@LizardSF @hu_logic @dyslexxicon @rodhilton until not so long ago, the master key for the mainframe crypto cards had to be kept in three 3,5 floppy disks, handled by three different people (who should not know each other) in different safes.
Then, to recover the key they should come one by one to insert they floppy in an old thinkpad running OS/2. That thinkpad should be placed in a safe room with the keys stored in a safe protected by armed guards.