Unformatted text preview: wouldn’t. What happens if you double the key size?  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.  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 1-to-1, i.e., we can recover the old state from the new state and the key.  Q.4 (a). What is the main drawback of the one time pad cryptosystem?  Q.4 (b). Show that the transposition cipher is vulnerable to a known plaintext attack.  ********** No. of Pages = 1 No. of Questions = 4...
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- Spring '11
- Cryptography, Greatest common divisor, brute force attack, Pilani Distance Learning, Course Title Nature, Exam Weightage Duration