Questions
Syllabus
Qns. By Syllabus

Semester

Subject

Year

Tribhuwan University

Institute of Science and Technology

2080

Bachelor Level / Third Year / Fifth Semester / Science

B.Sc in Computer Science and Information Technology (CSC327)

(Cryptography)

Full Marks: 60

Pass Marks: 24

Time: 3 Hours

Candidates are required to give their answers in their own words as for as practicable.

The figures in the margin indicate full marks.

Section A

Long Answers Questions

Attempt any TWO questions.
[2*10=20]
1.
Define discrete logarithms. How key generation, encryption and decryption is done in RSA. In a RSA cryptosystem, given p=13 and q=7, determine private key, public key and perform encryption and decryption for the text M='hi' using 0 to 25 for letters from a to z. [10]
2.
Write down the encryption and decryption process at 2-DES and 3-DES. Explain the Fiestal cipher structure. Divide 5x2+4x+65x^2 + 4x + 6 by 2x+12x + 1 over GF(7). [10]
3.
What are the applications of hash functions? Discuss how SHA-1 algorithm generates hash value from a given message. [10]
Section B

Short Answers Questions

Attempt any Eight questions.
[8*5=40]
4.
Show encryption and decryption of "csit" using hill cipher having key, [5]
5.
Give the formal definition of authentication system. Describe about one way and mutual authentication system.
[3257]\begin{bmatrix} 3 & 2 \\ 5 & 7 \end{bmatrix}
[5]
6.
List the stage of certificate life cycle. What are the types of firewalls? [5]
7.
What is malicious logic? How zombies are different from trojan horses? [5]
8.
How Miller Rabin test is used for primality testing? Show whether the number 561 passes the test. [5]
9.
Show that the set of integers is Ring under addition and multiplication. [5]
10.
How substitution ciphers are different from transposition ciphers? Given a message M="CSIT PROGRAM IS A HOT CAKE", encrypt M using Rail Fence cipher with rail size 3. [5]
11.
Describe about IPSec. List the five services of PGP. [5]
12.
How does meet in middle attack work in Diffie Helman key exchange protocol? Explain. [5]