Why do we need discrete logarithm? Illustrate with an example. Consider a Diffie-Hellman scheme with a common prime p = 13 between user A and user B. Suppose public key of A is 10 and public key of B is 8. Now determine their private keys and shared secret key. Select any valid primitive root of 13. [10]
2.
Write short notes on (any two) a. Totient value of any positive integer. b. Properties of hash function. c. Virus or Worms. [5]
Authentication
1.
Discuss the working mechanism of kerberos protocol. [5]
Cryptographic Hash Functions and Digital Signatures
1.
What is Message Authentication Code? List the operation of computing digest value in different passes of MD4. Describe about Needhom-Schroeder protocol. [10]
Malicious Logic
1.
What is intrusion? Explain any two types of intrusion detection system. [5]
2.
What is DoS attack? Discuss about PKI trust model. [5]
Network Security and Public Key Infrastructure
1.
What is the use of firewall? How circuit level gateway differs from stateful inspection firewall? [5]
Symmetric Ciphers
1.
Let us consider the 4 bits key set as {1100, 1010, 0000, 1111, 0101, 1001} and input text as {1011, 1110, 1011, 1000}. Now trace the first full round operation of IDEA algorithm. [10]
2.
Show the encryption of plain text "ALGORITHM" using the key "PSEUDOCODE" using playfair cipher. [5]
3.
Find the multiplicative inverse of polynomial (95) using extended euclidean Algorithm. [5]
4.
Using Vigenere cipher with key = “worlds”, encrypt the plain text “hello everyone”. [5]