1 /* 2 * Copyright (C) 2008 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include <errno.h> 18 #include <malloc.h> 19 #include <stdio.h> 20 #include <string.h> 21 22 #include <algorithm> 23 #include <memory> 24 25 #include <openssl/ecdsa.h> 26 #include <openssl/obj_mac.h> 27 28 #include "asn1_decoder.h" 29 #include "common.h" 30 #include "print_sha1.h" 31 #include "ui.h" 32 #include "verifier.h" 33 34 extern RecoveryUI* ui; 35 36 static constexpr size_t MiB = 1024 * 1024; 37 38 /* 39 * Simple version of PKCS#7 SignedData extraction. This extracts the 40 * signature OCTET STRING to be used for signature verification. 41 * 42 * For full details, see http://www.ietf.org/rfc/rfc3852.txt 43 * 44 * The PKCS#7 structure looks like: 45 * 46 * SEQUENCE (ContentInfo) 47 * OID (ContentType) 48 * [0] (content) 49 * SEQUENCE (SignedData) 50 * INTEGER (version CMSVersion) 51 * SET (DigestAlgorithmIdentifiers) 52 * SEQUENCE (EncapsulatedContentInfo) 53 * [0] (CertificateSet OPTIONAL) 54 * [1] (RevocationInfoChoices OPTIONAL) 55 * SET (SignerInfos) 56 * SEQUENCE (SignerInfo) 57 * INTEGER (CMSVersion) 58 * SEQUENCE (SignerIdentifier) 59 * SEQUENCE (DigestAlgorithmIdentifier) 60 * SEQUENCE (SignatureAlgorithmIdentifier) 61 * OCTET STRING (SignatureValue) 62 */ 63 static bool read_pkcs7(uint8_t* pkcs7_der, size_t pkcs7_der_len, uint8_t** sig_der, 64 size_t* sig_der_length) { 65 asn1_context_t* ctx = asn1_context_new(pkcs7_der, pkcs7_der_len); 66 if (ctx == NULL) { 67 return false; 68 } 69 70 asn1_context_t* pkcs7_seq = asn1_sequence_get(ctx); 71 if (pkcs7_seq != NULL && asn1_sequence_next(pkcs7_seq)) { 72 asn1_context_t *signed_data_app = asn1_constructed_get(pkcs7_seq); 73 if (signed_data_app != NULL) { 74 asn1_context_t* signed_data_seq = asn1_sequence_get(signed_data_app); 75 if (signed_data_seq != NULL 76 && asn1_sequence_next(signed_data_seq) 77 && asn1_sequence_next(signed_data_seq) 78 && asn1_sequence_next(signed_data_seq) 79 && asn1_constructed_skip_all(signed_data_seq)) { 80 asn1_context_t *sig_set = asn1_set_get(signed_data_seq); 81 if (sig_set != NULL) { 82 asn1_context_t* sig_seq = asn1_sequence_get(sig_set); 83 if (sig_seq != NULL 84 && asn1_sequence_next(sig_seq) 85 && asn1_sequence_next(sig_seq) 86 && asn1_sequence_next(sig_seq) 87 && asn1_sequence_next(sig_seq)) { 88 uint8_t* sig_der_ptr; 89 if (asn1_octet_string_get(sig_seq, &sig_der_ptr, sig_der_length)) { 90 *sig_der = (uint8_t*) malloc(*sig_der_length); 91 if (*sig_der != NULL) { 92 memcpy(*sig_der, sig_der_ptr, *sig_der_length); 93 } 94 } 95 asn1_context_free(sig_seq); 96 } 97 asn1_context_free(sig_set); 98 } 99 asn1_context_free(signed_data_seq); 100 } 101 asn1_context_free(signed_data_app); 102 } 103 asn1_context_free(pkcs7_seq); 104 } 105 asn1_context_free(ctx); 106 107 return *sig_der != NULL; 108 } 109 110 // Look for an RSA signature embedded in the .ZIP file comment given 111 // the path to the zip. Verify it matches one of the given public 112 // keys. 113 // 114 // Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered 115 // or no key matches the signature). 116 117 int verify_file(unsigned char* addr, size_t length, 118 const std::vector<Certificate>& keys) { 119 ui->SetProgress(0.0); 120 121 // An archive with a whole-file signature will end in six bytes: 122 // 123 // (2-byte signature start) $ff $ff (2-byte comment size) 124 // 125 // (As far as the ZIP format is concerned, these are part of the 126 // archive comment.) We start by reading this footer, this tells 127 // us how far back from the end we have to start reading to find 128 // the whole comment. 