1 /*
2 * Copyright (C) 2016 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 "KeyStorage.h"
18
19 #include "Keymaster.h"
20 #include "ScryptParameters.h"
21 #include "Utils.h"
22
23 #include <vector>
24
25 #include <errno.h>
26 #include <sys/stat.h>
27 #include <sys/types.h>
28 #include <sys/wait.h>
29 #include <unistd.h>
30
31 #include <openssl/sha.h>
32
33 #include <android-base/file.h>
34 #include <android-base/logging.h>
35
36 #include <cutils/properties.h>
37
38 #include <hardware/hw_auth_token.h>
39
40 #include <keymaster/authorization_set.h>
41
42 extern "C" {
43
44 #include "crypto_scrypt.h"
45 }
46
47 namespace android {
48 namespace vold {
49
50 const KeyAuthentication kEmptyAuthentication{"", ""};
51
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;
58
59 static constexpr uint32_t AUTH_TIMEOUT = 30; // Seconds
60
61 static const char* kCurrentVersion = "1";
62 static const char* kRmPath = "/system/bin/rm";
63 static const char* kSecdiscardPath = "/system/bin/secdiscard";
64 static const char* kStretch_none = "none";
65 static const char* kStretch_nopassword = "nopassword";
66 static const std::string kStretchPrefix_scrypt = "scrypt ";
67 static const char* kFn_encrypted_key = "encrypted_key";
68 static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
69 static const char* kFn_salt = "salt";
70 static const char* kFn_secdiscardable = "secdiscardable";
71 static const char* kFn_stretching = "stretching";
72 static const char* kFn_version = "version";
73
checkSize(const std::string & kind,size_t actual,size_t expected)74 static bool checkSize(const std::string& kind, size_t actual, size_t expected) {
75 if (actual != expected) {
76 LOG(ERROR) << "Wrong number of bytes in " << kind << ", expected " << expected << " got "
77 << actual;
78 return false;
79 }
80 return true;
81 }
82
hashSecdiscardable(const std::string & secdiscardable)83 static std::string hashSecdiscardable(const std::string& secdiscardable) {
84 SHA512_CTX c;
85
86 SHA512_Init(&c);
87 // Personalise the hashing by introducing a fixed prefix.
88 // Hashing applications should use personalization except when there is a
89 // specific reason not to; see section 4.11 of https://www.schneier.com/skein1.3.pdf
90 std::string secdiscardableHashingPrefix = "Android secdiscardable SHA512";
91 secdiscardableHashingPrefix.resize(SHA512_CBLOCK);
92 SHA512_Update(&c, secdiscardableHashingPrefix.data(), secdiscardableHashingPrefix.size());
93 SHA512_Update(&c, secdiscardable.data(), secdiscardable.size());
94 std::string res(SHA512_DIGEST_LENGTH, '\0');
95 SHA512_Final(reinterpret_cast<uint8_t*>(&res[0]), &c);
96 return res;
97 }
98
generateKeymasterKey(Keymaster & keymaster,const KeyAuthentication & auth,const std::string & appId,std::string * key)99 static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth,
100 const std::string& appId, std::string* key) {
101 auto paramBuilder = keymaster::AuthorizationSetBuilder()
102 .AesEncryptionKey(AES_KEY_BYTES * 8)
103 .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
104 .Authorization(keymaster::TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
105 .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
106 addStringParam(¶mBuilder, keymaster::TAG_APPLICATION_ID, appId);
107 if (auth.token.empty()) {
108 LOG(DEBUG) << "Creating key that doesn't need auth token";
109 paramBuilder.Authorization(keymaster::TAG_NO_AUTH_REQUIRED);
110 } else {
111 LOG(DEBUG) << "Auth token required for key";
112 if (auth.token.size() != sizeof(hw_auth_token_t)) {
113 LOG(ERROR) << "Auth token should be " << sizeof(hw_auth_token_t) << " bytes, was "
114 << auth.token.size() << " bytes";
115 return false;
116 }
117 const hw_auth_token_t* at = reinterpret_cast<const hw_auth_token_t*>(auth.token.data());
118 paramBuilder.Authorization(keymaster::TAG_USER_SECURE_ID, at->user_id);
119 paramBuilder.Authorization(keymaster::TAG_USER_AUTH_TYPE, HW_AUTH_PASSWORD);
120 paramBuilder.Authorization(keymaster::TAG_AUTH_TIMEOUT, AUTH_TIMEOUT);
121 }
122 return keymaster.generateKey(paramBuilder.build(), key);
123 }
124
beginParams(const KeyAuthentication & auth,const std::string & appId)125 static keymaster::AuthorizationSetBuilder beginParams(const KeyAuthentication& auth,
126 const std::string& appId) {
127 auto paramBuilder = keymaster::AuthorizationSetBuilder()
128 .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
129 .Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
130 .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
131 addStringParam(¶mBuilder, keymaster::TAG_APPLICATION_ID, appId);
132 if (!auth.token.empty()) {
133 LOG(DEBUG) << "Supplying auth token to Keymaster";
134 addStringParam(¶mBuilder, keymaster::TAG_AUTH_TOKEN, auth.token);
135 }
136 return paramBuilder;
137 }
138
encryptWithKeymasterKey(Keymaster & keymaster,const std::string & key,const KeyAuthentication & auth,const std::string & appId,const std::string & message,std::string * ciphertext)139 static bool encryptWithKeymasterKey(Keymaster& keymaster, const std::string& key,
140 const KeyAuthentication& auth, const std::string& appId,
141 const std::string& message, std::string* ciphertext) {
142 auto params = beginParams(auth, appId).build();
143 keymaster::AuthorizationSet outParams;
