对明文进行加密
        :param text: 需要加密的明文
        :param app_id: 微信公众平台的 AppID
        :return: 加密后的字符串

def encrypt(self, text, app_id):
        """
        对明文进行加密
        :param text: 需要加密的明文
        :param app_id: 微信公众平台的 AppID
        :return: 加密后的字符串
        """
        text = b"".join(
            [
                to_binary(self.get_random_string()),
                struct.pack(b"I", socket.htonl(len(to_binary(text)))),
                to_binary(text),
                to_binary(app_id)
            ]
        )
        text = pkcs7.encode(text)
        encryptor = self.cipher.encryptor()
        ciphertext = to_binary(encryptor.update(text) + encryptor.finalize())
        return base64.b64encode(ciphertext)