Javascript bitwise encoding

gistfile1.js

var Encryption = (function() {

  function generateKey(seed) {
    var key = ""
    while (key.length < seed) key += Math.srand(seed)
    return key
  }

  /*
   * @param 'val' - a String to encode or a byte[] to decode.
   * @param 'salt' - (Optional) salt to perform bitwise encode/decode operation.
   */
  function xorHash(val, salt) {
    var encrypt = typeof val == 'string'
    var byteArr = encrypt ? val.toByteArr() : val 
    var keyBytes = typeof salt == 'undefined' ? 
      generateKey(byteArr.length).toByteArr() : salt.toByteArr()
    for (var i = 0; i < byteArr.length; i++) {
      byteArr[i] = byteArr[i] ^ keyBytes[i % keyBytes.length]
    }
    return (encrypt ? byteArr : String.fromCharCode.apply(String, byteArr))
  }
  
  return {
    /**
     *
     */
    encode : function(str, salt) {
      var encoded = []
      var bytes = xorHash(str, salt)
      for (var i = 0; i < bytes.length; i++) encoded.push(bytes[i].toString(16))
      return encoded.join(",")
    },
    /**
     *
     */
    decode : function(hsh, salt) {
      var decoded = []
      var hshArr = hsh.split(",")
      for (var i = 0; i < hshArr.length; i++) decoded.push(parseInt(hshArr[i], 16))
      return xorHash(decoded, salt)
    }
  }
})()

Math.srand = function(seed) {
  if (!seed) seed = new Date().getTime()
  seed = (seed*9301+49297) % 233280
  return seed/(233280.0)
}

String.prototype.toByteArr = function() {
  var arr = []
  for (var i = 0;i < this.length; i++) arr.push(this.charCodeAt(i))
  return arr
}