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Simplified DES

Simplified DES. 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

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Simplified DES

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  1. Simplified DES

  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 Encryption Decryption P10 8-bit plaintext 8-bit plaintext SHIFT IP IP - 1 P8 K1 K1 fk fk SHIFT SW SW K2 P8 K2 fk fk IP - 1 IP 8-bit ciphertext 8-bit ciphertext

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

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

  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) Expand 4 bits into 8 and permutate them… k1 k2 k3 k4 k4 k1 k2 k3 k2 k3 k4 k1

  8. Key Generation 10 P10 5 5 LS-1 LS-1 5 5 P8 8 K1 LS-2 LS-2 5 5 P8 8 K2

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

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

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

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