Computer and Network Security

1. Describe the S-Boxes in DES.

2. Is F-box in DES reversible? If yes, why Inverse F-box is not used in DES decryption?

3. F box takes the right 32 bits ( R )from previous round and a sub round key (K) as two inputs and produce a 32 bit output. Assume R=Ox12345678, K=Ox111122223333 Manually work out F(R,K).

4. Why double DES is not used and 3DES is the more popular cipher?

5. Show GF(23) and its operations with some examples

6. Describe the substitution Box in AES

7. Describe Shiffrows, MixColumns and AddRoundKey in AES










Sample Solution