L10-Block Ciphers-2 - Initial and Final Permutations •...

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Initial and Final Permutations Initial and Final Permutations • “Final Permutation” is the inverse of “Initial Permutation” • Purpose of “Initial Permutation” and “Final Permutation” is to make software implementations of DES slow
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Initial Permutation Initial Permutation 58 th bit value of Input becomes 1 st bit of Output 7 th bit value of Input becomes 64 th bit of Output
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Final Permutation (Inverse of Initial Permutation Final Permutation (Inverse of Initial Permutation ) ) 4 08 4 81 65 62 46 43 2 3 97 4 71 55 52 36 33 1 3 86 4 61 45 42 26 23 0 3 75 4 51 35 32 16 12 9 3 64 4 41 25 22 06 02 8 3 53 4 31 15 11 95 92 7 3 4 21 05 01 85 82 6 33 1 41 9 49 17 57 25 33 rd bit value of Input moves to 57 th bit of Output 25 th bit value of Input moves to 64 th bit of Output
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Expansion Permutation (E) Expansion Permutation (E) 32 nd bit value of Input moves to 1 st bit of Output 4 th bit value of Input moves to 7 th bit of Output
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Permutation (P) Permutation (P) 16 th bit value of Input moves to 1 st bit of Output 1 st bit value of Input moves to 9 th bit of Output
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Substitution (S Substitution (S - - box) box) (6 inputs / 4 outputs) (6 inputs / 4 outputs)
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L10-Block Ciphers-2 - Initial and Final Permutations •...

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