hw8-sol_Security

hw8-sol_Security - udaya shankar Page 1 of 3 December 10,...

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udaya shankar Page 1 of 3 December 10, 2007 CMSC 414: HW 5 ___________________________________________________________ 1. Show a protocol for an augmented form of EKE. Solution (one way to get EKE augmented): A B A stores password pw W and W’ are two keys obtained from pw (e.g., different hashes) B stores ( A, W’, T A ’) where T A ’ = g W mod-p Public g and p (prime) choose rn a T A g a mod-p send [A, B, W’{T A }] receive msg extract T A from W’{T A } using W’ choose rn b T B g b mod-p K B ± (T A ) b mod-p K B ± (T A ’) b mod-p H ± hash( K B , K B ’ ) send [B, A, W’{T B }, H] receive msg extract T B from W’{T B } using W’ K A ± (T B ) a mod-p K A ± (T B ) W mod-p verify H = hash(K A , K A ’) to authenticate B H’ ± hash’(K A , K A ’ ), where hash’ is another hash function send [A, B, H’] receive msg verify H’ = hash’(K B , K B ’) to authenticate A A and B are mutually authenticated and share strong key K = g ab mod p
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hw8-sol_Security - udaya shankar Page 1 of 3 December 10,...

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