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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(&paramBuilder, 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(&paramBuilder, keymaster::TAG_APPLICATION_ID, appId);
132     if (!auth.token.empty()) {
133         LOG(DEBUG) << "Supplying auth token to Keymaster";
134         addStringParam(&paramBuilder, 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