Prior to transmission, a message is divided into multiple transmission units. A sub-message authentication code is obtained for each of the transmission units. A composed message authentication code is obtained for the whole message based on the sub-message authentication codes of the multiple transmission units. The multiple transmission units and the composed message authentication code are then transmitted. A receiver of the message receives a plurality of transmission units corresponding to the message. A local sub-message authentication code is calculated by the receiver for each transmission unit. A local composed message authentication code is calculated by the receiver based on the local sub-message authentication codes for the plurality of transmission units. The local composed message authentication code is compared to a received composed message authentication code to determine the integrity and/or authenticity of the received message.