Digital Timestamping

[tcmay@netcom.com (Timothy C. May)]

Douglas Floyd writes:

> In the RSA FAQ, it states how one can set up a server to do time and date
> stamping of documents, but I know of no Internet service that will
> do this.
> 
> Is there a way I can send a document to some agency/server and have it
> time and date stamped with their public key?
> 
> Thanks in advance,

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

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.

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

The MIT server is an experiment, and is probably useful for
experimenting. But it is undoubtedly even less legally significant, of
course.

--Tim May


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