194 return constant_time_select_int(good, 1, -1); 195} 196 197/*- 198 * ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in 199 * constant time (independent of the concrete value of rec->length, which may 200 * vary within a 256-byte window). 201 * 202 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to 203 * this function. 204 * 205 * On entry: 206 * rec->orig_len >= md_size 207 * md_size <= EVP_MAX_MD_SIZE 208 * 209 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with 210 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into 211 * a single or pair of cache-lines, then the variable memory accesses don't 212 * actually affect the timing. CPUs with smaller cache-lines [if any] are 213 * not multi-core and are not considered vulnerable to cache-timing attacks. 214 */ 215#define CBC_MAC_ROTATE_IN_PLACE 216 217void ssl3_cbc_copy_mac(unsigned char *out, 218 const SSL3_RECORD *rec, 219 unsigned md_size, unsigned orig_len) 220{ 221#if defined(CBC_MAC_ROTATE_IN_PLACE) 222 unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; 223 unsigned char *rotated_mac; 224#else 225 unsigned char rotated_mac[EVP_MAX_MD_SIZE]; 226#endif 227 228 /* 229 * mac_end is the index of |rec->data| just after the end of the MAC. 230 */ 231 unsigned mac_end = rec->length; 232 unsigned mac_start = mac_end - md_size; 233 /* 234 * scan_start contains the number of bytes that we can ignore because the 235 * MAC's position can only vary by 255 bytes. 236 */ 237 unsigned scan_start = 0; 238 unsigned i, j; 239 unsigned div_spoiler; 240 unsigned rotate_offset; 241 242 OPENSSL_assert(orig_len >= md_size); 243 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 244 245#if defined(CBC_MAC_ROTATE_IN_PLACE) 246 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf) & 63); 247#endif 248 249 /* This information is public so it's safe to branch based on it. */ 250 if (orig_len > md_size + 255 + 1) 251 scan_start = orig_len - (md_size + 255 + 1); 252 /* 253 * div_spoiler contains a multiple of md_size that is used to cause the 254 * modulo operation to be constant time. Without this, the time varies 255 * based on the amount of padding when running on Intel chips at least. 256 * The aim of right-shifting md_size is so that the compiler doesn't 257 * figure out that it can remove div_spoiler as that would require it to 258 * prove that md_size is always even, which I hope is beyond it. 259 */ 260 div_spoiler = md_size >> 1; 261 div_spoiler <<= (sizeof(div_spoiler) - 1) * 8; 262 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; 263 264 memset(rotated_mac, 0, md_size); 265 for (i = scan_start, j = 0; i < orig_len; i++) { 266 unsigned char mac_started = constant_time_ge_8(i, mac_start); 267 unsigned char mac_ended = constant_time_ge_8(i, mac_end); 268 unsigned char b = rec->data[i]; 269 rotated_mac[j++] |= b & mac_started & ~mac_ended; 270 j &= constant_time_lt(j, md_size); 271 } 272 273 /* Now rotate the MAC */ 274#if defined(CBC_MAC_ROTATE_IN_PLACE) 275 j = 0; 276 for (i = 0; i < md_size; i++) { 277 /* in case cache-line is 32 bytes, touch second line */ 278 ((volatile unsigned char *)rotated_mac)[rotate_offset ^ 32]; 279 out[j++] = rotated_mac[rotate_offset++]; 280 rotate_offset &= constant_time_lt(rotate_offset, md_size); 281 } 282#else 283 memset(out, 0, md_size); 284 rotate_offset = md_size - rotate_offset; 285 rotate_offset &= constant_time_lt(rotate_offset, md_size); 286 for (i = 0; i < md_size; i++) { 287 for (j = 0; j < md_size; j++) 288 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); 289 rotate_offset++; 290 rotate_offset &= constant_time_lt(rotate_offset, md_size); 291 } 292#endif 293} 294 295/* 296 * u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 297 * little-endian order. The value of p is advanced by four. 298 */ 299#define u32toLE(n, p) \ 300 (*((p)++)=(unsigned char)(n), \ 301 *((p)++)=(unsigned char)(n>>8), \ 302 *((p)++)=(unsigned char)(n>>16), \ 303 *((p)++)=(unsigned char)(n>>24)) 304 305/* 306 * These functions serialize the state of a hash and thus perform the 307 * standard "final" operation without adding the padding and length that such 308 * a function typically does. 309 */ 310static void tls1_md5_final_raw(void *ctx, unsigned char *md_out) 311{ 312 MD5_CTX *md5 = ctx; 313 u32toLE(md5->A, md_out); 314 u32toLE(md5->B, md_out); 315 u32toLE(md5->C, md_out); 316 u32toLE(md5->D, md_out); 317} 318 319static void tls1_sha1_final_raw(void *ctx, unsigned char *md_out) 320{ 321 SHA_CTX *sha1 = ctx; 322 l2n(sha1->h0, md_out); 323 l2n(sha1->h1, md_out); 324 l2n(sha1->h2, md_out); 325 l2n(sha1->h3, md_out); 326 l2n(sha1->h4, md_out); 327} 328 329#define LARGEST_DIGEST_CTX SHA_CTX 330 331#ifndef OPENSSL_NO_SHA256 332static void tls1_sha256_final_raw(void *ctx, unsigned char *md_out) 333{ 334 SHA256_CTX *sha256 = ctx; 335 unsigned i; 336 337 for (i = 0; i < 8; i++) { 338 l2n(sha256->h[i], md_out); 339 } 340} 341 342# undef LARGEST_DIGEST_CTX 343# define LARGEST_DIGEST_CTX SHA256_CTX 344#endif 345 346#ifndef OPENSSL_NO_SHA512 347static void tls1_sha512_final_raw(void *ctx, unsigned char *md_out) 348{ 349 SHA512_CTX *sha512 = ctx; 350 unsigned i; 351 352 for (i = 0; i < 8; i++) { 353 l2n8(sha512->h[i], md_out); 354 } 355} 356 357# undef LARGEST_DIGEST_CTX 358# define LARGEST_DIGEST_CTX SHA512_CTX 359#endif 360 361/* 362 * ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 363 * which ssl3_cbc_digest_record supports. 364 */ 365char ssl3_cbc_record_digest_supported(const EVP_MD *digest) 366{ 367#ifdef OPENSSL_FIPS 368 if (FIPS_mode()) 369 return 0; 370#endif 371 switch (EVP_MD_type(digest)) { 372 case NID_md5: 373 case NID_sha1: 374#ifndef OPENSSL_NO_SHA256 375 case NID_sha224: 376 case NID_sha256: 377#endif 378#ifndef OPENSSL_NO_SHA512 379 case NID_sha384: 380 case NID_sha512: 381#endif 382 return 1; 383 default: 384 return 0; 385 } 386} 387 388/*- 389 * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS 390 * record. 391 * 392 * ctx: the EVP_MD_CTX from which we take the hash function. 393 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 394 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 395 * md_out_size: if non-NULL, the number of output bytes is written here. 396 * header: the 13-byte, TLS record header. 397 * data: the record data itself, less any preceeding explicit IV. 398 * data_plus_mac_size: the secret, reported length of the data and MAC 399 * once the padding has been removed. 400 * data_plus_mac_plus_padding_size: the public length of the whole 401 * record, including padding. 402 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS. 403 * 404 * On entry: by virtue of having been through one of the remove_padding 405 * functions, above, we know that data_plus_mac_size is large enough to contain 406 * a padding byte and MAC. (If the padding was invalid, it might contain the 407 * padding too. ) 408 */ 409void ssl3_cbc_digest_record(const EVP_MD *digest, 410 unsigned char *md_out, 411 size_t *md_out_size, 412 const unsigned char header[13], 413 const unsigned char *data, 414 size_t data_plus_mac_size, 415 size_t data_plus_mac_plus_padding_size, 416 const unsigned char *mac_secret, 417 unsigned mac_secret_length, char is_sslv3) 418{ 419 union { 420 double align; 421 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; 422 } md_state; 423 void (*md_final_raw) (void *ctx, unsigned char *md_out); 424 void (*md_transform) (void *ctx, const unsigned char *block); 425 unsigned md_size, md_block_size = 64; 426 unsigned sslv3_pad_length = 40, header_length, variance_blocks, 427 len, max_mac_bytes, num_blocks, 428 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 429 unsigned int bits; /* at most 18 bits */ 430 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 431 /* hmac_pad is the masked HMAC key. */ 432 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 433 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 434 unsigned char mac_out[EVP_MAX_MD_SIZE]; 435 unsigned i, j, md_out_size_u; 436 EVP_MD_CTX md_ctx; 437 /* 438 * mdLengthSize is the number of bytes in the length field that 439 * terminates * the hash. 440 */ 441 unsigned md_length_size = 8; 442 char length_is_big_endian = 1; 443 444 /* 445 * This is a, hopefully redundant, check that allows us to forget about 446 * many possible overflows later in this function. 