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 <errno.h> 30 #include <malloc.h> 31 #include <stdio.h> 32 #include <string.h> 33 34 extern RecoveryUI* ui; 35 36 /* 37 * Simple version of PKCS#7 SignedData extraction. This extracts the 38 * signature OCTET STRING to be used for signature verification. 39 * 40 * For full details, see http://www.ietf.org/rfc/rfc3852.txt 41 * 42 * The PKCS#7 structure looks like: 43 * 44 * SEQUENCE (ContentInfo) 45 * OID (ContentType) 46 * [0] (content) 47 * SEQUENCE (SignedData) 48 * INTEGER (version CMSVersion) 49 * SET (DigestAlgorithmIdentifiers) 50 * SEQUENCE (EncapsulatedContentInfo) 51 * [0] (CertificateSet OPTIONAL) 52 * [1] (RevocationInfoChoices OPTIONAL) 53 * SET (SignerInfos) 54 * SEQUENCE (SignerInfo) 55 * INTEGER (CMSVersion) 56 * SEQUENCE (SignerIdentifier) 57 * SEQUENCE (DigestAlgorithmIdentifier) 58 * SEQUENCE (SignatureAlgorithmIdentifier) 59 * OCTET STRING (SignatureValue) 60 */ 61 static bool read_pkcs7(uint8_t* pkcs7_der, size_t pkcs7_der_len, uint8_t** sig_der, 62 size_t* sig_der_length) { 63 asn1_context_t* ctx = asn1_context_new(pkcs7_der, pkcs7_der_len); 64 if (ctx == NULL) { 65 return false; 66 } 67 68 asn1_context_t* pkcs7_seq = asn1_sequence_get(ctx); 69 if (pkcs7_seq != NULL && asn1_sequence_next(pkcs7_seq)) { 70 asn1_context_t *signed_data_app = asn1_constructed_get(pkcs7_seq); 71 if (signed_data_app != NULL) { 72 asn1_context_t* signed_data_seq = asn1_sequence_get(signed_data_app); 73 if (signed_data_seq != NULL 74 && asn1_sequence_next(signed_data_seq) 75 && asn1_sequence_next(signed_data_seq) 76 && asn1_sequence_next(signed_data_seq) 77 && asn1_constructed_skip_all(signed_data_seq)) { 78 asn1_context_t *sig_set = asn1_set_get(signed_data_seq); 79 if (sig_set != NULL) { 80 asn1_context_t* sig_seq = asn1_sequence_get(sig_set); 81 if (sig_seq != NULL 82 && asn1_sequence_next(sig_seq) 83 && asn1_sequence_next(sig_seq) 84 && asn1_sequence_next(sig_seq) 85 && asn1_sequence_next(sig_seq)) { 86 uint8_t* sig_der_ptr; 87 if (asn1_octet_string_get(sig_seq, &sig_der_ptr, sig_der_length)) { 88 *sig_der = (uint8_t*) malloc(*sig_der_length); 89 if (*sig_der != NULL) { 90 memcpy(*sig_der, sig_der_ptr, *sig_der_length); 91 } 92 } 93 asn1_context_free(sig_seq); 94 } 95 asn1_context_free(sig_set); 96 } 97 asn1_context_free(signed_data_seq); 98 } 99 asn1_context_free(signed_data_app); 100 } 101 asn1_context_free(pkcs7_seq); 102 } 103 asn1_context_free(ctx); 104 105 return *sig_der != NULL; 106 } 107 108 // Look for an RSA signature embedded in the .ZIP file comment given 109 // the path to the zip. Verify it matches one of the given public 110 // keys. 111 // 112 // Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered 113 // or no key matches the signature). 114 115 int verify_file(unsigned char* addr, size_t length, 116 const Certificate* pKeys, unsigned int numKeys) { 117 ui->SetProgress(0.0); 118 119 // An archive with a whole-file signature will end in six bytes: 120 // 121 // (2-byte signature start) $ff $ff (2-byte comment size) 122 // 123 // (As far as the ZIP format is concerned, these are part of the 124 // archive comment.) We start by reading this footer, this tells 125 // us how far back from the end we have to start reading to find 126 // the whole comment. 