Earlier I said I would forward to the list a posting I did on digital time-stamping, describing the Haber and Stornetta system. But I'll instead repost Stu Haber's comments, for more detail. --Tim

Date: Sun, 19 Jun 1994 21:52:29 -0700 From: stuarth@netcom.com (Stuart Haber) To: cypherpunks@toad.com Cc: stuarth@netcom.com Subject: coming soon: secure digital time-stamping in practice Sender: owner-cypherpunks@toad.com Precedence: bulk Status: RO

On Thursday, June 16 Tim May very nicely described a digital time-stamping scheme:

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The canonical reference for digital timestamping is the work of Stu Haber and Scott Stornetta, of Bellcore. Papers presented at various Crypto conferences.

See below for pointers to the papers.

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Their work involves having the user compute a hash of the document he wishes to be stamped and sending the hash to them, where they merge this hash with other hashes (and all previous hashes, via a tree system) and then they *publish* the resultant hash in a very public and hard-to-alter forum, such as in an ad in the Sunday New York Times.

In their parlance, such an ad is a "widely witnessed event," and attempts to alter all or even many copies of the newspaper would be very difficult. (In a sense, this WWE is similar to the "beacon" term Eric Hughes used recently in connection with timed-release crypto.)

Haber and Stornetta plan some sort of commercial operation to do this, and, last I heard, Stornetta was moving to the Bay Area (where else?) to get it started.

We do indeed plan to do just that. Bellcore has spun off a company, Surety Technologies, whose charter is to bring digital time-stamping into widespread use. Resisting the charms of the Bay Area, we decided to stay in New Jersey.

Instead of closing off our trees once a week and publishing their roots in the national edition of the Sunday New York Times, as we've been doing for over two years now (including this week: look for the Public and Commercial Notices towards the end of the main news section of today's paper -- on p. 30 if you get the NY-area edition), we are planning to close our trees at sub-minute intervals and make their roots widely available. By the end of the summer, we plan to have a service bureau (to build the trees) up and running, and client software available to access the service -- both for time-stamping documents and for validating (document, time-stamp certificate) pairs.

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This service has not yet been tested in court, so far as I know.

Nor as far as I know. But we do plan to push this issue, on several legal and regulatory fronts, so as to enhance the legal acceptance of appropriately authenticated digital documents.

Here are the references: "How to Time-Stamp a Digital Document," S. Haber and W.S. Stornetta, Journal of Cryptology, vol. 3, pp. 99-111 (1991). A similar version appeared in the CRYPTO '90 Proceedings (Springer-Verlag LNCS, Vol. 537), pp. 437-455.

"Improving the Efficiency and Reliability of Digital Time-Stamping," D. Bayer, S. Haber, and W.S. Stornetta, Sequences II: Methods in Communication, Security, and Computer Science, ed. R.M. Capocelli, A. DeSantis, U. Vaccaro, pp. 329-334, Springer-Verlag (1993).

Stuart Haber | Surety Technologies provides Chief Scientist | Digital Notary(sm) service on the Internet. Surety Technologies, Inc. | General info: info@notary.com stuart@notary.com | (201) 993-8178, fax -8748

.......................................................................... Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@netcom.com | anonymous networks, digital pseudonyms, zero 408-688-5409 | knowledge, reputations, information markets, W.A.S.T.E.: Aptos, CA | black markets, collapse of governments. Higher Power: 2^859433 | Public Key: PGP and MailSafe available. "National borders are just speed bumps on the information superhighway."