Cryptography & System Security - Dec 2016

Computer Engineering (Semester 7)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1(a) What are block ciphers? Explain with examples the CBC and ECB modes of block ciphers.(5 marks) 1(b) Encrypt the string " This is an easy task" using a playfair cipher with key "monarchy".(5 marks) 1(c) Define authentication and non-repudiation and show with examples how each one can be achieved.(5 marks) 1(d) Describe triple DES with two DES keys. Is main in the middle attack possible on triple DES?(5 marks) 2(a) A and B decide to use Diffie Hellman algorithm to share a key. They choose p=23 and g=5 as the public parameters. Their secret keys are 6 and 15 respectively. Compute the secret key that they share.(10 marks) 2(b) Compare DES and IDEA. Explain the round key generation scheme in both these alorithms.(10 marks) 3(a) What are the different types of viruses and worms? How do they propogate?(10 marks) 3(b) What are the various ways for memory and address protection in Operating systems? How is authentication achieved in O.S?(10 marks) 4(a) Explain briefly with examples, how the following attacks occur:
i) Salami attack
ii) Denial of service attack
iii) session hijacking attack
iv) Cross-cite scripting attack(10 marks) 4(b) How is security achieved in the transport and tunnel modes of IPSec? Describe the role of AH and ESP.(10 marks) 5(a) How is confidentiality achieved in emails using either S/MIME or PGP?(5 marks) 5(b) A and B wish to use RSA to communicate securely. A chooses public key (e,n) as (7,247) And B chooses public key (e,n) as (5,221). Calculate their private keys. What will be the cipher text sent byA to B if A wishes to send message m=5 securely to B?(10 marks) 5(c) What is a digital signature? Explain andy digital signature algorithm.(5 marks) 6(a) Comapare and contrast(Any two):
i) Block and stream ciphers
ii) MD-5 versus SHA
iii) KDC versus CA(10 marks) 6(b) What are firewalls. Explain the different types of firewalls and mention the layer in which they operate.(10 marks)