1 // Copyright 2015 The Android Open Source Project 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #define LOG_TAG "keystore_client" 16 17 #include "keystore/keystore_client_impl.h" 18 19 #include <string> 20 #include <vector> 21 22 #include "binder/IBinder.h" 23 #include "binder/IInterface.h" 24 #include "binder/IServiceManager.h" 25 #include "keystore/IKeystoreService.h" 26 #include "keystore/keystore.h" 27 #include "log/log.h" 28 #include "utils/String16.h" 29 #include "utils/String8.h" 30 31 #include "keystore_client.pb.h" 32 33 using android::ExportResult; 34 using android::KeyCharacteristics; 35 using android::KeymasterArguments; 36 using android::OperationResult; 37 using android::String16; 38 using keymaster::AuthorizationSet; 39 using keymaster::AuthorizationSetBuilder; 40 41 namespace { 42 43 // Use the UID of the current process. 44 const int kDefaultUID = -1; 45 const char kEncryptSuffix[] = "_ENC"; 46 const char kAuthenticateSuffix[] = "_AUTH"; 47 const uint32_t kAESKeySize = 256; // bits 48 const uint32_t kHMACKeySize = 256; // bits 49 const uint32_t kHMACOutputSize = 256; // bits 50 51 const uint8_t* StringAsByteArray(const std::string& s) { 52 return reinterpret_cast<const uint8_t*>(s.data()); 53 } 54 55 std::string ByteArrayAsString(const uint8_t* data, size_t data_size) { 56 return std::string(reinterpret_cast<const char*>(data), data_size); 57 } 58 59 void CopyParameters(const AuthorizationSet& in, std::vector<keymaster_key_param_t>* out) { 60 keymaster_key_param_set_t tmp; 61 in.CopyToParamSet(&tmp); 62 out->assign(&tmp.params[0], &tmp.params[tmp.length]); 63 free(tmp.params); 64 } 65 66 } // namespace 67 68 namespace keystore { 69 70 KeystoreClientImpl::KeystoreClientImpl() { 71 service_manager_ = android::defaultServiceManager(); 72 keystore_binder_ = service_manager_->getService(String16("android.security.keystore")); 73 keystore_ = android::interface_cast<android::IKeystoreService>(keystore_binder_); 74 } 75 76 bool KeystoreClientImpl::encryptWithAuthentication(const std::string& key_name, 77 const std::string& data, 78 std::string* encrypted_data) { 79 // The encryption algorithm is AES-256-CBC with PKCS #7 padding and a random 80 // IV. The authentication algorithm is HMAC-SHA256 and is computed over the 81 // cipher-text (i.e. Encrypt-then-MAC approach). This was chosen over AES-GCM 82 // because hardware support for GCM is not mandatory for all Brillo devices. 83 std::string encryption_key_name = key_name + kEncryptSuffix; 84 if (!createOrVerifyEncryptionKey(encryption_key_name)) { 85 return false; 86 } 87 std::string authentication_key_name = key_name + kAuthenticateSuffix; 88 if (!createOrVerifyAuthenticationKey(authentication_key_name)) { 89 return false; 90 } 91 AuthorizationSetBuilder encrypt_params; 92 encrypt_params.Padding(KM_PAD_PKCS7); 93 encrypt_params.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_CBC); 94 AuthorizationSet output_params; 95 std::string raw_encrypted_data; 96 if (!oneShotOperation(KM_PURPOSE_ENCRYPT, encryption_key_name, encrypt_params.build(), data, 97 std::string(), /* signature_to_verify */ 98 &output_params, &raw_encrypted_data)) { 99 ALOGE("Encrypt: AES operation failed."); 100 return false; 101 } 102 keymaster_blob_t init_vector_blob; 103 if (!output_params.GetTagValue(keymaster::TAG_NONCE, &init_vector_blob)) { 104 ALOGE("Encrypt: Missing initialization vector."); 105 return false; 106 } 107 std::string init_vector = 108 ByteArrayAsString(init_vector_blob.data, init_vector_blob.data_length); 109 110 AuthorizationSetBuilder authenticate_params; 111 authenticate_params.Digest(KM_DIGEST_SHA_2_256); 112 authenticate_params.Authorization(keymaster::TAG_MAC_LENGTH, kHMACOutputSize); 113 