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Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 0471128457 Publication Date: 01/01/96 Search this book:
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 12.5 The Real Design Criteria
After differential cryptanalysis became public, IBM published the design criteria for the Sboxes and the Pbox [373,374]. The criteria for the Sboxes are: — Each Sbox has 6 input bits and 4 output bits. (This was the largest size that could be accommodated in a single chip with 1974 technology.) — No output bit of an Sbox should be too close to a linear function of the input bits. — If you fix the leftmost and rightmost bits of an Sbox and vary the 4 middle bits, each possible 4bit output is attained exactly once. — If two inputs to an Sbox differ in exactly 1 bit, the outputs must differ in at least 2 bits. — If two inputs to an Sbox differ in the 2 middle bits exactly, the outputs must differ in at least 2 bits. — If two inputs to an Sbox differ in their first 2 bits and are identical in their last 2 bits, the two outputs must not be the same. — For any nonzero 6bit difference between inputs, no more than 8 of the 32 pairs of inputs exhibiting that difference may result in the same output difference. — A criterion similar to the previous one, but for the case of three active Sboxes. The criteria for the Pbox are: — The 4...
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