Proper encryption isn't vulnerable to moles.
Somewhere at least one someone has access (key to the ark of the covenant). So somewhere a vulnerability exists. And moles exploit that.
Like I said, in a locked safe, on an air-gapped flash drive
At that point if you still have a security problem, it's a
physical security problem. Keycard accessed doors, alarms, and good safes are generally good protection against that. Don't give the combo to the safe to the janitor and you should be ok.
