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 "asn1_decoder.h" 18 #include "common.h" 19 #include "ui.h" 20 #include "verifier.h" 21 22 #include "mincrypt/dsa_sig.h" 23 #include "mincrypt/p256.h" 24 #include "mincrypt/p256_ecdsa.h" 25 #include "mincrypt/rsa.h" 26 #include "mincrypt/sha.h" 27 #include "mincrypt/sha256.h" 28 29 #include <string.h> 30 #include <stdio.h> 31 #include <errno.h> 32 33 extern RecoveryUI* ui; 34 35 /* 36 * Simple version of PKCS#7 SignedData extraction. This extracts the 37 * signature OCTET STRING to be used for signature verification. 38 * 39 * For full details, see http://www.ietf.org/rfc/rfc3852.txt 40 * 41 * The PKCS#7 structure looks like: 42 * 43 * SEQUENCE (ContentInfo) 44 * OID (ContentType) 45 * [0] (content) 46 * SEQUENCE (SignedData) 47 * INTEGER (version CMSVersion) 48 * SET (DigestAlgorithmIdentifiers) 49 * SEQUENCE (EncapsulatedContentInfo) 50 * [0] (CertificateSet OPTIONAL) 51 * [1] (RevocationInfoChoices OPTIONAL) 52 * SET (SignerInfos) 53 * SEQUENCE (SignerInfo) 54 * INTEGER (CMSVersion) 55 * SEQUENCE (SignerIdentifier) 56 * SEQUENCE (DigestAlgorithmIdentifier) 57 * SEQUENCE (SignatureAlgorithmIdentifier) 58 * OCTET STRING (SignatureValue) 59 */ 60 static bool read_pkcs7(uint8_t* pkcs7_der, size_t pkcs7_der_len, uint8_t** sig_der, 61 size_t* sig_der_length) { 62 asn1_context_t* ctx = asn1_context_new(pkcs7_der, pkcs7_der_len); 63 if (ctx == NULL) { 64 return false; 65 } 66 67 asn1_context_t* pkcs7_seq = asn1_sequence_get(ctx); 68 if (pkcs7_seq != NULL && asn1_sequence_next(pkcs7_seq)) { 69 asn1_context_t *signed_data_app = asn1_constructed_get(pkcs7_seq); 70 if (signed_data_app != NULL) { 71 asn1_context_t* signed_data_seq = asn1_sequence_get(signed_data_app); 72 if (signed_data_seq != NULL 73 && asn1_sequence_next(signed_data_seq) 74 && asn1_sequence_next(signed_data_seq) 75 && asn1_sequence_next(signed_data_seq) 76 && asn1_constructed_skip_all(signed_data_seq)) { 77 asn1_context_t *sig_set = asn1_set_get(signed_data_seq); 78 if (sig_set != NULL) { 79 asn1_context_t* sig_seq = asn1_sequence_get(sig_set); 80 if (sig_seq != NULL 81 && asn1_sequence_next(sig_seq) 82 && asn1_sequence_next(sig_seq) 83 && asn1_sequence_next(sig_seq) 84 && asn1_sequence_next(sig_seq)) { 85 uint8_t* sig_der_ptr; 86 if (asn1_octet_string_get(sig_seq, &sig_der_ptr, sig_der_length)) { 87 *sig_der = (uint8_t*) malloc(*sig_der_length); 88 if (*sig_der != NULL) { 89 memcpy(*sig_der, sig_der_ptr, *sig_der_length); 90 } 91 } 92 asn1_context_free(sig_seq); 93 } 94 asn1_context_free(sig_set); 95 } 96 asn1_context_free(signed_data_seq); 97 } 98 asn1_context_free(signed_data_app); 99 } 100 asn1_context_free(pkcs7_seq); 101 } 102 asn1_context_free(ctx); 103 104 return *sig_der != NULL; 105 } 106 107 // Look for an RSA signature embedded in the .ZIP file comment given 108 // the path to the zip. Verify it matches one of the given public 109 // keys. 110 // 111 // Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered 112 // or no key matches the signature). 113 114 int verify_file(unsigned char* addr, size_t length, 115 const Certificate* pKeys, unsigned int numKeys) { 116 ui->SetProgress(0.0); 117 118 // An archive with a whole-file signature will end in six bytes: 119 // 120 // (2-byte signature start) $ff $ff (2-byte comment size) 121 // 122 // (As far as the ZIP format is concerned, these are part of the 123 // archive comment.) We start by reading this footer, this tells 124 // us how far back from the end we have to start reading to find 125 // the whole comment. 