KeyStorage.cpp - platform/system/vold - Gitiles

 /*
  * 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 <vector>

 #include <errno.h>
 #include <stdio.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>

 #include <openssl/err.h>
 #include <openssl/evp.h>
 #include <openssl/sha.h>

 #include <android-base/file.h>
 #include <android-base/logging.h>

 #include <cutils/properties.h>

 #include <hardware/hw_auth_token.h>

 #include <keystore/authorization_set.h>
 #include <keystore/keystore_hidl_support.h>

 extern "C" {

 #include "crypto_scrypt.h"
 }

 namespace android {
 namespace vold {
 using namespace keystore;

 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 std::string hashWithPrefix(char const* prefix, const std::string& tohash) {
     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());
     std::string res(SHA512_DIGEST_LENGTH, '\0');
     SHA512_Final(reinterpret_cast<uint8_t*>(&res[0]), &c);
     return res;
 }

 static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth,
                                  const std::string& appId, std::string* key) {
     auto paramBuilder = AuthorizationSetBuilder()
                             .AesEncryptionKey(AES_KEY_BYTES * 8)
                             .Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
                             .Authorization(TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
                             .Authorization(TAG_PADDING, PaddingMode::NONE)
                             .Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
     if (auth.token.empty()) {
         LOG(DEBUG) << "Creating key that doesn't need auth token";
         paramBuilder.Authorization(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<const hw_auth_token_t*>(auth.token.data());
         paramBuilder.Authorization(TAG_USER_SECURE_ID, at->user_id);
         paramBuilder.Authorization(TAG_USER_AUTH_TYPE, HardwareAuthenticatorType::PASSWORD);
         paramBuilder.Authorization(TAG_AUTH_TIMEOUT, AUTH_TIMEOUT);
     }
     return keymaster.generateKey(paramBuilder, key);
 }

 static AuthorizationSet beginParams(const KeyAuthentication& auth,
                                                const std::string& appId) {
     auto paramBuilder = AuthorizationSetBuilder()
                             .Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
                             .Authorization(TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
                             .Authorization(TAG_PADDING, PaddingMode::NONE)
                             .Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
     if (!auth.token.empty()) {
         LOG(DEBUG) << "Supplying auth token to Keymaster";
         paramBuilder.Authorization(TAG_AUTH_TOKEN, blob2hidlVec(auth.token));
     }
     return paramBuilder;
 }

 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) {
     if (!android::base::WriteStringToFile(payload, filename)) {
         PLOG(ERROR) << "Failed to write to " << filename;
         return false;
     }
     return true;
 }

 static KeymasterOperation begin(Keymaster& keymaster, const std::string& dir,
                                 KeyPurpose purpose,
                                 const AuthorizationSet &keyParams,
                                 const AuthorizationSet &opParams,
                                 AuthorizationSet* outParams) {
     auto kmKeyPath = dir + "/" + kFn_keymaster_key_blob;
     std::string kmKey;
     if (!readFileToString(kmKeyPath, &kmKey)) return KeymasterOperation();
     AuthorizationSet inParams(keyParams);
     inParams.append(opParams.begin(), opParams.end());
     for (;;) {
         auto opHandle = keymaster.begin(purpose, kmKey, inParams, outParams);
         if (opHandle) {
             return opHandle;
         }
         if (opHandle.errorCode() != 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 AuthorizationSet &keyParams,
                                     const std::string& message, std::string* ciphertext) {
     AuthorizationSet opParams;
     AuthorizationSet outParams;
     auto opHandle = begin(keymaster, dir, KeyPurpose::ENCRYPT, keyParams, opParams, &outParams);
     if (!opHandle) return false;
     auto nonceBlob = outParams.GetTagValue(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<const char*>(&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 AuthorizationSet &keyParams,
                                     const std::string& ciphertext, std::string* message) {
     auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
     auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
     auto opParams = AuthorizationSetBuilder()
             .Authorization(TAG_NONCE, blob2hidlVec(nonce));
     auto opHandle = begin(keymaster, dir, KeyPurpose::DECRYPT, keyParams, opParams, 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<const uint8_t*>(secret.data()), secret.size(),
                           reinterpret_cast<const uint8_t*>(salt.data()), salt.size(),
                           1 << Nf, 1 << rf, 1 << pf,
                           reinterpret_cast<uint8_t*>(&(*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,
                           std::string* appId) {
     std::string stretched;
     if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
     *appId = hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable) + stretched;
     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;
 }

