[kevkrom]

The idea here is that these files can’t be accessed even with a warrant.

Yes, they can be accessed with a warrant... unless the target refuses to cooperate with the warrant, which puts him in legal jeopardy anyway. As far as I know, you can't claim the 5th on documents covered by a warrant.

[Sherman Logan]

Here’s an interesting discussion of whether you can be compelled to provide a password.

http://boards.straightdope.com/sdmb/showthread.php?t=580986

From a practical perspective, all they can do is imprison you, I presume for contempt of court, until you do give up the password. If doing so would provide evidence sufficient to convict you of a really serious crime, possibly a capital one, I find it difficult to see what incentive the accused would have to do so, regardless of what a court may order.