127 128 #define FOOTER_SIZE 6 129 130 if (length < FOOTER_SIZE) { 131 LOGE("not big enough to contain footer\n"); 132 return VERIFY_FAILURE; 133 } 134 135 unsigned char* footer = addr + length - FOOTER_SIZE; 136 137 if (footer[2] != 0xff || footer[3] != 0xff) { 138 LOGE("footer is wrong\n"); 139 return VERIFY_FAILURE; 140 } 141 142 size_t comment_size = footer[4] + (footer[5] << 8); 143 size_t signature_start = footer[0] + (footer[1] << 8); 144 LOGI("comment is %zu bytes; signature %zu bytes from end\n", 145 comment_size, signature_start); 146 147 if (signature_start <= FOOTER_SIZE) { 148 LOGE("Signature start is in the footer"); 149 return VERIFY_FAILURE; 150 } 151 152 #define EOCD_HEADER_SIZE 22 153 154 // The end-of-central-directory record is 22 bytes plus any 155 // comment length. 156 size_t eocd_size = comment_size + EOCD_HEADER_SIZE; 157 158 if (length < eocd_size) { 159 LOGE("not big enough to contain EOCD\n"); 160 return VERIFY_FAILURE; 161 } 162 163 // Determine how much of the file is covered by the signature. 164 // This is everything except the signature data and length, which 165 // includes all of the EOCD except for the comment length field (2 166 // bytes) and the comment data. 167 size_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2; 168 169 unsigned char* eocd = addr + length - eocd_size; 170 171 // If this is really is the EOCD record, it will begin with the 172 // magic number $50 $4b $05 $06. 173 if (eocd[0] != 0x50 || eocd[1] != 0x4b || 174 eocd[2] != 0x05 || eocd[3] != 0x06) { 175 LOGE("signature length doesn't match EOCD marker\n"); 176 return VERIFY_FAILURE; 177 } 178 179 size_t i; 180 for (i = 4; i < eocd_size-3; ++i) { 181 if (eocd[i ] == 0x50 && eocd[i+1] == 0x4b && 182 eocd[i+2] == 0x05 && eocd[i+3] == 0x06) { 183 // if the sequence $50 $4b $05 $06 appears anywhere after 184 // the real one, minzip will find the later (wrong) one, 185 // which could be exploitable. Fail verification if 186 // this sequence occurs anywhere after the real one. 187 LOGE("EOCD marker occurs after start of EOCD\n"); 188 return VERIFY_FAILURE; 189 } 190 } 191 192 #define BUFFER_SIZE 4096 193 194 bool need_sha1 = false; 195 bool need_sha256 = false; 196 for (i = 0; i < numKeys; ++i) { 197 switch (pKeys[i].hash_len) { 198 case SHA_DIGEST_SIZE: need_sha1 = true; break; 199 case SHA256_DIGEST_SIZE: need_sha256 = true; break; 200 } 201 } 202 203 SHA_CTX sha1_ctx; 204 SHA256_CTX sha256_ctx; 205 SHA_init(&sha1_ctx); 206 SHA256_init(&sha256_ctx); 207 208 double frac = -1.0; 209 size_t so_far = 0; 210 while (so_far < signed_len) { 211 size_t size = signed_len - so_far; 212 if (size > BUFFER_SIZE) size = BUFFER_SIZE; 213 214 if (need_sha1) SHA_update(&sha1_ctx, addr + so_far, size); 215 if (need_sha256) SHA256_update(&sha256_ctx, addr + so_far, size); 216 so_far += size; 217 218 double f = so_far / (double)signed_len; 219 if (f > frac + 0.02 || size == so_far) { 220 ui->SetProgress(f); 221 frac = f; 222 } 223 } 224 225 const uint8_t* sha1 = SHA_final(&sha1_ctx); 226 const uint8_t* sha256 = SHA256_final(&sha256_ctx); 227 228 uint8_t* sig_der = NULL; 229 size_t sig_der_length = 0; 230 231 size_t signature_size = signature_start - FOOTER_SIZE; 232 if (!read_pkcs7(eocd + eocd_size - signature_start, signature_size, &sig_der, 233 &sig_der_length)) { 234 LOGE("Could not find signature DER block\n"); 235 return VERIFY_FAILURE; 236 } 237 238 /* 239 * Check to make sure at least one of the keys matches the signature. Since 240 * any key can match, we need to try each before determining a verification 241 * failure has happened. 