In a reply, @ErrataRob brings up (perhaps inadvertently) a really interesting question that deserves its own thread, that I need to think more about: What's the connection b/w burden to show foregone conclusion and to get punishment for contempt? A thread....
Here's the issue. The burden of proof for a foregone conclusion comes up when the subject is ordered to act and pleads the 5th. Court then rules on whether the order can be enforced. But there's a second step to this: The contempt burden.
That is, what if the court says that the order is enforceable but the subject of the order then says, "okay, well, maybe I once knew the password, but I forgot." The government moves to hold subject in contempt, which has its own burden of proof depending on the punishment.
The standard for criminal contempt is proof beyond a reasonable doubt under the constitution, but for civil contempt there is much less const protection and standards can vary. See Hicks v. Feiock, 485 U.S. 624 (1988). scholar.google.com/scholar_case?c… 
BTW, roughy speaking, criminal contempt is "we're punishing you for pretending you can't comply," and civil contempt is "we're putting you in jail until you comply, and then we'll set you free."
I need to think more about the relationship between these two steps. One answer may be that they're just independent: The govt has to show the subject knows the password by clear and convincing evidence at stage 1, and then whatever burden depending on the sanction at stage 2.
On the other hand, if the two stages come up at once, and they are asking the same basic questions but raising different burdens, maybe the issue here is more a const limit on civil contempt b/c crim contempt will still require proof BRD.
Anyway, sorry for thinking through this in real-time, rather than having a clear answer. I blame @ErrataRob, who had the poor manners to raise this after my brief was filed and not before. :)
