Well there are plenty of safes without physical keys that use pin-pads. To to bring that analogy a little closer to reality then, they are trying to force him t

Well there are plenty of safes without physical keys that use pin-pads. To to bring that analogy a little closer to reality then, they are trying to force him to enter the pin into the safe. And again the current argument is not about whether he knows the pin or not, just whether he can refuse to enter it by arguing that this would be "being witness against himself", i.e. protected by the fifth.