447 */ 448 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024 * 1024); 449 450 switch (EVP_MD_type(digest)) { 451 case NID_md5: 452 MD5_Init((MD5_CTX *)md_state.c); 453 md_final_raw = tls1_md5_final_raw; 454 md_transform = 455 (void (*)(void *ctx, const unsigned char *block))MD5_Transform; 456 md_size = 16; 457 sslv3_pad_length = 48; 458 length_is_big_endian = 0; 459 break; 460 case NID_sha1: 461 SHA1_Init((SHA_CTX *)md_state.c); 462 md_final_raw = tls1_sha1_final_raw; 463 md_transform = 464 (void (*)(void *ctx, const unsigned char *block))SHA1_Transform; 465 md_size = 20; 466 break; 467#ifndef OPENSSL_NO_SHA256 468 case NID_sha224: 469 SHA224_Init((SHA256_CTX *)md_state.c); 470 md_final_raw = tls1_sha256_final_raw; 471 md_transform = 472 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform; 473 md_size = 224 / 8; 474 break; 475 case NID_sha256: 476 SHA256_Init((SHA256_CTX *)md_state.c); 477 md_final_raw = tls1_sha256_final_raw; 478 md_transform = 479 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform; 480 md_size = 32; 481 break; 482#endif 483#ifndef OPENSSL_NO_SHA512 484 case NID_sha384: 485 SHA384_Init((SHA512_CTX *)md_state.c); 486 md_final_raw = tls1_sha512_final_raw; 487 md_transform = 488 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform; 489 md_size = 384 / 8; 490 md_block_size = 128; 491 md_length_size = 16; 492 break; 493 case NID_sha512: 494 SHA512_Init((SHA512_CTX *)md_state.c); 495 md_final_raw = tls1_sha512_final_raw; 496 md_transform = 497 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform; 498 md_size = 64; 499 md_block_size = 128; 500 md_length_size = 16; 501 break; 502#endif 503 default: 504 /* 505 * ssl3_cbc_record_digest_supported should have been called first to 506 * check that the hash function is supported. 507 */ 508 OPENSSL_assert(0); 509 if (md_out_size) 510 *md_out_size = -1; 511 return; 512 } 513 514 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 515 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 516 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 517 518 header_length = 13; 519 if (is_sslv3) { 520 header_length = mac_secret_length + sslv3_pad_length + 8 /* sequence 521 * number */ + 522 1 /* record type */ + 523 2 /* record length */ ; 524 } 525 526 /* 527 * variance_blocks is the number of blocks of the hash that we have to 528 * calculate in constant time because they could be altered by the 529 * padding value. In SSLv3, the padding must be minimal so the end of 530 * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively 531 * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes 532 * of hash termination (0x80 + 64-bit length) don't fit in the final 533 * block, we say that the final two blocks can vary based on the padding. 534 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 535 * required to be minimal. Therefore we say that the final six blocks can 536 * vary based on the padding. Later in the function, if the message is 537 * short and there obviously cannot be this many blocks then 538 * variance_blocks can be reduced. 539 */ 540 variance_blocks = is_sslv3 ? 2 : 6; 541 /* 542 * From now on we're dealing with the MAC, which conceptually has 13 543 * bytes of `header' before the start of the data (TLS) or 71/75 bytes 544 * (SSLv3) 545 */ 546 len = data_plus_mac_plus_padding_size + header_length; 547 /* 548 * max_mac_bytes contains the maximum bytes of bytes in the MAC, 549 * including * |header|, assuming that there's no padding. 550 */ 551 max_mac_bytes = len - md_size - 1; 552 /* num_blocks is the maximum number of hash blocks. */ 553 num_blocks = 554 (max_mac_bytes + 1 + md_length_size + md_block_size - 555 1) / md_block_size; 556 /* 557 * In order to calculate the MAC in constant time we have to handle the 558 * final blocks specially because the padding value could cause the end 559 * to appear somewhere in the final |variance_blocks| blocks and we can't 560 * leak where. However, |num_starting_blocks| worth of data can be hashed 561 * right away because no padding value can affect whether they are 562 * plaintext. 