2 * Copyright (C) 2016 The Android Open Source Project
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
17 #include "KeyStorage.h"
19 #include "Keymaster.h"
20 #include "ScryptParameters.h"
28 #include <sys/types.h>
32 #include <openssl/err.h>
33 #include <openssl/evp.h>
34 #include <openssl/sha.h>
36 #include <android-base/file.h>
37 #include <android-base/logging.h>
39 #include <cutils/properties.h>
41 #include <hardware/hw_auth_token.h>
43 #include <keystore/authorization_set.h>
44 #include <keystore/keystore_hidl_support.h>
48 #include "crypto_scrypt.h"
53 using namespace keystore;
55 const KeyAuthentication kEmptyAuthentication{"", ""};
57 static constexpr size_t AES_KEY_BYTES = 32;
58 static constexpr size_t GCM_NONCE_BYTES = 12;
59 static constexpr size_t GCM_MAC_BYTES = 16;
60 static constexpr size_t SALT_BYTES = 1 << 4;
61 static constexpr size_t SECDISCARDABLE_BYTES = 1 << 14;
62 static constexpr size_t STRETCHED_BYTES = 1 << 6;
64 static constexpr uint32_t AUTH_TIMEOUT = 30; // Seconds
66 static const char* kCurrentVersion = "1";
67 static const char* kRmPath = "/system/bin/rm";
68 static const char* kSecdiscardPath = "/system/bin/secdiscard";
69 static const char* kStretch_none = "none";
70 static const char* kStretch_nopassword = "nopassword";
71 static const std::string kStretchPrefix_scrypt = "scrypt ";
72 static const char* kHashPrefix_secdiscardable = "Android secdiscardable SHA512";
73 static const char* kHashPrefix_keygen = "Android key wrapping key generation SHA512";
74 static const char* kFn_encrypted_key = "encrypted_key";
75 static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
76 static const char* kFn_keymaster_key_blob_upgraded = "keymaster_key_blob_upgraded";
77 static const char* kFn_salt = "salt";
78 static const char* kFn_secdiscardable = "secdiscardable";
79 static const char* kFn_stretching = "stretching";
80 static const char* kFn_version = "version";
82 static bool checkSize(const std::string& kind, size_t actual, size_t expected) {
83 if (actual != expected) {
84 LOG(ERROR) << "Wrong number of bytes in " << kind << ", expected " << expected << " got "
91 static std::string hashWithPrefix(char const* prefix, const std::string& tohash) {
95 // Personalise the hashing by introducing a fixed prefix.
96 // Hashing applications should use personalization except when there is a
97 // specific reason not to; see section 4.11 of https://www.schneier.com/skein1.3.pdf
98 std::string hashingPrefix = prefix;
99 hashingPrefix.resize(SHA512_CBLOCK);
100 SHA512_Update(&c, hashingPrefix.data(), hashingPrefix.size());
101 SHA512_Update(&c, tohash.data(), tohash.size());
102 std::string res(SHA512_DIGEST_LENGTH, '\0');
103 SHA512_Final(reinterpret_cast<uint8_t*>(&res[0]), &c);
107 static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth,
108 const std::string& appId, std::string* key) {
109 auto paramBuilder = AuthorizationSetBuilder()
110 .AesEncryptionKey(AES_KEY_BYTES * 8)
111 .Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
112 .Authorization(TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
113 .Authorization(TAG_PADDING, PaddingMode::NONE)
114 .Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
115 if (auth.token.empty()) {
116 LOG(DEBUG) << "Creating key that doesn't need auth token";
117 paramBuilder.Authorization(TAG_NO_AUTH_REQUIRED);
119 LOG(DEBUG) << "Auth token required for key";
120 if (auth.token.size() != sizeof(hw_auth_token_t)) {
121 LOG(ERROR) << "Auth token should be " << sizeof(hw_auth_token_t) << " bytes, was "
122 << auth.token.size() << " bytes";
125 const hw_auth_token_t* at = reinterpret_cast<const hw_auth_token_t*>(auth.token.data());
126 paramBuilder.Authorization(TAG_USER_SECURE_ID, at->user_id);
127 paramBuilder.Authorization(TAG_USER_AUTH_TYPE, HardwareAuthenticatorType::PASSWORD);
128 paramBuilder.Authorization(TAG_AUTH_TIMEOUT, AUTH_TIMEOUT);
130 return keymaster.generateKey(paramBuilder, key);
133 static AuthorizationSet beginParams(const KeyAuthentication& auth,
134 const std::string& appId) {
135 auto paramBuilder = AuthorizationSetBuilder()
136 .Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
137 .Authorization(TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
