[spinron]

What's actually needed is a secure time stamping service. You can read about those at:

http://en.wikipedia.org/wiki/Trusted_timestamping

A personal favorite which I highly recommend is the following:

http://www.itconsult.co.uk/stamper.htm

Under normal circumstances, one would need an expert witness to authenticate the signature, but in several jurisdictions which enacted digital signature laws statues, that may not be necessary depending on the evidentiary status of e-signatures.

[JulianTosh]

ah ya beat me to it. double vote for bamf right here.