 static void logOpensslError() {
     LOG(ERROR) << "Openssl error: " << ERR_get_error();
 }

 static bool encryptWithoutKeymaster(const std::string& preKey,
                                     const std::string& plaintext, std::string* ciphertext) {
     auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
     key.resize(AES_KEY_BYTES);
     if (!readRandomBytesOrLog(GCM_NONCE_BYTES, ciphertext)) return false;
     auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
         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<const uint8_t*>(key.data()),
             reinterpret_cast<const uint8_t*>(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<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES), &outlen,
         reinterpret_cast<const uint8_t*>(plaintext.data()), plaintext.size())) {
         logOpensslError();
         return false;
     }
     if (outlen != static_cast<int>(plaintext.size())) {
         LOG(ERROR) << "GCM ciphertext length should be " << plaintext.size() << " was " << outlen;
         return false;
     }
     if (1 != EVP_EncryptFinal_ex(ctx.get(),
         reinterpret_cast<uint8_t*>(&(*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<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()))) {
         logOpensslError();
         return false;
     }
     return true;
 }

 static bool decryptWithoutKeymaster(const std::string& preKey,
                                     const std::string& ciphertext, std::string* plaintext) {
     if (ciphertext.size() < GCM_NONCE_BYTES + GCM_MAC_BYTES) {
         LOG(ERROR) << "GCM ciphertext too small: " << ciphertext.size();
         return false;
     }
     auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
     key.resize(AES_KEY_BYTES);
     auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
         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<const uint8_t*>(key.data()),
             reinterpret_cast<const uint8_t*>(ciphertext.data()))) {
         logOpensslError();
         return false;
     }
     plaintext->resize(ciphertext.size() - GCM_NONCE_BYTES - GCM_MAC_BYTES);
     int outlen;
     if (1 != EVP_DecryptUpdate(ctx.get(),
         reinterpret_cast<uint8_t*>(&(*plaintext)[0]), &outlen,
         reinterpret_cast<const uint8_t*>(ciphertext.data() + GCM_NONCE_BYTES), plaintext->size())) {
         logOpensslError();
         return false;
     }
     if (outlen != static_cast<int>(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<void *>(
             reinterpret_cast<const void*>(ciphertext.data() + GCM_NONCE_BYTES + plaintext->size())))) {
         logOpensslError();
         return false;
     }
     if (1 != EVP_DecryptFinal_ex(ctx.get(),
         reinterpret_cast<uint8_t*>(&(*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 std::string& 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;
     if (!readRandomBytesOrLog(SECDISCARDABLE_BYTES, &secdiscardable)) return false;
     if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) 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, &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;
         auto keyParams = beginParams(auth, appId);
         if (!encryptWithKeymasterKey(keymaster, dir, keyParams, key, &encryptedKey)) return false;
     } else {
         if (!encryptWithoutKeymaster(appId, key, &encryptedKey)) return false;
     }
     if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
     return true;
 }

 bool storeKeyAtomically(const std::string& key_path, const std::string& tmp_path,
                         const KeyAuthentication& auth, const std::string& 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, std::string* 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;
     if (!readFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) 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, &appId)) return false;
     std::string encryptedMessage;
     if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
     if (auth.usesKeymaster()) {
         Keymaster keymaster;
         if (!keymaster) return false;
         auto keyParams = beginParams(auth, appId);
         if (!decryptWithKeymasterKey(keymaster, dir, keyParams, 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;
 }

 static bool runSecdiscard(const std::string& dir) {
     if (ForkExecvp(
             std::vector<std::string>{kSecdiscardPath, "--",
                 dir + "/" + kFn_encrypted_key,
                 dir + "/" + kFn_keymaster_key_blob,
                 dir + "/" + kFn_secdiscardable,
                 }) != 0) {
         LOG(ERROR) << "secdiscard failed";
         return false;
     }
     return true;
 }

 bool runSecdiscardSingle(const std::string& file) {
     if (ForkExecvp(
             std::vector<std::string>{kSecdiscardPath, "--",
                 file}) != 0) {
         LOG(ERROR) << "secdiscard failed";
         return false;
     }
     return true;
 }

 static bool recursiveDeleteKey(const std::string& dir) {
     if (ForkExecvp(std::vector<std::string>{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.
     success &= deleteKey(dir);
     success &= runSecdiscard(dir);
     success &= recursiveDeleteKey(dir);
     return success;
 }