126 127 #define FOOTER_SIZE 6 128 129 if (length < FOOTER_SIZE) { 130 LOGE("not big enough to contain footer\n"); 131 return VERIFY_FAILURE; 132 } 133 134 unsigned char* footer = addr + length - FOOTER_SIZE; 135 136 if (footer[2] != 0xff || footer[3] != 0xff) { 137 LOGE("footer is wrong\n"); 138 return VERIFY_FAILURE; 139 } 140 141 size_t comment_size = footer[4] + (footer[5] << 8); 142 size_t signature_start = footer[0] + (footer[1] << 8); 143 LOGI("comment is %zu bytes; signature %zu bytes from end\n", 144 comment_size, signature_start); 145 146 if (signature_start <= FOOTER_SIZE) { 147 LOGE("Signature start is in the footer"); 148 return VERIFY_FAILURE; 149 } 150 151 #define EOCD_HEADER_SIZE 22 152 153 // The end-of-central-directory record is 22 bytes plus any 154 // comment length. 155 size_t eocd_size = comment_size + EOCD_HEADER_SIZE; 156 157 if (length < eocd_size) { 158 LOGE("not big enough to contain EOCD\n"); 159 return VERIFY_FAILURE; 160 } 161 162 // Determine how much of the file is covered by the signature. 163 // This is everything except the signature data and length, which 164 // includes all of the EOCD except for the comment length field (2 165 // bytes) and the comment data. 166 size_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2; 167 168 unsigned char* eocd = addr + length - eocd_size; 169 170 // If this is really is the EOCD record, it will begin with the 171 // magic number $50 $4b $05 $06. 172 if (eocd[0] != 0x50 || eocd[1] != 0x4b || 173 eocd[2] != 0x05 || eocd[3] != 0x06) { 174 LOGE("signature length doesn't match EOCD marker\n"); 175 return VERIFY_FAILURE; 176 } 177 178 size_t i; 179 for (i = 4; i < eocd_size-3; ++i) { 180 if (eocd[i ] == 0x50 && eocd[i+1] == 0x4b && 181 eocd[i+2] == 0x05 && eocd[i+3] == 0x06) { 182 // if the sequence $50 $4b $05 $06 appears anywhere after 183 // the real one, minzip will find the later (wrong) one, 184 // which could be exploitable. Fail verification if 185 // this sequence occurs anywhere after the real one. 186 LOGE("EOCD marker occurs after start of EOCD\n"); 187 return VERIFY_FAILURE; 188 } 189 } 190 191 #define BUFFER_SIZE 4096 192 193 bool need_sha1 = false; 194 bool need_sha256 = false; 195 for (i = 0; i < numKeys; ++i) { 196 switch (pKeys[i].hash_len) { 197 case SHA_DIGEST_SIZE: need_sha1 = true; break; 198 case SHA256_DIGEST_SIZE: need_sha256 = true; break; 199 } 200 } 201 202 SHA_CTX sha1_ctx; 203 SHA256_CTX sha256_ctx; 204 SHA_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 size_t size = signed_len - so_far; 211 if (size > BUFFER_SIZE) size = BUFFER_SIZE; 212 213 if (need_sha1) SHA_update(&sha1_ctx, addr + so_far, size); 214 if (need_sha256) SHA256_update(&sha256_ctx, addr + so_far, size); 215 so_far += size; 216 217 double f = so_far / (double)signed_len; 218 if (f > frac + 0.02 || size == so_far) { 219 ui->SetProgress(f); 220 frac = f; 221 } 222 } 223 224 const uint8_t* sha1 = SHA_final(&sha1_ctx); 225 const uint8_t* sha256 = SHA256_final(&sha256_ctx); 226 227 uint8_t* sig_der = NULL; 228 size_t sig_der_length = 0; 229 230 size_t signature_size = signature_start - FOOTER_SIZE; 231 if (!read_pkcs7(eocd + eocd_size - signature_start, signature_size, &sig_der, 232 &sig_der_length)) { 233 LOGE("Could not find signature DER block\n"); 234 return VERIFY_FAILURE; 235 } 236 237 /* 238 * Check to make sure at least one of the keys matches the signature. Since 239 * any key can match, we need to try each before determining a verification 240 * failure has happened. 