242 */ 243 for (i = 0; i < numKeys; ++i) { 244 const uint8_t* hash; 245 switch (pKeys[i].hash_len) { 246 case SHA_DIGEST_SIZE: hash = sha1; break; 247 case SHA256_DIGEST_SIZE: hash = sha256; break; 248 default: continue; 249 } 250 251 // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that 252 // the signing tool appends after the signature itself. 253 if (pKeys[i].key_type == Certificate::RSA) { 254 if (sig_der_length < RSANUMBYTES) { 255 // "signature" block isn't big enough to contain an RSA block. 256 LOGI("signature is too short for RSA key %zu\n", i); 257 continue; 258 } 259 260 if (!RSA_verify(pKeys[i].rsa, sig_der, RSANUMBYTES, 261 hash, pKeys[i].hash_len)) { 262 LOGI("failed to verify against RSA key %zu\n", i); 263 continue; 264 } 265 266 LOGI("whole-file signature verified against RSA key %zu\n", i); 267 free(sig_der); 268 return VERIFY_SUCCESS; 269 } else if (pKeys[i].key_type == Certificate::EC 270 && pKeys[i].hash_len == SHA256_DIGEST_SIZE) { 271 p256_int r, s; 272 if (!dsa_sig_unpack(sig_der, sig_der_length, &r, &s)) { 273 LOGI("Not a DSA signature block for EC key %zu\n", i); 274 continue; 275 } 276 277 p256_int p256_hash; 278 p256_from_bin(hash, &p256_hash); 279 if (!p256_ecdsa_verify(&(pKeys[i].ec->x), &(pKeys[i].ec->y), 280 &p256_hash, &r, &s)) { 281 LOGI("failed to verify against EC key %zu\n", i); 282 continue; 283 } 284 285 LOGI("whole-file signature verified against EC key %zu\n", i); 286 free(sig_der); 287 return VERIFY_SUCCESS; 288 } else { 289 LOGI("Unknown key type %d\n", pKeys[i].key_type); 290 } 291 } 292 free(sig_der); 293 LOGE("failed to verify whole-file signature\n"); 294 return VERIFY_FAILURE; 295 } 296 297 // Reads a file containing one or more public keys as produced by 298 // DumpPublicKey: this is an RSAPublicKey struct as it would appear 299 // as a C source literal, eg: 300 // 301 // "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" 302 // 303 // For key versions newer than the original 2048-bit e=3 keys 304 // supported by Android, the string is preceded by a version 305 // identifier, eg: 306 // 307 // "v2 {64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" 308 // 309 // (Note that the braces and commas in this example are actual 310 // characters the parser expects to find in the file; the ellipses 311 // indicate more numbers omitted from this example.) 312 // 313 // The file may contain multiple keys in this format, separated by 314 // commas. The last key must not be followed by a comma. 315 // 316 // A Certificate is a pair of an RSAPublicKey and a particular hash 317 // (we support SHA-1 and SHA-256; we store the hash length to signify 318 // which is being used). The hash used is implied by the version number. 319 // 320 // 1: 2048-bit RSA key with e=3 and SHA-1 hash 321 // 2: 2048-bit RSA key with e=65537 and SHA-1 hash 322 // 3: 2048-bit RSA key with e=3 and SHA-256 hash 323 // 4: 2048-bit RSA key with e=65537 and SHA-256 hash 324 // 5: 256-bit EC key using the NIST P-256 curve parameters and SHA-256 hash 325 // 326 // Returns NULL if the file failed to parse, or if it contain zero keys. 327 Certificate* 328 load_keys(const char* filename, int* numKeys) { 329 Certificate* out = NULL; 330 *numKeys = 0; 331 332 FILE* f = fopen(filename, "r"); 333 if (f == NULL) { 334 LOGE("opening %s: %s\n", filename, strerror(errno)); 335 goto exit; 336 } 337 338 { 339 int i; 340 bool done = false; 341 while (!done) { 342 ++*numKeys; 343 out = (Certificate*)realloc(out, *numKeys * sizeof(Certificate)); 344 Certificate* cert = out + (*numKeys - 1); 345 memset(cert, '\0', sizeof(Certificate)); 346 347 char start_char; 348 if (fscanf(f, " %c", &start_char) != 1) goto exit; 349 if (start_char == '{') { 350 // a version 1 key has no version specifier. 