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"
27 #include <sys/types.h>
31 #include <openssl/sha.h>
33 #include <android-base/file.h>
34 #include <android-base/logging.h>
36 #include <cutils/properties.h>
38 #include <hardware/hw_auth_token.h>
40 #include <keymaster/authorization_set.h>
44 #include "crypto_scrypt.h"
50 const KeyAuthentication kEmptyAuthentication{"", ""};
52 static constexpr size_t AES_KEY_BYTES = 32;
53 static constexpr size_t GCM_NONCE_BYTES = 12;
54 static constexpr size_t GCM_MAC_BYTES = 16;
55 static constexpr size_t SALT_BYTES = 1 << 4;
56 static constexpr size_t SECDISCARDABLE_BYTES = 1 << 14;
57 static constexpr size_t STRETCHED_BYTES = 1 << 6;
59 static const char* kCurrentVersion = "1";
60 static const char* kRmPath = "/system/bin/rm";
61 static const char* kSecdiscardPath = "/system/bin/secdiscard";
62 static const char* kStretch_none = "none";
63 static const char* kStretch_nopassword = "nopassword";
64 static const std::string kStretchPrefix_scrypt = "scrypt ";
65 static const char* kFn_encrypted_key = "encrypted_key";
66 static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
67 static const char* kFn_salt = "salt";
68 static const char* kFn_secdiscardable = "secdiscardable";
69 static const char* kFn_stretching = "stretching";
70 static const char* kFn_version = "version";
72 static bool checkSize(const std::string& kind, size_t actual, size_t expected) {
73 if (actual != expected) {
74 LOG(ERROR) << "Wrong number of bytes in " << kind << ", expected " << expected << " got "
81 static std::string hashSecdiscardable(const std::string& secdiscardable) {
85 // Personalise the hashing by introducing a fixed prefix.
86 // Hashing applications should use personalization except when there is a
87 // specific reason not to; see section 4.11 of https://www.schneier.com/skein1.3.pdf
88 std::string secdiscardableHashingPrefix = "Android secdiscardable SHA512";
89 secdiscardableHashingPrefix.resize(SHA512_CBLOCK);
90 SHA512_Update(&c, secdiscardableHashingPrefix.data(), secdiscardableHashingPrefix.size());
91 SHA512_Update(&c, secdiscardable.data(), secdiscardable.size());
92 std::string res(SHA512_DIGEST_LENGTH, '\0');
93 SHA512_Final(reinterpret_cast<uint8_t*>(&res[0]), &c);
97 static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth,
98 const std::string& appId, std::string* key) {
99 auto paramBuilder = keymaster::AuthorizationSetBuilder()
100 .AesEncryptionKey(AES_KEY_BYTES * 8)
101 .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
102 .Authorization(keymaster::TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
103 .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
104 addStringParam(¶mBuilder, keymaster::TAG_APPLICATION_ID, appId);
105 if (auth.token.empty()) {
106 LOG(DEBUG) << "Creating key that doesn't need auth token";
107 paramBuilder.Authorization(keymaster::TAG_NO_AUTH_REQUIRED);
109 LOG(DEBUG) << "Auth token required for key";
110 if (auth.token.size() != sizeof(hw_auth_token_t)) {
111 LOG(ERROR) << "Auth token should be " << sizeof(hw_auth_token_t) << " bytes, was "
112 << auth.token.size() << " bytes";
115 const hw_auth_token_t* at = reinterpret_cast<const hw_auth_token_t*>(auth.token.data());
116 paramBuilder.Authorization(keymaster::TAG_USER_SECURE_ID, at->user_id);
117 paramBuilder.Authorization(keymaster::TAG_USER_AUTH_TYPE, HW_AUTH_PASSWORD);
118 paramBuilder.Authorization(keymaster::TAG_AUTH_TIMEOUT, 5);
120 return keymaster.generateKey(paramBuilder.build(), key);
123 static keymaster::AuthorizationSetBuilder beginParams(const KeyAuthentication& auth,
124 const std::string& appId) {
125 auto paramBuilder = keymaster::AuthorizationSetBuilder()
126 .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
127 .Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
128 .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
129 addStringParam(¶mBuilder, keymaster::TAG_APPLICATION_ID, appId);
130 if (!auth.token.empty()) {
131 LOG(DEBUG) << "Supplying auth token to Keymaster";
132 addStringParam(¶mBuilder, keymaster::TAG_AUTH_TOKEN, auth.token);
137 static bool encryptWithKeymasterKey(Keymaster& keymaster, const std::string& key,
138 const KeyAuthentication& auth, const std::string& appId,
139 const std::string& message, std::string* ciphertext) {
140 auto params = beginParams(auth, appId).build();
141 keymaster::AuthorizationSet outParams;
142 auto opHandle = keymaster.begin(KM_PURPOSE_ENCRYPT, key, params, &outParams);
143 if (!opHandle) return false;
144 keymaster_blob_t nonceBlob;
145 if (!outParams.GetTagValue(keymaster::TAG_NONCE, &nonceBlob)) {
146 LOG(ERROR) << "GCM encryption but no nonce generated";
149 // nonceBlob here is just a pointer into existing data, must not be freed
150 std::string nonce(reinterpret_cast<const char*>(nonceBlob.data), nonceBlob.data_length);
151 if (!checkSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
153 if (!opHandle.updateCompletely(message, &body)) return false;
156 if (!opHandle.finishWithOutput(&mac)) return false;
157 if (!checkSize("mac", mac.size(), GCM_MAC_BYTES)) return false;
158 *ciphertext = nonce + body + mac;
162 static bool decryptWithKeymasterKey(Keymaster& keymaster, const std::string& key,
163 const KeyAuthentication& auth, const std::string& appId,
164 const std::string& ciphertext, std::string* message) {
165 auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
166 auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
167 auto params = addStringParam(beginParams(auth, appId), keymaster::TAG_NONCE, nonce).build();
