[1166] in cryptography@c2.net mail archive
Re: Better DES challenge update
daemon@ATHENA.MIT.EDU (David Wagner)
Fri Jul 4 12:49:11 1997
To: cryptography@c2.net
From: daw@cs.berkeley.edu (David Wagner)
Date: 3 Jul 1997 18:43:59 -0700
In article <v03007812afe0eca1b155@[207.94.249.161]>,
Bill Frantz <frantz@netcom.com> wrote:
> At 5:21 PM -0700 7/2/97, Steven Bellovin wrote:
> >The former, by David Wagner and myself, describes a programmable plaintext
> >recognizer designed to fit on-chip with a Wiener engine. The latter, by
> >me, analyzes IPSEC for probable plaintext. The hardware feature you want
> >for the latter is a "population count under mask" -- you XOR the target
> >word with the trial decryption, then count how many 0 bits are in selected
> >positions...
>
> And now you know why machines designed by Cray have an instruction which
> counts the number of 1 bits in a register (in one machine cycle).
An alternate (or additional) theory: popcount is extremely useful
for implementing LSFRs, so perhaps the NSA wants to do lots of LSFR
analysis on their Crays...
