... is the one you don't ask. So here I go... #1 Isn't "part of the deal" of patent granting a requirement that the details of the thing being patented be revealed. If so, why isn't IBM required to reveal the details of s-box design? After all, they hold the patent on DES. #2 Skipjack has a 80 bit key which is proposed to be "escrowed" in two parts. Now considering that the likeliest attack on DES is a brute force key search of 2^55 keys, isn't it true that a compromise of one half of a "Clipper key" would allow a brute force attack to "discover the remaining 40 bits. If 2^55 is possible, then 2^40 is even easier, no? Brian