Unformatted text preview: wouldn’t. What happens if you double the key size? [10] Q.2 Use the extended Euclidean algorithm to compute the greatest common divisor d of 654 and 123 and to find integers m and n such that 654m + 123n = d. [10] Q.3 In a Feistel system, we divide the state into left and right halves LiRi and then define the new state by Li+1 = Ri and Ri+1 = Li f(Ki,Ri) where Ki is the key for the i th round and f is a function of the key and half of the state. Prove that no matter what the function f is, the round transformation is 1to1, i.e., we can recover the old state from the new state and the key. [10] Q.4 (a). What is the main drawback of the one time pad cryptosystem? [5] Q.4 (b). Show that the transposition cipher is vulnerable to a known plaintext attack. [5] ********** No. of Pages = 1 No. of Questions = 4...
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 Spring '11
 raj
 Cryptography, Greatest common divisor, brute force attack, Pilani Distance Learning, Course Title Nature, Exam Weightage Duration

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