129 130 #define FOOTER_SIZE 6 131 132 if (length < FOOTER_SIZE) { 133 LOGE("not big enough to contain footer\n"); 134 return VERIFY_FAILURE; 135 } 136 137 unsigned char* footer = addr + length - FOOTER_SIZE; 138 139 if (footer[2] != 0xff || footer[3] != 0xff) { 140 LOGE("footer is wrong\n"); 141 return VERIFY_FAILURE; 142 } 143 144 size_t comment_size = footer[4] + (footer[5] << 8); 145 size_t signature_start = footer[0] + (footer[1] << 8); 146 LOGI("comment is %zu bytes; signature %zu bytes from end\n", 147 comment_size, signature_start); 148 149 if (signature_start <= FOOTER_SIZE) { 150 LOGE("Signature start is in the footer"); 151 return VERIFY_FAILURE; 152 } 153 154 #define EOCD_HEADER_SIZE 22 155 156 // The end-of-central-directory record is 22 bytes plus any 157 // comment length. 158 size_t eocd_size = comment_size + EOCD_HEADER_SIZE; 159 160 if (length < eocd_size) { 161 LOGE("not big enough to contain EOCD\n"); 162 return VERIFY_FAILURE; 163 } 164 165 // Determine how much of the file is covered by the signature. 166 // This is everything except the signature data and length, which 167 // includes all of the EOCD except for the comment length field (2 168 // bytes) and the comment data. 169 size_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2; 170 171 unsigned char* eocd = addr + length - eocd_size; 172 173 // If this is really is the EOCD record, it will begin with the 174 // magic number $50 $4b $05 $06. 175 if (eocd[0] != 0x50 || eocd[1] != 0x4b || 176 eocd[2] != 0x05 || eocd[3] != 0x06) { 177 LOGE("signature length doesn't match EOCD marker\n"); 178 return VERIFY_FAILURE; 179 } 180 181 for (size_t i = 4; i < eocd_size-3; ++i) { 182 if (eocd[i ] == 0x50 && eocd[i+1] == 0x4b && 183 eocd[i+2] == 0x05 && eocd[i+3] == 0x06) { 184 // if the sequence $50 $4b $05 $06 appears anywhere after 185 // the real one, minzip will find the later (wrong) one, 186 // which could be exploitable. Fail verification if 187 // this sequence occurs anywhere after the real one. 188 LOGE("EOCD marker occurs after start of EOCD\n"); 189 return VERIFY_FAILURE; 190 } 191 } 192 193 bool need_sha1 = false; 194 bool need_sha256 = false; 195 for (const auto& key : keys) { 196 switch (key.hash_len) { 197 case SHA_DIGEST_LENGTH: need_sha1 = true; break; 198 case SHA256_DIGEST_LENGTH: need_sha256 = true; break; 199 } 200 } 201 202 SHA_CTX sha1_ctx; 203 SHA256_CTX sha256_ctx; 204 SHA1_Init(&sha1_ctx); 205 SHA256_Init(&sha256_ctx); 206 207 double frac = -1.0; 208 size_t so_far = 0; 209 while (so_far < signed_len) { 210 // On a Nexus 5X, experiment showed 16MiB beat 1MiB by 6% faster for a 211 // 1196MiB full OTA and 60% for an 89MiB incremental OTA. 212 // http://b/28135231. 213 size_t size = std::min(signed_len - so_far, 16 * MiB); 214 215 if (need_sha1) SHA1_Update(&sha1_ctx, addr + so_far, size); 216 if (need_sha256) SHA256_Update(&sha256_ctx, addr + so_far, size); 217 so_far += size; 218 219 double f = so_far / (double)signed_len; 220 if (f > frac + 0.02 || size == so_far) { 221 ui->SetProgress(f); 222 frac = f; 223 } 224 } 225 226 uint8_t sha1[SHA_DIGEST_LENGTH]; 227 SHA1_Final(sha1, &sha1_ctx); 228 uint8_t sha256[SHA256_DIGEST_LENGTH]; 229 SHA256_Final(sha256, &sha256_ctx); 230 231 