S Boxes Properties of S-boxes in dES (per NSA) Each s-box has 6 input bits and 4 output bits This was the largest that could be put on one chip back in 1974 All rows of all the s-boxes are permutations of 0, 1 15 S-Boxes are not affine transformations of their input Change in an input bit changes at least two output bits of the s-box For any X and any S-box S, S(X), s(X 0001100)differs by at least two bits 2222 • Properties of S-boxes in DES (per NSA) – Each S-box has 6 input bits and 4 output bits. This was the largest that could be put on one chip back in 1974. – All rows of all the S-boxes are permutations of 0, 1, …, 15 – S-Boxes are not affine transformations of their input – Change in an input bit changes at least two output bits of the S-box – For any x and any S-box S, S(x), S(x 001100) differs by at least two bits S Boxes