std::string raw_authentication_data; 114 if (!oneShotOperation(KM_PURPOSE_SIGN, authentication_key_name, authenticate_params.build(), 115 init_vector + raw_encrypted_data, std::string(), /* signature_to_verify */ 116 &output_params, &raw_authentication_data)) { 117 ALOGE("Encrypt: HMAC operation failed."); 118 return false; 119 } 120 EncryptedData protobuf; 121 protobuf.set_init_vector(init_vector); 122 protobuf.set_authentication_data(raw_authentication_data); 123 protobuf.set_encrypted_data(raw_encrypted_data); 124 if (!protobuf.SerializeToString(encrypted_data)) { 125 ALOGE("Encrypt: Failed to serialize EncryptedData protobuf."); 126 return false; 127 } 128 return true; 129 } 130 131 bool KeystoreClientImpl::decryptWithAuthentication(const std::string& key_name, 132 const std::string& encrypted_data, 133 std::string* data) { 134 EncryptedData protobuf; 135 if (!protobuf.ParseFromString(encrypted_data)) { 136 ALOGE("Decrypt: Failed to parse EncryptedData protobuf."); 137 } 138 // Verify authentication before attempting decryption. 139 std::string authentication_key_name = key_name + kAuthenticateSuffix; 140 AuthorizationSetBuilder authenticate_params; 141 authenticate_params.Digest(KM_DIGEST_SHA_2_256); 142 AuthorizationSet output_params; 143 std::string output_data; 144 if (!oneShotOperation(KM_PURPOSE_VERIFY, authentication_key_name, authenticate_params.build(), 145 protobuf.init_vector() + protobuf.encrypted_data(), 146 protobuf.authentication_data(), &output_params, &output_data)) { 147 ALOGE("Decrypt: HMAC operation failed."); 148 return false; 149 } 150 std::string encryption_key_name = key_name + kEncryptSuffix; 151 AuthorizationSetBuilder encrypt_params; 152 encrypt_params.Padding(KM_PAD_PKCS7); 153 encrypt_params.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_CBC); 154 encrypt_params.Authorization(keymaster::TAG_NONCE, protobuf.init_vector().data(), 155 protobuf.init_vector().size()); 156 if (!oneShotOperation(KM_PURPOSE_DECRYPT, encryption_key_name, encrypt_params.build(), 157 protobuf.encrypted_data(), std::string(), /* signature_to_verify */ 158 &output_params, data)) { 159 ALOGE("Decrypt: AES operation failed."); 160 return false; 161 } 162 return true; 163 } 164 165 bool KeystoreClientImpl::oneShotOperation(keymaster_purpose_t purpose, const std::string& key_name, 166 const keymaster::AuthorizationSet& input_parameters, 167 const std::string& input_data, 168 const std::string& signature_to_verify, 169 keymaster::AuthorizationSet* output_parameters, 170 std::string* output_data) { 171 keymaster_operation_handle_t handle; 172 int32_t result = 173 beginOperation(purpose, key_name, input_parameters, output_parameters, &handle); 174 if (result != KM_ERROR_OK) { 175 ALOGE("BeginOperation failed: %d", result); 176 return false; 177 } 178 AuthorizationSet empty_params; 179 size_t num_input_bytes_consumed; 180 AuthorizationSet ignored_params; 181 result = updateOperation(handle, empty_params, input_data, &num_input_bytes_consumed, 182 &ignored_params, output_data); 183 if (result != KM_ERROR_OK) { 184 ALOGE("UpdateOperation failed: %d", result); 185 return false; 186 } 187 result = 188 finishOperation(handle, empty_params, signature_to_verify, &ignored_params, output_data); 189 if (result != KM_ERROR_OK) { 190 ALOGE("FinishOperation failed: %d", result); 191 return false; 192 } 193 return true; 194 } 195 196 int32_t KeystoreClientImpl::addRandomNumberGeneratorEntropy(const std::string& entropy) { 197 return mapKeystoreError(keystore_->addRngEntropy(StringAsByteArray(entropy), entropy.size())); 198 } 199 200 int32_t KeystoreClientImpl::generateKey(const std::string& key_name, 201 const AuthorizationSet& key_parameters, 202 