THE NOBLEST CRYPTOLOGIST
Gerhard F. Strasser · Cryptologia · 1983
Using the eight parity bits of the DES key to select from 256 alternative sets of substitution (S-) boxes increases key space from 256 to 264, permits operating in an autokeying mode if desired, and allows up to $\left(\matrix{65,536 \cr 8,192}\right) variants of the algorithm. We employ multi-level binary derivative sequences to show that our S-boxes scramble the bits of crypt-text as well as unmodified DES does.