Questions
Syllabus
Qns. By Syllabus

Semester

Subject

Year

Tribhuwan University

Institute of Science and Technology

2076

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.
Among monoalphabetic and polyalphabetic cipher, which one is more vulnerable? Justify your statement. Which types of keys are considered weak keys in DES? Explain the round operation in IDEA.[10]
2.
State Fermat’s theorem with an example. Given the prime number p=29 and its primitive root g=8, private key sender with X=9 and random integer K=11, encrypt the message m=13 using ElGamal cryptosystem.[10]
3.
Compare the SHA parameters between SHA-1 and SHA-2 families. Decrypt the cipher text DRIJ with the key using the Hill cipher.

$\begin{pmatrix} 7 & 8 \\ 11 & 11 \end{pmatrix}$
[10]
Section B

Short Answers Questions

Attempt any Eight questions.
[8*5=40]
4.
Define discrete logarithm. Explain the procedure of sharing the secret key in Diffie Hellman. [5]
5.
Distinguish between stream cipher and block cipher. Encrypt the message WE ARE IN SAME RACE UNTILL OVER LIVE END using Rail fence cipher using 4 as a number of rails. [5]
6.
Define digital signature. Describe the approaches of DSS. [5]
7.
What is the task of a firewall? List the elements of X.509. [5]
8.
How does the nature of worms differ from viruses? Define PKI with its architecture model. [5]
9.
Explain the procedure of mix column transformation in AES with an example. [5]
10.
What is the role of the prime number in the Euler totient Function? Find the GCD of 12 and 16 using the Euclidean algorithm. [5]
11.
Write down any two limitations of MAC. What do policy and mechanism mean in cryptography? Describe with a scenario. [5]
12.
Write short notes on: a. Classes of Intruder b. SSL c. DoS Attack [5]