Challenge-Response protocols Unilateral authentication( timestamp-based Ato B: MACK(tA, B) Unilateral authentication(nonce-based . bto a Ato B: MACK(rB, B) Mutual authentication(nonce-based b to a: Ato B: rA, MACK(rA, rB, B) B to A: MACK(rB, rA 17Challenge-Response Protocols • Unilateral authentication (timestamp-based) • A to B: MACK(tA, B) • Unilateral authentication (nonce-based) • B to A: rB • A to B: MACK(rB, B) • Mutual authentication (nonce-based) • B to A: rB • A to B: rA, MACK(rA, rB, B) • B to A: MACK(rB, rA) Topic 3: User Authentication 172/3/2021