JNTU – Supplimentary Examinations- Network Security And Cryptography-February 2008

JNTU paper

JNTU Supplimentary Examinations, February 2008

Network Security And Cryptography

(Computer Science & Engineering)


1. This problem provides a numerical example of encryption using a one-round version

of DES. We start with the same bit pattern for the key and plain text, namely, In hexadecimal notation 0 1 2 3 4 5 6 7 8 9 A B C D E F

Inbinary notation: 0000 0001 0010 0011 0100 0101 0110 0111

1000 1001 1010 1011 1100 1101 1110 1111

(a) Derive K1, the first – round subkey.

(b) Derive L0,R0

(c) Expand R0 to get E[R0]

(d) Calculate A=E[R0] _ K1.

(e) Group the 48-bit result of (d) into sets of 6 bits and evaluate the corresponding

S-box substitutions.

(f) Cancatenate the results of (e) to get a 32-bit result,B.

(g) Apply the permutation to get P(B).

(h) Calculate R1=P(B) _ L0

(i) write down the cipher text.


2. (a) List the characteristics of advanced block ciphers.

(b) What are the differences between RC5 and RC2?


3. (a) What is an Elliptic Curve?

(b) Explain the additive rules of Elliptic Curve Cryptography?


4. (a) Explain Miller-Robin test algorithm.

(b) Explain Chinese Remainder Theorem.


5. Define digital Signature. Explain its role in network security.


6. (a) What problem was Kerberos designed to address?

(b) What are three threats associated with user authentication over a network or Internet?

(c) List three approaches to secure user authentication over a network or Internet?



7. (a) What are the basic approaches to building SAs?

(b) What are the roles of the Oakley key determination protocol and ISAKMP in



8. (a) What are the three benefits that can be provided by an intrusion detection system?

(b) What is the difference between rule-based anomaly detection and rule-based

penetration identification?

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