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 http://mattjensen.com Seattle

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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