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// Copyright 2011 The Closure Library Authors. All Rights Reserved.
//
// 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.
/**
* @fileoverview Provides a convenient API for data persistence with key and
* object encryption. Without a valid secret, the existence of a particular
* key can't be verified and values can't be decrypted. The value encryption
* is salted, so subsequent writes of the same cleartext result in different
* ciphertext. The ciphertext is *not* authenticated, so there is no protection
* against data manipulation.
*
* The metadata is *not* encrypted, so expired keys can be cleaned up without
* decrypting them. If sensitive metadata is added in subclasses, it is up
* to the subclass to protect this information, perhaps by embedding it in
* the object.
*
*/
goog.provide('goog.storage.EncryptedStorage');
goog.require('goog.crypt');
goog.require('goog.crypt.Arc4');
goog.require('goog.crypt.Sha1');
goog.require('goog.crypt.base64');
goog.require('goog.json');
goog.require('goog.json.Serializer');
goog.require('goog.storage.CollectableStorage');
goog.require('goog.storage.ErrorCode');
goog.require('goog.storage.RichStorage');
goog.require('goog.storage.RichStorage.Wrapper');
goog.require('goog.storage.mechanism.IterableMechanism');
/**
* Provides an encrypted storage. The keys are hashed with a secret, so
* their existence cannot be verified without the knowledge of the secret.
* The values are encrypted using the key, a salt, and the secret, so
* stream cipher initialization varies for each stored value.
*
* @param {!goog.storage.mechanism.IterableMechanism} mechanism The underlying
* storage mechanism.
* @param {string} secret The secret key used to encrypt the storage.
* @constructor
* @extends {goog.storage.CollectableStorage}
*/
goog.storage.EncryptedStorage = function(mechanism, secret) {
goog.base(this, mechanism);
this.secret_ = goog.crypt.stringToByteArray(secret);
this.cleartextSerializer_ = new goog.json.Serializer();
};
goog.inherits(goog.storage.EncryptedStorage, goog.storage.CollectableStorage);
/**
* Metadata key under which the salt is stored.
*
* @type {string}
* @protected
*/
goog.storage.EncryptedStorage.SALT_KEY = 'salt';
/**
* The secret used to encrypt the storage.
*
* @type {Array.<number>}
* @private
*/
goog.storage.EncryptedStorage.prototype.secret_ = null;
/**
* The JSON serializer used to serialize values before encryption. This can
* be potentially different from serializing for the storage mechanism (see
* goog.storage.Storage), so a separate serializer is kept here.
*
* @type {goog.json.Serializer}
* @private
*/
goog.storage.EncryptedStorage.prototype.cleartextSerializer_ = null;
/**
* Hashes a key using the secret.
*
* @param {string} key The key.
* @return {string} The hash.
* @private
*/
goog.storage.EncryptedStorage.prototype.hashKeyWithSecret_ = function(key) {
var sha1 = new goog.crypt.Sha1();
sha1.update(goog.crypt.stringToByteArray(key));
sha1.update(this.secret_);
return goog.crypt.base64.encodeByteArray(sha1.digest(), true);
};
/**
* Encrypts a value using a key, a salt, and the secret.
*
* @param {!Array.<number>} salt The salt.
* @param {string} key The key.
* @param {string} value The cleartext value.
* @return {string} The encrypted value.
* @private
*/
goog.storage.EncryptedStorage.prototype.encryptValue_ = function(
salt, key, value) {
if (!(salt.length > 0)) {
throw Error('Non-empty salt must be provided');
}
var sha1 = new goog.crypt.Sha1();
sha1.update(goog.crypt.stringToByteArray(key));
sha1.update(salt);
sha1.update(this.secret_);
var arc4 = new goog.crypt.Arc4();
arc4.setKey(sha1.digest());
// Warm up the streamcypher state, see goog.crypt.Arc4 for details.
arc4.discard(1536);
var bytes = goog.crypt.stringToByteArray(value);
arc4.crypt(bytes);
return goog.crypt.byteArrayToString(bytes);
};
/**
* Decrypts a value using a key, a salt, and the secret.
*
* @param {!Array.<number>} salt The salt.
* @param {string} key The key.
* @param {string} value The encrypted value.
* @return {string} The decrypted value.
* @private
*/
goog.storage.EncryptedStorage.prototype.decryptValue_ = function(
salt, key, value) {
// ARC4 is symmetric.
return this.encryptValue_(salt, key, value);
};
/** @override */
goog.storage.EncryptedStorage.prototype.set = function(
key, value, opt_expiration) {
if (!goog.isDef(value)) {
goog.storage.EncryptedStorage.prototype.remove.call(this, key);
return;
}
var salt = [];
// 64-bit random salt.
for (var i = 0; i < 8; ++i) {
salt[i] = Math.floor(Math.random() * 0x100);
}
var wrapper = new goog.storage.RichStorage.Wrapper(
this.encryptValue_(salt, key,
this.cleartextSerializer_.serialize(value)));
wrapper[goog.storage.EncryptedStorage.SALT_KEY] = salt;
goog.base(this, 'set', this.hashKeyWithSecret_(key), wrapper, opt_expiration);
};
/** @override */
goog.storage.EncryptedStorage.prototype.getWrapper = function(
key, opt_expired) {
var wrapper = goog.base(this, 'getWrapper',
this.hashKeyWithSecret_(key), opt_expired);
if (!wrapper) {
return undefined;
}
var value = goog.storage.RichStorage.Wrapper.unwrap(wrapper);
var salt = wrapper[goog.storage.EncryptedStorage.SALT_KEY];
if (!goog.isString(value) || !goog.isArray(salt) || !salt.length) {
throw goog.storage.ErrorCode.INVALID_VALUE;
}
var json = this.decryptValue_(salt, key, value);
/** @preserveTry */
try {
wrapper[goog.storage.RichStorage.DATA_KEY] = goog.json.parse(json);
} catch (e) {
throw goog.storage.ErrorCode.DECRYPTION_ERROR;
}
return wrapper;
};
/** @override */
goog.storage.EncryptedStorage.prototype.remove = function(key) {
goog.base(this, 'remove', this.hashKeyWithSecret_(key));
};
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