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// Copyright 2005 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 ARC4 streamcipher implementation. A description of the
* algorithm can be found at:
* http://www.mozilla.org/projects/security/pki/nss/draft-kaukonen-cipher-arcfour-03.txt.
*
* Usage:
* <code>
* var arc4 = new goog.crypt.Arc4();
* arc4.setKey(key);
* arc4.discard(1536);
* arc4.crypt(bytes);
* </code>
*
* Note: For converting between strings and byte arrays, goog.crypt.base64 may
* be useful.
*
*/
goog.provide('goog.crypt.Arc4');
goog.require('goog.asserts');
/**
* ARC4 streamcipher implementation.
* @constructor
*/
goog.crypt.Arc4 = function() {
/**
* A permutation of all 256 possible bytes.
* @type {Array.<number>}
* @private
*/
this.state_ = [];
/**
* 8 bit index pointer into this.state_.
* @type {number}
* @private
*/
this.index1_ = 0;
/**
* 8 bit index pointer into this.state_.
* @type {number}
* @private
*/
this.index2_ = 0;
};
/**
* Initialize the cipher for use with new key.
* @param {Array.<number>} key A byte array containing the key.
* @param {number=} opt_length Indicates # of bytes to take from the key.
*/
goog.crypt.Arc4.prototype.setKey = function(key, opt_length) {
goog.asserts.assertArray(key, 'Key parameter must be a byte array');
if (!opt_length) {
opt_length = key.length;
}
var state = this.state_;
for (var i = 0; i < 256; ++i) {
state[i] = i;
}
var j = 0;
for (var i = 0; i < 256; ++i) {
j = (j + state[i] + key[i % opt_length]) & 255;
var tmp = state[i];
state[i] = state[j];
state[j] = tmp;
}
this.index1_ = 0;
this.index2_ = 0;
};
/**
* Discards n bytes of the keystream.
* These days 1536 is considered a decent amount to drop to get the key state
* warmed-up enough for secure usage. This is not done in the constructor to
* preserve efficiency for use cases that do not need this.
* NOTE: Discard is identical to crypt without actually xoring any data. It's
* unfortunate to have this code duplicated, but this was done for performance
* reasons. Alternatives which were attempted:
* 1. Create a temp array of the correct length and pass it to crypt. This
* works but needlessly allocates an array. But more importantly this
* requires choosing an array type (Array or Uint8Array) in discard, and
* choosing a different type than will be passed to crypt by the client
* code hurts the javascript engines ability to optimize crypt (7x hit in
* v8).
* 2. Make data option in crypt so discard can pass null, this has a huge
* perf hit for crypt.
* @param {number} length Number of bytes to disregard from the stream.
*/
goog.crypt.Arc4.prototype.discard = function(length) {
var i = this.index1_;
var j = this.index2_;
var state = this.state_;
for (var n = 0; n < length; ++n) {
i = (i + 1) & 255;
j = (j + state[i]) & 255;
var tmp = state[i];
state[i] = state[j];
state[j] = tmp;
}
this.index1_ = i;
this.index2_ = j;
};
/**
* En- or decrypt (same operation for streamciphers like ARC4)
* @param {Array.<number>|Uint8Array} data The data to be xor-ed in place.
* @param {number=} opt_length The number of bytes to crypt.
*/
goog.crypt.Arc4.prototype.crypt = function(data, opt_length) {
if (!opt_length) {
opt_length = data.length;
}
var i = this.index1_;
var j = this.index2_;
var state = this.state_;
for (var n = 0; n < opt_length; ++n) {
i = (i + 1) & 255;
j = (j + state[i]) & 255;
var tmp = state[i];
state[i] = state[j];
state[j] = tmp;
data[n] ^= state[(state[i] + state[j]) & 255];
}
this.index1_ = i;
this.index2_ = j;
};
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