[FoRK] Does the web have a public timestamper?

Matt Jensen mattj at newsblip.com
Sun May 8 07:21:42 PDT 2005

> A Surety patent in the area appears to have been successfully
> challenged in 1999:
>   http://www.entrust.com/news/files/11_09_99_258.htm
> - Gordon

That challenge only defeated Surety's general claim to all forms of digital
timestamping. There are other claims in the patent which still stand. The most
useful of these is the chaining of hashes from one document to the next.  Every
week, Surety publishes a cumulative hash in the New York Times.  Each new
document is signed by hashing the document, and sigining that hash combined
with the current, global, cumulative hash.  This ensures that nobody can
backdate a faked document.

I had long thought about implementing this technique in a user-friendly app,
where initial document hashing is done in client-side JavaScript. That would
protect customer data, yet not require a software download (as Surety does). 
Applications include everything from dating the condition of something you take
possession of (car, apartment, etc.), to dating blog entries to prove your
journalistic integrity (i.e., to prove you don't backdate).  With user-friendly
software, you could offer timestamping for free and make your money with AdSense
on your validation pages.

It's funny, because this was a back-burner project I was planning on working on
this morning.  But this thread led me to check the patent situation more
closely, and it seems to this layman that Surety's remaining patent claims are
too powerful.

-Matt Jensen

> Russell Turpin wrote:
> > Long ago, I thought some site -- maybe a
> > certificate source like Thawte? -- should
> > provide a provable timestamping service
> > over the web. The basic idea is that when
> > an application wants to timestamp some
> > item, such as an entry in QuickBooks or
> > an executed PDF or whatever, it would
> > (1) generate a signature of the item,
> > using SHA1 or the favorite hash function
> > du jour, (2) then post a request to the
> > timestamp site with the signature,
> > (3) in the hope of receiving (a) a global
> > timestamp and (b) a validation signature
> > of the timestamp and item signature.
> >
> > The website also would maintain a
> > globally accessible log, by time, of what
> > validation signatures it had generated.
> > These provide independent proof if
> > ever needed that the item was indeed
> > timestamped -- and hence, existed --
> > when claimed.
> >
> > It seems to me that this would be useful
> > for a broad range of applications, from
> > bookkeepping to facility monitoring. I
> > can imagine all sorts of reasons for wanting
> > a verified timestamp, from the legal to
> > the mundane. Is anyone doing this?
> >
> >
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