Question

which is based on Feistal design AES or DES?

Answer 1

The DES working and design are based on Feistel Design :

1. In the DES design, there are a number of rounds each round as a design structure like Feistel Design.

2. For every round, in the DES, the input bits to each round is divided into two parts of equal size.

3. On part is called the Left(Le) part and the other part is called Right(Ri) Part.

4. For the computation of input to the network round with left and right part, following equation are used.

5. Consider the round k with Left part as Le(k) and Right Part as Ri(k) and the key for the kth round as Key(k)

6. The input values for the next round in DES cipher i.e for round k+1, equations are :

• Le(k+1) = Ri(k)
• Ri(k+1) = F(Key(k),Ri(k))  XOR Le(k)

7. Here, we have used the swapping function to find out the left part of the k+1 found . This type of design is the same as Feistel Cipher.

8. For the right part of the k+1 round, a function F takes the input as the right part of the kth round and the key fo kth round . The result of his function is XORed with the left part of the kth round.