1 /* 2 * Copyright 2012-2018 The OpenSSL Project Authors. All Rights Reserved. 3 * 4 * Licensed under the OpenSSL license (the "License"). You may not use 5 * this file except in compliance with the License. You can obtain a copy 6 * in the file LICENSE in the source distribution or at 7 * https://www.openssl.org/source/license.html 8 */ 9 10 #include "internal/constant_time.h" 11 #include "ssl_local.h" 12 #include "internal/cryptlib.h" 13 14 #include <openssl/md5.h> 15 #include <openssl/sha.h> 16 17 /* 18 * MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's 19 * length field. (SHA-384/512 have 128-bit length.) 20 */ 21 #define MAX_HASH_BIT_COUNT_BYTES 16 22 23 /* 24 * MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support. 25 * Currently SHA-384/512 has a 128-byte block size and that's the largest 26 * supported by TLS.) 27 */ 28 #define MAX_HASH_BLOCK_SIZE 128 29 30 /* 31 * u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 32 * little-endian order. The value of p is advanced by four. 33 */ 34 #define u32toLE(n, p) \ 35 (*((p)++)=(unsigned char)(n), \ 36 *((p)++)=(unsigned char)(n>>8), \ 37 *((p)++)=(unsigned char)(n>>16), \ 38 *((p)++)=(unsigned char)(n>>24)) 39 40 /* 41 * These functions serialize the state of a hash and thus perform the 42 * standard "final" operation without adding the padding and length that such 43 * a function typically does. 44 */ 45 static void tls1_md5_final_raw(void *ctx, unsigned char *md_out) 46 { 47 MD5_CTX *md5 = ctx; 48 u32toLE(md5->A, md_out); 49 u32toLE(md5->B, md_out); 50 u32toLE(md5->C, md_out); 51 u32toLE(md5->D, md_out); 52 } 53 54 static void tls1_sha1_final_raw(void *ctx, unsigned char *md_out) 55 { 56 SHA_CTX *sha1 = ctx; 57 l2n(sha1->h0, md_out); 58 l2n(sha1->h1, md_out); 59 l2n(sha1->h2, md_out); 60 l2n(sha1->h3, md_out); 61 l2n(sha1->h4, md_out); 62 } 63 64 static void tls1_sha256_final_raw(void *ctx, unsigned char *md_out) 65 { 66 SHA256_CTX *sha256 = ctx; 67 unsigned i; 68 69 for (i = 0; i < 8; i++) { 70 l2n(sha256->h[i], md_out); 71 } 72 } 73 74 static void tls1_sha512_final_raw(void *ctx, unsigned char *md_out) 75 { 76 SHA512_CTX *sha512 = ctx; 77 unsigned i; 78 79 for (i = 0; i < 8; i++) { 80 l2n8(sha512->h[i], md_out); 81 } 82 } 83 84 #undef LARGEST_DIGEST_CTX 85 #define LARGEST_DIGEST_CTX SHA512_CTX 86 87 /* 88 * ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 89 * which ssl3_cbc_digest_record supports. 90 */ 91 char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) 92 { 93 switch (EVP_MD_CTX_type(ctx)) { 94 case NID_md5: 95 case NID_sha1: 96 case NID_sha224: 97 case NID_sha256: 98 case NID_sha384: 99 case NID_sha512: 100 return 1; 101 default: 102 return 0; 103 } 104 } 105 106 /*- 107 * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS 108 * record. 109 * 110 * ctx: the EVP_MD_CTX from which we take the hash function. 111 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 112 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 113 * md_out_size: if non-NULL, the number of output bytes is written here. 114 * header: the 13-byte, TLS record header. 115 * data: the record data itself, less any preceding explicit IV. 116 * data_plus_mac_size: the secret, reported length of the data and MAC 117 * once the padding has been removed. 118 * data_plus_mac_plus_padding_size: the public length of the whole 119 * record, including padding. 120 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS. 121 * 122 * On entry: by virtue of having been through one of the remove_padding 123 * functions, above, we know that data_plus_mac_size is large enough to contain 124 * a padding byte and MAC. (If the padding was invalid, it might contain the 125 * padding too. ) 126 * Returns 1 on success or 0 on error 127 */ 128 int ssl3_cbc_digest_record(const EVP_MD_CTX *ctx, 129 unsigned char *md_out, 130 size_t *md_out_size, 131 const unsigned char header[13], 132 const unsigned char *data, 133 size_t data_plus_mac_size, 134 size_t data_plus_mac_plus_padding_size, 135 const unsigned char *mac_secret, 136 size_t mac_secret_length, char is_sslv3) 137 { 138 