uint8_t* sig_der = nullptr; 232 size_t sig_der_length = 0; 233 234 uint8_t* signature = eocd + eocd_size - signature_start; 235 size_t signature_size = signature_start - FOOTER_SIZE; 236 237 LOGI("signature (offset: 0x%zx, length: %zu): %s\n", 238 length - signature_start, signature_size, 239 print_hex(signature, signature_size).c_str()); 240 241 if (!read_pkcs7(signature, signature_size, &sig_der, &sig_der_length)) { 242 LOGE("Could not find signature DER block\n"); 243 return VERIFY_FAILURE; 244 } 245 246 /* 247 * Check to make sure at least one of the keys matches the signature. Since 248 * any key can match, we need to try each before determining a verification 249 * failure has happened. 250 */ 251 size_t i = 0; 252 for (const auto& key : keys) { 253 const uint8_t* hash; 254 int hash_nid; 255 switch (key.hash_len) { 256 case SHA_DIGEST_LENGTH: 257 hash = sha1; 258 hash_nid = NID_sha1; 259 break; 260 case SHA256_DIGEST_LENGTH: 261 hash = sha256; 262 hash_nid = NID_sha256; 263 break; 264 default: 265 continue; 266 } 267 268 // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that 269 // the signing tool appends after the signature itself. 270 if (key.key_type == Certificate::KEY_TYPE_RSA) { 271 if (!RSA_verify(hash_nid, hash, key.hash_len, sig_der, 272 sig_der_length, key.rsa.get())) { 273 LOGI("failed to verify against RSA key %zu\n", i); 274 continue; 275 } 276 277 LOGI("whole-file signature verified against RSA key %zu\n", i); 278 free(sig_der); 279 return VERIFY_SUCCESS; 280 } else if (key.key_type == Certificate::KEY_TYPE_EC 281 && key.hash_len == SHA256_DIGEST_LENGTH) { 282 if (!ECDSA_verify(0, hash, key.hash_len, sig_der, 283 sig_der_length, key.ec.get())) { 284 LOGI("failed to verify against EC key %zu\n", i); 285 continue; 286 } 287 288 LOGI("whole-file signature verified against EC key %zu\n", i); 289 free(sig_der); 290 return VERIFY_SUCCESS; 291 } else { 292 LOGI("Unknown key type %d\n", key.key_type); 293 } 294 i++; 295 } 296 297 if (need_sha1) { 298 LOGI("SHA-1 digest: %s\n", print_hex(sha1, SHA_DIGEST_LENGTH).c_str()); 299 } 300 if (need_sha256) { 301 LOGI("SHA-256 digest: %s\n", print_hex(sha256, SHA256_DIGEST_LENGTH).c_str()); 302 } 303 free(sig_der); 304 LOGE("failed to verify whole-file signature\n"); 305 return VERIFY_FAILURE; 306 } 307 308 std::unique_ptr<RSA, RSADeleter> parse_rsa_key(FILE* file, uint32_t exponent) { 309 // Read key length in words and n0inv. n0inv is a precomputed montgomery 310 // parameter derived from the modulus and can be used to speed up 311 // verification. n0inv is 32 bits wide here, assuming the verification logic 312 // uses 32 bit arithmetic. However, BoringSSL may use a word size of 64 bits 313 // internally, in which case we don't have a valid n0inv. Thus, we just 314 // ignore the montgomery parameters and have BoringSSL recompute them 315 // internally. If/When the speedup from using the montgomery parameters 316 // becomes relevant, we can add more sophisticated code here to obtain a 317 // 64-bit n0inv and initialize the montgomery parameters in the key object. 318 uint32_t key_len_words = 0; 319 uint32_t n0inv = 0; 320 if (fscanf(file, " %i , 0x%x", &key_len_words, &n0inv) != 2) { 321 return nullptr; 322 } 323 324 if (key_len_words > 8192 / 32) { 325 LOGE("key length (%d) too large\n", key_len_words); 326 return nullptr; 327 } 328 329 // Read the modulus. 