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 (at) 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 (at) cryptsoft.com). This product includes software written by Tim 51 * Hudson (tjh (at) cryptsoft.com). */ 52 53 #include <assert.h> 54 #include <string.h> 55 56 #include <openssl/digest.h> 57 #include <openssl/obj.h> 58 #include <openssl/sha.h> 59 60 #include "../internal.h" 61 62 63 /* TODO(davidben): unsigned should be size_t. The various constant_time 64 * functions need to be switched to size_t. */ 65 66 /* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length 67 * field. (SHA-384/512 have 128-bit length.) */ 68 #define MAX_HASH_BIT_COUNT_BYTES 16 69 70 /* MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support. 71 * Currently SHA-384/512 has a 128-byte block size and that's the largest 72 * supported by TLS.) */ 73 #define MAX_HASH_BLOCK_SIZE 128 74 75 int EVP_tls_cbc_remove_padding(unsigned *out_len, 76 const uint8_t *in, unsigned in_len, 77 unsigned block_size, unsigned mac_size) { 78 unsigned padding_length, good, to_check, i; 79 const unsigned overhead = 1 /* padding length byte */ + mac_size; 80 81 /* These lengths are all public so we can test them in non-constant time. */ 82 if (overhead > in_len) { 83 return 0; 84 } 85 86 padding_length = in[in_len - 1]; 87 88 good = constant_time_ge(in_len, overhead + padding_length); 89 /* The padding consists of a length byte at the end of the record and 90 * then that many bytes of padding, all with the same value as the 91 * length byte. Thus, with the length byte included, there are i+1 92 * bytes of padding. 93 * 94 * We can't check just |padding_length+1| bytes because that leaks 95 * decrypted information. Therefore we always have to check the maximum 96 * amount of padding possible. (Again, the length of the record is 97 * public information so we can use it.) */ 98 to_check = 256; /* maximum amount of padding, inc length byte. */ 99 if (to_check > in_len) { 100 to_check = in_len; 101 } 102 103 for (i = 0; i < to_check; i++) { 104 uint8_t mask = constant_time_ge_8(padding_length, i); 105 uint8_t b = in[in_len - 1 - i]; 106 /* The final |padding_length+1| bytes should all have the value 107 * |padding_length|. Therefore the XOR should be zero. */ 108 good &= ~(mask & (padding_length ^ b)); 109 } 110 111 /* If any of the final |padding_length+1| bytes had the wrong value, 112 * one or more of the lower eight bits of |good| will be cleared. */ 113 good = constant_time_eq(0xff, good & 0xff); 114 115 /* Always treat |padding_length| as zero on error. If, assuming block size of 116 * 16, a padding of [<15 arbitrary bytes> 15] treated |padding_length| as 16 117 * and returned -1, distinguishing good MAC and bad padding from bad MAC and 118 * bad padding would give POODLE's padding oracle. */ 119 padding_length = good & (padding_length + 1); 120 *out_len = in_len - padding_length; 121 122 return constant_time_select_int(good, 1, -1); 123 } 124 125 /* If CBC_MAC_ROTATE_IN_PLACE is defined then EVP_tls_cbc_copy_mac is performed 126 * with variable accesses in a 64-byte-aligned buffer. Assuming that this fits 127 * into a single or pair of cache-lines, then the variable memory accesses don't 128 * actually affect the timing. CPUs with smaller cache-lines [if any] are not 129 * multi-core and are not considered vulnerable to cache-timing attacks. */ 130 #define CBC_MAC_ROTATE_IN_PLACE 131 132 void EVP_tls_cbc_copy_mac(uint8_t *out, unsigned md_size, 133 const uint8_t *in, unsigned in_len, 134 unsigned orig_len) { 135 #if defined(CBC_MAC_ROTATE_IN_PLACE) 136 uint8_t rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; 137 uint8_t *rotated_mac; 138 #else 139 uint8_t rotated_mac[EVP_MAX_MD_SIZE]; 140 #endif 141 142 /* mac_end is the index of |in| just after the end of the MAC. */ 143 unsigned mac_end = in_len; 144 unsigned mac_start = mac_end - md_size; 145 /* scan_start contains the number of bytes that we can ignore because 146 * the MAC's position can only vary by 255 bytes. */ 147 unsigned scan_start = 0; 148 unsigned i, j; 149 unsigned div_spoiler; 150 unsigned rotate_offset; 151 152 assert(orig_len >= in_len); 153 assert(in_len >= md_size); 154 assert(md_size <= EVP_MAX_MD_SIZE); 155 156 #if defined(CBC_MAC_ROTATE_IN_PLACE) 157 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf) & 63); 158 #endif 159 160 /* This information is public so it's safe to branch based on it. */ 161 if (orig_len > md_size + 255 + 1) { 162 scan_start = orig_len - (md_size + 255 + 1); 163 } 164 /* div_spoiler contains a multiple of md_size that is used to cause the 165 * modulo operation to be constant time. Without this, the time varies 166 * based on the amount of padding when running on Intel chips at least. 