1 /* 2 * Copyright 2015 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 #include <UniquePtr.h> 17 #include <gatekeeper/gatekeeper.h> 18 19 #include <endian.h> 20 21 #define DAY_IN_MS (1000 * 60 * 60 * 24) 22 23 namespace gatekeeper { 24 25 void GateKeeper::Enroll(const EnrollRequest &request, EnrollResponse *response) { 26 if (response == NULL) return; 27 28 if (!request.provided_password.buffer.get()) { 29 response->error = ERROR_INVALID; 30 return; 31 } 32 33 secure_id_t user_id = 0;// todo: rename to policy 34 uint32_t uid = request.user_id; 35 36 if (request.password_handle.buffer.get() == NULL) { 37 // Password handle does not match what is stored, generate new SecureID 38 GetRandom(&user_id, sizeof(secure_id_t)); 39 } else { 40 password_handle_t *pw_handle = 41 reinterpret_cast<password_handle_t *>(request.password_handle.buffer.get()); 42 43 if (pw_handle->version > HANDLE_VERSION) { 44 response->error = ERROR_INVALID; 45 return; 46 } 47 48 user_id = pw_handle->user_id; 49 50 uint64_t timestamp = GetMillisecondsSinceBoot(); 51 52 uint32_t timeout = 0; 53 bool throttle = (pw_handle->version >= HANDLE_VERSION_THROTTLE); 54 if (throttle) { 55 bool throttle_secure = pw_handle->flags & HANDLE_FLAG_THROTTLE_SECURE; 56 failure_record_t record; 57 if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) { 58 response->error = ERROR_UNKNOWN; 59 return; 60 } 61 62 if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return; 63 64 if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) { 65 response->error = ERROR_UNKNOWN; 66 return; 67 } 68 69 timeout = ComputeRetryTimeout(&record); 70 } 71 72 if (!DoVerify(pw_handle, request.enrolled_password)) { 73 // incorrect old password 74 if (throttle && timeout > 0) { 75 response->SetRetryTimeout(timeout); 76 } else { 77 response->error = ERROR_INVALID; 78 } 79 return; 80 } 81 } 82 83 uint64_t flags = 0; 84 if (ClearFailureRecord(uid, user_id, true)) { 85 flags |= HANDLE_FLAG_THROTTLE_SECURE; 86 } else { 87 ClearFailureRecord(uid, user_id, false); 88 } 89 90 salt_t salt; 91 GetRandom(&salt, sizeof(salt)); 92 93 SizedBuffer password_handle; 94 if (!CreatePasswordHandle(&password_handle, 95 salt, user_id, flags, HANDLE_VERSION, request.provided_password.buffer.get(), 96 request.provided_password.length)) { 97 response->error = ERROR_INVALID; 98 return; 99 } 100 101 response->SetEnrolledPasswordHandle(&password_handle); 102 } 103 104 void GateKeeper::Verify(const VerifyRequest &request, VerifyResponse *response) { 105 if (response == NULL) return; 106 107 if (!request.provided_password.buffer.get() || !request.password_handle.buffer.get()) { 108 response->error = ERROR_INVALID; 109 return; 110 } 111 112 password_handle_t *password_handle = reinterpret_cast<password_handle_t *>( 113 request.password_handle.buffer.get()); 114 115 if (password_handle->version > HANDLE_VERSION) { 116 response->error = ERROR_INVALID; 117 return; 118 } 119 120 secure_id_t user_id = password_handle->user_id; 121 secure_id_t authenticator_id = 0; 122 uint32_t uid = request.user_id; 123 124 uint64_t timestamp = GetMillisecondsSinceBoot(); 125 126 uint32_t timeout = 0; 127 bool throttle = (password_handle->version >= HANDLE_VERSION_THROTTLE); 128 bool throttle_secure = password_handle->flags & HANDLE_FLAG_THROTTLE_SECURE; 129 if (throttle) { 130 failure_record_t record; 131 if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) { 132 response->error = ERROR_UNKNOWN; 133 return; 134 } 135 136 if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return; 137 138 if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) { 139 response->error = ERROR_UNKNOWN; 140 return; 141 } 142 143 timeout = ComputeRetryTimeout(&record); 144 } else { 145 response->request_reenroll = true; 146 } 147 148 if (DoVerify(password_handle, request.provided_password)) { 149 // Signature matches 150 UniquePtr<uint8_t> auth_token_buffer; 151 uint32_t auth_token_len; 152 MintAuthToken(&auth_token_buffer, &auth_token_len, timestamp, 153 user_id, authenticator_id, request.challenge); 154 155 SizedBuffer auth_token(auth_token_len); 156 memcpy(auth_token.buffer.get(), auth_token_buffer.get(), auth_token_len); 157 response->SetVerificationToken(&auth_token); 158 if (throttle) ClearFailureRecord(uid, user_id, throttle_secure); 159 } else { 160 // compute the new timeout given the incremented record 161 if (throttle && timeout > 0) { 162 response->SetRetryTimeout(timeout); 163 } else { 164 response->error = ERROR_INVALID; 165 } 166 } 167 } 168 169 bool GateKeeper::CreatePasswordHandle(SizedBuffer *password_handle_buffer, salt_t salt, 170 secure_id_t user_id, uint64_t flags, uint8_t handle_version, const uint8_t *password, 171 uint32_t password_length) { 172 password_handle_buffer->buffer.reset(new uint8_t[sizeof(password_handle_t)]); 173 password_handle_buffer->length = sizeof(password_handle_t); 174 175 password_handle_t *password_handle = reinterpret_cast<password_handle_t *>( 176 password_handle_buffer->buffer.get()); 177 