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

 #include <openssl/sha.h>

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

 #include <cutils/properties.h>

 #include <keymaster/authorization_set.h>

 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 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* kFn_encrypted_key = "encrypted_key";
 static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
 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 hashSecdiscardable(const std::string &secdiscardable) {
     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 secdiscardableHashingPrefix = "Android secdiscardable SHA512";
     secdiscardableHashingPrefix.resize(SHA512_CBLOCK);
     SHA512_Update(&c, secdiscardableHashingPrefix.data(), secdiscardableHashingPrefix.size());
     SHA512_Update(&c, secdiscardable.data(), secdiscardable.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 keymaster::AuthorizationSet &extraParams,
         std::string &key) {
     auto params = keymaster::AuthorizationSetBuilder()
         .AesEncryptionKey(AES_KEY_BYTES * 8)
         .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
         .Authorization(keymaster::TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
         .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
         .Authorization(keymaster::TAG_NO_AUTH_REQUIRED) // FIXME integrate with gatekeeper
         .build();
     params.push_back(extraParams);
     return keymaster.generateKey(params, key);
 }

 static bool encryptWithKeymasterKey(
         Keymaster &keymaster,
         const std::string &key,
         const keymaster::AuthorizationSet &extraParams,
         const std::string &message,
         std::string &ciphertext) {
     // FIXME fix repetition
     auto params = keymaster::AuthorizationSetBuilder()
         .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
         .Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
         .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
         .build();
     params.push_back(extraParams);
     keymaster::AuthorizationSet outParams;
     auto opHandle = keymaster.begin(KM_PURPOSE_ENCRYPT, key, params, outParams);
     if (!opHandle) return false;
     keymaster_blob_t nonceBlob;
     if (!outParams.GetTagValue(keymaster::TAG_NONCE, &nonceBlob)) {
         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.data), nonceBlob.data_length);
     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.finishWithOutput(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 &key,
         const keymaster::AuthorizationSet &extraParams,
         const std::string &ciphertext,
         std::string &message) {
     auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
     auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
     // FIXME fix repetition
     auto params = addStringParam(keymaster::AuthorizationSetBuilder(), keymaster::TAG_NONCE, nonce)
         .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
         .Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
         .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
         .build();
     params.push_back(extraParams);

     auto opHandle = keymaster.begin(KM_PURPOSE_DECRYPT, key, params);
     if (!opHandle) return false;
     if (!opHandle.updateCompletely(bodyAndMac, message)) return false;
     if (!opHandle.finish()) return false;
     return true;
 }

 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 std::string getStretching() {
     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(ERROR) << "Password present but stretching is nopasswd";
             // 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 buildParams(const KeyAuthentication &auth, const std::string &stretching,
         const std::string &salt, const std::string &secdiscardable,
         keymaster::AuthorizationSet &result) {
     std::string stretched;
     if (!stretchSecret(stretching, auth.secret, salt, stretched)) return false;
     auto appId = hashSecdiscardable(secdiscardable) + stretched;
     keymaster::AuthorizationSetBuilder paramBuilder;
     addStringParam(paramBuilder, keymaster::TAG_APPLICATION_ID, appId);
     if (!auth.token.empty()) {
         addStringParam(paramBuilder, keymaster::TAG_AUTH_TOKEN, auth.token);
     }
     result = paramBuilder.build();
     return true;
 }

 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 (ReadRandomBytes(SECDISCARDABLE_BYTES, secdiscardable) != OK) {
         // TODO status_t plays badly with PLOG, fix it.
         LOG(ERROR) << "Random read failed";
         return false;
     }
     if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
     std::string stretching = auth.secret.empty() ? kStretch_nopassword : getStretching();
     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;
     }
     keymaster::AuthorizationSet extraParams;
     if (!buildParams(auth, stretching, salt, secdiscardable, extraParams)) return false;
     Keymaster keymaster;
     if (!keymaster) return false;
     std::string kmKey;
     if (!generateKeymasterKey(keymaster, extraParams, kmKey)) return false;
     std::string encryptedKey;
     if (!encryptWithKeymasterKey(keymaster, kmKey, extraParams, key, encryptedKey)) return false;
     if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
     if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
     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;
     }
     keymaster::AuthorizationSet extraParams;
     if (!buildParams(auth, stretching, salt, secdiscardable, extraParams)) return false;
     std::string kmKey;
     if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, kmKey)) return false;
     std::string encryptedMessage;
     if (!readFileToString(dir + "/" + kFn_encrypted_key, encryptedMessage)) return false;
     Keymaster keymaster;
     if (!keymaster) return false;
     return decryptWithKeymasterKey(keymaster, kmKey, extraParams, encryptedMessage, key);
 }

 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 secdiscardSecdiscardable(const std::string &dir) {
     if (ForkExecvp(std::vector<std::string> {
             kSecdiscardPath, "--", dir + "/" + kFn_secdiscardable}) != 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 &= secdiscardSecdiscardable(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 <sys/stat.h>
	#include <sys/types.h>
	#include <sys/wait.h>
	#include <unistd.h>

