Therein is the current question. This is not a box. It is a metaphorical box, that can only be opened by information. This information is only contained in the head of the defendant. Say there is something incriminating in the box. The 5th amendment protects you from being compelled to self incriminate. So, the court could not legally order the box opened, without providing immunity to the defendant.

Your reasoning and my reasoning are the current modes of thought about encryption in a legal context. Neither has been proved correct in that context.