AuthorizationSet* hardware_enforced_characteristics, 203 AuthorizationSet* software_enforced_characteristics) { 204 String16 key_name16(key_name.data(), key_name.size()); 205 KeymasterArguments key_arguments; 206 CopyParameters(key_parameters, &key_arguments.params); 207 KeyCharacteristics characteristics; 208 int32_t result = 209 keystore_->generateKey(key_name16, key_arguments, NULL /*entropy*/, 0 /*entropyLength*/, 210 kDefaultUID, KEYSTORE_FLAG_NONE, &characteristics); 211 hardware_enforced_characteristics->Reinitialize(characteristics.characteristics.hw_enforced); 212 software_enforced_characteristics->Reinitialize(characteristics.characteristics.sw_enforced); 213 return mapKeystoreError(result); 214 } 215 216 int32_t 217 KeystoreClientImpl::getKeyCharacteristics(const std::string& key_name, 218 AuthorizationSet* hardware_enforced_characteristics, 219 AuthorizationSet* software_enforced_characteristics) { 220 String16 key_name16(key_name.data(), key_name.size()); 221 keymaster_blob_t client_id_blob = {nullptr, 0}; 222 keymaster_blob_t app_data_blob = {nullptr, 0}; 223 KeyCharacteristics characteristics; 224 int32_t result = keystore_->getKeyCharacteristics(key_name16, &client_id_blob, &app_data_blob, 225 kDefaultUID, &characteristics); 226 hardware_enforced_characteristics->Reinitialize(characteristics.characteristics.hw_enforced); 227 software_enforced_characteristics->Reinitialize(characteristics.characteristics.sw_enforced); 228 return mapKeystoreError(result); 229 } 230 231 int32_t KeystoreClientImpl::importKey(const std::string& key_name, 232 const AuthorizationSet& key_parameters, 233 keymaster_key_format_t key_format, 234 const std::string& key_data, 235 AuthorizationSet* hardware_enforced_characteristics, 236 AuthorizationSet* software_enforced_characteristics) { 237 String16 key_name16(key_name.data(), key_name.size()); 238 KeymasterArguments key_arguments; 239 CopyParameters(key_parameters, &key_arguments.params); 240 KeyCharacteristics characteristics; 241 int32_t result = 242 keystore_->importKey(key_name16, key_arguments, key_format, StringAsByteArray(key_data), 243 key_data.size(), kDefaultUID, KEYSTORE_FLAG_NONE, &characteristics); 244 hardware_enforced_characteristics->Reinitialize(characteristics.characteristics.hw_enforced); 245 software_enforced_characteristics->Reinitialize(characteristics.characteristics.sw_enforced); 246 return mapKeystoreError(result); 247 } 248 249 int32_t KeystoreClientImpl::exportKey(keymaster_key_format_t export_format, 250 const std::string& key_name, std::string* export_data) { 251 String16 key_name16(key_name.data(), key_name.size()); 252 keymaster_blob_t client_id_blob = {nullptr, 0}; 253 keymaster_blob_t app_data_blob = {nullptr, 0}; 254 ExportResult export_result; 255 keystore_->exportKey(key_name16, export_format, &client_id_blob, &app_data_blob, 256 kDefaultUID, &export_result); 257 *export_data = ByteArrayAsString(export_result.exportData.get(), export_result.dataLength); 258 return mapKeystoreError(export_result.resultCode); 259 } 260 261 int32_t KeystoreClientImpl::deleteKey(const std::string& key_name) { 262 String16 key_name16(key_name.data(), key_name.size()); 263 return mapKeystoreError(keystore_->del(key_name16, kDefaultUID)); 264 } 265 266 int32_t KeystoreClientImpl::deleteAllKeys() { 267 return mapKeystoreError(keystore_->clear_uid(kDefaultUID)); 268 } 269 270 int32_t KeystoreClientImpl::beginOperation(keymaster_purpose_t purpose, const std::string& key_name, 271 const AuthorizationSet& input_parameters, 272 AuthorizationSet* output_parameters, 273 keymaster_operation_handle_t* handle) { 274 android::sp<android::IBinder> token(new android::BBinder); 275 String16 key_name16(key_name.data(), key_name.size()); 276 