Re: Challenge-response passwords (Was: big word listing)

["Perry E. Metzger" <perry@imsi.com>]

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