Class for MAC generation on IECISA Secure payment

iecisaApi.php

<?php

/**
 * Class IecisaApi
 *
 * MAC generation for IECISA secure payment.
 *
 * $message = CF_XtnType + CF_User + CF_Date + CF_Time + CF_Amount +CF_Currency +  CF_TicketNumber + CF_Lang
 *
 * Example usage:
 *   $message = 'V000002120212021217022014032553T51111111111111111104151500EUR000123asdfasdfasdfasdfasdf';
 *   $secret = '133D59719B1B2134A3DB3A4FF2667A3B';
 *
 *   $iecisaApi = new IecisaApi($message, $secret);
 *   $mac = $iecisaApi->getMAC();
 *
 *
 * @author  Adrián Navarro <adrian.navarro.lopez@gmail.com>
 * @author  Juan Pastor <juantoleillo@gmail.com>
 *
 */
class IecisaApi
{
    protected $mac;

    /**
     * @param $data String concat transaction fields in order.
     * @param $secret Secret key for your IECISA user
     */
    public function __construct($data, $secret)
    {
        $zeros = '0000000000000000';
        $dataPadding = $data . hex2bin('80');
        $total = strlen($dataPadding);
        if (0 !== $total % 8) {
            for ($i = 0; $i < 8 -($total % 8); $i++) {
                $dataPadding .= pack('H*', '0');
            }
        }
        $tempKey = $zeros;
        for ($i = 0; $i < strlen($dataPadding)/8; $i++) {
            $string = bin2hex(substr($dataPadding, $i*8, 8));
            $xor = bin2hex(pack('H*', $tempKey) ^ pack('H*', $string));
            $tempKey = $this->encrypt(pack('H*', $xor), pack('H*', substr($secret, 0, 16)));
        }
        $string = substr($secret, 16);
        $xor    = $this->decrypt(pack('H*', $tempKey), pack('H*', $string));

        $this->mac = $this->encrypt(pack('H*', $xor), pack('H*', substr($secret, 0, 16)));
    }

    public function getMAC()
    {
        return substr($this->mac, 0, 8);
    }

    /**
     * @param $data string
     * @param $key string
     * @return string
     */
    private function encrypt($data, $key)
    {
        return bin2hex(mcrypt_encrypt(MCRYPT_DES, $key, $data, MCRYPT_MODE_ECB));
    }

    /**
     * @param $data string
     * @param $key string
     * @return string
     */
    private function decrypt($data, $key)
    {
        return bin2hex(mcrypt_decrypt(MCRYPT_DES, $key, $data, MCRYPT_MODE_ECB));
    }
}