protected function IsSecurityCheckOk($trxuser_id, $trx_amount, $trx_currency, $trxpassword, $ret_trx_number, $sOldChecksum)
    {
        $bChecksumIsOk = true;
        $sSharedSecret = $this->GetConfigParameter('shared_secret');
        if (!empty($sSharedSecret)) {
            $sNewChecksum = md5($trxuser_id.$trx_amount.$trx_currency.$trxpassword.$ret_trx_number.$sSharedSecret);
            if ($sNewChecksum != $sOldChecksum) {
                $bChecksumIsOk = false;
            }
        }

        return $bChecksumIsOk;
    }