hw6-sol_Security - s KDC Y is B s KDC and Z is a KDC that...

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udaya shankar Page 1 of 1 Fall 2006 CMSC 414: Hw 3 Solution ___________________________________________________________ 1. (text 9.2) …. Is this an example of an authentication scheme that … guards against both eavesdropping and server database disclosure? No. An attacker, say C, that sees the server database gets Z, the hash of Alice’s password. Given Z, the attacker can impersonate Alice: C (has Z) B (Bob) (has Z) send [A, B, conn] to B send challenge R to A send [hash(Z, R)] to B received msg matches hash(Z,R) so B assumes sender is A ___________________________________________________________ 2. (text 9.3) Extend the scenario in § to a chain of three KDCs, say X, Y, and Z, where A wants to talk to B, X is A'
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Unformatted text preview: s KDC, Y is B' s KDC, and Z is a KDC that has shared keys with X and Y. A (has K AX ) X (has K AX , K XZ ) Z (has K XZ , K ZY ) Y (has K ZY , K YB ) B (has K BY ) • send [A wants to talk to Z] to X • generate session key K AZ • send [K XZ {talk to A; use K AZ }] to Z • send [K AX {talk to Z; use K AZ }] to A • send [A wants to talk to Y] to Z • generate session key K AY • send [K ZY {talk to A; use K AZ }] • send [K AZ {talk to Y; use K AZ }] to A • send [A wants to talk to B] to Y • generate session key K AB • send [K BY {talk to A; use K AB }] to B • send [K AY {talk to B; use K AB }] to A ___________________________________________________________...
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