You could always set up a cron job that would delete the key on your server. Then make sure you log in before the cron job executes to post date it to the following week. So as long as you log in weekly, you can set the new date. If you lose your key, within a week the key is erased from the server and the key on the thumb drive becomes invalid. Personally I'd simply ensure I have a good passphrase to accompany the key, then keep a backup of the key somewhere accessible where you can get it and log onto your server to change it if you lose your USB drive. Jacques B.