union { 139 double align; 140 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; 141 } md_state; 142 void (*md_final_raw) (void *ctx, unsigned char *md_out); 143 void (*md_transform) (void *ctx, const unsigned char *block); 144 size_t md_size, md_block_size = 64; 145 size_t sslv3_pad_length = 40, header_length, variance_blocks, 146 len, max_mac_bytes, num_blocks, 147 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 148 size_t bits; /* at most 18 bits */ 149 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 150 /* hmac_pad is the masked HMAC key. */ 151 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 152 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 153 unsigned char mac_out[EVP_MAX_MD_SIZE]; 154 size_t i, j; 155 unsigned md_out_size_u; 156 EVP_MD_CTX *md_ctx = NULL; 157 /* 158 * mdLengthSize is the number of bytes in the length field that 159 * terminates * the hash. 160 */ 161 size_t md_length_size = 8; 162 char length_is_big_endian = 1; 163 int ret; 164 165 /* 166 * This is a, hopefully redundant, check that allows us to forget about 167 * many possible overflows later in this function. 168 */ 169 if (!ossl_assert(data_plus_mac_plus_padding_size < 1024 * 1024)) 170 return 0; 171 172 switch (EVP_MD_CTX_type(ctx)) { 173 case NID_md5: 174 if (MD5_Init((MD5_CTX *)md_state.c) <= 0) 175 return 0; 176 md_final_raw = tls1_md5_final_raw; 177 md_transform = 178 (void (*)(void *ctx, const unsigned char *block))MD5_Transform; 179 md_size = 16; 180 sslv3_pad_length = 48; 181 length_is_big_endian = 0; 182 break; 183 case NID_sha1: 184 if (SHA1_Init((SHA_CTX *)md_state.c) <= 0) 185 return 0; 186 md_final_raw = tls1_sha1_final_raw; 187 md_transform = 188 (void (*)(void *ctx, const unsigned char *block))SHA1_Transform; 189 md_size = 20; 190 break; 191 case NID_sha224: 192 if (SHA224_Init((SHA256_CTX *)md_state.c) <= 0) 193 return 0; 194 md_final_raw = tls1_sha256_final_raw; 195 md_transform = 196 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform; 197 md_size = 224 / 8; 198 break; 199 case NID_sha256: 200 if (SHA256_Init((SHA256_CTX *)md_state.c) <= 0) 201 return 0; 202 md_final_raw = tls1_sha256_final_raw; 203 md_transform = 204 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform; 205 md_size = 32; 206 break; 207 case NID_sha384: 208 if (SHA384_Init((SHA512_CTX *)md_state.c) <= 0) 209 return 0; 210 md_final_raw = tls1_sha512_final_raw; 211 md_transform = 212 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform; 213 md_size = 384 / 8; 214 md_block_size = 128; 215 md_length_size = 16; 216 break; 217 case NID_sha512: 218 if (SHA512_Init((SHA512_CTX *)md_state.c) <= 0) 219 return 0; 220 md_final_raw = tls1_sha512_final_raw; 221 md_transform = 222 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform; 223 md_size = 64; 224 md_block_size = 128; 225 md_length_size = 16; 226 break; 227 default: 228 /* 229 * ssl3_cbc_record_digest_supported should have been called first to 230 * check that the hash function is supported. 231 */ 232 if (md_out_size != NULL) 233 *md_out_size = 0; 234 return ossl_assert(0); 235 } 236 237 if (!ossl_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES) 238 || !ossl_assert(md_block_size <= MAX_HASH_BLOCK_SIZE) 239 || !ossl_assert(md_size <= EVP_MAX_MD_SIZE)) 240 return 0; 241 242 header_length = 13; 243 if (is_sslv3) { 244 header_length = mac_secret_length + sslv3_pad_length + 8 /* sequence 245 * number */ + 246 1 /* record type */ + 247 2 /* record length */ ; 248 } 249 250 /* 251 * variance_blocks is the number of blocks of the hash that we have to 252 * calculate in constant time because they could be altered by the 253 * padding value. In SSLv3, the padding must be minimal so the end of 254 * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively 255 * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes 256 * of hash termination (0x80 + 64-bit length) don't fit in the final 257 * block, we say that the final two blocks can vary based on the padding. 