[cryptography] Point compression prior art?

David-Sarah Hopwood david-sarah at jacaranda.org
Mon May 16 18:55:14 EDT 2011

On 03/05/11 19:59, Zooko O'Whielacronx wrote:
> Have you seen DJB's "Irrelevant patents on elliptic-curve cryptography"
> http://cr.yp.to/ecdh/patents.html
> My Curve25519 software never computes y, so it is not covered by the
> patent. It should, in any case, be obvious to the reader that a patent
> cannot cover compression mechanisms published seven years before the
> patent was filed.
> """
> DJB also has this page, which goes into more detail about 6141420:
> http://cr.yp.to/patents/us/6141420.html
> Contrary to the "filed 1994.07.29" above, the patent was actually
> filed January 29, 1997:
> http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6,141,420.PN.&OS=PN/6,141,420&RS=PN/6,141,420

True, but it has the "related U.S. patent document" with application number
282263, which was filed in July 1994. That date is what is most relevant
for the "published seven years before the patent was filed" comment.

> Which means it expires January 29, 2017.

If a granted patent has prior art for a given claim, then it is invalid
for that claim, and cannot be infringed, so its expiration date is not
important. (The holder can of course claim that it is infringed, but they
could do that for any random patent they hold, regardless of relevance.)

David-Sarah Hopwood ⚥ http://davidsarah.livejournal.com

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