True or false: "A MAC provides non-repudiation of origin."

False — a MAC uses a shared symmetric key, so either party could have generated it. Only digital signatures provide non-repudiation.

Why MACs can't provide non-repudiation:

Since $K_G = K_V$ (the same key generates and verifies), both Alice and Bob possess the key. If a dispute arises:

• Alice claims: "I didn't send that message — Bob generated the MAC himself"
• There is no way to prove otherwise, because Bob has the same key

For non-repudiation you need digital signatures:

• Only Alice has $K_{priv,A}$
• If the signature verifies with $K_{pub,A}$, it proves Alice signed it
• This holds up even in legal disputes (electronic signature laws)

Tip: Think of a MAC like a shared password on a door — if someone enters, you can't tell which key holder it was. A digital signature is like a fingerprint — uniquely traceable.