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// Copyright 2012 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 Implementation of CBC mode for block ciphers. See
* http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
* #Cipher-block_chaining_.28CBC.29. for description.
*
* @author nnaze@google.com (Nathan Naze)
*/
goog.provide('goog.crypt.Cbc');
goog.require('goog.array');
/**
* Implements the CBC mode for block ciphers. See
* http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
* #Cipher-block_chaining_.28CBC.29
*
* @param {!goog.crypt.BlockCipher} cipher The block cipher to use.
* @param {number=} opt_blockSize The block size of the cipher in bytes.
* Defaults to 16 bytes.
* @constructor
*/
goog.crypt.Cbc = function(cipher, opt_blockSize) {
/**
* Block cipher.
* @type {!goog.crypt.BlockCipher}
* @private
*/
this.cipher_ = cipher;
/**
* Block size in bytes.
* @type {number}
* @private
*/
this.blockSize_ = opt_blockSize || 16;
};
/**
* Encrypt a message.
*
* @param {!Array.<number>} plainText Message to encrypt. An array of bytes.
* The length should be a multiple of the block size.
* @param {!Array.<number>} initialVector Initial vector for the CBC mode.
* An array of bytes with the same length as the block size.
* @return {!Array.<number>} Encrypted message.
*/
goog.crypt.Cbc.prototype.encrypt = function(plainText, initialVector) {
goog.asserts.assert(
plainText.length % this.blockSize_ == 0,
'Data\'s length must be multiple of block size.');
goog.asserts.assert(
initialVector.length == this.blockSize_,
'Initial vector must be size of one block.');
// Implementation of
// http://en.wikipedia.org/wiki/File:Cbc_encryption.png
var cipherText = [];
var vector = initialVector;
// Generate each block of the encrypted cypher text.
for (var blockStartIndex = 0;
blockStartIndex < plainText.length;
blockStartIndex += this.blockSize_) {
// Takes one block from the input message.
var plainTextBlock = goog.array.slice(
plainText,
blockStartIndex,
blockStartIndex + this.blockSize_);
var input = goog.crypt.Cbc.xorByteArray_(plainTextBlock, vector);
var resultBlock = this.cipher_.encrypt(input);
goog.array.extend(cipherText, resultBlock);
vector = resultBlock;
}
return cipherText;
};
/**
* Decrypt a message.
*
* @param {!Array.<number>} cipherText Message to decrypt. An array of bytes.
* The length should be a multiple of the block size.
* @param {!Array.<number>} initialVector Initial vector for the CBC mode.
* An array of bytes with the same length as the block size.
* @return {!Array.<number>} Decrypted message.
*/
goog.crypt.Cbc.prototype.decrypt = function(cipherText, initialVector) {
goog.asserts.assert(
cipherText.length % this.blockSize_ == 0,
'Data\'s length must be multiple of block size.');
goog.asserts.assert(
initialVector.length == this.blockSize_,
'Initial vector must be size of one block.');
// Implementation of
// http://en.wikipedia.org/wiki/File:Cbc_decryption.png
var plainText = [];
var blockStartIndex = 0;
var vector = initialVector;
// Generate each block of the decrypted plain text.
while (blockStartIndex < cipherText.length) {
// Takes one block.
var cipherTextBlock = goog.array.slice(
cipherText,
blockStartIndex,
blockStartIndex + this.blockSize_);
var resultBlock = this.cipher_.decrypt(cipherTextBlock);
var plainTextBlock = goog.crypt.Cbc.xorByteArray_(vector, resultBlock);
goog.array.extend(plainText, plainTextBlock);
vector = cipherTextBlock;
blockStartIndex += this.blockSize_;
}
return plainText;
};
/**
* XOR two byte arrays.
* @param {!Array.<number>} arr1 Byte array.
* @param {!Array.<number>} arr2 Byte array.
* @return {!Array.<number>} Resulting XOR of the two byte arrays.
* @private
*/
goog.crypt.Cbc.xorByteArray_ = function(arr1, arr2) {
goog.asserts.assert(arr1.length == arr2.length,
'XOR array lengths must match');
var result = [];
for (var i = 0; i < arr1.length; i++) {
result.push(arr1[i] ^ arr2[i]);
}
return result;
};
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