password_handle->version = handle_version; 178 password_handle->salt = salt; 179 password_handle->user_id = user_id; 180 password_handle->flags = flags; 181 password_handle->hardware_backed = IsHardwareBacked(); 182 183 uint32_t metadata_length = sizeof(user_id) + sizeof(flags) + sizeof(HANDLE_VERSION); 184 const size_t to_sign_size = password_length + metadata_length; 185 UniquePtr<uint8_t> to_sign(new uint8_t[to_sign_size]); 186 187 if (to_sign.get() == nullptr) { 188 return false; 189 } 190 191 memcpy(to_sign.get(), password_handle, metadata_length); 192 memcpy(to_sign.get() + metadata_length, password, password_length); 193 194 const uint8_t *password_key = NULL; 195 uint32_t password_key_length = 0; 196 GetPasswordKey(&password_key, &password_key_length); 197 198 if (!password_key || password_key_length == 0) { 199 return false; 200 } 201 202 ComputePasswordSignature(password_handle->signature, sizeof(password_handle->signature), 203 password_key, password_key_length, to_sign.get(), to_sign_size, salt); 204 return true; 205 } 206 207 bool GateKeeper::DoVerify(const password_handle_t *expected_handle, const SizedBuffer &password) { 208 if (!password.buffer.get()) return false; 209 210 SizedBuffer provided_handle; 211 if (!CreatePasswordHandle(&provided_handle, expected_handle->salt, expected_handle->user_id, 212 expected_handle->flags, expected_handle->version, 213 password.buffer.get(), password.length)) { 214 return false; 215 } 216 217 password_handle_t *generated_handle = 218 reinterpret_cast<password_handle_t *>(provided_handle.buffer.get()); 219 return memcmp_s(generated_handle->signature, expected_handle->signature, 220 sizeof(expected_handle->signature)) == 0; 221 } 222 223 void GateKeeper::MintAuthToken(UniquePtr<uint8_t> *auth_token, uint32_t *length, 224 uint64_t timestamp, secure_id_t user_id, secure_id_t authenticator_id, 225 uint64_t challenge) { 226 if (auth_token == NULL) return; 227 228 hw_auth_token_t *token = new hw_auth_token_t; 229 SizedBuffer serialized_auth_token; 230 231 token->version = HW_AUTH_TOKEN_VERSION; 232 token->challenge = challenge; 233 token->user_id = user_id; 234 token->authenticator_id = authenticator_id; 235 token->authenticator_type = htonl(HW_AUTH_PASSWORD); 236 token->timestamp = htobe64(timestamp); 237 238 const uint8_t *auth_token_key = NULL; 239 uint32_t key_len = 0; 240 if (GetAuthTokenKey(&auth_token_key, &key_len)) { 241 uint32_t hash_len = (uint32_t)((uint8_t *)&token->hmac - (uint8_t *)token); 242 ComputeSignature(token->hmac, sizeof(token->hmac), auth_token_key, key_len, 243 reinterpret_cast<uint8_t *>(token), hash_len); 244 delete[] auth_token_key; 245 } else { 246 memset(token->hmac, 0, sizeof(token->hmac)); 247 } 248 249 if (length != NULL) *length = sizeof(*token); 250 auth_token->reset(reinterpret_cast<uint8_t *>(token)); 251 } 252 253 /* 254 * Calculates the timeout in milliseconds as a function of the failure 255 * counter 'x' as follows: 256 * 257 * [0. 5) -> 0 258 * 5 -> 30 259 * [6, 10) -> 0 260 * [11, 30) -> 30 261 * [30, 140) -> 30 * (2^((x - 30)/10)) 262 * [140, inf) -> 1 day 263 * 264 */ 265 uint32_t GateKeeper::ComputeRetryTimeout(const failure_record_t *record) { 266 static const int failure_timeout_ms = 30000; 267 if (record->failure_counter == 0) return 0; 268 269 if (record->failure_counter > 0 && record->failure_counter <= 10) { 270 if (record->failure_counter % 5 == 0) { 271 return failure_timeout_ms; 272 } else { 273 return 0; 274 } 275 } else if (record->failure_counter < 30) { 276 return failure_timeout_ms; 277 } else if (record->failure_counter < 140) { 278 return failure_timeout_ms << ((record->failure_counter - 30) / 10); 279 } 280 281 return DAY_IN_MS; 282 } 283 284 bool GateKeeper::ThrottleRequest(uint32_t uid, uint64_t timestamp, 285 failure_record_t *record, bool secure, GateKeeperMessage *response) { 286 287 uint64_t last_checked = record->last_checked_timestamp; 288 uint32_t timeout = ComputeRetryTimeout(record); 289 290 if (timeout > 0) { 291 // we have a pending timeout 292 if (timestamp < last_checked + timeout && timestamp > last_checked) { 293 // attempt before timeout expired, return remaining time 294 response->SetRetryTimeout(timeout - (timestamp - last_checked)); 295 return true; 296 } else if (timestamp <= last_checked) { 297 // device was rebooted or timer reset, don't count as new failure but 298 // reset timeout 299 record->last_checked_timestamp = timestamp; 300 if (!WriteFailureRecord(uid, record, secure)) { 301 response->error = ERROR_UNKNOWN; 302 return true; 303 } 304 response->SetRetryTimeout(timeout); 305 return true; 306 } 307 } 308 309 return false; 310 } 311 312 bool GateKeeper::IncrementFailureRecord(uint32_t uid, secure_id_t user_id, uint64_t timestamp, 313 failure_record_t *record, bool secure) { 314 record->secure_user_id = user_id; 315 record->failure_counter++; 316 record->last_checked_timestamp = timestamp; 317 318 return WriteFailureRecord(uid, record, secure); 319 } 320 } // namespace gatekeeper 321 322