# sol5 - CS346 Cryptography, Fall 2009 Homework 5, SOLUTIONS...

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CS346 Cryptography, Fall 2009 Homework 5, SOLUTIONS 1. (10 points) Problem 6, Chapter 4.9 (page 147) Solution: The meet-in-the middle attack is a “known plaintext” attack, so we can assume that Oscar (the attacker) has access to a plaintext-ciphertext pair ( m,c ). Oscar can make a list of the values E K ( E K ( m )) for all possible values of K , and another list D K ( c ) for all possible values of K . Since (m,c) is a valid plaintext-ciphertext pair, there will be at least one match between the two lists, such that for some values K 1 and K 2 E K 1 ( E K 1 ( m )) = D K 2 ( c ). NOTE: If there are several matches, then more plaintext-ciphertext pairs would help to identify the correct keys being used. 2. (10 points) Problem 7, Chapter 4.9 (page 147) Solution: A. The solution is similar to the previous question: The meet-in-the middle attack is a “known plaintext” attack, so we can assume that Oscar (the attacker) has access to a plaintext-ciphertext pair ( m,c ). Oscar can make a list of the values

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## This note was uploaded on 10/07/2010 for the course C S 52475 taught by Professor Gal during the Fall '10 term at University of Texas.

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sol5 - CS346 Cryptography, Fall 2009 Homework 5, SOLUTIONS...

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