563 */ 564 num_starting_blocks = 0; 565 /* 566 * k is the starting byte offset into the conceptual header||data where 567 * we start processing. 568 */ 569 k = 0; 570 /* 571 * mac_end_offset is the index just past the end of the data to be MACed. 572 */ 573 mac_end_offset = data_plus_mac_size + header_length - md_size; 574 /* 575 * c is the index of the 0x80 byte in the final hash block that contains 576 * application data. 577 */ 578 c = mac_end_offset % md_block_size; 579 /* 580 * index_a is the hash block number that contains the 0x80 terminating 581 * value. 582 */ 583 index_a = mac_end_offset / md_block_size; 584 /* 585 * index_b is the hash block number that contains the 64-bit hash length, 586 * in bits. 587 */ 588 index_b = (mac_end_offset + md_length_size) / md_block_size; 589 /* 590 * bits is the hash-length in bits. It includes the additional hash block 591 * for the masked HMAC key, or whole of |header| in the case of SSLv3. 592 */ 593 594 /* 595 * For SSLv3, if we're going to have any starting blocks then we need at 596 * least two because the header is larger than a single block. 597 */ 598 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) { 599 num_starting_blocks = num_blocks - variance_blocks; 600 k = md_block_size * num_starting_blocks; 601 } 602 603 bits = 8 * mac_end_offset; 604 if (!is_sslv3) { 605 /* 606 * Compute the initial HMAC block. For SSLv3, the padding and secret 607 * bytes are included in |header| because they take more than a 608 * single block. 609 */ 610 bits += 8 * md_block_size; 611 memset(hmac_pad, 0, md_block_size); 612 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad)); 613 memcpy(hmac_pad, mac_secret, mac_secret_length); 614 for (i = 0; i < md_block_size; i++) 615 hmac_pad[i] ^= 0x36; 616 617 md_transform(md_state.c, hmac_pad); 618 } 619 620 if (length_is_big_endian) { 621 memset(length_bytes, 0, md_length_size - 4); 622 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); 623 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); 624 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); 625 length_bytes[md_length_size - 1] = (unsigned char)bits; 626 } else { 627 memset(length_bytes, 0, md_length_size); 628 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); 629 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); 630 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); 631 length_bytes[md_length_size - 8] = (unsigned char)bits; 632 } 633 634 if (k > 0) { 635 if (is_sslv3) { 636 /* 637 * The SSLv3 header is larger than a single block. overhang is 638 * the number of bytes beyond a single block that the header 639 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5). 640 */ 641 unsigned overhang = header_length - md_block_size; 642 md_transform(md_state.c, header); 643 memcpy(first_block, header + md_block_size, overhang); 644 memcpy(first_block + overhang, data, md_block_size - overhang); 645 md_transform(md_state.c, first_block); 646 for (i = 1; i < k / md_block_size - 1; i++) 647 md_transform(md_state.c, data + md_block_size * i - overhang); 648 } else { 649 /* k is a multiple of md_block_size. */ 650 memcpy(first_block, header, 13); 651 memcpy(first_block + 13, data, md_block_size - 13); 652 md_transform(md_state.c, first_block); 653 for (i = 1; i < k / md_block_size; i++) 654 md_transform(md_state.c, data + md_block_size * i - 13); 655 } 656 } 657 658 memset(mac_out, 0, sizeof(mac_out)); 659 660 /* 661 * We now process the final hash blocks. For each block, we construct it 662 * in constant time. If the |i==index_a| then we'll include the 0x80 663 * bytes and zero pad etc. For each block we selectively copy it, in 664 * constant time, to |mac_out|. 