# CRYPTOGRAPHY AND NETWORK SECURITY AKTU 2020-21 Question Paper

## B.Tech

### CRYPTOGRAPHY AND NETWORK SECURITY

[Time: 3:00 Hours] Total Marks: 70

Note: Attempt all Sections. If require any missing data: then choose suitably.

### SECTION-A

1. Attempt all questions in brief.                                                                                  2 x 7 = 14
1. What do you mean Brute Force Attack?
2. Define CIA?
3. Define the concept of confusion and Diffusion?
4. Find all the primitive roots of 11.
5. Find gcd(24140, 16762) using Euclid’s algorithm?
6. List out the services provided by the Digital Signature.
7. What are the five principal services provided by PGP?

## SECTION-B

2 . Attempt any three questions in brief.                                                                      7 x 3 = 21

1. Explain the Security Attack with Example.
2. Explain the Structure of DES Algorithm and define the role of fiestal cipher in DES in detail.
3. Explain symmetric and Asymmetric Cryptography with the help of diagrammatic representation. And how-to symmetric cryptography is different from asymmetric Cryptography.
4. State Chinese remainder theorem and find X for the given set of congruent equations using CRT: X=2(mod3), X=3(mod5), X=2(mod7).
5. Describe RSA algorithm, Suppose alice and bob uses a public key cryptosystem using RSA, the two prime no is P=13 and q=17 and e=7 the find out the decryption key d and Perform the encryption and decryption of the message “CRYPTOGRAPHY” Using 00 to 25 for letters A to Z.

## SECTION-B

3. Attempt any one part of the following:                                                                                            7 x 1 = 7

1. Explain Block modes of operation and also explain the Electronic Code Book (ECB) mode is not a secured mode of encryption and highlight the problems with this mode.
2. Give a real-life example where both confidentiality and integrity are needed. Explain why encryption alone does not provide integrity of information.

4. Attempt any one part of the following:                                                                                            7 x 1 = 7

1. Compare Substitution and Transposition techniques.
2. Encrypt the following using play fair cipher using the keyword:

MONARCHY. “SWARAJ IS MY BIRT RIGHT”. Use X as blank space.

5. Attempt any one part of the following:                                                                                            7 x 1 = 7

1. Define Primality Test and also explain Miller Rabin Algorithm using base 2 to test whether the number 341 is composite or not?
2. Explain AES algorithm What is the difference between the AES decryption algorithm and the DES algorithm.

6. Attempt any one part of the following:                                                                                          7 x 1 = 7

1. Explain the Kerberos protocol for key distribution? Explain the functionality of each step.
2. How does worms and viruses compare? Describe the component of the virus and how does it protect from anti-virus software’s?

7. Attempt any one part of the following:                                                                                            7 x 1 = 7

1. What do you mean by SHA 1 algorithm What basic arithmetical and logical functions are used in SHA?
2. Explain in detail about S/MIME and what difference between S/MIME and PGP.