Intrinsic: MTech. Cryptography and Network Security.

MTech. Cryptography and Network Security -1 (2010)

1. Explain the various Services, Mechanisms and Attacks which are dealt with in the OSI Security Architecture. (10 marks)

2. (a) Draw the conventional Encryption model and explain. (5 marks)

(b) Use Hill cipher to decrypt the text M N K H A N S H Q A . The key given is

7 8

19 3 ( 5 marks)

3. (a) For the cipher text

S S E T N B O T H P E O S L I Y C H I E Y X T X

and key 241536 for both rounds find the plain text using column transposition.

(5 marks)

(b) Given S boxes

S₀ = 1 0 3 2 S₁ = 0 1 2 3

3 2 1 0 2 0 1 3

0 2 1 3 3 0 1 0

3 1 3 2 2 1 0 3

For the input combination 1001 and 1110 for S₀and S₁respectively, find the outputs of the S boxes. (5 marks)

4. (a) Mention the different applications of DES algorithm and explain the cipher feedback mode with diagram. (5 marks)

(b) Explain with diagram the Fiestel Cipher structure used for confusion and diffusion.

(5 marks)

5. With a neat diagram explain the S-DES encryption for 8-bit plain text.(10 marks)

6. Explain in detail a single round of DES encryption. (10 marks)

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Intrinsic