138 .Authorization(TAG_PADDING, PaddingMode::NONE)
139 .Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
140 if (!auth.token.empty()) {
141 LOG(DEBUG) << "Supplying auth token to Keymaster";
142 paramBuilder.Authorization(TAG_AUTH_TOKEN, blob2hidlVec(auth.token));
147 static bool readFileToString(const std::string& filename, std::string* result) {
148 if (!android::base::ReadFileToString(filename, result)) {
149 PLOG(ERROR) << "Failed to read from " << filename;
155 static bool writeStringToFile(const std::string& payload, const std::string& filename) {
156 if (!android::base::WriteStringToFile(payload, filename)) {
157 PLOG(ERROR) << "Failed to write to " << filename;
163 static KeymasterOperation begin(Keymaster& keymaster, const std::string& dir,
165 const AuthorizationSet &keyParams,
166 const AuthorizationSet &opParams,
167 AuthorizationSet* outParams) {
168 auto kmKeyPath = dir + "/" + kFn_keymaster_key_blob;
170 if (!readFileToString(kmKeyPath, &kmKey)) return KeymasterOperation();
171 AuthorizationSet inParams(keyParams);
172 inParams.append(opParams.begin(), opParams.end());
174 auto opHandle = keymaster.begin(purpose, kmKey, inParams, outParams);
178 if (opHandle.errorCode() != ErrorCode::KEY_REQUIRES_UPGRADE) return opHandle;
179 LOG(DEBUG) << "Upgrading key: " << dir;
181 if (!keymaster.upgradeKey(kmKey, keyParams, &newKey)) return KeymasterOperation();
182 auto newKeyPath = dir + "/" + kFn_keymaster_key_blob_upgraded;
183 if (!writeStringToFile(newKey, newKeyPath)) return KeymasterOperation();
184 if (rename(newKeyPath.c_str(), kmKeyPath.c_str()) != 0) {
185 PLOG(ERROR) << "Unable to move upgraded key to location: " << kmKeyPath;
186 return KeymasterOperation();
188 if (!keymaster.deleteKey(kmKey)) {
189 LOG(ERROR) << "Key deletion failed during upgrade, continuing anyway: " << dir;
192 LOG(INFO) << "Key upgraded: " << dir;
196 static bool encryptWithKeymasterKey(Keymaster& keymaster, const std::string& dir,
197 const AuthorizationSet &keyParams,
198 const std::string& message, std::string* ciphertext) {
199 AuthorizationSet opParams;
200 AuthorizationSet outParams;
201 auto opHandle = begin(keymaster, dir, KeyPurpose::ENCRYPT, keyParams, opParams, &outParams);
202 if (!opHandle) return false;
203 auto nonceBlob = outParams.GetTagValue(TAG_NONCE);
204 if (!nonceBlob.isOk()) {
205 LOG(ERROR) << "GCM encryption but no nonce generated";
208 // nonceBlob here is just a pointer into existing data, must not be freed
209 std::string nonce(reinterpret_cast<const char*>(&nonceBlob.value()[0]), nonceBlob.value().size());
210 if (!checkSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
212 if (!opHandle.updateCompletely(message, &body)) return false;
215 if (!opHandle.finish(&mac)) return false;
216 if (!checkSize("mac", mac.size(), GCM_MAC_BYTES)) return false;
217 *ciphertext = nonce + body + mac;
221 static bool decryptWithKeymasterKey(Keymaster& keymaster, const std::string& dir,
222 const AuthorizationSet &keyParams,
223 const std::string& ciphertext, std::string* message) {
224 auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
225 auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
226 auto opParams = AuthorizationSetBuilder()
227 .Authorization(TAG_NONCE, blob2hidlVec(nonce));
228 auto opHandle = begin(keymaster, dir, KeyPurpose::DECRYPT, keyParams, opParams, nullptr);
229 if (!opHandle) return false;
230 if (!opHandle.updateCompletely(bodyAndMac, message)) return false;
231 if (!opHandle.finish(nullptr)) return false;
235 static std::string getStretching(const KeyAuthentication& auth) {
236 if (!auth.usesKeymaster()) {
237 return kStretch_none;
238 } else if (auth.secret.empty()) {
239 return kStretch_nopassword;
241 char paramstr[PROPERTY_VALUE_MAX];
243 property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
244 return std::string() + kStretchPrefix_scrypt + paramstr;
248 static bool stretchingNeedsSalt(const std::string& stretching) {
249 return stretching != kStretch_nopassword && stretching != kStretch_none;
252 static bool stretchSecret(const std::string& stretching, const std::string& secret,
253 const std::string& salt, std::string* stretched) {
254 if (stretching == kStretch_nopassword) {
