applied cryptography - protocols, algorithms, and source code in c

1 lucifer in the late 1960s led by horst feistel and

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Unformatted text preview: , s3DES, was presented in [839] and shown to be worse than DES against linear cryptanalysis [856,1491,1527,858,838]. Biham suggested a minor change to make s3DES secure against both linear and differential cryptanalysis [165]. The group went back to their computers and developed better techniques for S-box design [835,837]. They proposed s4DES [836] and then s5DES [838,944]. Table 12.16 gives the s3DES S-boxes with S-box 1 and S-box 2 reversed, which are secure against both differential and linear cryptanalysis. Sticking this variant in a triple-DES mix is sure to irritate cryptanalysts. DES with Key-Dependent S-Boxes Linear and differential cryptanalysis work only if the analyst knows the composition of the S-boxes. If the S-boxes are key-dependent and chosen by a cryptographically strong method, then linear and differential cryptanalysis are much more difficult. Remember though, that randomly generated S-boxes have very poor differential and linear characteristics; even if they are secret. s3DES Table 12.16 S-Boxes (with S-box 1 and S-box 2 reversed) 13 8 14 1 S-box 1: 14 0 3 10 4 7 2 11 13 4 1 14 9 3 10 0 7 13 4 14 7 11 13 8 S-box 2: 9 11 8 12 6 1 15 2 5 7 5 15 0 3 10 6 9 12 4 8 5 6 15 11 12 1 2 2 6 3 5 10 12 0 15 9 15 8 3 6 15 9 9 14 5 10 5 3 S-box 3: 13 3 11 4 13 1 658 1 11 7 S-box 4: 907 5 10 12 10 7 9 3 9 15 S-box 5: 5 15 9 693 15 0 10 12 5 0 S-box 6: 437 14 13 11 13 0 10 174 S-box 7: 4 10 15 10 15 6 2 12 9 12 6 3 S-box 8: 13 10 0 2 7 13 4 13 14 8 11 7 14 4 2 9 5 3 12 10 8 2 4 15 15 12 9 0 5 0 11 10 1 13 7 6 12 0 13 8 4 11 14 2 1 7 3 10 7 6 13 1 11 12 0 6 1 2 8 4 11 14 7 13 2 10 9 506 7 15 12 095 5 14 8 0 6 4 15 1 12 7 8 7 2 14 11 15 10 12 3 9 11 13 14 3 0 9 2 4 1 10 2 8 13 4 14 6 12 10 15 3 11 12 5 10 6 15 3 1 14 2 8 4 13 6 0 15 3 9 8 13 11 1 7 2 14 4 12 5 0 6 11 3 14 4 2 8 13 15 1 0 6 10 5 12 14 2 1 7 13 4 8 11 10 0 3 14 4 15 5 12 0 10 9 3 5 4 14 6 15 10 9 3 10 9 42 94 14 11 2 12 7 1 13 6 8 11 8 7 13 4 2 11 14 1 8 11 1 7 6 12 13 2 7 2 14 11 8 1 4 13 8 6 2 9 0 14 13 15...
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