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1 st Authentication. h n-1 (k). h n-1 (k). k. h n (k). 2 nd Authentication. h n-2 (k). h n-2 (k). k. h n-1 (k). Lamport ’ s Scheme. How do user and server synchronize on which password to use? h: one-way hash function (e.g., MD5 or SHA-1) h n (k) : h(h(h(...h(k)...))). Server.
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1st Authentication hn-1(k) hn-1(k) k hn(k) 2nd Authentication hn-2(k) hn-2(k) k hn-1(k) Lamport’s Scheme • How do user and server synchronize on which password to use? • h: one-way hash function (e.g., MD5 or SHA-1) • hn(k): h(h(h(...h(k)...))) Server User n Registration secure channel hn-1(k) hn(k) k k