Return digest of the given message and key

		:param key: secret HMAC key
		:param message: code (message) to authenticate

		:return: bytes

def hash(self, key, message=None):
		""" Return digest of the given message and key

		:param key: secret HMAC key
		:param message: code (message) to authenticate

		:return: bytes
		"""
		hmac_obj = hmac.HMAC(key, self.__digest_generator, backend=default_backend())
		if message is not None:
			hmac_obj.update(message)
		return hmac_obj.finalize()