258 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 259 * required to be minimal. Therefore we say that the final |variance_blocks| 260 * blocks can 261 * vary based on the padding. Later in the function, if the message is 262 * short and there obviously cannot be this many blocks then 263 * variance_blocks can be reduced. 264 */ 265 variance_blocks = is_sslv3 ? 2 : ( ((255 + 1 + md_size + md_block_size - 1) / md_block_size) + 1); 266 /* 267 * From now on we're dealing with the MAC, which conceptually has 13 268 * bytes of `header' before the start of the data (TLS) or 71/75 bytes 269 * (SSLv3) 270 */ 271 len = data_plus_mac_plus_padding_size + header_length; 272 /* 273 * max_mac_bytes contains the maximum bytes of bytes in the MAC, 274 * including * |header|, assuming that there's no padding. 275 */ 276 max_mac_bytes = len - md_size - 1; 277 /* num_blocks is the maximum number of hash blocks. */ 278 num_blocks = 279 (max_mac_bytes + 1 + md_length_size + md_block_size - 280 1) / md_block_size; 281 /* 282 * In order to calculate the MAC in constant time we have to handle the 283 * final blocks specially because the padding value could cause the end 284 * to appear somewhere in the final |variance_blocks| blocks and we can't 285 * leak where. However, |num_starting_blocks| worth of data can be hashed 286 * right away because no padding value can affect whether they are 287 * plaintext. 288 */ 289 num_starting_blocks = 0; 290 /* 291 * k is the starting byte offset into the conceptual header||data where 292 * we start processing. 293 */ 294 k = 0; 295 /* 296 * mac_end_offset is the index just past the end of the data to be MACed. 297 */ 298 mac_end_offset = data_plus_mac_size + header_length - md_size; 299 /* 300 * c is the index of the 0x80 byte in the final hash block that contains 301 * application data. 302 */ 303 c = mac_end_offset % md_block_size; 304 /* 305 * index_a is the hash block number that contains the 0x80 terminating 306 * value. 307 */ 308 index_a = mac_end_offset / md_block_size; 309 /* 310 * index_b is the hash block number that contains the 64-bit hash length, 311 * in bits. 312 */ 313 index_b = (mac_end_offset + md_length_size) / md_block_size; 314 /* 315 * bits is the hash-length in bits. It includes the additional hash block 316 * for the masked HMAC key, or whole of |header| in the case of SSLv3. 317 */ 318 319 /* 320 * For SSLv3, if we're going to have any starting blocks then we need at 321 * least two because the header is larger than a single block. 322 */ 323 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) { 324 num_starting_blocks = num_blocks - variance_blocks; 325 k = md_block_size * num_starting_blocks; 326 } 327 328 bits = 8 * mac_end_offset; 329 if (!is_sslv3) { 330 /* 331 * Compute the initial HMAC block. For SSLv3, the padding and secret 332 * bytes are included in |header| because they take more than a 333 * single block. 334 */ 335 bits += 8 * md_block_size; 336 memset(hmac_pad, 0, md_block_size); 337 if (!ossl_assert(mac_secret_length <= sizeof(hmac_pad))) 338 return 0; 339 memcpy(hmac_pad, mac_secret, mac_secret_length); 340 for (i = 0; i < md_block_size; i++) 341 hmac_pad[i] ^= 0x36; 342 343 md_transform(md_state.c, hmac_pad); 344 } 345 346 if (length_is_big_endian) { 347 memset(length_bytes, 0, md_length_size - 4); 348 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); 349 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); 350 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); 351 length_bytes[md_length_size - 1] = (unsigned char)bits; 352 } else { 353 memset(length_bytes, 0, md_length_size); 354 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); 355 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); 356 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); 357 length_bytes[md_length_size - 8] = (unsigned char)bits; 358 } 359 360 if (k > 0) { 361 if (is_sslv3) { 362 size_t overhang; 363 364 /* 365 * The SSLv3 header is larger than a single block. overhang is 366 * the number of bytes beyond a single block that the header 367 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5). There are no 368 * ciphersuites in SSLv3 that are not SHA1 