255 if (!secret.empty()) {
256 LOG(WARNING) << "Password present but stretching is nopassword";
260 } else if (stretching == kStretch_none) {
262 } else if (std::equal(kStretchPrefix_scrypt.begin(), kStretchPrefix_scrypt.end(),
263 stretching.begin())) {
265 if (!parse_scrypt_parameters(stretching.substr(kStretchPrefix_scrypt.size()).c_str(), &Nf,
267 LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching;
270 stretched->assign(STRETCHED_BYTES, '\0');
271 if (crypto_scrypt(reinterpret_cast<const uint8_t*>(secret.data()), secret.size(),
272 reinterpret_cast<const uint8_t*>(salt.data()), salt.size(),
273 1 << Nf, 1 << rf, 1 << pf,
274 reinterpret_cast<uint8_t*>(&(*stretched)[0]), stretched->size()) != 0) {
275 LOG(ERROR) << "scrypt failed with params: " << stretching;
279 LOG(ERROR) << "Unknown stretching type: " << stretching;
285 static bool generateAppId(const KeyAuthentication& auth, const std::string& stretching,
286 const std::string& salt, const std::string& secdiscardable,
287 std::string* appId) {
288 std::string stretched;
289 if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
290 *appId = hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable) + stretched;
294 static bool readRandomBytesOrLog(size_t count, std::string* out) {
295 auto status = ReadRandomBytes(count, *out);
297 LOG(ERROR) << "Random read failed with status: " << status;
303 static void logOpensslError() {
304 LOG(ERROR) << "Openssl error: " << ERR_get_error();
307 static bool encryptWithoutKeymaster(const std::string& preKey,
308 const std::string& plaintext, std::string* ciphertext) {
309 auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
310 key.resize(AES_KEY_BYTES);
311 if (!readRandomBytesOrLog(GCM_NONCE_BYTES, ciphertext)) return false;
312 auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
313 EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
318 if (1 != EVP_EncryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL,
319 reinterpret_cast<const uint8_t*>(key.data()),
320 reinterpret_cast<const uint8_t*>(ciphertext->data()))) {
324 ciphertext->resize(GCM_NONCE_BYTES + plaintext.size() + GCM_MAC_BYTES);
326 if (1 != EVP_EncryptUpdate(ctx.get(),
327 reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES), &outlen,
328 reinterpret_cast<const uint8_t*>(plaintext.data()), plaintext.size())) {
332 if (outlen != static_cast<int>(plaintext.size())) {
333 LOG(ERROR) << "GCM ciphertext length should be " << plaintext.size() << " was " << outlen;
336 if (1 != EVP_EncryptFinal_ex(ctx.get(),
337 reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()), &outlen)) {
342 LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen;
345 if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_GET_TAG, GCM_MAC_BYTES,
346 reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()))) {
353 static bool decryptWithoutKeymaster(const std::string& preKey,
354 const std::string& ciphertext, std::string* plaintext) {
355 if (ciphertext.size() < GCM_NONCE_BYTES + GCM_MAC_BYTES) {
356 LOG(ERROR) << "GCM ciphertext too small: " << ciphertext.size();
359 auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
360 key.resize(AES_KEY_BYTES);
361 auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
362 EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
367 if (1 != EVP_DecryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL,
368 reinterpret_cast<const uint8_t*>(key.data()),
369 reinterpret_cast<const uint8_t*>(ciphertext.data()))) {
373 plaintext->resize(ciphertext.size() - GCM_NONCE_BYTES - GCM_MAC_BYTES);
375 if (1 != EVP_DecryptUpdate(ctx.get(),
376 reinterpret_cast<uint8_t*>(&(*plaintext)[0]), &outlen,
377 reinterpret_cast<const uint8_t*>(ciphertext.data() + GCM_NONCE_BYTES), plaintext->size())) {
381 if (outlen != static_cast<int>(plaintext->size())) {
382 LOG(ERROR) << "GCM plaintext length should be " << plaintext->size() << " was " << outlen;
385 if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_SET_TAG, GCM_MAC_BYTES,
387 reinterpret_cast<const void*>(ciphertext.data() + GCM_NONCE_BYTES + plaintext->size())))) {
391 if (1 != EVP_DecryptFinal_ex(ctx.get(),
392 reinterpret_cast<uint8_t*>(&(*plaintext)[0] + plaintext->size()), &outlen)) {
