This will be interesting to watch: A judge in Colorado has issued a court order for a defendant to decrypt her laptop hard drive so police can search for evidence which would likely be used against her. The tech website CNET.com has this bit:
Much of the discussion has been about what analogy comes closest. Prosecutors tend to view PGP passphrases as akin to someone possessing a key to a safe filled with incriminating documents. That person can, in general, be legally compelled to hand over the key. Other examples include the U.S. Supreme Court saying that defendants can be forced to provide fingerprints, blood samples, or voice recordings.
On the other hand are civil libertarians citing other Supreme Court cases that conclude Americans can't be forced to give "compelled testimonial communications" and extending the legal shield of the Fifth Amendment to encryption passphrases. Courts already have ruled that that such protection extends to the contents of a defendant's minds, the argument goes, so why shouldn't a passphrase be shielded as well?
I have a feeling this fight is going to last a while in the courts. In fact I wouldn't be surprised if it makes it to the US Supreme Court.