1. Simplified DES CS-480b Network Security Dick Steflik

2. What is Simplified DES Developed 1996 as a teaching tool Santa Clara University\ Prof. Edward Schaefer Takes an 8-bit block plaintext, a 10 –bit key and produces an 8-bit block of ciphertext Decryption takes the 8-bit block of ciphertext, the same 10-bit key and produces the original 8-bit block of plaintext

3. S-DES Scheme IP fkfk SW fkfk IP - 1 P10 P8 IP fkfk SW fkfk IP - 1 SHIFT P8 Encryption Decryption 8-bit plaintext 8-bit ciphertext K1K1 K1K1 K2K2 K2K2

4. Five Functions to Encrypt IP – an initial permutation f k - a complex, 2-input function SW – a simple permutation that swaps the two nybles f k - a complex, 2-input function; again IP – inverse permutation of the initial permutation

5. Encryption Detail I P E/P S0 S1 P4 E/P S0 S1 P4 SW I P -1 K 1 K 2 4 4 8 4 4 22 4

6. Initial Permutation (IP)‏ Move the bits of the original character around a little… k1 k2 k3 k4 k5 k6 k7 k8 k2 k6 k3 k1 k4 k8 k5 k7

7. Expansion/Permutation (E/P)‏ k4 k1 k2 k3 k2 k3 k4 k1 k1 k2 k3 k4 Expand 4 bits into 8 and permutate them…

8. Key Generation P10 P8 LS-1 LS-2 8 8 55 55 55 K1K1 K2K2 10

9. P10 Permutation k1 k2 k3 k4 k5 k6 k7 k8 k9 k10 k3 k5 k2 k7 k4 k10 k1 k9 k8 k6

10. P8 Permutation k1 k2 k3 k4 k5 k6 k7 k8 k9 k10 k6 k3 k7 k4 k8 k5 k10 k9 Permutate 10 into 8

11. LS-1 k3 k 5 k 2 k 7 k 4 k5 k 2 k 7 k 4 k 3 k10 k1 k9 k8 k6 k1 k9 k8 k6 k10 Left circular shift 1 each 5 bit group

12. LS-2 k3 k 5 k 2 k 7 k 4 k2 k7 k4 k3 k5 k10 k1 k9 k8 k6 k9 k8 k6 k10 k1 Left circular shift 2 each 5 bit group

13. Substitution Boxes 1 0 3 2 3 2 1 0 0 2 1 3 3 1 3 2 0 1 2 3 2 0 1 3 3 0 1 0 2 1 0 3 S0 S1