public function useEncryption($key)
    {
        $this->encryptor = new \sb\Encryption\ForTransmission($key);
        $this->encryption_key = $key;

        //decrypt cookies if sent
        foreach (\sb\Gateway::$cookie as $k => $v) {
            \sb\Gateway::$cookie[$k] = $this->encryptor->decrypt($v);
        }
    }