330 std::unique_ptr<uint32_t[]> modulus(new uint32_t[key_len_words]); 331 if (fscanf(file, " , { %u", &modulus[0]) != 1) { 332 return nullptr; 333 } 334 for (uint32_t i = 1; i < key_len_words; ++i) { 335 if (fscanf(file, " , %u", &modulus[i]) != 1) { 336 return nullptr; 337 } 338 } 339 340 // Cconvert from little-endian array of little-endian words to big-endian 341 // byte array suitable as input for BN_bin2bn. 342 std::reverse((uint8_t*)modulus.get(), 343 (uint8_t*)(modulus.get() + key_len_words)); 344 345 // The next sequence of values is the montgomery parameter R^2. Since we 346 // generally don't have a valid |n0inv|, we ignore this (see comment above). 347 uint32_t rr_value; 348 if (fscanf(file, " } , { %u", &rr_value) != 1) { 349 return nullptr; 350 } 351 for (uint32_t i = 1; i < key_len_words; ++i) { 352 if (fscanf(file, " , %u", &rr_value) != 1) { 353 return nullptr; 354 } 355 } 356 if (fscanf(file, " } } ") != 0) { 357 return nullptr; 358 } 359 360 // Initialize the key. 361 std::unique_ptr<RSA, RSADeleter> key(RSA_new()); 362 if (!key) { 363 return nullptr; 364 } 365 366 key->n = BN_bin2bn((uint8_t*)modulus.get(), 367 key_len_words * sizeof(uint32_t), NULL); 368 if (!key->n) { 369 return nullptr; 370 } 371 372 key->e = BN_new(); 373 if (!key->e || !BN_set_word(key->e, exponent)) { 374 return nullptr; 375 } 376 377 return key; 378 } 379 380 struct BNDeleter { 381 void operator()(BIGNUM* bn) { 382 BN_free(bn); 383 } 384 }; 385 386 std::unique_ptr<EC_KEY, ECKEYDeleter> parse_ec_key(FILE* file) { 387 uint32_t key_len_bytes = 0; 388 if (fscanf(file, " %i", &key_len_bytes) != 1) { 389 return nullptr; 390 } 391 392 std::unique_ptr<EC_GROUP, void (*)(EC_GROUP*)> group( 393 EC_GROUP_new_by_curve_name(NID_X9_62_prime256v1), EC_GROUP_free); 394 if (!group) { 395 return nullptr; 396 } 397 398 // Verify that |key_len| matches the group order. 399 if (key_len_bytes != BN_num_bytes(EC_GROUP_get0_order(group.get()))) { 400 return nullptr; 401 } 402 403 // Read the public key coordinates. Note that the byte order in the file is 404 // little-endian, so we convert to big-endian here. 405 std::unique_ptr<uint8_t[]> bytes(new uint8_t[key_len_bytes]); 406 std::unique_ptr<BIGNUM, BNDeleter> point[2]; 407 for (int i = 0; i < 2; ++i) { 408 unsigned int byte = 0; 409 if (fscanf(file, " , { %u", &byte) != 1) { 410 return nullptr; 411 } 412 bytes[key_len_bytes - 1] = byte; 413 414 for (size_t i = 1; i < key_len_bytes; ++i) { 415 if (fscanf(file, " , %u", &byte) != 1) { 416 return nullptr; 417 } 418 bytes[key_len_bytes - i - 1] = byte; 419 } 420 421 point[i].reset(BN_bin2bn(bytes.get(), key_len_bytes, nullptr)); 422 if (!point[i]) { 423 return nullptr; 424 } 425 426 if (fscanf(file, " }") != 0) { 427 return nullptr; 428 } 429 } 430 431 if (fscanf(file, " } ") != 0) { 432 return nullptr; 433 } 434 435 // Create and initialize the key. 436 std::unique_ptr<EC_KEY, ECKEYDeleter> key(EC_KEY_new()); 437 if (!key || !EC_KEY_set_group(key.get(), group.get()) || 438 !EC_KEY_set_public_key_affine_coordinates(key.get(), point[0].get(), 439 point[1].get())) { 440 return nullptr; 441 } 442 443 return key; 444 } 445 446 // Reads a file containing one or more public keys as produced by 447 // DumpPublicKey: this is an RSAPublicKey struct as it would appear 448 // as a C source literal, eg: 449 // 450 // "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" 451 // 452 // For key versions newer than the original 2048-bit e=3 keys 453 // supported by Android, the string is preceded by a version 454 // identifier, eg: 455 // 456 // "v2 {64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" 457 // 458 // (Note that the braces and commas in this example are actual 459 // characters the parser expects to find in the file; the ellipses 460 // indicate more numbers omitted from this example.) 