KeymasterArguments input_arguments; 277 CopyParameters(input_parameters, &input_arguments.params); 278 OperationResult result; 279 keystore_->begin(token, key_name16, purpose, true /*pruneable*/, input_arguments, 280 NULL /*entropy*/, 0 /*entropyLength*/, kDefaultUID, &result); 281 int32_t error_code = mapKeystoreError(result.resultCode); 282 if (error_code == KM_ERROR_OK) { 283 *handle = getNextVirtualHandle(); 284 active_operations_[*handle] = result.token; 285 if (!result.outParams.params.empty()) { 286 output_parameters->Reinitialize(&*result.outParams.params.begin(), 287 result.outParams.params.size()); 288 } 289 } 290 return error_code; 291 } 292 293 int32_t KeystoreClientImpl::updateOperation(keymaster_operation_handle_t handle, 294 const AuthorizationSet& input_parameters, 295 const std::string& input_data, 296 size_t* num_input_bytes_consumed, 297 AuthorizationSet* output_parameters, 298 std::string* output_data) { 299 if (active_operations_.count(handle) == 0) { 300 return KM_ERROR_INVALID_OPERATION_HANDLE; 301 } 302 KeymasterArguments input_arguments; 303 CopyParameters(input_parameters, &input_arguments.params); 304 OperationResult result; 305 keystore_->update(active_operations_[handle], input_arguments, StringAsByteArray(input_data), 306 input_data.size(), &result); 307 int32_t error_code = mapKeystoreError(result.resultCode); 308 if (error_code == KM_ERROR_OK) { 309 *num_input_bytes_consumed = result.inputConsumed; 310 if (!result.outParams.params.empty()) { 311 output_parameters->Reinitialize(&*result.outParams.params.begin(), 312 result.outParams.params.size()); 313 } 314 output_data->append(ByteArrayAsString(result.data.get(), result.dataLength)); 315 } 316 return error_code; 317 } 318 319 int32_t KeystoreClientImpl::finishOperation(keymaster_operation_handle_t handle, 320 const AuthorizationSet& input_parameters, 321 const std::string& signature_to_verify, 322 AuthorizationSet* output_parameters, 323 std::string* output_data) { 324 if (active_operations_.count(handle) == 0) { 325 return KM_ERROR_INVALID_OPERATION_HANDLE; 326 } 327 KeymasterArguments input_arguments; 328 CopyParameters(input_parameters, &input_arguments.params); 329 OperationResult result; 330 keystore_->finish(active_operations_[handle], input_arguments, 331 StringAsByteArray(signature_to_verify), signature_to_verify.size(), 332 NULL /*entropy*/, 0 /*entropyLength*/, &result); 333 int32_t error_code = mapKeystoreError(result.resultCode); 334 if (error_code == KM_ERROR_OK) { 335 if (!result.outParams.params.empty()) { 336 output_parameters->Reinitialize(&*result.outParams.params.begin(), 337 result.outParams.params.size()); 338 } 339 output_data->append(ByteArrayAsString(result.data.get(), result.dataLength)); 340 active_operations_.erase(handle); 341 } 342 return error_code; 343 } 344 345 int32_t KeystoreClientImpl::abortOperation(keymaster_operation_handle_t handle) { 346 if (active_operations_.count(handle) == 0) { 347 return KM_ERROR_INVALID_OPERATION_HANDLE; 348 } 349 int32_t error_code = mapKeystoreError(keystore_->abort(active_operations_[handle])); 350 if (error_code == KM_ERROR_OK) { 351 active_operations_.erase(handle); 352 } 353 return error_code; 354 } 355 356 bool KeystoreClientImpl::doesKeyExist(const std::string& key_name) { 357 String16 key_name16(key_name.data(), key_name.size()); 358 int32_t error_code = mapKeystoreError(keystore_->exist(key_name16, kDefaultUID)); 359 return (error_code == KM_ERROR_OK); 360 } 361 362 bool KeystoreClientImpl::listKeys(const std::string& prefix, 363 std::vector<std::string>* key_name_list) { 364 String16 prefix16(prefix.data(), prefix.size()); 365 android::Vector<String16> matches; 366 int32_t error_code = mapKeystoreError(keystore_->list(prefix16, kDefaultUID, &matches)); 367 if (error_code == KM_ERROR_OK) { 368 for (const auto& match : matches) { 369 android::String8 key_name(match); 370 key_name_list->push_back(prefix + std::string(key_name.string(), key_name.size())); 371 } 372 return true; 373 } 374 return false; 375 } 376 377 keymaster_operation_handle_t KeystoreClientImpl::getNextVirtualHandle() { 378 return next_virtual_handle_++; 379 } 380 381 int32_t KeystoreClientImpl::mapKeystoreError(int32_t keystore_error) { 382 // See notes in keystore_client.h for rationale. 383 if (keystore_error == ::NO_ERROR) { 384 return KM_ERROR_OK; 385 } 386 return keystore_error; 387 } 388 389 bool KeystoreClientImpl::createOrVerifyEncryptionKey(const std::string& key_name) { 390 bool key_exists = doesKeyExist(key_name); 391 if (key_exists) { 392 bool verified = false; 393 if (!verifyEncryptionKeyAttributes(key_name, &verified)) { 394 return false; 395 } 396 if (!verified) { 397 int32_t result = deleteKey(key_name); 398 if (result != KM_ERROR_OK) { 399 ALOGE("Failed to delete invalid encryption key: %d", result); 400 return false; 401 } 402 key_exists = false; 403 } 404 } 405 if (!key_exists) { 406 AuthorizationSetBuilder key_parameters; 407 key_parameters.AesEncryptionKey(kAESKeySize) 408 .Padding(KM_PAD_PKCS7) 409 .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_CBC) 410 .Authorization(keymaster::TAG_NO_AUTH_REQUIRED); 411 AuthorizationSet hardware_enforced_characteristics; 412 AuthorizationSet software_enforced_characteristics; 413 int32_t result = 414 generateKey(key_name, key_parameters.build(), &hardware_enforced_characteristics, 415 &software_enforced_characteristics); 416 if (result != KM_ERROR_OK) { 417 ALOGE("Failed to generate encryption key: %d", result); 418 return false; 419 } 420 if (hardware_enforced_characteristics.size() == 0) { 421 ALOGW("WARNING: Encryption key is not hardware-backed."); 422 } 423 } 424 return true; 425 } 426 427 bool KeystoreClientImpl::createOrVerifyAuthenticationKey(const std::string& key_name) { 428 bool key_exists = doesKeyExist(key_name); 429 if (key_exists) { 430 bool verified = false; 431 if (!verifyAuthenticationKeyAttributes(key_name, &verified)) { 432 return false; 433 } 434 if (!verified) { 435 int32_t result = deleteKey(key_name); 436 if (result != KM_ERROR_OK) { 437 ALOGE("Failed to delete invalid authentication key: %d", result); 438 return false; 439 } 440 key_exists = false; 441 } 442 } 443 if (!key_exists) { 444 AuthorizationSetBuilder key_parameters; 445 key_parameters.HmacKey(kHMACKeySize) 446 .Digest(KM_DIGEST_SHA_2_256) 447 .Authorization(keymaster::TAG_MIN_MAC_LENGTH, kHMACOutputSize) 448 .Authorization(keymaster::TAG_NO_AUTH_REQUIRED); 449 AuthorizationSet hardware_enforced_characteristics; 450 AuthorizationSet software_enforced_characteristics; 451 int32_t result = 452 generateKey(key_name, key_parameters.build(), &hardware_enforced_characteristics, 453 &software_enforced_characteristics); 454 if (result != KM_ERROR_OK) { 455 ALOGE("Failed to generate authentication key: %d", result); 456 return false; 457 } 458 if (hardware_enforced_characteristics.size() == 0) { 459 ALOGW("WARNING: Authentication key is not hardware-backed."); 460 } 461 } 462 return true; 463 } 464 465 bool KeystoreClientImpl::verifyEncryptionKeyAttributes(const std::string& key_name, 466 bool* verified) { 467 AuthorizationSet hardware_enforced_characteristics; 468 AuthorizationSet software_enforced_characteristics; 469 int32_t result = getKeyCharacteristics(key_name, &hardware_enforced_characteristics, 470 &software_enforced_characteristics); 471 if (result != KM_ERROR_OK) { 472 ALOGE("Failed to query encryption key: %d", result); 473 return false; 474 } 475 *verified = true; 476 keymaster_algorithm_t algorithm = KM_ALGORITHM_RSA; 477 if ((!hardware_enforced_characteristics.GetTagValue(keymaster::TAG_ALGORITHM, &algorithm) && 478 !software_enforced_characteristics.GetTagValue(keymaster::TAG_ALGORITHM, &algorithm)) || 479 algorithm != KM_ALGORITHM_AES) { 480 ALOGW("Found encryption key with invalid algorithm."); 481 *verified = false; 482 } 483 uint32_t key_size = 0; 484 if ((!hardware_enforced_characteristics.GetTagValue(keymaster::TAG_KEY_SIZE, &key_size) && 485 !software_enforced_characteristics.GetTagValue(keymaster::TAG_KEY_SIZE, &key_size)) || 486 key_size != kAESKeySize) { 487 ALOGW("Found encryption key with invalid size."); 488 *verified = false; 489 } 490 keymaster_block_mode_t block_mode = KM_MODE_ECB; 491 if ((!hardware_enforced_characteristics.GetTagValue(keymaster::TAG_BLOCK_MODE, &block_mode) && 492 !software_enforced_characteristics.GetTagValue(keymaster::TAG_BLOCK_MODE, &block_mode)) || 493 block_mode != KM_MODE_CBC) { 494 ALOGW("Found encryption key with invalid block mode."); 495 *verified = false; 496 } 497 keymaster_padding_t padding_mode = KM_PAD_NONE; 498 if ((!hardware_enforced_characteristics.GetTagValue(keymaster::TAG_PADDING, &padding_mode) && 499 !software_enforced_characteristics.GetTagValue(keymaster::TAG_PADDING, &padding_mode)) || 500 padding_mode != KM_PAD_PKCS7) { 501 ALOGW("Found encryption key with invalid padding mode."); 502 *verified = false; 503 } 504 if (hardware_enforced_characteristics.size() == 0) { 505 ALOGW("WARNING: Encryption key is not hardware-backed."); 506 } 507 return true; 508 } 509 510 bool KeystoreClientImpl::verifyAuthenticationKeyAttributes(const std::string& key_name, 511 bool* verified) { 512 AuthorizationSet hardware_enforced_characteristics; 513 AuthorizationSet software_enforced_characteristics; 514 int32_t result = getKeyCharacteristics(key_name, &hardware_enforced_characteristics, 515 &software_enforced_characteristics); 516 if (result != KM_ERROR_OK) { 517 ALOGE("Failed to query authentication key: %d", result); 518 return false; 519 } 520 *verified = true; 521 keymaster_algorithm_t algorithm = KM_ALGORITHM_RSA; 522 if ((!hardware_enforced_characteristics.GetTagValue(keymaster::TAG_ALGORITHM, &algorithm) && 523 !software_enforced_characteristics.GetTagValue(keymaster::TAG_ALGORITHM, &algorithm)) || 524 algorithm != KM_ALGORITHM_HMAC) { 525 ALOGW("Found authentication key with invalid algorithm."); 526 *verified = false; 527 } 528 uint32_t key_size = 0; 529 if ((!hardware_enforced_characteristics.GetTagValue(keymaster::TAG_KEY_SIZE, &key_size) && 530 !software_enforced_characteristics.GetTagValue(keymaster::TAG_KEY_SIZE, &key_size)) || 531 key_size != kHMACKeySize) { 532 ALOGW("Found authentication key with invalid size."); 533 *verified = false; 534 } 535 uint32_t mac_size = 0; 536 if ((!hardware_enforced_characteristics.GetTagValue(keymaster::TAG_MIN_MAC_LENGTH, &mac_size) && 537 !software_enforced_characteristics.GetTagValue(keymaster::TAG_MIN_MAC_LENGTH, 538 &mac_size)) || 539 mac_size != kHMACOutputSize) { 540 ALOGW("Found authentication key with invalid minimum mac size."); 541 *verified = false; 542 } 543 keymaster_digest_t digest = KM_DIGEST_NONE; 544 if ((!hardware_enforced_characteristics.GetTagValue(keymaster::TAG_DIGEST, &digest) && 545 !software_enforced_characteristics.GetTagValue(keymaster::TAG_DIGEST, &digest)) || 546 digest != KM_DIGEST_SHA_2_256) { 547 ALOGW("Found authentication key with invalid digest list."); 548 *verified = false; 549 } 550 if (hardware_enforced_characteristics.size() == 0) { 551 ALOGW("WARNING: Authentication key is not hardware-backed."); 552 } 553 return true; 554 } 555 556 } // namespace keystore 557
