Questions
Syllabus
Qns. By Syllabus

Semester

Subject

Year

Tribhuwan University

Institute of Science and Technology

2079

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.
Illustrate the concept of security policy and mechanism with an example. Differentiate between block cipher and stream cipher. Explain the process of key expansion in AES.[10]
2.
Describe the properties of hash functions. Discuss how hash value is generated using SHA-1 algorithm.[10]
3.
Show that Z 5 is a field. John publishes the ElGamal public key (q, α, YA) =(101, 2, 14). Jane desired to send the secret message CSIT to John. Using the equivalence A = 0, B=1, ..., Z=25, encrypt the message using John’s public key. Use a random number k = 4.[10]
Section B

Short Answers Questions

Attempt any Eight questions.
[8*5=40]
4.
Differentiate between Trojan horse and virus. Describe any two types of intruders. [5]
5.
The message “IMOGUN” was encrypted with a Playfair cipher using keyword “GALOIS”. Decrypt the message. [5]
6.
How encryption is done using IDEA algorithm. [5]
7.
Describe the services provided by Pretty Good Privacy protocol to secure email. [5]
8.
Define challenge response system. Why do we need Kerberos? [5]
9.
How direct digital signature different from arbitrated digital signature? How digital signature generation and verification is done using RSA. [5]
10.
Why do we need discrete logarithm over normal logarithm? Find out whether 3 is primitive root of 7 or not. [5]
11.
Which one is more secure, monoalphabetic cipher or poly alphabetic cipher? Justify. Using rail fence cipher encrypt the text 'LEARNING AND TEACHING ARE DIFFERENT' using 3 as rails. [5]
12.
What is the condition of for two integers, x and y, to be relatively prime? Find whether 61 is prime or not using Miller-Rabin algorithm. [5]