or MD5 based and 369 * therefore we can be confident that the header_length will be 370 * greater than |md_block_size|. However we add a sanity check just 371 * in case 372 */ 373 if (header_length <= md_block_size) { 374 /* Should never happen */ 375 return 0; 376 } 377 overhang = header_length - md_block_size; 378 md_transform(md_state.c, header); 379 memcpy(first_block, header + md_block_size, overhang); 380 memcpy(first_block + overhang, data, md_block_size - overhang); 381 md_transform(md_state.c, first_block); 382 for (i = 1; i < k / md_block_size - 1; i++) 383 md_transform(md_state.c, data + md_block_size * i - overhang); 384 } else { 385 /* k is a multiple of md_block_size. */ 386 memcpy(first_block, header, 13); 387 memcpy(first_block + 13, data, md_block_size - 13); 388 md_transform(md_state.c, first_block); 389 for (i = 1; i < k / md_block_size; i++) 390 md_transform(md_state.c, data + md_block_size * i - 13); 391 } 392 } 393 394 memset(mac_out, 0, sizeof(mac_out)); 395 396 /* 397 * We now process the final hash blocks. For each block, we construct it 398 * in constant time. If the |i==index_a| then we'll include the 0x80 399 * bytes and zero pad etc. For each block we selectively copy it, in 400 * constant time, to |mac_out|. 401 */ 402 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks; 403 i++) { 404 unsigned char block[MAX_HASH_BLOCK_SIZE]; 405 unsigned char is_block_a = constant_time_eq_8_s(i, index_a); 406 unsigned char is_block_b = constant_time_eq_8_s(i, index_b); 407 for (j = 0; j < md_block_size; j++) { 408 unsigned char b = 0, is_past_c, is_past_cp1; 409 if (k < header_length) 410 b = header[k]; 411 else if (k < data_plus_mac_plus_padding_size + header_length) 412 b = data[k - header_length]; 413 k++; 414 415 is_past_c = is_block_a & constant_time_ge_8_s(j, c); 416 is_past_cp1 = is_block_a & constant_time_ge_8_s(j, c + 1); 417 /* 418 * If this is the block containing the end of the application 419 * data, and we are at the offset for the 0x80 value, then 420 * overwrite b with 0x80. 421 */ 422 b = constant_time_select_8(is_past_c, 0x80, b); 423 /* 424 * If this block contains the end of the application data 425 * and we're past the 0x80 value then just write zero. 426 */ 427 b = b & ~is_past_cp1; 428 /* 429 * If this is index_b (the final block), but not index_a (the end 430 * of the data), then the 64-bit length didn't fit into index_a 431 * and we're having to add an extra block of zeros. 432 */ 433 b &= ~is_block_b | is_block_a; 434 435 /* 436 * The final bytes of one of the blocks contains the length. 437 */ 438 if (j >= md_block_size - md_length_size) { 439 /* If this is index_b, write a length byte. */ 440 b = constant_time_select_8(is_block_b, 441 length_bytes[j - 442 (md_block_size - 443 md_length_size)], b); 444 } 445 block[j] = b; 446 } 447 448 md_transform(md_state.c, block); 449 md_final_raw(md_state.c, block); 450 /* If this is index_b, copy the hash value to |mac_out|. */ 451 for (j = 0; j < md_size; j++) 452 mac_out[j] |= block[j] & is_block_b; 453 } 454 455 md_ctx = EVP_MD_CTX_new(); 456 if (md_ctx == NULL) 457 goto err; 458 if (EVP_DigestInit_ex(md_ctx, EVP_MD_CTX_md(ctx), NULL /* engine */ ) <= 0) 459 goto err; 460 if (is_sslv3) { 461 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */ 462 memset(hmac_pad, 0x5c, sslv3_pad_length); 463 464 if (EVP_DigestUpdate(md_ctx, mac_secret, mac_secret_length) <= 0 465 || EVP_DigestUpdate(md_ctx, hmac_pad, sslv3_pad_length) <= 0 466 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0) 467 goto err; 468 } else { 469 /* Complete the HMAC in the standard manner. */ 470 for (i = 0; i < md_block_size; i++) 471 hmac_pad[i] ^= 0x6a; 472 473 if (EVP_DigestUpdate(md_ctx, hmac_pad, md_block_size) <= 0 474 || EVP_DigestUpdate(md_ctx, mac_out, md_size) <= 0) 475 goto err; 476 } 477 /* TODO(size_t): Convert me */ 478 ret = EVP_DigestFinal(md_ctx, md_out, &md_out_size_u); 479 if (ret && md_out_size) 480 *md_out_size = md_out_size_u; 481 EVP_MD_CTX_free(md_ctx); 482 483 return 1; 484 err: 485 EVP_MD_CTX_free(md_ctx); 486 return 0; 487 } 488