144 auto opHandle = keymaster.begin(KM_PURPOSE_ENCRYPT, key, params, &outParams);
145 if (!opHandle) return false;
146 keymaster_blob_t nonceBlob;
147 if (!outParams.GetTagValue(keymaster::TAG_NONCE, &nonceBlob)) {
148 LOG(ERROR) << "GCM encryption but no nonce generated";
149 return false;
150 }
151 // nonceBlob here is just a pointer into existing data, must not be freed
152 std::string nonce(reinterpret_cast<const char*>(nonceBlob.data), nonceBlob.data_length);
153 if (!checkSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
154 std::string body;
155 if (!opHandle.updateCompletely(message, &body)) return false;
156
157 std::string mac;
158 if (!opHandle.finishWithOutput(&mac)) return false;
159 if (!checkSize("mac", mac.size(), GCM_MAC_BYTES)) return false;
160 *ciphertext = nonce + body + mac;
161 return true;
162 }
163
decryptWithKeymasterKey(Keymaster & keymaster,const std::string & key,const KeyAuthentication & auth,const std::string & appId,const std::string & ciphertext,std::string * message)164 static bool decryptWithKeymasterKey(Keymaster& keymaster, const std::string& key,
165 const KeyAuthentication& auth, const std::string& appId,
166 const std::string& ciphertext, std::string* message) {
167 auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
168 auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
169 auto params = addStringParam(beginParams(auth, appId), keymaster::TAG_NONCE, nonce).build();
170 auto opHandle = keymaster.begin(KM_PURPOSE_DECRYPT, key, params);
171 if (!opHandle) return false;
172 if (!opHandle.updateCompletely(bodyAndMac, message)) return false;
173 if (!opHandle.finish()) return false;
174 return true;
175 }
176
readFileToString(const std::string & filename,std::string * result)177 static bool readFileToString(const std::string& filename, std::string* result) {
178 if (!android::base::ReadFileToString(filename, result)) {
179 PLOG(ERROR) << "Failed to read from " << filename;
180 return false;
181 }
182 return true;
183 }
184
writeStringToFile(const std::string & payload,const std::string & filename)185 static bool writeStringToFile(const std::string& payload, const std::string& filename) {
186 if (!android::base::WriteStringToFile(payload, filename)) {
187 PLOG(ERROR) << "Failed to write to " << filename;
188 return false;
189 }
190 return true;
191 }
192
getStretching()193 static std::string getStretching() {
194 char paramstr[PROPERTY_VALUE_MAX];
195
196 property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
197 return std::string() + kStretchPrefix_scrypt + paramstr;
198 }
199
stretchingNeedsSalt(const std::string & stretching)200 static bool stretchingNeedsSalt(const std::string& stretching) {
201 return stretching != kStretch_nopassword && stretching != kStretch_none;
202 }
203
stretchSecret(const std::string & stretching,const std::string & secret,const std::string & salt,std::string * stretched)204 static bool stretchSecret(const std::string& stretching, const std::string& secret,
205 const std::string& salt, std::string* stretched) {
206 if (stretching == kStretch_nopassword) {
207 if (!secret.empty()) {
208 LOG(WARNING) << "Password present but stretching is nopassword";
209 // Continue anyway
210 }
211 stretched->clear();
212 } else if (stretching == kStretch_none) {
213 *stretched = secret;
214 } else if (std::equal(kStretchPrefix_scrypt.begin(), kStretchPrefix_scrypt.end(),
215 stretching.begin())) {
216 int Nf, rf, pf;
217 if (!parse_scrypt_parameters(stretching.substr(kStretchPrefix_scrypt.size()).c_str(), &Nf,
218 &rf, &pf)) {
219 LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching;
220 return false;
221 }
222 stretched->assign(STRETCHED_BYTES, '\0');
223 if (crypto_scrypt(reinterpret_cast<const uint8_t*>(secret.data()), secret.size(),
224 reinterpret_cast<const uint8_t*>(salt.data()), salt.size(),
225 1 << Nf, 1 << rf, 1 << pf,
226 reinterpret_cast<uint8_t*>(&(*stretched)[0]), stretched->size()) != 0) {
227 LOG(ERROR) << "scrypt failed with params: " << stretching;
228 return false;
229 }
230 } else {
231 LOG(ERROR) << "Unknown stretching type: " << stretching;
232 return false;
233 }
234 return true;
235 }
236
generateAppId(const KeyAuthentication & auth,const std::string & stretching,const std::string & salt,const std::string & secdiscardable,std::string * appId)237 static bool generateAppId(const KeyAuthentication& auth, const std::string& stretching,
238 const std::string& salt, const std::string& secdiscardable,
239 std::string* appId) {
240 std::string stretched;
241 if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
242 *appId = hashSecdiscardable(secdiscardable) + stretched;
243 return true;
244 }
245
storeKey(const std::string & dir,const KeyAuthentication & auth,const std::string & key)246 bool storeKey(const std::string& dir, const KeyAuthentication& auth, const std::string& key) {
247 if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) {
248 PLOG(ERROR) << "key mkdir " << dir;
249 return false;
250 }
251 if (!writeStringToFile(kCurrentVersion, dir + "/" + kFn_version)) return false;
252 std::string secdiscardable;
253 if (ReadRandomBytes(SECDISCARDABLE_BYTES, secdiscardable) != OK) {
254 // TODO status_t plays badly with PLOG, fix it.
