Gujarat Technological University 2011-6th Sem B.E , 160702 - Information Security on - Question Paper
GUJARAT TECHNOLOGICAL UNIVERSITY
B E Sem-VI exam May 2011
Subject code: 160702
Subject Name: info Security
Date: 17/05/2011 Time: 10.30 am – 01.00 pm
Total Marks: 70
Seat No. Enrolment No.
GUJARAT TECHNOLOGICAL UNIVERSITY
B E Sem-VI Examination May 2011
Subject Name: Information Security Date: 17/05/2011 Time: 10.30 am - 01.00 pm
Total Marks: 70
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) (i) Explain the various types of cryptanalytic attack, based on the amount 04 of information known to the cryptanalyst.
(ii) Explain the terms diffusion and confusion. 03
(b) (i) Which two criteria are used to validate that a sequence of numbers is 04 random? Explain the linear congruential method to generate pseudorandom numbers.
(ii) Write the key distribution scenario in which each user shares a unique 03 master key with key distribution center
Q.2 (a) (i) Why mode of operation is defined? Explain the simplest mode for 04 block cipher modes of operation?
(ii) What is the purpose of S-boxes in DES? Explain the avalanche effect. 03
(b) (i) In a public key system using RSA, the ciphertext intercepted is C=10 04 which is sent to the user whose public key is e=5, n=35. What is the plaintext M?
(ii) Write the differences between conventional encryption and public key 03 encryption.
OR
(b) (i) Briefly explain the Diffie-Hellman key exchange. 04
(ii) Perform encryption and decryption using the RSA algorithm for p=3, 03 q=11, e=7, M=5.
Q.3 (a) (i) How key exchange using elliptic curves can be done? 04
(ii) Construct a playfair matrix with the key occurrence. Generate the 03 cipher text for the plaintext Tall trees
(b) Explain how subkeys are generated in blowfish algorithm and also explain 07 the encryption in blowfish algorithm. How does the key-size in blowfish differ from cast-128?
OR
Q.3 (a) (i) Write the Euclids algorithm and show the steps of Euclids algorithm 04 to find gcd(1970,1066).
(ii) Encrypt the message Good morning using the Hill Cipher with the 03
"9 4
key
(b) Which parameters affect RC5 encryption algorithm. Explain RC5 07 encryption and decryption process.
Q.4 (a) Illustrate variety of ways in which hash code can be used to provide 07 message authentication.
(b) (i) Why is the segmentation and reassembly function in PGP(Pretty Good 04 Privacy) needed?
(ii)What are the security threats to E-commerce transactions? 03
OR
Q.4 (a) What is cryptographic checksum or message authentication code? 07 Describe the three situations in which message authentication code is used.
(b) (i) What is the difference between transport mode and tunnel mode? 04
(ii) What parameters characterize the nature of a particular security 03 association in IPSec.
Q.5 (a) Write the Digital Signature Algorithm. 07
(b) Explain the following properties of hash function
(i) One way property 02
(ii) Weak collision resistance 02
(iii) Compression function in hash algorithm. 03
OR
Q.5 (a) List and define the parameters that define secure socket layer connection 07 state.
(b) What is dual signature and explain construction of dual signature. 07
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