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Simplified DES : 

Simplified DES

What is Simplified DES : 

What is Simplified DES Developed 1996 as a teaching tool rather than a secure encryption algorithm 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

S-DES Scheme : 

S-DES Scheme 8-bit ciphertext 8-bit ciphertext Involves Substitution and permutation operation and depends on the input key

Five Functions to Encrypt : 

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

Initial Permutation (IP)‏ : 

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

Expansion/Permutation (E/P)‏ : 

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

Key Generation : 

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

P10 Permutation : 

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

P8 Permutation : 

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

LS-1 : 

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

LS-2 : 

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

Substitution Boxes : 

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

Analysis of S-DES : 

Analysis of S-DES A brute force attack on S-DES is certainly feasible. With a 10-bit key, there are only 210 = 1024 possibilities.

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