[5688] in cryptography@c2.net mail archive
Re: having source code for your CPU chip -- NOT
daemon@ATHENA.MIT.EDU (John Gilmore)
Sun Sep 19 22:15:33 1999
Message-Id: <199909200158.SAA29807@toad.com>
To: William Allen Simpson <wsimpson@greendragon.com>
Cc: cryptography@c2.net, gnu@toad.com
In-reply-to: <37E4495E.A831571F@greendragon.com>
Date: Sun, 19 Sep 1999 18:58:42 -0700
From: John Gilmore <gnu@toad.com>
> On the other hand, having the actual CPU source, we could stop worrying
> about Intel's ID gaffs, and RNG support, and "know" it is built correctly.
Even if you designed the chip and contracted out the fabrication,
you will not know that it is built correctly. Even if you ran the fab
and shuttled the wafers from machine to machine yourself.
I have done design verification for complex chips (in the SPARCstation-1
and -2). You can certainly test that it does everything you designed it
to do. You can't test for the *absence* of backdoors or trojan horses.
If someone jiggered your CAD software to insert circuitry that turns on
the supervisor bit for one instruction if you execute seventeen ADDs in
a row, you'll never find it unless someone points you at it. (And it
won't be in your "source code", only in your physical circuitry. You
could find it in the photographic masks, or in a chip, nowhere else.)
Remember Ken Thompson's _Reflections on Trusting Trust_:
http://www.acm.org/classics/sep95/
It's a very short paper, readable by everyone on the list. Read it now!
You'll be shocked.
John
