Tribhuvan University
Bachelor of Science in Computer Science and Information Technology
Semester 5 · TU Board 2079
Course Title: Cryptography (CSC316)
Full Marks: 60Pass Marks: 24Time: 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.
Group A
Answer any TWO(2 × 10 = 20)
- 1.10
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.
- 2.10
Describe the properties of hash functions. Discuss how hash value is generated using SHA-1 algorithm.
Answer comingAlso asked in 2082, 2080
- 3.10
Show that Z 5is 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.
Group B
Answer any EIGHT(8 × 5 = 40)
- 4.5
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.
- 6.5
How encryption is done using IDEA algorithm.
- 7.5
Describe the services provided by Pretty Good Privacy protocol to secure email.
- 8.5
Define challenge response system. Why do we need Kerberos?
- 9.5
How direct digital signature different from arbitrated digital signature? How digital signature generation and verification is done using RSA.
- 10.5
Why do we need discrete logarithm over normal logarithm? Find out whether 3 is primitive root of 7 or not.
- 11.5
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.
- 12.5
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.
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