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);
- πTi Fi are the mappings performed on the left-xL and right-xR 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.
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