## Wednesday, October 28, 2009

B.E./B.TECH. DEGREE EXAMINATION,APRIL/MAY 2008

SIXTH SEMESTER

INFORMATION TECHNOLOGY

IT 1352 - CRYTOGRAPHY AND NETWORK SECURITY

( REGULATION 2004 )

PART A - (10 X 2 = 20 )

1. What is the advantage and disadvantage of one time pad encryption algorithm?

2. If a bit error occurs in plain text block p1, how far does the error propagate in CBC mode of DES?

3. When do we say an integer a, less than n is a primitive root of n? State the conditions for having at least one primitive root for n.

4. What for the Miller-Rabin algorithm is used?

5. Draw a simple public key encryption model that provides authentication alone.

6. Identify any two applications where one way authentication is necessary.

7. Why the leading two octets of message digest are stored in PGP message along with the encrypted message digest?

8. State any two advantages of Oakley key determination protocol over Diffie Hellman key exchange protocol.

9. How are the passwords stored in password file in UNIX operating system?

10. What is meant by polymorphic viruses?

PART - B ( 5 x 16 = 80 )

11. (a) (i) Discuss any four substitution cipher encryption methods and list their merits and demerits.[ marks 8 ]

(ii) How are Diffusion and Confusion achieved in DES? [ mark 8 ]

or

(b) (i) In AES, explain how the encryption key is expanded to produce keys for the 10 rounds.

(ii) Explain the types of attacks on double DES and triple DES. [ mark 8 ]

12. (a) (i) How are arithmetic operations on integer carried out from their residues modulo a set of pair wise relatively prime moduli? Give the procedure to reconstruct the integers from the residues. [ mark 8 ]

(ii) How is discrete logarithm evaluated for a number? What is the role of discrete logarithm in the Diffie Hellman key exchange in exchanging yhe secret key among two users?[ marks 8 ]

or

(b) (i) Identify the possible threats for RSA algorithm and list their counter measures. [ mark 8 ]

(ii) Sate the requirements for the design of Elliptic curve crypto system. Using that, Explain how secret keys are exchanged and messeges are encrypted. [ mark 8 ]

13. (a) (i) Describe Digital Signature Algorithm and show how signing and verification is done using DSS. [ mark 8 ]

(ii) Consider any message M of length 4120 bits ending with "ABCDEF" in hexadecimal form. Construct the last block of message to be given as input for the MD5. [ mark 8 ]

or

(b) (i) Explain the processing of a message block of 512 bits using SHA1. [ mark 12 ]

(ii) Write about the symmetric encryption approach for digital signatures. [ mark 4 ]

14. (a) (i) Describe the authentication dialogue used by Kerberos for obtaining services from another Realm. [ mark 8 ]

(ii) Explain with the help of an example how a user's certificate is obtained from another Cerification Authority in X509 scheme. [ mark 8 ]

or

(b) (i) What are the functions included in MIME in order to enchance security? How are they done? [ mark 8 ]

(ii) Why does PGP maintain key rings with every user? Explain how the messages are generated and recived by PGP? [ mark 8 ]

15. (a) (i) Explain any two approaches for intrusion detection. [ mark 10 ]

(ii) Suggest any three password selection strategies and identify their advantages and disadvantages if any. [ mark 6 ]

or

(b) (i) Identify a few malicious program that need a host program for their existence. [ mark 6 ]

(ii) Describe the familiar types of firewall configurations. [ mark 10 ]

Click the following link to download:

http://www.ziddu.com/download/7201227/cns.pdf.html