397 LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen;
403 bool pathExists(const std::string& path) {
404 return access(path.c_str(), F_OK) == 0;
407 bool storeKey(const std::string& dir, const KeyAuthentication& auth, const std::string& key) {
408 if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) {
409 PLOG(ERROR) << "key mkdir " << dir;
412 if (!writeStringToFile(kCurrentVersion, dir + "/" + kFn_version)) return false;
413 std::string secdiscardable;
414 if (!readRandomBytesOrLog(SECDISCARDABLE_BYTES, &secdiscardable)) return false;
415 if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
416 std::string stretching = getStretching(auth);
417 if (!writeStringToFile(stretching, dir + "/" + kFn_stretching)) return false;
419 if (stretchingNeedsSalt(stretching)) {
420 if (ReadRandomBytes(SALT_BYTES, salt) != OK) {
421 LOG(ERROR) << "Random read failed";
424 if (!writeStringToFile(salt, dir + "/" + kFn_salt)) return false;
427 if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
428 std::string encryptedKey;
429 if (auth.usesKeymaster()) {
431 if (!keymaster) return false;
433 if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
434 if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
435 auto keyParams = beginParams(auth, appId);
436 if (!encryptWithKeymasterKey(keymaster, dir, keyParams, key, &encryptedKey)) return false;
438 if (!encryptWithoutKeymaster(appId, key, &encryptedKey)) return false;
440 if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
444 bool storeKeyAtomically(const std::string& key_path, const std::string& tmp_path,
445 const KeyAuthentication& auth, const std::string& key) {
446 if (pathExists(key_path)) {
447 LOG(ERROR) << "Already exists, cannot create key at: " << key_path;
450 if (pathExists(tmp_path)) {
451 LOG(DEBUG) << "Already exists, destroying: " << tmp_path;
452 destroyKey(tmp_path); // May be partially created so ignore errors
454 if (!storeKey(tmp_path, auth, key)) return false;
455 if (rename(tmp_path.c_str(), key_path.c_str()) != 0) {
456 PLOG(ERROR) << "Unable to move new key to location: " << key_path;
459 LOG(DEBUG) << "Created key: " << key_path;
463 bool retrieveKey(const std::string& dir, const KeyAuthentication& auth, std::string* key) {
465 if (!readFileToString(dir + "/" + kFn_version, &version)) return false;
466 if (version != kCurrentVersion) {
467 LOG(ERROR) << "Version mismatch, expected " << kCurrentVersion << " got " << version;
470 std::string secdiscardable;
471 if (!readFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) return false;
472 std::string stretching;
473 if (!readFileToString(dir + "/" + kFn_stretching, &stretching)) return false;
475 if (stretchingNeedsSalt(stretching)) {
476 if (!readFileToString(dir + "/" + kFn_salt, &salt)) return false;
479 if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
480 std::string encryptedMessage;
481 if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
482 if (auth.usesKeymaster()) {
484 if (!keymaster) return false;
485 auto keyParams = beginParams(auth, appId);
486 if (!decryptWithKeymasterKey(keymaster, dir, keyParams, encryptedMessage, key)) return false;
488 if (!decryptWithoutKeymaster(appId, encryptedMessage, key)) return false;
493 static bool deleteKey(const std::string& dir) {
495 if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
497 if (!keymaster) return false;
498 if (!keymaster.deleteKey(kmKey)) return false;
502 static bool runSecdiscard(const std::string& dir) {
504 std::vector<std::string>{kSecdiscardPath, "--",
505 dir + "/" + kFn_encrypted_key,
506 dir + "/" + kFn_keymaster_key_blob,
507 dir + "/" + kFn_secdiscardable,
509 LOG(ERROR) << "secdiscard failed";
515 bool runSecdiscardSingle(const std::string& file) {
517 std::vector<std::string>{kSecdiscardPath, "--",
519 LOG(ERROR) << "secdiscard failed";
525 static bool recursiveDeleteKey(const std::string& dir) {
526 if (ForkExecvp(std::vector<std::string>{kRmPath, "-rf", dir}) != 0) {
527 LOG(ERROR) << "recursive delete failed";
533 bool destroyKey(const std::string& dir) {
535 // Try each thing, even if previous things failed.
536 success &= deleteKey(dir);
537 success &= runSecdiscard(dir);
538 success &= recursiveDeleteKey(dir);
543 } // namespace android