A very simple cryptography JavaScript module created for my xmas calendar 2013.

xmas-secret.js

var encryption = function() {

  // Works with ASCII chars from 32 (space) 
  // to 248 (å). 

  var shiftCharCode = function(code, shift) {
    if (shift < 0) shift += (248 - 32 + 1)
    return 32 + (((code - 32) + shift) % (248 - 32 + 1));
  };

  var shiftString = function(s, shift) {
    var s2 = "";
    for(var i in s) {
      var char_code = s.charCodeAt(i);
      var new_char_code = shiftCharCode(char_code, shift);
      s2 += String.fromCharCode(new_char_code);
    }
    return s2;
  };

  var shiftRight = function(s) {
    return shiftString(s, 1);
  };

  var shiftLeft = function(s) {
    return shiftString(s, -1);
  };

  var moveRight = function(s) {
    var lastIndex = s.length - 1;
    return s[lastIndex] + s.substring(0,lastIndex);
  };

  var moveLeft = function(s) {
    return s.substring(1) + s[0];
  };

  var addNoice = function(s) {
    var randomChar = Math.floor(Math.random()*(122-65+1)) + 65;
    return s + String.fromCharCode(randomChar);
  };

  var removeNoice = function(s) {
    return s.substring(0, s.length-1);
  };

  var encrypters = [shiftRight, moveRight, addNoice];
  var decrypters = [shiftLeft, moveLeft, removeNoice];

  return {
    shiftLeft : shiftLeft,
    encrypt: function(text, strength) {
      var result = { encrypted:text, key:'' };
      while (strength-- > 0) {
        var nextKeyPart = Math.floor(Math.random()*encrypters.length);
        var nextEncrypter = encrypters[nextKeyPart];
        result.encrypted = nextEncrypter(result.encrypted);
        result.key += nextKeyPart;
      }
      return result;
    },
    decrypt: function(text, key) {
      for(var i=key.length-1; i >= 0 ; i--) {
        text = decrypters[key[i]](text);
      }
      return text;
    }
  };
}();