665 */ 666 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks; 667 i++) { 668 unsigned char block[MAX_HASH_BLOCK_SIZE]; 669 unsigned char is_block_a = constant_time_eq_8(i, index_a); 670 unsigned char is_block_b = constant_time_eq_8(i, index_b); 671 for (j = 0; j < md_block_size; j++) { 672 unsigned char b = 0, is_past_c, is_past_cp1; 673 if (k < header_length) 674 b = header[k]; 675 else if (k < data_plus_mac_plus_padding_size + header_length) 676 b = data[k - header_length]; 677 k++; 678 679 is_past_c = is_block_a & constant_time_ge_8(j, c); 680 is_past_cp1 = is_block_a & constant_time_ge_8(j, c + 1); 681 /* 682 * If this is the block containing the end of the application 683 * data, and we are at the offset for the 0x80 value, then 684 * overwrite b with 0x80. 685 */ 686 b = constant_time_select_8(is_past_c, 0x80, b); 687 /* 688 * If this the the block containing the end of the application 689 * data and we're past the 0x80 value then just write zero. 690 */ 691 b = b & ~is_past_cp1; 692 /* 693 * If this is index_b (the final block), but not index_a (the end 694 * of the data), then the 64-bit length didn't fit into index_a 695 * and we're having to add an extra block of zeros. 696 */ 697 b &= ~is_block_b | is_block_a; 698 699 /* 700 * The final bytes of one of the blocks contains the length. 701 */ 702 if (j >= md_block_size - md_length_size) { 703 /* If this is index_b, write a length byte. */ 704 b = constant_time_select_8(is_block_b, 705 length_bytes[j - 706 (md_block_size - 707 md_length_size)], b); 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, digest, NULL /* engine */ ); 721 if (is_sslv3) { 722 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */ 723 memset(hmac_pad, 0x5c, sslv3_pad_length); 724 725 EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length); 726 EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length); 727 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 728 } else { 729 /* Complete the HMAC in the standard manner. */ 730 for (i = 0; i < md_block_size; i++) 731 hmac_pad[i] ^= 0x6a; 732 733 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 734 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 735 } 736 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 737 if (md_out_size) 738 *md_out_size = md_out_size_u; 739 EVP_MD_CTX_cleanup(&md_ctx); 740} 741 742#ifdef OPENSSL_FIPS 743 744/* 745 * Due to the need to use EVP in FIPS mode we can't reimplement digests but 746 * we can ensure the number of blocks processed is equal for all cases by 747 * digesting additional data. 748 */ 749 750void tls_fips_digest_extra(const EVP_CIPHER_CTX *cipher_ctx, 751 const EVP_MD *hash, HMAC_CTX *hctx, 752 const unsigned char *data, size_t data_len, 753 size_t orig_len) 754{ 755 size_t block_size, digest_pad, blocks_data, blocks_orig; 756 if (EVP_CIPHER_CTX_mode(cipher_ctx) != EVP_CIPH_CBC_MODE) 757 return; 758 block_size = EVP_MD_block_size(hash); 759 /* 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. Minimum digest padding length is 17 for 762 * SHA384/SHA512 and 9 otherwise. Additional header is 13 bytes. To get 763 * the number of digest blocks processed round up the amount of data plus 764 * padding to the nearest block length. Block length is 128 for 765 * SHA384/SHA512 and 64 otherwise. So we have: blocks = (payload_len + 766 * digest_pad + 13 + block_size - 1)/block_size equivalently: blocks = 767 * (payload_len + digest_pad + 12)/block_size + 1 HMAC adds a constant 768 * overhead. We're ultimately only interested in differences so this 769 * becomes blocks = (payload_len + 29)/128 for SHA384/SHA512 and blocks = 770 * (payload_len + 21)/64 otherwise. 771 */ 772 digest_pad = block_size == 64 ? 21 : 29; 773 blocks_orig = (orig_len + digest_pad) / block_size; 774 blocks_data = (data_len + digest_pad) / block_size; 775 /* 776 * MAC enough blocks to make up the difference between the original and 777 * actual lengths plus one extra block to ensure this is never a no op. 778 * The "data" pointer should always have enough space to perform this 779 * operation as it is large enough for a maximum length TLS buffer. 780 */ 781 HMAC_Update(hctx, data, (blocks_orig - blocks_data + 1) * block_size); 782} 783#endif 784