In the course of my work I produce a substantial amount of source code, CAD drawings, and 3D models. Since little of it is ever published I'm left looking for a good way to prove that the backup copies of these files existed on a given date and have been unmodified since.
Proving that the files are unmodified is trivial enough. We have a number of fine hashing functions for that. The issue is in proving the date. The file date stamps are, of course, quite useless. Lacking any other clear options I've been taring up the file sets for my completed projects, printing out their checksums, and getting that notarized.
While this is something, it's not exactly ideal. This process is tedious, and may not hold as much weight in court as one would hope. (Coming up with clever ways to explain to the judge just how big 2^[whatever] is all well and good, but this method does not prove the date with similar confidence.)
My ideal solution would be to send the checksum list to some trusted-third-party and have them sign it for me with GPG or something. Does anyone know of a reputable service that will do this for a reasonable fee, or perhaps a better scheme entirely?
(If it doesn't exist please nobody patent a "business model" based on it. We have enough problems already, and I think this Ask Slashdot constitutes some sort of prior art.)