/* * Copyright (C) 2016 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include "KeyStorage.h" #include "Keymaster.h" #include "ScryptParameters.h" #include "Utils.h" #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include extern "C" { #include "crypto_scrypt.h" } namespace android { namespace vold { const KeyAuthentication kEmptyAuthentication{"", ""}; static constexpr size_t AES_KEY_BYTES = 32; static constexpr size_t GCM_NONCE_BYTES = 12; static constexpr size_t GCM_MAC_BYTES = 16; static constexpr size_t SALT_BYTES = 1 << 4; static constexpr size_t SECDISCARDABLE_BYTES = 1 << 14; static constexpr size_t STRETCHED_BYTES = 1 << 6; static constexpr uint32_t AUTH_TIMEOUT = 30; // Seconds static const char* kCurrentVersion = "1"; static const char* kRmPath = "/system/bin/rm"; static const char* kSecdiscardPath = "/system/bin/secdiscard"; static const char* kStretch_none = "none"; static const char* kStretch_nopassword = "nopassword"; static const std::string kStretchPrefix_scrypt = "scrypt "; static const char* kHashPrefix_secdiscardable = "Android secdiscardable SHA512"; static const char* kHashPrefix_keygen = "Android key wrapping key generation SHA512"; static const char* kFn_encrypted_key = "encrypted_key"; static const char* kFn_keymaster_key_blob = "keymaster_key_blob"; static const char* kFn_keymaster_key_blob_upgraded = "keymaster_key_blob_upgraded"; static const char* kFn_salt = "salt"; static const char* kFn_secdiscardable = "secdiscardable"; static const char* kFn_stretching = "stretching"; static const char* kFn_version = "version"; static bool checkSize(const std::string& kind, size_t actual, size_t expected) { if (actual != expected) { LOG(ERROR) << "Wrong number of bytes in " << kind << ", expected " << expected << " got " << actual; return false; } return true; } static void hashWithPrefix(char const* prefix, const std::string& tohash, std::string* res) { SHA512_CTX c; SHA512_Init(&c); // Personalise the hashing by introducing a fixed prefix. // Hashing applications should use personalization except when there is a // specific reason not to; see section 4.11 of https://www.schneier.com/skein1.3.pdf std::string hashingPrefix = prefix; hashingPrefix.resize(SHA512_CBLOCK); SHA512_Update(&c, hashingPrefix.data(), hashingPrefix.size()); SHA512_Update(&c, tohash.data(), tohash.size()); res->assign(SHA512_DIGEST_LENGTH, '\0'); SHA512_Final(reinterpret_cast(&(*res)[0]), &c); } static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth, const std::string& appId, std::string* key) { auto paramBuilder = km::AuthorizationSetBuilder() .AesEncryptionKey(AES_KEY_BYTES * 8) .GcmModeMinMacLen(GCM_MAC_BYTES * 8) .Authorization(km::TAG_APPLICATION_ID, km::support::blob2hidlVec(appId)); if (auth.token.empty()) { LOG(DEBUG) << "Creating key that doesn't need auth token"; paramBuilder.Authorization(km::TAG_NO_AUTH_REQUIRED); } else { LOG(DEBUG) << "Auth token required for key"; if (auth.token.size() != sizeof(hw_auth_token_t)) { LOG(ERROR) << "Auth token should be " << sizeof(hw_auth_token_t) << " bytes, was " << auth.token.size() << " bytes"; return false; } const hw_auth_token_t* at = reinterpret_cast(auth.token.data()); paramBuilder.Authorization(km::TAG_USER_SECURE_ID, at->user_id); paramBuilder.Authorization(km::TAG_USER_AUTH_TYPE, km::HardwareAuthenticatorType::PASSWORD); paramBuilder.Authorization(km::TAG_AUTH_TIMEOUT, AUTH_TIMEOUT); } return keymaster.generateKey(paramBuilder, key); } static std::pair beginParams( const KeyAuthentication& auth, const std::string& appId) { auto paramBuilder = km::AuthorizationSetBuilder() .GcmModeMacLen(GCM_MAC_BYTES * 8) .Authorization(km::TAG_APPLICATION_ID, km::support::blob2hidlVec(appId)); km::HardwareAuthToken