168 auto opHandle = keymaster.begin(KM_PURPOSE_DECRYPT, key, params);
169 if (!opHandle) return false;
170 if (!opHandle.updateCompletely(bodyAndMac, message)) return false;
171 if (!opHandle.finish()) return false;
175 static bool readFileToString(const std::string& filename, std::string* result) {
176 if (!android::base::ReadFileToString(filename, result)) {
177 PLOG(ERROR) << "Failed to read from " << filename;
183 static bool writeStringToFile(const std::string& payload, const std::string& filename) {
184 if (!android::base::WriteStringToFile(payload, filename)) {
185 PLOG(ERROR) << "Failed to write to " << filename;
191 static std::string getStretching() {
192 char paramstr[PROPERTY_VALUE_MAX];
194 property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
195 return std::string() + kStretchPrefix_scrypt + paramstr;
198 static bool stretchingNeedsSalt(const std::string& stretching) {
199 return stretching != kStretch_nopassword && stretching != kStretch_none;
202 static bool stretchSecret(const std::string& stretching, const std::string& secret,
203 const std::string& salt, std::string* stretched) {
204 if (stretching == kStretch_nopassword) {
205 if (!secret.empty()) {
206 LOG(WARNING) << "Password present but stretching is nopassword";
210 } else if (stretching == kStretch_none) {
212 } else if (std::equal(kStretchPrefix_scrypt.begin(), kStretchPrefix_scrypt.end(),
213 stretching.begin())) {
215 if (!parse_scrypt_parameters(stretching.substr(kStretchPrefix_scrypt.size()).c_str(), &Nf,
217 LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching;
220 stretched->assign(STRETCHED_BYTES, '\0');
221 if (crypto_scrypt(reinterpret_cast<const uint8_t*>(secret.data()), secret.size(),
222 reinterpret_cast<const uint8_t*>(salt.data()), salt.size(),
223 1 << Nf, 1 << rf, 1 << pf,
224 reinterpret_cast<uint8_t*>(&(*stretched)[0]), stretched->size()) != 0) {
225 LOG(ERROR) << "scrypt failed with params: " << stretching;
229 LOG(ERROR) << "Unknown stretching type: " << stretching;
235 static bool generateAppId(const KeyAuthentication& auth, const std::string& stretching,
236 const std::string& salt, const std::string& secdiscardable,
237 std::string* appId) {
238 std::string stretched;
239 if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
240 *appId = hashSecdiscardable(secdiscardable) + stretched;
244 bool storeKey(const std::string& dir, const KeyAuthentication& auth, const std::string& key) {
245 if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) {
246 PLOG(ERROR) << "key mkdir " << dir;
249 if (!writeStringToFile(kCurrentVersion, dir + "/" + kFn_version)) return false;
250 std::string secdiscardable;
251 if (ReadRandomBytes(SECDISCARDABLE_BYTES, secdiscardable) != OK) {
252 // TODO status_t plays badly with PLOG, fix it.
253 LOG(ERROR) << "Random read failed";
256 if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
257 std::string stretching = auth.secret.empty() ? kStretch_nopassword : getStretching();
258 if (!writeStringToFile(stretching, dir + "/" + kFn_stretching)) return false;
260 if (stretchingNeedsSalt(stretching)) {
261 if (ReadRandomBytes(SALT_BYTES, salt) != OK) {
262 LOG(ERROR) << "Random read failed";
265 if (!writeStringToFile(salt, dir + "/" + kFn_salt)) return false;
268 if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
270 if (!keymaster) return false;
272 if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
273 if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
274 std::string encryptedKey;
275 if (!encryptWithKeymasterKey(keymaster, kmKey, auth, appId, key, &encryptedKey)) return false;
276 if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
280 bool retrieveKey(const std::string& dir, const KeyAuthentication& auth, std::string* key) {
282 if (!readFileToString(dir + "/" + kFn_version, &version)) return false;
283 if (version != kCurrentVersion) {
284 LOG(ERROR) << "Version mismatch, expected " << kCurrentVersion << " got " << version;
287 std::string secdiscardable;
288 if (!readFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) return false;
289 std::string stretching;
290 if (!readFileToString(dir + "/" + kFn_stretching, &stretching)) return false;
292 if (stretchingNeedsSalt(stretching)) {
293 if (!readFileToString(dir + "/" + kFn_salt, &salt)) return false;
296 if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
298 if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
299 std::string encryptedMessage;
300 if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
302 if (!keymaster) return false;
303 return decryptWithKeymasterKey(keymaster, kmKey, auth, appId, encryptedMessage, key);
306 static bool deleteKey(const std::string& dir) {
308 if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
310 if (!keymaster) return false;
311 if (!keymaster.deleteKey(kmKey)) return false;
315 static bool secdiscardSecdiscardable(const std::string& dir) {
317 std::vector<std::string>{kSecdiscardPath, "--", dir + "/" + kFn_secdiscardable}) != 0) {
318 LOG(ERROR) << "secdiscard failed";
324 static bool recursiveDeleteKey(const std::string& dir) {
325 if (ForkExecvp(std::vector<std::string>{kRmPath, "-rf", dir}) != 0) {
326 LOG(ERROR) << "recursive delete failed";
332 bool destroyKey(const std::string& dir) {
334 // Try each thing, even if previous things failed.
335 success &= deleteKey(dir);
336 success &= secdiscardSecdiscardable(dir);
337 success &= recursiveDeleteKey(dir);
342 } // namespace android