🚀 go-pugleaf

In article <1483@faline.bellcore.com> karn@faline.bellcore.com (Phil R. Karn) writes:
>Each round in DES involves an expansion, exclusive-OR, a ROM table
>lookup (the S-boxes) followed by a permutation (P-boxes) and then
>another exclusive-OR.

If it helps, the S-box step can be done with Boolean operators: each of
the 4 output bits of each S box can be represented as a Boolean function
of the 6 input bits.  Some of them are simpler than one might expect, as
has been pointed out in the literature.  I suspect this would be faster in
hardware than a ROM lookup, but it would presumably take more chip area
and reinforce the bottom line of Phil's argument.
-- 
	Jim Gillogly
	{hplabs, ihnp4}!sdcrdcf!randvax!jim
	jim@rand-unix.arpa