How to decrypt php Gkencode class?

How to decrypt php Gkencode class?

I'm have script but don't looking Decrypt function. I'm tried for decrypt
this has but not lucky
<?php
include("Gkencode.php");
$secretKey = "Key";
$string = "Encrypt Text";
$gkencode = new Gkencode();
$encrypted = $gkencode->encrypt($string,$secretKey); //
b956bbb922a5be143614b04b16efe6db
$decrypted = $gkencode->decrypt($encrypted,$secretKey); // ???
?>
File Gkencode.php