255 LOG(ERROR) << "Random read failed";
256 return false;
257 }
258 if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
259 std::string stretching = auth.secret.empty() ? kStretch_nopassword : getStretching();
260 if (!writeStringToFile(stretching, dir + "/" + kFn_stretching)) return false;
261 std::string salt;
262 if (stretchingNeedsSalt(stretching)) {
263 if (ReadRandomBytes(SALT_BYTES, salt) != OK) {
264 LOG(ERROR) << "Random read failed";
265 return false;
266 }
267 if (!writeStringToFile(salt, dir + "/" + kFn_salt)) return false;
268 }
269 std::string appId;
270 if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
271 Keymaster keymaster;
272 if (!keymaster) return false;
273 std::string kmKey;
274 if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
275 if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
276 std::string encryptedKey;
277 if (!encryptWithKeymasterKey(keymaster, kmKey, auth, appId, key, &encryptedKey)) return false;
278 if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
279 return true;
280 }
281
retrieveKey(const std::string & dir,const KeyAuthentication & auth,std::string * key)282 bool retrieveKey(const std::string& dir, const KeyAuthentication& auth, std::string* key) {
283 std::string version;
284 if (!readFileToString(dir + "/" + kFn_version, &version)) return false;
285 if (version != kCurrentVersion) {
286 LOG(ERROR) << "Version mismatch, expected " << kCurrentVersion << " got " << version;
287 return false;
288 }
289 std::string secdiscardable;
290 if (!readFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) return false;
291 std::string stretching;
292 if (!readFileToString(dir + "/" + kFn_stretching, &stretching)) return false;
293 std::string salt;
294 if (stretchingNeedsSalt(stretching)) {
295 if (!readFileToString(dir + "/" + kFn_salt, &salt)) return false;
296 }
297 std::string appId;
298 if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
299 std::string kmKey;
300 if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
301 std::string encryptedMessage;
302 if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
303 Keymaster keymaster;
304 if (!keymaster) return false;
305 return decryptWithKeymasterKey(keymaster, kmKey, auth, appId, encryptedMessage, key);
306 }
307
deleteKey(const std::string & dir)308 static bool deleteKey(const std::string& dir) {
309 std::string kmKey;
310 if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
311 Keymaster keymaster;
312 if (!keymaster) return false;
313 if (!keymaster.deleteKey(kmKey)) return false;
314 return true;
315 }
316
runSecdiscard(const std::string & dir)317 static bool runSecdiscard(const std::string& dir) {
318 if (ForkExecvp(
319 std::vector<std::string>{kSecdiscardPath, "--",
320 dir + "/" + kFn_encrypted_key,
321 dir + "/" + kFn_keymaster_key_blob,
322 dir + "/" + kFn_secdiscardable,
323 }) != 0) {
324 LOG(ERROR) << "secdiscard failed";
325 return false;
326 }
327 return true;
328 }
329
recursiveDeleteKey(const std::string & dir)330 static bool recursiveDeleteKey(const std::string& dir) {
331 if (ForkExecvp(std::vector<std::string>{kRmPath, "-rf", dir}) != 0) {
332 LOG(ERROR) << "recursive delete failed";
333 return false;
334 }
335 return true;
336 }
337
destroyKey(const std::string & dir)338 bool destroyKey(const std::string& dir) {
339 bool success = true;
340 // Try each thing, even if previous things failed.
341 success &= deleteKey(dir);
342 success &= runSecdiscard(dir);
343 success &= recursiveDeleteKey(dir);
344 return success;
345 }
346
347 } // namespace vold
348 } // namespace android
349