E 00000CS409121902 Pages: 2

Reg No.: Name:
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY

Seventh semester B.Tech examinations (S), September 2020

Course Code: CS409
Course Name: CRYPTOGRAPHY AND NETWORKSECURITY

Max. Marks: 100 Duration: 3 Hours
PARTA
Answer all questions, each carries 4 marks. Marks
1 Which parameters and design choices determine the actual algorithm of a (4)
Fiestel Cipher.
2 Encrypt the message “the house is being sold tonight” using Vigenere cipher (4)

with key “dollars”. Ignore the space between words. Decrypt the message to

get the plain text.

3 Compare stream cipher and block cipher with example. (4)

4 Find gced(252,105). (4)

5 List different types of attacks addressed by message authentication. (4)

6 Illustrate Needham and Schroedor protocol for mutual authentication. (4)

7 Compare transport mode and tunnel mode functionalities in IPSec. (4)

8 List out the five header fields and their meaning defined in MIME. (4)

9 What are the steps involved in the SSL record protocol transmission? (4)

10 Compare SSL and TLS. (4)
PART ‏تا‎

Answer any two full questions, each carries 9 marks.

11 a) Discuss about different polyalphabetic cipher substitution techniques. (4)

b) Explain single round of DES algorithm. (5)

12 a) Differentiate between Confusion and Diffusion. (4)

b) Explain the key generation in IDEA. (5)

13 Explain AES algorithm in detail. (9)
PART C

Answer any two full questions, each carries 9 marks.
14 a) Alice and Bob agreed to use RSA algorithm for the secret communication. (6)

Alice securely choose two primes, p=5 and q=11 and a secret key d=7. Find the
corresponding public key. Bob uses this public key and sends a cipher text 18
to Alice. Find the plain text.

b) State and prove Euler’s theorem. (3)

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