AES-256 Decryption with PHP Mcrypt (CodeIgniter)

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
//http://blog.absolutedisaster.co.uk/aes-256-decryption-with-php-mcrypt

class Aes extends CI_Controller {

    private $encrypted,
            $key,
            $iv;

    public function index()
    {

        $this->config->load('aes');

        $this->key = $this->config->item('aes_secret');

        $this->iv = $this->config->item('aes_iv');

        $this->encrypted = $this->input->post('accesstoken');

        echo $this->aes256_decrypt();

    }

    private function aes256_decrypt()
    {

        return trim(
            mcrypt_decrypt(
                MCRYPT_RIJNDAEL_128,// AES 256 decryption is acheived with Rijndael 128
                                    // http://kix.in/2008/07/22/aes-256-using-php-mcrypt/
                $this->key,
                base64_decode($this->encrypted),
                MCRYPT_MODE_CBC,
                $this->iv
            )
        );

    }
}
/*End of file aes.php*/
/*Location .application/controllers/aes.php*/