167 * 168 * The aim of right-shifting md_size is so that the compiler doesn't 169 * figure out that it can remove div_spoiler as that would require it 170 * to prove that md_size is always even, which I hope is beyond it. */ 171 div_spoiler = md_size >> 1; 172 div_spoiler <<= (sizeof(div_spoiler) - 1) * 8; 173 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; 174 175 memset(rotated_mac, 0, md_size); 176 for (i = scan_start, j = 0; i < orig_len; i++) { 177 uint8_t mac_started = constant_time_ge_8(i, mac_start); 178 uint8_t mac_ended = constant_time_ge_8(i, mac_end); 179 uint8_t b = in[i]; 180 rotated_mac[j++] |= b & mac_started & ~mac_ended; 181 j &= constant_time_lt(j, md_size); 182 } 183 184 /* Now rotate the MAC */ 185 #if defined(CBC_MAC_ROTATE_IN_PLACE) 186 j = 0; 187 for (i = 0; i < md_size; i++) { 188 /* in case cache-line is 32 bytes, touch second line */ 189 ((volatile uint8_t *)rotated_mac)[rotate_offset ^ 32]; 190 out[j++] = rotated_mac[rotate_offset++]; 191 rotate_offset &= constant_time_lt(rotate_offset, md_size); 192 } 193 #else 194 memset(out, 0, md_size); 195 rotate_offset = md_size - rotate_offset; 196 rotate_offset &= constant_time_lt(rotate_offset, md_size); 197 for (i = 0; i < md_size; i++) { 198 for (j = 0; j < md_size; j++) { 199 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); 200 } 201 rotate_offset++; 202 rotate_offset &= constant_time_lt(rotate_offset, md_size); 203 } 204 #endif 205 } 206 207 /* u32toBE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 208 * big-endian order. The value of p is advanced by four. */ 209 #define u32toBE(n, p) \ 210 (*((p)++)=(uint8_t)(n>>24), \ 211 *((p)++)=(uint8_t)(n>>16), \ 212 *((p)++)=(uint8_t)(n>>8), \ 213 *((p)++)=(uint8_t)(n)) 214 215 /* u64toBE serialises an unsigned, 64-bit number (n) as eight bytes at (p) in 216 * big-endian order. The value of p is advanced by eight. */ 217 #define u64toBE(n, p) \ 218 (*((p)++)=(uint8_t)(n>>56), \ 219 *((p)++)=(uint8_t)(n>>48), \ 220 *((p)++)=(uint8_t)(n>>40), \ 221 *((p)++)=(uint8_t)(n>>32), \ 222 *((p)++)=(uint8_t)(n>>24), \ 223 *((p)++)=(uint8_t)(n>>16), \ 224 *((p)++)=(uint8_t)(n>>8), \ 225 *((p)++)=(uint8_t)(n)) 226 227 /* These functions serialize the state of a hash and thus perform the standard 228 * "final" operation without adding the padding and length that such a function 229 * typically does. */ 230 static void tls1_sha1_final_raw(void *ctx, uint8_t *md_out) { 231 SHA_CTX *sha1 = ctx; 232 u32toBE(sha1->h[0], md_out); 233 u32toBE(sha1->h[1], md_out); 234 u32toBE(sha1->h[2], md_out); 235 u32toBE(sha1->h[3], md_out); 236 u32toBE(sha1->h[4], md_out); 237 } 238 #define LARGEST_DIGEST_CTX SHA_CTX 239 240 static void tls1_sha256_final_raw(void *ctx, uint8_t *md_out) { 241 SHA256_CTX *sha256 = ctx; 242 unsigned i; 243 244 for (i = 0; i < 8; i++) { 245 u32toBE(sha256->h[i], md_out); 246 } 247 } 248 #undef LARGEST_DIGEST_CTX 249 #define LARGEST_DIGEST_CTX SHA256_CTX 250 251 static void tls1_sha512_final_raw(void *ctx, uint8_t *md_out) { 252 SHA512_CTX *sha512 = ctx; 253 unsigned i; 254 255 for (i = 0; i < 8; i++) { 256 u64toBE(sha512->h[i], md_out); 257 } 258 } 259 #undef LARGEST_DIGEST_CTX 260 #define LARGEST_DIGEST_CTX SHA512_CTX 261 262 int EVP_tls_cbc_record_digest_supported(const EVP_MD *md) { 263 switch (EVP_MD_type(md)) { 264 case NID_sha1: 265 case NID_sha256: 266 case NID_sha384: 267 return 1; 268 269 default: 270 return 0; 271 } 272 } 273 274 int EVP_tls_cbc_digest_record(const EVP_MD *md, uint8_t *md_out, 275 size_t *md_out_size, const