From: Adam Shostack <adam@bwh.harvard.edu>
Date: Sat, 17 Dec 94 21:16:55 PST
To: cactus@seabsd.hks.net (L. Todd Masco)
Subject: Re: QUERY: S/Keyish PGP?
In-Reply-To: <199412180038.TAA03190@bb.hks.net>
Message-ID: <199412180516.AAA21349@bwh.harvard.edu>
MIME-Version: 1.0
Content-Type: text/plain



| A quick question: Has anybody considered the possibility of hacking
| something into PGP's password protection to allow an S/Key like access?

	I thought of this, bounced it off a few people, none of whom
caught the flaw.  When I got around to implementing it, I realized
that for it to work, your key would have to be securely stored on your
unix box without encryption.

	The way S/key works is it uses your ability to provide the
input to a one way function whose expected output S/key knows.  There
is no secret data stored on the server.  In contrast, PGP needs secret
data which it uses to encrypt your key while it is stored.

	Offhand, I doubt it can be done without storing your key in
the clear, or trusting the local CPU.  If you can store your key in
the clear because you feel the comprimise of your key is an acceptable
risk, you are all set.  Similarly, if you trust the local CPU, you can
probably do an encrypted telnet or somesuch.

	Don't take that to mean it can't be done; I'm not even an
amateur cryptographer, and there may well be some clever way of doing
this that I haven't thought of.

Adam


-- 
"It is seldom that liberty of any kind is lost all at once."
						       -Hume