My wife's friend Stuart haber is co-inventor of the standard way to do this
(cryptographically chained timestamped hash codes). There are a few URLs of
citations, etc. And they did start a company (Surety), to commercialize the
technology. I don't know healthy the business is.
I stuck in one of the many other sites offering some variation of this service.
The thing I like about Stuart's service is that there's a need to have a
public "hash code of record," every so often so that clients and courts
don't have to depend on trusting the hash authotirty. They use dead-tree
broadcast replication of identical bits: by publishing a classified ad in
the NYT every day -- thus leaving a tough-to-falsify audit trail of
sufficient permanence for commercial transactions.
David Durand firstname.lastname@example.org \ david@dynamicDiagrams.com
Boston University Computer Science \ Sr. Analyst
http://www.cs.bu.edu/students/grads/dgd/ \ Dynamic Diagrams
MAPA: mapping for the WWW \__________________________