Declan McCullagh has an article on an important case in the US, where a federal judge has demanded a defendant decrypt a PGP-encrypted drive for the authorities. Case law in the area of decryption is unsettled, as McCullagh notes:
The question of whether a criminal defendant can be legally compelled to cough up his encryption passphrase remains an unsettled one, with law review articles for at least the last 15 years arguing the merits of either approach. (A U.S. Justice Department attorney wrote an article in 1996, for instance, titled “Compelled Production of Plaintext and Keys.”)
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?
Eventually the case law around encryption has to be addressed by SCOTUS. There are too many differing positions at the moment; clarity is needed both for users of encryption in the US, and for counsel seeking to prosecute and defence clients.