241 */ 242 for (i = 0; i < numKeys; ++i) { 243 const uint8_t* hash; 244 switch (pKeys[i].hash_len) { 245 case SHA_DIGEST_SIZE: hash = sha1; break; 246 case SHA256_DIGEST_SIZE: hash = sha256; break; 247 default: continue; 248 } 249 250 // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that 251 // the signing tool appends after the signature itself. 252 if (pKeys[i].key_type == Certificate::RSA) { 253 if (sig_der_length < RSANUMBYTES) { 254 // "signature" block isn't big enough to contain an RSA block. 255 LOGI("signature is too short for RSA key %zu\n", i); 256 continue; 257 } 258 259 if (!RSA_verify(pKeys[i].rsa, sig_der, RSANUMBYTES, 260 hash, pKeys[i].hash_len)) { 261 LOGI("failed to verify against RSA key %zu\n", i); 262 continue; 263 } 264 265 LOGI("whole-file signature verified against RSA key %zu\n", i); 266 free(sig_der); 267 return VERIFY_SUCCESS; 268 } else if (pKeys[i].key_type == Certificate::EC 269 && pKeys[i].hash_len == SHA256_DIGEST_SIZE) { 270 p256_int r, s; 271 if (!dsa_sig_unpack(sig_der, sig_der_length, &r, &s)) { 272 LOGI("Not a DSA signature block for EC key %zu\n", i); 273 continue; 274 } 275 276 p256_int p256_hash; 277 p256_from_bin(hash, &p256_hash); 278 if (!p256_ecdsa_verify(&(pKeys[i].ec->x), &(pKeys[i].ec->y), 279 &p256_hash, &r, &s)) { 280 LOGI("failed to verify against EC key %zu\n", i); 281 continue; 282 } 283 284 LOGI("whole-file signature verified against EC key %zu\n", i); 285 free(sig_der); 286 return VERIFY_SUCCESS; 287 } else { 288 LOGI("Unknown key type %d\n", pKeys[i].key_type); 289 } 290 } 291 free(sig_der); 292 LOGE("failed to verify whole-file signature\n"); 293 return VERIFY_FAILURE; 294 } 295 296 // Reads a file containing one or more public keys as produced by 297 // DumpPublicKey: this is an RSAPublicKey struct as it would appear 298 // as a C source literal, eg: 299 // 300 // "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" 301 // 302 // For key versions newer than the original 2048-bit e=3 keys 303 // supported by Android, the string is preceded by a version 304 // identifier, eg: 305 // 306 // "v2 {64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" 307 // 308 // (Note that the braces and commas in this example are actual 309 // characters the parser expects to find in the file; the ellipses 310 // indicate more numbers omitted from this example.) 311 // 312 // The file may contain multiple keys in this format, separated by 313 // commas. The last key must not be followed by a comma. 314 // 315 // A Certificate is a pair of an RSAPublicKey and a particular hash 316 // (we support SHA-1 and SHA-256; we store the hash length to signify 317 // which is being used). The hash used is implied by the version number. 318 // 319 // 1: 2048-bit RSA key with e=3 and SHA-1 hash 320 // 2: 2048-bit RSA key with e=65537 and SHA-1 hash 321 // 3: 2048-bit RSA key with e=3 and SHA-256 hash 322 // 4: 2048-bit RSA key with e=65537 and SHA-256 hash 323 // 5: 256-bit EC key using the NIST P-256 curve parameters and SHA-256 hash 324 // 325 // Returns NULL if the file failed to parse, or if it contain zero keys. 326 Certificate* 327 load_keys(const char* filename, int* numKeys) { 328 Certificate* out = NULL; 329 *numKeys = 0; 330 331 FILE* f = fopen(filename, "r"); 332 if (f == NULL) { 333 LOGE("opening %s: %s\n", filename, strerror(errno)); 334 goto exit; 335 } 336 337 { 338 int i; 339 bool done = false; 340 while (!done) { 341 ++*numKeys; 342 out = (Certificate*)realloc(out, *numKeys * sizeof(Certificate)); 343 Certificate* cert = out + (*numKeys - 1); 344 memset(cert, '\0', sizeof(Certificate)); 345 346 char start_char; 347 if (fscanf(f, " %c", &start_char) != 1) goto exit; 348 if (start_char == '{') { 349 // a version 1 key has no version specifier. 