As a scientist I would like to keep some official record of the time I check something into my Git repository. This in order to later back up claims of who invented what first during for instance patent disputes.
At the moment I from time to time add a tag to my repository like so:
git tag -s -m "`date`" 2012-08-20
and push the tags to the central server:
git push --tags
Pulling up a tag shows the date I signed it with my key:
git tag -v 2012-08-20
object 2d6f6035270e8e44c035431e99be8da3fccee095
type commit
tag 2012-08-20
tagger My Full Name <name@institution> 1345466433 +0200
Mon Aug 20 14:40:33 CEST 2012
gpg: Signature made Mon Aug 20 14:40:37 2012 CEST using RSA key ID somekey
gpg: Good signature from "My Full Name <name@institution>"
gpg: aka "My Full Name <personal-email>"
My question is how secure these dates are? Is it possible tamper with them later on?
EDIT: to clarify a but further, I wish to be able to prove that it would be very unlikely that I tampered with the tags later on.