	#include <openssl/sha.h>

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

	#include <cutils/properties.h>

	#include <keymaster/authorization_set.h>

	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 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* kFn_encrypted_key = "encrypted_key";
	static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
	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 hashSecdiscardable(const std::string &secdiscardable) {
	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 secdiscardableHashingPrefix = "Android secdiscardable SHA512";
	secdiscardableHashingPrefix.resize(SHA512_CBLOCK);
	SHA512_Update(&c, secdiscardableHashingPrefix.data(), secdiscardableHashingPrefix.size());
	SHA512_Update(&c, secdiscardable.data(), secdiscardable.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 keymaster::AuthorizationSet &extraParams,
	std::string &key) {
	auto params = keymaster::AuthorizationSetBuilder()
	.AesEncryptionKey(AES_KEY_BYTES * 8)
	.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
	.Authorization(keymaster::TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
	.Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
	.Authorization(keymaster::TAG_NO_AUTH_REQUIRED) // FIXME integrate with gatekeeper
	.build();
	params.push_back(extraParams);
	return keymaster.generateKey(params, key);
	}

	static bool encryptWithKeymasterKey(
	Keymaster &keymaster,
	const std::string &key,
	const keymaster::AuthorizationSet &extraParams,
	const std::string &message,
	std::string &ciphertext) {
	// FIXME fix repetition
	auto params = keymaster::AuthorizationSetBuilder()
	.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
	.Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
	.Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
	.build();
	params.push_back(extraParams);
	keymaster::AuthorizationSet outParams;
	auto opHandle = keymaster.begin(KM_PURPOSE_ENCRYPT, key, params, outParams);
	if (!opHandle) return false;
	keymaster_blob_t nonceBlob;
	if (!outParams.GetTagValue(keymaster::TAG_NONCE, &nonceBlob)) {
	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.data), nonceBlob.data_length);
	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.finishWithOutput(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 &key,
	const keymaster::AuthorizationSet &extraParams,
	const std::string &ciphertext,
	std::string &message) {
	auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
	auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
	// FIXME fix repetition
	auto params = addStringParam(keymaster::AuthorizationSetBuilder(), keymaster::TAG_NONCE, nonce)
	.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
	.Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
	.Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
	.build();
	params.push_back(extraParams);

	auto opHandle = keymaster.begin(KM_PURPOSE_DECRYPT, key, params);
	if (!opHandle) return false;
	if (!opHandle.updateCompletely(bodyAndMac, message)) return false;
	if (!opHandle.finish()) return false;
	return true;
	}

	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 std::string getStretching() {
	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(ERROR) << "Password present but stretching is nopasswd";
	// 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 buildParams(const KeyAuthentication &auth, const std::string &stretching,
	const std::string &salt, const std::string &secdiscardable,
	keymaster::AuthorizationSet &result) {
	std::string stretched;
	if (!stretchSecret(stretching, auth.secret, salt, stretched)) return false;
	auto appId = hashSecdiscardable(secdiscardable) + stretched;
	keymaster::AuthorizationSetBuilder paramBuilder;
	addStringParam(paramBuilder, keymaster::TAG_APPLICATION_ID, appId);
	if (!auth.token.empty()) {
	addStringParam(paramBuilder, keymaster::TAG_AUTH_TOKEN, auth.token);
	}
	result = paramBuilder.build();
	return true;
	}

	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 (ReadRandomBytes(SECDISCARDABLE_BYTES, secdiscardable) != OK) {
	// TODO status_t plays badly with PLOG, fix it.
	LOG(ERROR) << "Random read failed";
	return false;
	}
	if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
	std::string stretching = auth.secret.empty() ? kStretch_nopassword : getStretching();
	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;
	}
	keymaster::AuthorizationSet extraParams;
	if (!buildParams(auth, stretching, salt, secdiscardable, extraParams)) return false;
	Keymaster keymaster;
	if (!keymaster) return false;
	std::string kmKey;
	if (!generateKeymasterKey(keymaster, extraParams, kmKey)) return false;
	std::string encryptedKey;
	if (!encryptWithKeymasterKey(keymaster, kmKey, extraParams, key, encryptedKey)) return false;
	if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
	if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
	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;
	}
	keymaster::AuthorizationSet extraParams;
	if (!buildParams(auth, stretching, salt, secdiscardable, extraParams)) return false;
	std::string kmKey;
	if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, kmKey)) return false;
	std::string encryptedMessage;
	if (!readFileToString(dir + "/" + kFn_encrypted_key, encryptedMessage)) return false;
	Keymaster keymaster;
	if (!keymaster) return false;
	return decryptWithKeymasterKey(keymaster, kmKey, extraParams, encryptedMessage, key);
	}

	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 secdiscardSecdiscardable(const std::string &dir) {
	if (ForkExecvp(std::vector<std::string> {
	kSecdiscardPath, "--", dir + "/" + kFn_secdiscardable}) != 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 &= secdiscardSecdiscardable(dir);
	success &= recursiveDeleteKey(dir);
	return success;
	}

	} // namespace vold
	} // namespace android