From: eric@remailer.net (Eric Hughes)
Date: Tue, 27 Dec 94 23:13:16 PST
To: cypherpunks@toad.com
Subject: Re: Why I have a 512 bit PGP key
In-Reply-To: <9412281627.ZM11604@wiley.sydney.sgi.com>
Message-ID: <199412280713.XAA02404@largo.remailer.net>
MIME-Version: 1.0
Content-Type: text/plain


   From: "Ian Farquhar" <ianf@sydney.sgi.com>

   > Recompile the binary from newly uploaded source each time.  MD5 source
   > isn't more than about 10K long.  That's all of a few seconds of upload
   > time.

   Irritating [...]

???  An upload can be automated, just like anything other solution.

   [...] and also insecure (system admin intercepts the upload and
   replaces it with source of his or her own).

_Every_ solution to this problem is insecure, when it comes down to
it.  What you asked for is something that makes things more difficult.

Interception can be made quite difficult.  Make the "upload" consist
of simulating a keyboard typing the source code into emacs.  Change
the file name each time.  Obfuscate the source by redefining variables
each time.  Pipe the output directly into the compiler; hell, compile
straight from stdin!

You can't go about protecting against the modification of binaries by
relying upon one of your binaries being better protected than the
rest.  There's an infinite regress involved here.  The solution is to
go outside the regress.  Recreating the binary from scratch is one
way.  I'm sure there are others.

   >    I am pretty much certain that to make such
   >    a system perfectly secure under these conditions is impossible.

   Is there a standard proof for this, though?  I suspect that there is, but
   have not discovered it.

Get the essay that Perry mentioned and start there.  Keep in mind that
object code can be interpreted in many different ways, only one of
them typically expected.

Eric