The MAC value protects a message’s data integrity, as well as its authenticity, by allowing verifiers (who also possess the secret key) to detect any changes to the message content.

Does a MAC provide confidentiality?

Encryption provides confidentiality, a MAC provides integrity. Using encryption alone makes your messages vulnerable to a ciphertext only attack. The sender, with the symmetric key, can encrypt the message and send E(M) . No one should be able to send a valid message other than the holder of the key.

Does MAC protect against replay attacks?

MACs provide no protection against replay attacks. The problem is that MACs do not incorporate any notion of state in their verification algorithms.