public function toBankCard(array $params)
    {
        foreach (['bank_code', 'partner_trade_no', 'enc_bank_no', 'enc_true_name', 'amount'] as $key) {
            if (empty($params[$key])) {
                throw new RuntimeException(\sprintf('"%s" is required.', $key));
            }
        }

        $publicKey = file_get_contents($this->app['config']->get('rsa_public_key_path'));

        $params['enc_bank_no'] = rsa_public_encrypt($params['enc_bank_no'], $publicKey);
        $params['enc_true_name'] = rsa_public_encrypt($params['enc_true_name'], $publicKey);

        return $this->safeRequest('mmpaysptrans/pay_bank', $params);
    }