Lamport's One-Time Password Setting: A wants to authenticate itself to B Initialization A selects an arbitrary value S, a hash function Ho, and integer value t A computes Wo= H(S)and sends Wo, and Ho to B B stores Wo Protocol: To authenticate to b at time i where 1<=i<= t A sends to B: A, i, W;=Ht(S) B checks: i=A, H Wi=Wi-1 If both holds, IA =IA 15Lamport’s One-Time Password • Setting: A wants to authenticate itself to B • Initialization: • A selects an arbitrary value S, a hash function H(), and integer value t • A computes w0 = Ht (S) and sends w0 , and H() to B • B stores w0 • Protocol: To authenticate to B at time i where 1 <= i <= t • A sends to B: A, i, wi = Ht-i (S) • B checks: i = iA, H(wi ) = wi-1 • If both holds, iA = iA + 1 Topic 3: User Authentication 152/3/2021