From: "Perry E. Metzger" <perry@imsi.com>
Date: Wed, 26 Jul 95 12:52:52 PDT
To: stewarts@ix.netcom.com (Bill Stewart)
Subject: Re: Challenge-response passwords (Was: big word listing)
In-Reply-To: <199507261944.MAA20832@ix9.ix.netcom.com>
Message-ID: <9507261952.AA28574@snark.imsi.com>
MIME-Version: 1.0
Content-Type: text/plain



Bill Stewart writes:
> It's _not_ free after 1997!  I thought of it last fall, was
> surprised I couldn't find it anywhere in the literature, given that
> it's pretty obvious, but eventually found that a guy from Siemens
> had patented it in Germany and then gotten a US patent in ~1994.
> Unfortunately, he phrased it in terms of
> "commutative hash functions", with g^X mod p as an example, so it's more
> general.

Given all the prior art, I have a solid suspicion that the patent
wouldn't hold up. The existance of the publically published Diffie
Hellman patent, for instance, makes it rather hard to patent the
more general case.

Perry