IT1352 – CRYPTOGRAPHY AND NETWORK SECURITY MAY08

  T3315
B.E DEGREE EXAMINATION, MAY 2008
IT1352 – CRYPTOGRAPHY AND NETWORK SECURITY

Part –a 
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 or 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 tow 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
11. A) i. Discuss any four substitution cipher encryption methods and list their merits and demerits .

ii. how are diffusion and confusion achieved in DES.
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.

12. A)  
i. How are arithmetic operations on integers carried out from their residues modulo a set of pair wise relatively prime moduli. Give the procedure to reconstruct the integers form the residue.
ii. How is discrete logarithm evaluated for a number . what is the role of discrete logarithms in the diffie hellman key exchange in exchanging the secret key among two users.
 
Or
b) i. Identify the possible threats for RSA algorithm and list their counter measures.
ii. state the requirements for the design of an elliptic curve crypto system. Using that , explain how secret keys are exchanged and messages are encrypted.

13. A).  
i. Describe digital signature algorithm and show how signing and verification is done using DSS.
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.
 
Or
  b) i. Explain the processing of a message block of 512 bits using SHA1.
ii. write about the symmetric encryption approach for digital signatures.

14. a) i.Describe the authentication dialogue used by Kerberos for obtaining services from another realm.
ii. Explain with the help of an example how a user’s certificate is obtained from another certification authority in x509 scheme.
Or
b). i. what are the functions included in MIME in order to enchance security how are they done..
ii. why does PGP maintain key rings with every users. Explain how the messages are generated and received by pgp.
15). A)  
i. Explain any tow approached for intrusion detection.
ii. Suggest any three password selection strategies and identify their advantages and disadvantages if any.
Or
b). i. Identify a few malicious programs that need a host program for their existence.
ii. Describe the familiar types of firewall configurations.