Anna University Questions  CS9402 Cryptography and Security April May 2014, Computer Science and Engineering (CSE), Seventh Semester, Regulation 2008
Exam

B.E/B.Tech. (Full
Time) DEGREE END SEMESTER EXAMINATIONS

Academic
Year

April May 2014

Subject
Code

CS9402 
Subject
Name

Cryptography and Security 
Branch

Computer Science and Engineering

Semester

Seventh Semester

Regulation

2008

B.E
/ B.Tech. (Full Time) DEGREE END SEMESTER EXAMINATIONS, APRIL / MAY 2014
Computer Science
and Engineering
Seventh Semester
CS9402
CRYPTOGRAPHY AND SECURITY
(Regulation 2008)
Time : 3 Hours Answer A L L Questions Max. Marks 100
PARTA
(10 x 2 = 20 Marks)
1. Suppose we work mod 27 instead of
mod 26 for affine ciphers. How many keys are possible?
2. Determine (231). (Eulers Totient
function)
3. Give the differences between RC4
and RC5.
4. Discuss the timing attack on RSA
and how it can be overcome.
5. What is meant by birthday attack in
hash functions?
6. How MAC is different from hash
techniques?
7. What is the purpose of X.509
certificate?
8. What problem was Kerberos designed
to address?
9. List the key features of a trusted
operating system.
10. What are the factors to be
considered while determining the sensitive data in data base security?
PartB
(5* 16 = 80 Marks)
11. (i) Suppose we build an LFSR
machine that works mod 3 instead of mod 2. It uses a recurrence of length 2 of
the form (8)
X_{N+2} =C_{0}X_{n}+
C_{1}X_{n+1} (mod 3)
To generate the sequence
1,1,0,2,2,0,1,1. Set up and solve the matrix equation to find the coefficients
C_{0} and C_{1}.
(ii) A group of people are arranging
themselves for a parade. If they line up three to a row, one person is left
over. If they line up four to a row, two people are left over and if they line
up five to a row three people are left over. What is the smallest possible number
of people? What is the next smallest number? (interpret this problem in terms of
the CRT) (8)
12. a) (i) Show how 12 is transformed
to C9 by subbyte routine using GF(28) field with the irreducible
polynomial (x^{8}+x^{4}+x^{3}+x+1) in AES algorithm.
(8)
(ii) Discuss the key expansion in AES
 128. (8)
OR
b) (i) Discuss any one primality
testing algorithm that is used to test whether a given number is a prime or a
composite number. (8)
(ii) Perform encryption and decryption
using the RSA algorithm p = 7,q = 11,e = 17,M = 8 (8)
13. a) (i) Consider a DiffieHellman
scheme with a common prime q = 11 and a primitive root a = 2.
• Show that 2 is a primitive root of
11. (2)
• If user A has public key Y_{A}
= 9, what is A's private key X_{A}? (3)
• If user B has public key Y_{B}
= 3, what is the shared secret key K? (3)
(ii) Discuss in detail about the
secure hash algorithm. (8)
OR
b) (i) Discuss in detail about the
digital signature standard algorithm. (8)
(ii) Discuss how the key exchange is
done using elliptic curve cryptography. (8)
14. a) Discuss briefly about the PGP
used for Email security. (16)
OR
b) Discuss briefly about IP security
architecture. (16)
15. a) Discuss briefly about the
security models involved in trusted operating systems. (16)
OR
b) Discuss in detail about the
multilevel secure database. (16)
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