 }  // namespace vold
 }  // namespace android
	/*
	* 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 <vector>

	#include <errno.h>
	#include <stdio.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <sys/wait.h>
	#include <unistd.h>

	#include <openssl/err.h>
	#include <openssl/evp.h>
	#include <openssl/sha.h>

	#include <android-base/file.h>
	#include <android-base/logging.h>

	#include <cutils/properties.h>

	#include <hardware/hw_auth_token.h>

	#include <keystore/authorization_set.h>
	#include <keystore/keystore_hidl_support.h>

	extern "C" {

	#include "crypto_scrypt.h"
	}

	namespace android {
	namespace vold {
	using namespace keystore;

	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 std::string hashWithPrefix(char const* prefix, const std::string& tohash) {
	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());
	std::string res(SHA512_DIGEST_LENGTH, '\0');
	SHA512_Final(reinterpret_cast<uint8_t*>(&res[0]), &c);
	return res;
	}

	static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth,
	const std::string& appId, std::string* key) {
	auto paramBuilder = AuthorizationSetBuilder()
	.AesEncryptionKey(AES_KEY_BYTES * 8)
	.Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
	.Authorization(TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
	.Authorization(TAG_PADDING, PaddingMode::NONE)
	.Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
	if (auth.token.empty()) {
	LOG(DEBUG) << "Creating key that doesn't need auth token";
	paramBuilder.Authorization(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<const hw_auth_token_t*>(auth.token.data());
	paramBuilder.Authorization(TAG_USER_SECURE_ID, at->user_id);
	paramBuilder.Authorization(TAG_USER_AUTH_TYPE, HardwareAuthenticatorType::PASSWORD);
	paramBuilder.Authorization(TAG_AUTH_TIMEOUT, AUTH_TIMEOUT);
	}
	return keymaster.generateKey(paramBuilder, key);
	}

	static AuthorizationSet beginParams(const KeyAuthentication& auth,
	const std::string& appId) {
	auto paramBuilder = AuthorizationSetBuilder()
	.Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
	.Authorization(TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
	.Authorization(TAG_PADDING, PaddingMode::NONE)
	.Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
	if (!auth.token.empty()) {
	LOG(DEBUG) << "Supplying auth token to Keymaster";
	paramBuilder.Authorization(TAG_AUTH_TOKEN, blob2hidlVec(auth.token));
	}
	return paramBuilder;
	}

	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) {
	if (!android::base::WriteStringToFile(payload, filename)) {
	PLOG(ERROR) << "Failed to write to " << filename;
	return false;
	}
	return true;
	}

	static KeymasterOperation begin(Keymaster& keymaster, const std::string& dir,
	KeyPurpose purpose,
	const AuthorizationSet &keyParams,
	const AuthorizationSet &opParams,
	AuthorizationSet* outParams) {
	auto kmKeyPath = dir + "/" + kFn_keymaster_key_blob;
	std::string kmKey;
	if (!readFileToString(kmKeyPath, &kmKey)) return KeymasterOperation();
	AuthorizationSet inParams(keyParams);
	inParams.append(opParams.begin(), opParams.end());
	for (;;) {
	auto opHandle = keymaster.begin(purpose, kmKey, inParams, outParams);
	if (opHandle) {
	return opHandle;
	}
	if (opHandle.errorCode() != 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 AuthorizationSet &keyParams,
	const std::string& message, std::string* ciphertext) {
	AuthorizationSet opParams;
	AuthorizationSet outParams;
	auto opHandle = begin(keymaster, dir, KeyPurpose::ENCRYPT, keyParams, opParams, &outParams);
	if (!opHandle) return false;
	auto nonceBlob = outParams.GetTagValue(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<const char*>(&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 AuthorizationSet &keyParams,
	const std::string& ciphertext, std::string* message) {
	auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
	auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
	auto opParams = AuthorizationSetBuilder()
	.Authorization(TAG_NONCE, blob2hidlVec(nonce));
	auto opHandle = begin(keymaster, dir, KeyPurpose::DECRYPT, keyParams, opParams, 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<const uint8_t*>(secret.data()), secret.size(),
	reinterpret_cast<const uint8_t*>(salt.data()), salt.size(),
	1 << Nf, 1 << rf, 1 << pf,
	reinterpret_cast<uint8_t>(&(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,
	std::string* appId) {
	std::string stretched;
	if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
	*appId = hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable) + stretched;
	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;
	}

	static void logOpensslError() {
	LOG(ERROR) << "Openssl error: " << ERR_get_error();
	}

