How does MAA work?
Figure showing how an MAA works
An authenticator is a number sent along with a message so that a check can be made by the receiver that it has not been altered since it left the sender. The sender and receiver share the knowledge of a key K which is secret. If M is the message and C be the authenticator, then C is the function of M and K,
i.e. C = f(M, K).
If the value of the authenticator calculated by the receiver is equal to that from the sender, the message is assumed to be correct; otherwise it shows that there have been some changes in the message since it left the sender.