351 cert->key_type = Certificate::RSA; 352 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey)); 353 cert->rsa->exponent = 3; 354 cert->hash_len = SHA_DIGEST_SIZE; 355 } else if (start_char == 'v') { 356 int version; 357 if (fscanf(f, "%d {", &version) != 1) goto exit; 358 switch (version) { 359 case 2: 360 cert->key_type = Certificate::RSA; 361 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey)); 362 cert->rsa->exponent = 65537; 363 cert->hash_len = SHA_DIGEST_SIZE; 364 break; 365 case 3: 366 cert->key_type = Certificate::RSA; 367 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey)); 368 cert->rsa->exponent = 3; 369 cert->hash_len = SHA256_DIGEST_SIZE; 370 break; 371 case 4: 372 cert->key_type = Certificate::RSA; 373 cert->rsa = (RSAPublicKey*)malloc(sizeof(RSAPublicKey)); 374 cert->rsa->exponent = 65537; 375 cert->hash_len = SHA256_DIGEST_SIZE; 376 break; 377 case 5: 378 cert->key_type = Certificate::EC; 379 cert->ec = (ECPublicKey*)calloc(1, sizeof(ECPublicKey)); 380 cert->hash_len = SHA256_DIGEST_SIZE; 381 break; 382 default: 383 goto exit; 384 } 385 } 386 387 if (cert->key_type == Certificate::RSA) { 388 RSAPublicKey* key = cert->rsa; 389 if (fscanf(f, " %i , 0x%x , { %u", 390 &(key->len), &(key->n0inv), &(key->n[0])) != 3) { 391 goto exit; 392 } 393 if (key->len != RSANUMWORDS) { 394 LOGE("key length (%d) does not match expected size\n", key->len); 395 goto exit; 396 } 397 for (i = 1; i < key->len; ++i) { 398 if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit; 399 } 400 if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit; 401 for (i = 1; i < key->len; ++i) { 402 if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit; 403 } 404 fscanf(f, " } } "); 405 406 LOGI("read key e=%d hash=%d\n", key->exponent, cert->hash_len); 407 } else if (cert->key_type == Certificate::EC) { 408 ECPublicKey* key = cert->ec; 409 int key_len; 410 unsigned int byte; 411 uint8_t x_bytes[P256_NBYTES]; 412 uint8_t y_bytes[P256_NBYTES]; 413 if (fscanf(f, " %i , { %u", &key_len, &byte) != 2) goto exit; 414 if (key_len != P256_NBYTES) { 415 LOGE("Key length (%d) does not match expected size %d\n", key_len, P256_NBYTES); 416 goto exit; 417 } 418 x_bytes[P256_NBYTES - 1] = byte; 419 for (i = P256_NBYTES - 2; i >= 0; --i) { 420 if (fscanf(f, " , %u", &byte) != 1) goto exit; 421 x_bytes[i] = byte; 422 } 423 if (fscanf(f, " } , { %u", &byte) != 1) goto exit; 424 y_bytes[P256_NBYTES - 1] = byte; 425 for (i = P256_NBYTES - 2; i >= 0; --i) { 426 if (fscanf(f, " , %u", &byte) != 1) goto exit; 427 y_bytes[i] = byte; 428 } 429 fscanf(f, " } } "); 430 p256_from_bin(x_bytes, &key->x); 431 p256_from_bin(y_bytes, &key->y); 432 } else { 433 LOGE("Unknown key type %d\n", cert->key_type); 434 goto exit; 435 } 436 437 // if the line ends in a comma, this file has more keys. 438 switch (fgetc(f)) { 439 case ',': 440 // more keys to come. 441 break; 442 443 case EOF: 444 done = true; 445 break; 446 447 default: 448 LOGE("unexpected character between keys\n"); 449 goto exit; 450 } 451 } 452 } 453 454 fclose(f); 455 return out; 456 457 exit: 458 if (f) fclose(f); 459 free(out); 460 *numKeys = 0; 461 return NULL; 462 } 463
