def encrypt(self, k, a, m):
        """ Encrypt accoriding to the selected encryption and hashing
        functions.

        :param k: Encryption key (optional)
        :param a: Additional Authentication Data
        :param m: Plaintext

        Returns a dictionary with the computed data.
        """
        iv = _randombits(96)
        cipher = Cipher(algorithms.AES(k), modes.GCM(iv),
                        backend=self.backend)
        encryptor = cipher.encryptor()
        encryptor.authenticate_additional_data(a)
        e = encryptor.update(m) + encryptor.finalize()

        return (iv, e, encryptor.tag)
Encrypt accoriding to the selected encryption and hashing
        functions.

        :param k: Encryption key (optional)
        :param a: Additional Authentication Data
        :param m: Plaintext

        Returns a dictionary with the computed data.