rc4.js

var CryptoJS = require('./core');
require('./enc-base64');
require('./md5');
require('./evpkdf');
require('./cipher-core');

(function() {
  // Shortcuts
  var C = CryptoJS;
  var C_lib = C.lib;
  var StreamCipher = C_lib.StreamCipher;
  var C_algo = C.algo;

  /**
   * RC4 stream cipher algorithm.
   */
  var RC4 = C_algo.RC4 = StreamCipher.extend({
    _doReset: function() {
      // Shortcuts
      var key = this._key;
      var keyWords = key.words;
      var keySigBytes = key.sigBytes;

      // Init sbox
      var S = this._S = [];
      for (var i = 0; i < 256; i++) {
        S[i] = i;
      }

      // Key setup
      for (var i = 0, j = 0; i < 256; i++) {
        var keyByteIndex = i % keySigBytes;
        var keyByte = (keyWords[keyByteIndex >>> 2] >>> (24 - (keyByteIndex % 4) * 8)) & 0xff;

        j = (j + S[i] + keyByte) % 256;

        // Swap
        var t = S[i];
        S[i] = S[j];
        S[j] = t;
      }

      // Counters
      this._i = this._j = 0;
    },

    _doProcessBlock: function(M, offset) {
      M[offset] ^= generateKeystreamWord.call(this);
    },

    keySize: 256 / 32,

    ivSize: 0
  });

  function generateKeystreamWord() {
    // Shortcuts
    var S = this._S;
    var i = this._i;
    var j = this._j;

    // Generate keystream word
    var keystreamWord = 0;
    for (var n = 0; n < 4; n++) {
      i = (i + 1) % 256;
      j = (j + S[i]) % 256;

      // Swap
      var t = S[i];
      S[i] = S[j];
      S[j] = t;

      keystreamWord |= S[(S[i] + S[j]) % 256] << (24 - n * 8);
    }

    // Update counters
    this._i = i;
    this._j = j;

    return keystreamWord;
  }

  /**
   * Shortcut functions to the cipher's object interface.
   *
   * @example
   *
   *     var ciphertext = CryptoJS.RC4.encrypt(message, key, cfg);
   *     var plaintext  = CryptoJS.RC4.decrypt(ciphertext, key, cfg);
   */
  C.RC4 = StreamCipher._createHelper(RC4);

  /**
   * Modified RC4 stream cipher algorithm.
   */
  var RC4Drop = C_algo.RC4Drop = RC4.extend({
    /**
     * Configuration options.
     *
     * @property {number} drop The number of keystream words to drop. Default 192
     */
    cfg: RC4.cfg.extend({
      drop: 192
    }),

    _doReset: function() {
      RC4._doReset.call(this);

      // Drop
      for (var i = this.cfg.drop; i > 0; i--) {
        generateKeystreamWord.call(this);
      }
    }
  });

  /**
   * Shortcut functions to the cipher's object interface.
   *
   * @example
   *
   *     var ciphertext = CryptoJS.RC4Drop.encrypt(message, key, cfg);
   *     var plaintext  = CryptoJS.RC4Drop.decrypt(ciphertext, key, cfg);
   */
  C.RC4Drop = StreamCipher._createHelper(RC4Drop);
}());

module.exports = CryptoJS.RC4;