uint8_t header[13], 276 const uint8_t *data, size_t data_plus_mac_size, 277 size_t data_plus_mac_plus_padding_size, 278 const uint8_t *mac_secret, 279 unsigned mac_secret_length) { 280 union { 281 double align; 282 uint8_t c[sizeof(LARGEST_DIGEST_CTX)]; 283 } md_state; 284 void (*md_final_raw)(void *ctx, uint8_t *md_out); 285 void (*md_transform)(void *ctx, const uint8_t *block); 286 unsigned md_size, md_block_size = 64; 287 unsigned len, max_mac_bytes, num_blocks, num_starting_blocks, k, 288 mac_end_offset, c, index_a, index_b; 289 unsigned int bits; /* at most 18 bits */ 290 uint8_t length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 291 /* hmac_pad is the masked HMAC key. */ 292 uint8_t hmac_pad[MAX_HASH_BLOCK_SIZE]; 293 uint8_t first_block[MAX_HASH_BLOCK_SIZE]; 294 uint8_t mac_out[EVP_MAX_MD_SIZE]; 295 unsigned i, j, md_out_size_u; 296 EVP_MD_CTX md_ctx; 297 /* mdLengthSize is the number of bytes in the length field that terminates 298 * the hash. */ 299 unsigned md_length_size = 8; 300 301 /* This is a, hopefully redundant, check that allows us to forget about 302 * many possible overflows later in this function. */ 303 assert(data_plus_mac_plus_padding_size < 1024 * 1024); 304 305 switch (EVP_MD_type(md)) { 306 case NID_sha1: 307 SHA1_Init((SHA_CTX *)md_state.c); 308 md_final_raw = tls1_sha1_final_raw; 309 md_transform = 310 (void (*)(void *ctx, const uint8_t *block))SHA1_Transform; 311 md_size = 20; 312 break; 313 314 case NID_sha256: 315 SHA256_Init((SHA256_CTX *)md_state.c); 316 md_final_raw = tls1_sha256_final_raw; 317 md_transform = 318 (void (*)(void *ctx, const uint8_t *block))SHA256_Transform; 319 md_size = 32; 320 break; 321 322 case NID_sha384: 323 SHA384_Init((SHA512_CTX *)md_state.c); 324 md_final_raw = tls1_sha512_final_raw; 325 md_transform = 326 (void (*)(void *ctx, const uint8_t *block))SHA512_Transform; 327 md_size = 384 / 8; 328 md_block_size = 128; 329 md_length_size = 16; 330 break; 331 332 default: 333 /* EVP_tls_cbc_record_digest_supported should have been called first to 334 * check that the hash function is supported. */ 335 assert(0); 336 *md_out_size = 0; 337 return 0; 338 } 339 340 assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 341 assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 342 assert(md_size <= EVP_MAX_MD_SIZE); 343 344 static const unsigned kHeaderLength = 13; 345 346 /* kVarianceBlocks is the number of blocks of the hash that we have to 347 * calculate in constant time because they could be altered by the 348 * padding value. 349 * 350 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 351 * required to be minimal. Therefore we say that the final six blocks 352 * can vary based on the padding. */ 353 static const unsigned kVarianceBlocks = 6; 354 355 /* From now on we're dealing with the MAC, which conceptually has 13 356 * bytes of `header' before the start of the data. */ 357 len = data_plus_mac_plus_padding_size + kHeaderLength; 358 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including 359 * |header|, assuming that there's no padding. */ 360 max_mac_bytes = len - md_size - 1; 361 /* num_blocks is the maximum number of hash blocks. */ 362 num_blocks = 363 (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size; 364 /* In order to calculate the MAC in constant time we have to handle 365 * the final blocks specially because the padding value could cause the 366 * end to appear somewhere in the final |kVarianceBlocks| blocks and we 367 * can't leak where. However, |num_starting_blocks| worth of data can 368 * be hashed right away because no padding value can affect whether 369 * they are plaintext. */ 370 num_starting_blocks = 0; 371 /* k is the starting byte offset into the conceptual header||data where 372 * we start processing. */ 373 k = 0; 374 /* mac_end_offset is the index just past the end of the data to be 375 * MACed. */ 376 mac_end_offset = data_plus_mac_size + kHeaderLength - md_size; 377 /* c is the index of the 0x80 byte in the final hash block that 378 * contains application data. */ 379 c = mac_end_offset % md_block_size; 380 /* index_a is the hash block