Restoring `System.keychain` from a Time Machine backup without access to system `/var/db/SystemKey` I have an old backup that (hopefully) holds the encryption keys to some encrypted disks in the System.keychain. To unlock that properly, I seem to need the /var/db/SystemKey that does not seem to be present in the backup.
I've been searcing around and can't seem to find any solutions that don't need the SystemKey file (which makes sense if it is the encryption key), but since that computer has since been wiped and given on, I can't imagine any way of restoring it (though if it can somehow be deterministically created on the specific computer, I could ask the new user to create the key if I knew how)
If I can't recover the SystemKey, what other options are there? Are the keys in my System.keychain gone for good?
Yes, unfortunately for all practical purposes the keys are gone for good.
You need the SystemKey file corresponding to that System.keychain in order to restore anything from it. If you haven't got a backup, you'll have to resort to bruteforcing the contents of the SystemKey file - which is not practically possible.