PHP，如何在不丢失信息的情况下缩短字符串

I'm using codeigniter 3 ecryption library with default settings from the codeigniter PHP framework to crypt some simple alphanumeric strings.

Here's a small example on how it works inside a codeigniter helper:

<?php
    function shortCrypt($string) {
        $CI =& get_instance();
        $CI->load->library('encryption');
        return $CI->encryption->encrypt($string);
    }

The returned crypted string is too long for my purposes and i would like to make it shorter without losing any information. I thought to pass the AES-128 crypted string via md5 to reach a 32 characters lenght but the only problem is i can't obtain the original string back.

Is there a way to "compress" the AES-128 crypted string to obtain a shorter one without losing the original?

Sorry for my bad english.