A communication device is described including a receiver configured to receive a message including message data and a message authentication code, a first register for storing a received message authentication code and a second register for storing a computed message authentication code. The device also includes a first processor configured to extract the message authentication code from the message and to store the message authentication code in the first register, a second processor configured to compute a message authentication code based on the message data and to store the computed message authentication code in the second register, and a comparing circuit configured to compare the contents of the first register and the second register and to provide a comparison result. The device includes access control circuitry configured to prevent access by the second processor to the first register and to allow access by the first processor to the first register and to prevent access by the first processor to the second register and to allow access by the second processor to the second register.