**JNTU IV B.Tech I Semester Supplimentary Examinations, February 2008**

**NETWORK SECURITY AND CRYPTOGRAPHY**

**(Computer Science & Engineering)**

**SET-I**

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 are two different uses of public – key cryptography related to key Distribution?

(b) Explain RSA Algorithm?

4. (a) Explain in detail about Euclidâ€™s Algorithm.

(b) Determine gcd(1970,1066).

5. (a) What is a difference between little-endian and big-endian format?

(b) What basic arithmetical and logical functions are used in MD5?

6. (a) List limitations of SMTP/822 scheme?

(b) What are the MIME specifications?

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

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

8. (a) what information used by a typical packet-filtering router?

(b) What are some weaknesses of a packet-filtering router?

(c) What is the difference between a packet-filtering router and a stateful inspection firewall?