A Super simple encryption cipher using XOR and Base64 in JavaScript

XORCipher.js

// XORCipher - Super simple encryption using XOR and Base64
//
// Depends on [Underscore](http://underscorejs.org/).
//
// As a warning, this is **not** a secure encryption algorythm. It uses a very
// simplistic keystore and will be easy to crack.
//
// The Base64 algorythm is a modification of the one used in phpjs.org
// * http://phpjs.org/functions/base64_encode/
// * http://phpjs.org/functions/base64_decode/
//
// Examples
// --------
//
//     XORCipher.encode("test", "foobar");   // => "EgocFhUX"
//     XORCipher.decode("test", "EgocFhUX"); // => "foobar"
//
// Copyright © 2013 Devin Weaver <suki@tritarget.org>
//
// This program is free software. It comes without any warranty, to
// the extent permitted by applicable law. You can redistribute it
// and/or modify it under the terms of the Do What The Fuck You Want
// To Public License, Version 2, as published by Sam Hocevar. See
// http://www.wtfpl.net/ for more details.

/* jshint forin:true, noarg:true, noempty:true, eqeqeq:true, strict:true,
   undef:true, unused:true, curly:true, browser:true, indent:2, maxerr:50 */
(function(exports) {
  "use strict";

  var XORCipher = {
    encode: function(key, data) {
      data = xor_encrypt(key, data);
      return b64_encode(data);
    },
    decode: function(key, data) {
      data = b64_decode(data);
      return xor_decrypt(key, data);
    }
  };

  var b64_table =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

  function b64_encode(data) {
    var o1,
      o2,
      o3,
      h1,
      h2,
      h3,
      h4,
      bits,
      r,
      i = 0,
      enc = "";
    if (!data) {
      return data;
    }
    do {
      o1 = data[i++];
      o2 = data[i++];
      o3 = data[i++];
      bits = (o1 << 16) | (o2 << 8) | o3;
      h1 = (bits >> 18) & 0x3f;
      h2 = (bits >> 12) & 0x3f;
      h3 = (bits >> 6) & 0x3f;
      h4 = bits & 0x3f;
      enc +=
        b64_table.charAt(h1) +
        b64_table.charAt(h2) +
        b64_table.charAt(h3) +
        b64_table.charAt(h4);
    } while (i < data.length);
    r = data.length % 3;
    return (r ? enc.slice(0, r - 3) : enc) + "===".slice(r || 3);
  }

  function b64_decode(data) {
    var o1,
      o2,
      o3,
      h1,
      h2,
      h3,
      h4,
      bits,
      i = 0,
      result = [];
    if (!data) {
      return data;
    }
    data += "";
    do {
      h1 = b64_table.indexOf(data.charAt(i++));
      h2 = b64_table.indexOf(data.charAt(i++));
      h3 = b64_table.indexOf(data.charAt(i++));
      h4 = b64_table.indexOf(data.charAt(i++));
      bits = (h1 << 18) | (h2 << 12) | (h3 << 6) | h4;
      o1 = (bits >> 16) & 0xff;
      o2 = (bits >> 8) & 0xff;
      o3 = bits & 0xff;
      result.push(o1);
      if (h3 !== 64) {
        result.push(o2);
        if (h4 !== 64) {
          result.push(o3);
        }
      }
    } while (i < data.length);
    return result;
  }

  function keyCharAt(key, i) {
    return key.charCodeAt(Math.floor(i % key.length));
  }

  function map(list, callback) {
    var output = [];
    for (var index = 0; index < list.length; index++) {
      output.push(callback(list[index], index));
    }
    return output;
  }

  function xor_encrypt(key, data) {
    return map(data, function(c, i) {
      return c.charCodeAt(0) ^ keyCharAt(key, i);
    });
  }

  function xor_decrypt(key, data) {
    return map(data, function(c, i) {
      return String.fromCharCode(c ^ keyCharAt(key, i));
    }).join("");
  }

  exports.XORCipher = XORCipher;
})(this);