Authentication: Summary Proof of knowledge By text encrypted with secret key(authenticator Not by secret key itself Proof of freshness By included timevarying parameter Timestamp, counter, nonce(challenge-response) Alice Alice, Alice, N KAB Bob 1313 Authentication: Summary • Proof of knowledge – By text encrypted with secret key (authenticator) – Not by secret key itself • Proof of freshness – By included timevarying parameter – Timestamp, counter, nonce (challenge-response) Alice Bob Alice, {Alice, N}KAB N