Tribhuvan University

Institute of Science and Technology

2078

Bachelor Level / fifth-semester / Science

Computer Science and Information Technology( CSC316 )

Cryptography

Full Marks: 60 + 20 + 20

Pass Marks: 24 + 8 + 8

Time: 3 Hours

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

The figures in the margin indicate full marks.

**Section A**

**Attempt Any Two Questions**

1

Define CIA triad. State the encryption process of double and triple DES. What is the task of S-Box in DES ? Discuss with an example.

2

Explain the generic model of digital signature process. Consider the two prime numbers 7 and 19. Select 29 as public key and 41 as private key. Encrypt the plaintext 4 and decrypt the cipher text 3 using RSA.

3

Define Galois field with an example. Explain any two modes of block cipher encryption. Deterimine the quadratic residues of 7.

**Section B**

**Attempt Eight Questions**

4

What does intrusion mean? How the system detect intrusion? List any four types of firewall.

5

Decrypt the message “GVPJ” using Hill cipher taking the key as {Row1 = 3 7, Row2= 5 12}.

6

Describe the PKI trust model.

7

Define authentication system. Illustrate the need of mutual authentication over one way authentication with an example.

8

Find the value of 7^2019 MOD 13 using Fermat’s Little theorem. Define Euler totient function with

an example.

9

List the properties of hash function. Discuss the first pass of MD4.

10

Differentiate between Symmetric and Asymmetric cipher. Encrypt the message “HELL” using

the key “FAIL” using Vernanm cipher.

11

Divide 3x^{2} + 4x +3 by 5x +6 over GF(7).

12

Define SSL protocol. Mention the services provided by PGP.

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