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]
2.
Why do we need discrete logarithm over normal logarithm? Find out whether 3 is primitive root of 7 or not. [5]
3.
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]
Authentication
1.
Define challenge response system. Why do we need Kerberos? [5]
Cryptographic Hash Functions and Digital Signatures
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.
How direct digital signature different from arbitrated digital signature? How digital signature generation and verification is done using RSA. [5]
Introduction and Classical Ciphers
1.
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]
Malicious Logic
1.
Differentiate between Trojan horse and virus. Describe any two types of intruders. [5]
Network Security and Public Key Infrastructure
1.
Describe the services provided by Pretty Good Privacy protocol to secure email. [5]
Symmetric Ciphers
1.
The message “IMOGUN” was encrypted with a Playfair cipher using keyword “GALOIS”. Decrypt the message. [5]