private function encryptorFactory($classFullName, $secretKey) {
        $refClass = new \ReflectionClass($classFullName);
        if ($refClass->implementsInterface(self::ENCRYPTOR_INTERFACE_NS)) {
            return new $classFullName($secretKey);
        } else {
            throw new \RuntimeException('Encryptor must implements interface EncryptorInterface');
        }
    }