If I use tarsnap-keymgmt to create a key that can only create new archives, and another key that can list and delete old ones, and want to use them from different machines, what's the best way to do that?
I don't want an attacker who gains access to the machine I'm backing up to be able to delete old backups, but I don't want to keep old backups indefinitely, so my plan is to delete old backups from a different machine.
I'm guessing the best plan is to use rsync to keep the cache folders in sync on the two machines, but do they need to be synced in both directions, or is it enough to copy from the machine which creates archives to the one which deletes them?
If it needs to go both ways then I guess I also need to put some kind of semaphore in place to make sure only one machine is using tarsnap at a time.