	static bool encryptWithoutKeymaster(const std::string& preKey,
	const std::string& plaintext, std::string* ciphertext) {
	auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
	key.resize(AES_KEY_BYTES);
	if (!readRandomBytesOrLog(GCM_NONCE_BYTES, ciphertext)) return false;
	auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
	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<const uint8_t*>(key.data()),
	reinterpret_cast<const uint8_t*>(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<uint8_t>(&(ciphertext)[0] + GCM_NONCE_BYTES), &outlen,
	reinterpret_cast<const uint8_t*>(plaintext.data()), plaintext.size())) {
	logOpensslError();
	return false;
	}
	if (outlen != static_cast<int>(plaintext.size())) {
	LOG(ERROR) << "GCM ciphertext length should be " << plaintext.size() << " was " << outlen;
	return false;
	}
	if (1 != EVP_EncryptFinal_ex(ctx.get(),
	reinterpret_cast<uint8_t>(&(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<uint8_t>(&(ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()))) {
	logOpensslError();
	return false;
	}
	return true;
	}

	static bool decryptWithoutKeymaster(const std::string& preKey,
	const std::string& ciphertext, std::string* plaintext) {
	if (ciphertext.size() < GCM_NONCE_BYTES + GCM_MAC_BYTES) {
	LOG(ERROR) << "GCM ciphertext too small: " << ciphertext.size();
	return false;
	}
	auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
	key.resize(AES_KEY_BYTES);
	auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
	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<const uint8_t*>(key.data()),
	reinterpret_cast<const uint8_t*>(ciphertext.data()))) {
	logOpensslError();
	return false;
	}
	plaintext->resize(ciphertext.size() - GCM_NONCE_BYTES - GCM_MAC_BYTES);
	int outlen;
	if (1 != EVP_DecryptUpdate(ctx.get(),
	reinterpret_cast<uint8_t>(&(plaintext)[0]), &outlen,
	reinterpret_cast<const uint8_t*>(ciphertext.data() + GCM_NONCE_BYTES), plaintext->size())) {
	logOpensslError();
	return false;
	}
	if (outlen != static_cast<int>(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<void *>(
	reinterpret_cast<const void*>(ciphertext.data() + GCM_NONCE_BYTES + plaintext->size())))) {
	logOpensslError();
	return false;
	}
	if (1 != EVP_DecryptFinal_ex(ctx.get(),
	reinterpret_cast<uint8_t>(&(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 std::string& 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;
	if (!readRandomBytesOrLog(SECDISCARDABLE_BYTES, &secdiscardable)) return false;
	if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) 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, &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;
	auto keyParams = beginParams(auth, appId);
	if (!encryptWithKeymasterKey(keymaster, dir, keyParams, key, &encryptedKey)) return false;
	} else {
	if (!encryptWithoutKeymaster(appId, key, &encryptedKey)) return false;
	}
	if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
	return true;
	}

	bool storeKeyAtomically(const std::string& key_path, const std::string& tmp_path,
	const KeyAuthentication& auth, const std::string& 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, std::string* 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;
	if (!readFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) 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, &appId)) return false;
	std::string encryptedMessage;
	if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
	if (auth.usesKeymaster()) {
	Keymaster keymaster;
	if (!keymaster) return false;
	auto keyParams = beginParams(auth, appId);
	if (!decryptWithKeymasterKey(keymaster, dir, keyParams, 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;
	}

	static bool runSecdiscard(const std::string& dir) {
	if (ForkExecvp(
	std::vector<std::string>{kSecdiscardPath, "--",
	dir + "/" + kFn_encrypted_key,
	dir + "/" + kFn_keymaster_key_blob,
	dir + "/" + kFn_secdiscardable,
	}) != 0) {
	LOG(ERROR) << "secdiscard failed";
	return false;
	}
	return true;
	}

	bool runSecdiscardSingle(const std::string& file) {
	if (ForkExecvp(
	std::vector<std::string>{kSecdiscardPath, "--",
	file}) != 0) {
	LOG(ERROR) << "secdiscard failed";
	return false;
	}
	return true;
	}

	static bool recursiveDeleteKey(const std::string& dir) {
	if (ForkExecvp(std::vector<std::string>{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.
	success &= deleteKey(dir);
	success &= runSecdiscard(dir);
	success &= recursiveDeleteKey(dir);
	return success;
	}

	} // namespace vold
	} // namespace android