number that contains the 0x80 terminating 381 * value. */ 382 index_a = mac_end_offset / md_block_size; 383 /* index_b is the hash block number that contains the 64-bit hash 384 * length, in bits. */ 385 index_b = (mac_end_offset + md_length_size) / md_block_size; 386 /* bits is the hash-length in bits. It includes the additional hash 387 * block for the masked HMAC key. */ 388 389 if (num_blocks > kVarianceBlocks) { 390 num_starting_blocks = num_blocks - kVarianceBlocks; 391 k = md_block_size * num_starting_blocks; 392 } 393 394 bits = 8 * mac_end_offset; 395 396 /* Compute the initial HMAC block. */ 397 bits += 8 * md_block_size; 398 memset(hmac_pad, 0, md_block_size); 399 assert(mac_secret_length <= sizeof(hmac_pad)); 400 memcpy(hmac_pad, mac_secret, mac_secret_length); 401 for (i = 0; i < md_block_size; i++) { 402 hmac_pad[i] ^= 0x36; 403 } 404 405 md_transform(md_state.c, hmac_pad); 406 407 memset(length_bytes, 0, md_length_size - 4); 408 length_bytes[md_length_size - 4] = (uint8_t)(bits >> 24); 409 length_bytes[md_length_size - 3] = (uint8_t)(bits >> 16); 410 length_bytes[md_length_size - 2] = (uint8_t)(bits >> 8); 411 length_bytes[md_length_size - 1] = (uint8_t)bits; 412 413 if (k > 0) { 414 /* k is a multiple of md_block_size. */ 415 memcpy(first_block, header, 13); 416 memcpy(first_block + 13, data, md_block_size - 13); 417 md_transform(md_state.c, first_block); 418 for (i = 1; i < k / md_block_size; i++) { 419 md_transform(md_state.c, data + md_block_size * i - 13); 420 } 421 } 422 423 memset(mac_out, 0, sizeof(mac_out)); 424 425 /* We now process the final hash blocks. For each block, we construct 426 * it in constant time. If the |i==index_a| then we'll include the 0x80 427 * bytes and zero pad etc. For each block we selectively copy it, in 428 * constant time, to |mac_out|. */ 429 for (i = num_starting_blocks; i <= num_starting_blocks + kVarianceBlocks; 430 i++) { 431 uint8_t block[MAX_HASH_BLOCK_SIZE]; 432 uint8_t is_block_a = constant_time_eq_8(i, index_a); 433 uint8_t is_block_b = constant_time_eq_8(i, index_b); 434 for (j = 0; j < md_block_size; j++) { 435 uint8_t b = 0, is_past_c, is_past_cp1; 436 if (k < kHeaderLength) { 437 b = header[k]; 438 } else if (k < data_plus_mac_plus_padding_size + kHeaderLength) { 439 b = data[k - kHeaderLength]; 440 } 441 k++; 442 443 is_past_c = is_block_a & constant_time_ge_8(j, c); 444 is_past_cp1 = is_block_a & constant_time_ge_8(j, c + 1); 445 /* If this is the block containing the end of the 446 * application data, and we are at the offset for the 447 * 0x80 value, then overwrite b with 0x80. */ 448 b = constant_time_select_8(is_past_c, 0x80, b); 449 /* If this the the block containing the end of the 450 * application data and we're past the 0x80 value then 451 * just write zero. */ 452 b = b & ~is_past_cp1; 453 /* If this is index_b (the final block), but not 454 * index_a (the end of the data), then the 64-bit 455 * length didn't fit into index_a and we're having to 456 * add an extra block of zeros. */ 457 b &= ~is_block_b | is_block_a; 458 459 /* The final bytes of one of the blocks contains the 460 * length. */ 461 if (j >= md_block_size - md_length_size) { 462 /* If this is index_b, write a length byte. */ 463 b = constant_time_select_8( 464 is_block_b, length_bytes[j - (md_block_size - md_length_size)], b); 465 } 466 block[j] = b; 467 } 468 469 md_transform(md_state.c, block); 470 md_final_raw(md_state.c, block); 471 /* If this is index_b, copy the hash value to |mac_out|. */ 472 for (j = 0; j < md_size; j++) { 473 mac_out[j] |= block[j] & is_block_b; 474 } 475 } 476 477 EVP_MD_CTX_init(&md_ctx); 478 if (!EVP_DigestInit_ex(&md_ctx, md, NULL /* engine */)) { 479 EVP_MD_CTX_cleanup(&md_ctx); 480 return 0; 481 } 482 483 /* Complete the HMAC in the standard manner. */ 484 for (i = 0; i < md_block_size; i++) { 485 hmac_pad[i] ^= 0x6a; 486 } 487 488 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 489 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 490 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 491 *md_out_size = md_out_size_u; 492 EVP_MD_CTX_cleanup(&md_ctx); 493 494 return 1; 495 } 496
