Questions
Syllabus
Qns. By Syllabus

Semester

Subject

Year

Tribhuwan University

Institute of Science and Technology

2082

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.
Describe the Feistel Cipher structure. Given the key {2B, 7E, 15, 16, 28, AE, D2, A6, AB, F7, 97, 66, 01, 02, 03, 04}, compute the first 4 byte of next key after first iteration, using the following S-Box in AES.
S-Box0123456789ABCDEF0637C777BF26B6FC53001672BFED7AB76\begin{array}{c|cccccccccccccccc} \text{S-Box} & 0 & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & A & B & C & D & E & F \\ \hline 0 & 63 & 7C & 77 & 7B & F2 & 6B & 6F & C5 & 30 & 01 & 67 & 2B & FE & D7 & AB & 76 \end{array}
[10]
2.
Illustrate the man in middle attack in Diffie-Hellman key exchange protocol. Assume the prime number be 19 and 10 as its primitive root. Select 5 as private key and 4 as random integer. Find the cipher text of M = 2 using Elgamal crypto system. [10]
3.
Describe the properties of hash functions. Discuss how hash value is generated using SHA-1 algorithm. [10]
Section B

Short Answers Questions

Attempt any Eight questions.
[8*5=40]
4.
Describe any three types of malicious logic. [5]
5.
Given the key "HELLOWORLD", encrypt the plaintext "TURINGTEST" using Play fair cipher. [5]
6.
Explain any two modes of block cipher encryption. [5]
7.
Describe the working mechanism of digital signature algorithm. [5]
8.
State Fermat's theorem with example. What is the implication of discrete logarithm? [5]
9.
List and explain the types of firewall. [5]
10.
Define authentication system. Discuss about challenge response system. [5]
11.
Decrypt the ciphertext 'HI' using Hill Cipher where the key is.
Ciphertext: HI, Key: [5343]\text{Ciphertext: HI, Key: } \begin{bmatrix} 5 & 3 \\ 4 & 3 \end{bmatrix}
[5]
12.
What is digital certificate? Discuss the certificate life cycle. [5]