authToken; if (!auth.token.empty()) { LOG(DEBUG) << "Supplying auth token to Keymaster"; authToken = km::support::hidlVec2AuthToken(km::support::blob2hidlVec(auth.token)); } return {paramBuilder, authToken}; } static bool readFileToString(const std::string& filename, std::string* result) { if (!android::base::ReadFileToString(filename, result)) { PLOG(ERROR) << "Failed to read from " << filename; return false; } return true; } static bool writeStringToFile(const std::string& payload, const std::string& filename) { android::base::unique_fd fd(TEMP_FAILURE_RETRY( open(filename.c_str(), O_WRONLY | O_CREAT | O_NOFOLLOW | O_TRUNC | O_CLOEXEC, 0666))); if (fd == -1) { PLOG(ERROR) << "Failed to open " << filename; return false; } if (!android::base::WriteStringToFd(payload, fd)) { PLOG(ERROR) << "Failed to write to " << filename; unlink(filename.c_str()); return false; } // fsync as close won't guarantee flush data // see close(2), fsync(2) and b/68901441 if (fsync(fd) == -1) { if (errno == EROFS || errno == EINVAL) { PLOG(WARNING) << "Skip fsync " << filename << " on a file system does not support synchronization"; } else { PLOG(ERROR) << "Failed to fsync " << filename; unlink(filename.c_str()); return false; } } return true; } static bool readRandomBytesOrLog(size_t count, std::string* out) { auto status = ReadRandomBytes(count, *out); if (status != OK) { LOG(ERROR) << "Random read failed with status: " << status; return false; } return true; } bool createSecdiscardable(const std::string& filename, std::string* hash) { std::string secdiscardable; if (!readRandomBytesOrLog(SECDISCARDABLE_BYTES, &secdiscardable)) return false; if (!writeStringToFile(secdiscardable, filename)) return false; hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable, hash); return true; } bool readSecdiscardable(const std::string& filename, std::string* hash) { std::string secdiscardable; if (!readFileToString(filename, &secdiscardable)) return false; hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable, hash); return true; } static KeymasterOperation begin(Keymaster& keymaster, const std::string& dir, km::KeyPurpose purpose, const km::AuthorizationSet& keyParams, const km::AuthorizationSet& opParams, const km::HardwareAuthToken& authToken, km::AuthorizationSet* outParams) { auto kmKeyPath = dir + "/" + kFn_keymaster_key_blob; std::string kmKey; if (!readFileToString(kmKeyPath, &kmKey)) return KeymasterOperation(); km::AuthorizationSet inParams(keyParams); inParams.append(opParams.begin(), opParams.end()); for (;;) { auto opHandle = keymaster.begin(purpose, kmKey, inParams, authToken, outParams); if (opHandle) { return opHandle; } if (opHandle.errorCode() != km::ErrorCode::KEY_REQUIRES_UPGRADE) return opHandle; LOG(DEBUG) << "Upgrading key: " << dir; std::string newKey; if (!keymaster.upgradeKey(kmKey, keyParams, &newKey)) return KeymasterOperation(); auto newKeyPath = dir + "/" + kFn_keymaster_key_blob_upgraded; if (!writeStringToFile(newKey, newKeyPath)) return KeymasterOperation(); if (rename(newKeyPath.c_str(), kmKeyPath.c_str()) != 0) { PLOG(ERROR) << "Unable to move upgraded key to location: " << kmKeyPath; return KeymasterOperation(); } if (!keymaster.deleteKey(kmKey)) { LOG(ERROR) << "Key deletion failed during upgrade, continuing anyway: " << dir; } kmKey = newKey; LOG(INFO) << "Key upgraded: " << dir; } } static bool encryptWithKeymasterKey(Keymaster& keymaster, const std::string& dir, const km::AuthorizationSet& keyParams, const km::HardwareAuthToken& authToken, const KeyBuffer& message, std::string* ciphertext) { km::AuthorizationSet opParams; km::AuthorizationSet outParams; auto opHandle = begin(keymaster, dir, km::KeyPurpose::ENCRYPT, keyParams, opParams, authToken, &outParams); if (!opHandle) return false; auto nonceBlob = outParams.GetTagValue(km::TAG_NONCE); if (!nonceBlob.isOk()) { LOG(ERROR) << "GCM encryption but no nonce generated"; return false; } // nonceBlob here is just a pointer into existing data, must not be freed std::string nonce(reinterpret_cast(&nonceBlob.value()[0]), nonceBlob.value().size()); if (!checkSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false; std::string body; if (!opHandle.updateCompletely(message, &body)) return false; std::string mac; if (!opHandle.finish(&mac)) return false; if (!checkSize("mac", mac.size(), GCM_MAC_BYTES)) return false; *ciphertext = nonce + body + mac; return true; } static bool decryptWithKeymasterKey(Keymaster& keymaster, const std::string& dir, const km::AuthorizationSet& keyParams, const km::HardwareAuthToken& authToken, const std::string& ciphertext, KeyBuffer* message) { auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES); auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES); auto opParams = km::AuthorizationSetBuilder().Authorization(km::TAG_NONCE, km::support::blob2hidlVec(nonce)); auto opHandle = begin(keymaster, dir, km::KeyPurpose::DECRYPT, keyParams, opParams, authToken, nullptr); if (!opHandle) return false; if (!opHandle.updateCompletely(bodyAndMac, message)) return false; if (!opHandle.finish(nullptr)) return false; return true; } static std::string getStretching(const KeyAuthentication& auth) { if (!auth.usesKeymaster()) { return kStretch_none; } else if (auth.secret.empty()) { return kStretch_nopassword; } else { char paramstr[PROPERTY_VALUE_MAX]; property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS); return std::string() + kStretchPrefix_scrypt + paramstr; } } static bool stretchingNeedsSalt(const std::string& stretching) { return stretching != kStretch_nopassword && stretching != kStretch_none; } static bool stretchSecret(const std::string& stretching, const std::string& secret, const std::string& salt, std::string* stretched) { if (stretching == kStretch_nopassword) { if (!secret.empty()) { LOG(WARNING) << "Password present but stretching is nopassword"; // Continue anyway } stretched->clear(); } else if (stretching == kStretch_none) { *stretched = secret; } else if (std::equal(kStretchPrefix_scrypt.begin(), kStretchPrefix_scrypt.end(), stretching.begin())) { int Nf, rf, pf; if (!parse_scrypt_parameters(stretching.substr(kStretchPrefix_scrypt.size()).c_str(), &Nf, &rf, &pf)) { LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching; return false; } stretched->assign(STRETCHED_BYTES, '\0'); if (crypto_scrypt(reinterpret_cast(secret.data()), secret.size(), reinterpret_cast(salt.data()), salt.size(), 1 << Nf, 1 << rf, 1 << pf, reinterpret_cast(&(*stretched)[0]), stretched->size()) != 0) { LOG(ERROR) << "scrypt failed with params: " << stretching; return false; } } else { LOG(ERROR) << "Unknown stretching type: " << stretching; return false; } return true; } static bool generateAppId(const KeyAuthentication& auth, const std::string& stretching, const std::string& salt, const std::string& secdiscardable_hash, std::string* appId) { std::string stretched; if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false; *appId = secdiscardable_hash + stretched; return true; } static void logOpensslError() { LOG(ERROR) << "Openssl error: " << ERR_get_error(); } static bool encryptWithoutKeymaster(const std::string& preKey, const KeyBuffer& plaintext, std::string* ciphertext) { std::string key; hashWithPrefix(kHashPrefix_keygen, preKey, &key); key.resize(AES_KEY_BYTES); if (!readRandomBytesOrLog(GCM_NONCE_BYTES, ciphertext)) return false; auto ctx = std::unique_ptr( EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free); if (!ctx) { logOpensslError(); return false; } if (1 != EVP_EncryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL, reinterpret_cast(key.data()), reinterpret_cast(ciphertext->data()))) { logOpensslError(); return false; } ciphertext->resize(GCM_NONCE_BYTES + plaintext.size() + GCM_MAC_BYTES); int outlen; if (1 != EVP_EncryptUpdate( ctx.get(), reinterpret_cast(&(*ciphertext)[0] + GCM_NONCE_BYTES), &outlen, reinterpret_cast(plaintext.data()), plaintext.size())) { logOpensslError(); return false; } if (outlen != static_cast(plaintext.size())) { LOG(ERROR) << "GCM ciphertext length should be " << plaintext.size() << " was " << outlen; return false; } if (1 != EVP_EncryptFinal_ex( ctx.get(), reinterpret_cast(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()), &outlen)) { logOpensslError(); return false; } if (outlen != 0) { LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen; return false; } if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_GET_TAG, GCM_MAC_BYTES, reinterpret_cast(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()))) { logOpensslError(); return false; } return true; } static bool decryptWithoutKeymaster(const std::string& preKey, const std::string& ciphertext, KeyBuffer* plaintext) { if (ciphertext.size() < GCM_NONCE_BYTES + GCM_MAC_BYTES) { LOG(ERROR) << "GCM ciphertext too small: " << ciphertext.size(); return false; } std::string key; hashWithPrefix(kHashPrefix_keygen, preKey, &key); key.resize(AES_KEY_BYTES); auto ctx = std::unique_ptr( EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free); if (!ctx) { logOpensslError(); return false; } if (1 != EVP_DecryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL, reinterpret_cast(key.data()), reinterpret_cast(ciphertext.data()))) { logOpensslError(); return false; } *plaintext = KeyBuffer(ciphertext.size() - GCM_NONCE_BYTES - GCM_MAC_BYTES); int outlen; if (1 != EVP_DecryptUpdate(ctx.get(), reinterpret_cast(&(*plaintext)[0]), &outlen, reinterpret_cast(ciphertext.data() + GCM_NONCE_BYTES), plaintext->size())) { logOpensslError(); return false; } if (outlen != static_cast(plaintext->size())) { LOG(ERROR) << "GCM plaintext length should be " << plaintext->size() << " was " << outlen; return false; } if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_SET_TAG, GCM_MAC_BYTES, const_cast(reinterpret_cast( ciphertext.data() + GCM_NONCE_BYTES + plaintext->size())))) { logOpensslError(); return false; } if (1 != EVP_DecryptFinal_ex(ctx.get(), reinterpret_cast(&(*plaintext)[0] + plaintext->size()), &outlen)) { logOpensslError(); return false; } if (outlen != 0) { LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen; return false; } return true; } bool pathExists(const std::string& path) { return access(path.c_str(), F_OK) == 0; } bool storeKey(const std::string& dir, const KeyAuthentication& auth, const KeyBuffer& key) { if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) { PLOG(ERROR) << "key mkdir " << dir; return false; } if (!writeStringToFile(kCurrentVersion, dir + "/" + kFn_version)) return false; std::string secdiscardable_hash; if (!createSecdiscardable(dir + "/" + kFn_secdiscardable, &secdiscardable_hash)) return false; std::string stretching = getStretching(auth); if (!writeStringToFile(stretching, dir + "/" + kFn_stretching)) return false; std::string salt; if (stretchingNeedsSalt(stretching)) { if (ReadRandomBytes(SALT_BYTES, salt) != OK) { LOG(ERROR) << "Random read failed"; return false; } if (!writeStringToFile(salt, dir + "/" + kFn_salt)) return false; } std::string appId; if (!generateAppId(auth, stretching, salt, secdiscardable_hash, &appId)) return false; std::string encryptedKey; if (auth.usesKeymaster()) { Keymaster keymaster; if (!keymaster) return