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NSMID1 - (e What is Euler's totient function Q.2 Which...

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Birla Institute of Technology & Science, Pilani Work-Integrated Learning Programmes Division Second Semester 2009-2010 Mid-Semester Test (EC-1 Regular) Course No. : SS ZG513 Course Title : NETWORK SECURITY Nature of Exam : Closed Book Weightage : 40% Duration : 2 Hours Date of Exam : 06/02/2010 (FN) Note: 1. Please follow all the Instructions to Candidates given on the cover page of the answer book. 2. All parts of a question should be answered consecutively. Each answer should start from a fresh page. 3. Mobile phones and computers of any kind should not be used inside the examination hall. 4. Use of any unfair means will result in severe disciplinary action. Q.1. Answer the following to the point. [5 * 2 = 10] (a). What is the difference between diffusion and confusion? (b). What is the difference between an unconditionally secure cipher and a computationally secure cipher? (c). What is the difference between a monoalphabetic cipher and a polyalphabetic cipher? (d). What is a trapdoor one-way function?
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Unformatted text preview: (e). What is Euler's totient function? Q.2. Which parameters and design choices determine the actual algorithm of a Feistel cipher? [5] Q.3. Construct a Playfair matrix with the key “ largest”. Using this matrix encrypt this message: “Must see you over Cadogan West. Coming at once”. [5] Q.4. Explain how the DES algorithm can be strengthened by 3 DES. What is the effective key length of 3 DES? Justify. [5] Q.5. If a bit error occurs in the transmission of a ciphertext character in 8-bit CFB mode, how far does the error propagate? [5] Q.6. In a public-key system using RSA, you intercept the ciphertext C = 10 sent to a user whose public key is e = 5, n = 35. What is the plaintext M? [5] Q.7. Compare AES to DES. For each of the following elements of DES, indicate the comparable element in AES or explain why it is not needed in AES. [5] a. Permutation P b. Swapping of halves of the block ****** No. of Pages = 1 No. of Questions = 7...
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