Computer Security and Cryptography

9.2 DES

DES (Fig. 9.3) is a block cipher where

• plaintext
• ciphertext
• key

DES is the product (composition) of mappings

with inverse

• IP is the initial permutation (or wire-crossing, plugboard);
• π_Ti F_i are the mappings performed on the left-x_L and right-x_R halves of the input on the ith round;
• θ is the interchange involution

The operations involved in the mapping are portrayed in Figure 9.4.

Figure 9.3 DES.

Figure 9.4 The DES transformation .