350 cert->key_type = Certificate::RSA; 351 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey)); 352 cert->rsa->exponent = 3; 353 cert->hash_len = SHA_DIGEST_SIZE; 354 } else if (start_char == 'v') { 355 int version; 356 if (fscanf(f, "%d {", &version) != 1) goto exit; 357 switch (version) { 358 case 2: 359 cert->key_type = Certificate::RSA; 360 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey)); 361 cert->rsa->exponent = 65537; 362 cert->hash_len = SHA_DIGEST_SIZE; 363 break; 364 case 3: 365 cert->key_type = Certificate::RSA; 366 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey)); 367 cert->rsa->exponent = 3; 368 cert->hash_len = SHA256_DIGEST_SIZE; 369 break; 370 case 4: 371 cert->key_type = Certificate::RSA; 372 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey)); 373 cert->rsa->exponent = 65537; 374 cert->hash_len = SHA256_DIGEST_SIZE; 375 break; 376 case 5: 377 cert->key_type = Certificate::EC; 378 cert->ec = (ECPublicKey*)calloc(1, sizeof(ECPublicKey)); 379 cert->hash_len = SHA256_DIGEST_SIZE; 380 break; 381 default: 382 goto exit; 383 } 384 } 385 386 if (cert->key_type == Certificate::RSA) { 387 RSAPublicKey* key = cert->rsa; 388 if (fscanf(f, " %i , 0x%x , { %u", 389 &(key->len), &(key->n0inv), &(key->n[0])) != 3) { 390 goto exit; 391 } 392 if (key->len != RSANUMWORDS) { 393 LOGE("key length (%d) does not match expected size\n", key->len); 394 goto exit; 395 } 396 for (i = 1; i < key->len; ++i) { 397 if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit; 398 } 399 if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit; 400 for (i = 1; i < key->len; ++i) { 401 if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit; 402 } 403 fscanf(f, " } } "); 404 405 LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len); 406 } else if (cert->key_type == Certificate::EC) { 407 ECPublicKey* key = cert->ec; 408 int key_len; 409 unsigned int byte; 410 uint8_t x_bytes[P256_NBYTES]; 411 uint8_t y_bytes[P256_NBYTES]; 412 if (fscanf(f, " %i , { %u", &key_len, &byte) != 2) goto exit; 413 if (key_len != P256_NBYTES) { 414 LOGE("Key length (%d) does not match expected size %d\n", key_len, P256_NBYTES); 415 goto exit; 416 } 417 x_bytes[P256_NBYTES - 1] = byte; 418 for (i = P256_NBYTES - 2; i >= 0; --i) { 419 if (fscanf(f, " , %u", &byte) != 1) goto exit; 420 x_bytes[i] = byte; 421 } 422 if (fscanf(f, " } , { %u", &byte) != 1) goto exit; 423 y_bytes[P256_NBYTES - 1] = byte; 424 for (i = P256_NBYTES - 2; i >= 0; --i) { 425 if (fscanf(f, " , %u", &byte) != 1) goto exit; 426 y_bytes[i] = byte; 427 } 428 fscanf(f, " } } "); 429 p256_from_bin(x_bytes, &key->x); 430 p256_from_bin(y_bytes, &key->y); 431 } else { 432 LOGE("Unknown key type %d\n", cert->key_type); 433 goto exit; 434 } 435 436 // if the line ends in a comma, this file has more keys. 437 switch (fgetc(f)) { 438 case ',': 439 // more keys to come. 440 break; 441 442 case EOF: 443 done = true; 444 break; 445 446 default: 447 LOGE("unexpected character between keys\n"); 448 goto exit; 449 } 450 } 451 } 452 453 fclose(f); 454 return out; 455 456 exit: 457 if (f) fclose(f); 458 free(out); 459 *numKeys = 0; 460 return NULL; 461 } 462
