in file application/libraries/autoload.php, add load library encrption
$autoload['libraries'] = array('Encryption');
On encrypt and decrypt proses, you can use something like this
$this->encryption->encode('Your data'); $this->encryption->decode('Your encrypted data');
Referensi : http://www.99points.info/2010/06/php-encrypt-decrypt-functions-to-encrypt-url-data/