B.Tech VII (Seventh) Semester Examination 2011-12

Course Code:ECS708 Paper ID:0967114

Cryptography and Network Security

Time: 3 Hours Max. Marks: 70 Max Marks: 75

Note: Attempt six questions in all. Q. No. 1 is compulsory.

1. Answer any five of the following (limit your answer in 50 words). (4x5=20)

a) Distinguish between passive and active attacks. Give example of three active attacks.

b) What is block cipher encryption techniques. Differentiate between block cipher and stream cipher encryption technique. Are all stream ciphers are monoalphabetic cipher explain.

c) What is Tripple DES? Explain Tripple DES with two keys?

d) Define Euler’s Theorem? Explain its applications in cryptography. Find the value of f(240) and f(100.

e) Is it necessary to recover the secret key in order to attack a message authentication code algorithm?

f) What is difference between SSL Session and SSL Connection? What protocols comprise SSL?

g) Explain the services provided by IPSEC? What is difference between transport mode and tunnel mode?

h) Explain the authentication process involved in SET.

2. a) What is difference between an unconditionally secure cipher and computationally secure cipher? (5)

b) Distinguish between cryptography and Steganography. Determine which technique (Cryptography /Steganography) is used in each of following case:

i) A student writes the answer to a test on small piece of paper, rolls up the paper and insert in a ball – point pen and passes the pen to another student.

ii) A company uses special ink on its cheque to prevent forgeries.

(5)

3. a) What is avalanche effect? Explain linear and differential cryptanalysis of DES. (5)

b) What types of information might be derived from a traffic analysis attack? Differentiate between link and end to end encryption technique. (5)

4. a) Explain Fermat’s theorem. Using this calculate 3201 mod 11. (5)

b) Explain the security attacks on RSA encryption technique. (5)

5. a) Explain the basic arithmetic and logical functions used in MD5. (5)

b) Explain essentials of secure electronic transactions. (5)

6. a) What is digital signature? Explain RSA digital signature algorithm. (5)

b) Describe the digital signature standard algorithm. (5)

7. a) Explain the applications of S/MIME. Explain different formats supported by S/MIME. (5)

b) What do you mean by trusted system? Explain the concept of reference monitor. (5)

8. Write short notes on any two: (5x2=10)

a) Authentication protocol

b) Intrusion Detection System

c) Firewall