461 // 462 // The file may contain multiple keys in this format, separated by 463 // commas. The last key must not be followed by a comma. 464 // 465 // A Certificate is a pair of an RSAPublicKey and a particular hash 466 // (we support SHA-1 and SHA-256; we store the hash length to signify 467 // which is being used). The hash used is implied by the version number. 468 // 469 // 1: 2048-bit RSA key with e=3 and SHA-1 hash 470 // 2: 2048-bit RSA key with e=65537 and SHA-1 hash 471 // 3: 2048-bit RSA key with e=3 and SHA-256 hash 472 // 4: 2048-bit RSA key with e=65537 and SHA-256 hash 473 // 5: 256-bit EC key using the NIST P-256 curve parameters and SHA-256 hash 474 // 475 // Returns true on success, and appends the found keys (at least one) to certs. 476 // Otherwise returns false if the file failed to parse, or if it contains zero 477 // keys. The contents in certs would be unspecified on failure. 478 bool load_keys(const char* filename, std::vector<Certificate>& certs) { 479 std::unique_ptr<FILE, decltype(&fclose)> f(fopen(filename, "r"), fclose); 480 if (!f) { 481 LOGE("opening %s: %s\n", filename, strerror(errno)); 482 return false; 483 } 484 485 while (true) { 486 certs.emplace_back(0, Certificate::KEY_TYPE_RSA, nullptr, nullptr); 487 Certificate& cert = certs.back(); 488 uint32_t exponent = 0; 489 490 char start_char; 491 if (fscanf(f.get(), " %c", &start_char) != 1) return false; 492 if (start_char == '{') { 493 // a version 1 key has no version specifier. 494 cert.key_type = Certificate::KEY_TYPE_RSA; 495 exponent = 3; 496 cert.hash_len = SHA_DIGEST_LENGTH; 497 } else if (start_char == 'v') { 498 int version; 499 if (fscanf(f.get(), "%d {", &version) != 1) return false; 500 switch (version) { 501 case 2: 502 cert.key_type = Certificate::KEY_TYPE_RSA; 503 exponent = 65537; 504 cert.hash_len = SHA_DIGEST_LENGTH; 505 break; 506 case 3: 507 cert.key_type = Certificate::KEY_TYPE_RSA; 508 exponent = 3; 509 cert.hash_len = SHA256_DIGEST_LENGTH; 510 break; 511 case 4: 512 cert.key_type = Certificate::KEY_TYPE_RSA; 513 exponent = 65537; 514 cert.hash_len = SHA256_DIGEST_LENGTH; 515 break; 516 case 5: 517 cert.key_type = Certificate::KEY_TYPE_EC; 518 cert.hash_len = SHA256_DIGEST_LENGTH; 519 break; 520 default: 521 return false; 522 } 523 } 524 525 if (cert.key_type == Certificate::KEY_TYPE_RSA) { 526 cert.rsa = parse_rsa_key(f.get(), exponent); 527 if (!cert.rsa) { 528 return false; 529 } 530 531 LOGI("read key e=%d hash=%d\n", exponent, cert.hash_len); 532 } else if (cert.key_type == Certificate::KEY_TYPE_EC) { 533 cert.ec = parse_ec_key(f.get()); 534 if (!cert.ec) { 535 return false; 536 } 537 } else { 538 LOGE("Unknown key type %d\n", cert.key_type); 539 return false; 540 } 541 542 // if the line ends in a comma, this file has more keys. 543 int ch = fgetc(f.get()); 544 if (ch == ',') { 545 // more keys to come. 546 continue; 547 } else if (ch == EOF) { 548 break; 549 } else { 550 LOGE("unexpected character between keys\n"); 551 return false; 552 } 553 } 554 555 return true; 556 } 557