false; std::string kmKey; if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false; if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false; km::AuthorizationSet keyParams; km::HardwareAuthToken authToken; std::tie(keyParams, authToken) = beginParams(auth, appId); if (!encryptWithKeymasterKey(keymaster, dir, keyParams, authToken, key, &encryptedKey)) return false; } else { if (!encryptWithoutKeymaster(appId, key, &encryptedKey)) return false; } if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false; if (!FsyncDirectory(dir)) return false; return true; } bool storeKeyAtomically(const std::string& key_path, const std::string& tmp_path, const KeyAuthentication& auth, const KeyBuffer& key) { if (pathExists(key_path)) { LOG(ERROR) << "Already exists, cannot create key at: " << key_path; return false; } if (pathExists(tmp_path)) { LOG(DEBUG) << "Already exists, destroying: " << tmp_path; destroyKey(tmp_path); // May be partially created so ignore errors } if (!storeKey(tmp_path, auth, key)) return false; if (rename(tmp_path.c_str(), key_path.c_str()) != 0) { PLOG(ERROR) << "Unable to move new key to location: " << key_path; return false; } LOG(DEBUG) << "Created key: " << key_path; return true; } bool retrieveKey(const std::string& dir, const KeyAuthentication& auth, KeyBuffer* key) { std::string version; if (!readFileToString(dir + "/" + kFn_version, &version)) return false; if (version != kCurrentVersion) { LOG(ERROR) << "Version mismatch, expected " << kCurrentVersion << " got " << version; return false; } std::string secdiscardable_hash; if (!readSecdiscardable(dir + "/" + kFn_secdiscardable, &secdiscardable_hash)) return false; std::string stretching; if (!readFileToString(dir + "/" + kFn_stretching, &stretching)) return false; std::string salt; if (stretchingNeedsSalt(stretching)) { if (!readFileToString(dir + "/" + kFn_salt, &salt)) return false; } std::string appId; if (!generateAppId(auth, stretching, salt, secdiscardable_hash, &appId)) return false; std::string encryptedMessage; if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false; if (auth.usesKeymaster()) { Keymaster keymaster; if (!keymaster) return false; km::AuthorizationSet keyParams; km::HardwareAuthToken authToken; std::tie(keyParams, authToken) = beginParams(auth, appId); if (!decryptWithKeymasterKey(keymaster, dir, keyParams, authToken, encryptedMessage, key)) return false; } else { if (!decryptWithoutKeymaster(appId, encryptedMessage, key)) return false; } return true; } static bool deleteKey(const std::string& dir) { std::string kmKey; if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false; Keymaster keymaster; if (!keymaster) return false; if (!keymaster.deleteKey(kmKey)) return false; return true; } bool runSecdiscardSingle(const std::string& file) { if (ForkExecvp(std::vector{kSecdiscardPath, "--", file}) != 0) { LOG(ERROR) << "secdiscard failed"; return false; } return true; } static bool recursiveDeleteKey(const std::string& dir) { if (ForkExecvp(std::vector{kRmPath, "-rf", dir}) != 0) { LOG(ERROR) << "recursive delete failed"; return false; } return true; } bool destroyKey(const std::string& dir) { bool success = true; // Try each thing, even if previous things failed. bool uses_km = pathExists(dir + "/" + kFn_keymaster_key_blob); if (uses_km) { success &= deleteKey(dir); } auto secdiscard_cmd = std::vector{ kSecdiscardPath, "--", dir + "/" + kFn_encrypted_key, dir + "/" + kFn_secdiscardable, }; if (uses_km) { secdiscard_cmd.emplace_back(dir + "/" + kFn_keymaster_key_blob); } if (ForkExecvp(secdiscard_cmd) != 0) { LOG(ERROR) << "secdiscard failed"; success = false; } success &= recursiveDeleteKey(dir); return success; } } // namespace vold } // namespace android