You may want to read up on U.S. v Boucher, 2009.
Unless you're hiding evidence of something particularly heinous, refusing to provide a means of decryption may land you in more trouble than the crime of which you're suspected.
Unless you're hiding evidence of something particularly heinous, refusing to provide a means of decryption may land you in more trouble than the crime of which you're suspected.
Either way, the Constitution is clear on this issue: "no person ... shall be compelled in any criminal case to be a witness against himself". If a safe is found in your house, the government can do whatever they want to open it. They can blow it up, or they can ask your friends for the combination, or even just try every combination. But they can't punish you for not giving them the combination.
Cryptography is a very strong safe.
(A quick reading of related cases leads me to believe that this one is more relevant: http://supreme.justia.com/us/487/201/case.html. It holds that "In order to be "testimonial," an accused's oral or written communication, or act, must itself, explicitly or implicitly, relate a factual assertion or disclose information." Since reveling the decryption key is a factual assertion and discloses information, it is protected. Note that in Boucher, it is not clear that the key would disclose information.
But honestly, I think my Google skills are just better than the Appeals court in that case. I doubt that the decision would hold up in the Supreme court. And I especially doubt that one could be compelled to give up his or her key in normal, non-customs, criminal proceedings. IANAL.)
Yes, they can. If the judge has reasonable grounds to believe that you are withholding evidence or the knowledge necessary for law enforcement to collect this evidence then the judge can hold you in contempt of court and place you in jail until you agree to provide the information. While there have been a couple of aberrations in the general flow of case law to a standard consensus on the matter, the general consensus (at least at the federal level) is that being compelled to provide an encryption key is not covered by the 5th amendment's protection against self-incrimination.
Anyway, that doesn't really change the basic fact — if law enforcement has a warrant for information that's locked away, a defendant can be compelled to provide the information.
(And I'm not asking to be snarky. I need more information before I decide to run for public office and change the law :)
That page has a link to the District Court ruling in Boucher.
That's a little different than "we think you might possibly have something on this computer", which is still untested.
Also, they appealed. Considering child porn gets you more time than homicide these days, I would wait until the case if over before deciding that encrypting your hard drive is a waste.
You can always decrypt, you can't always encrypt.
The fifth amendment applies to words you say, not evidence. The "pass phrase" is access to the evidence, not testimony against yourself. It's a losing battle anyways, a judge demands you turn over the passphrase or unlock the data and throws you in jail until you do. You could attempt to take it to the supreme court or something, but you're in jail during that process. Likewise, you could try to give them the wrong key with truecrypt or something but that assumes that they are idiots. If you find yourself in court in this situation, you've already lost, you're almost certainly going to spend time in jail.
Either way, if you are paranoid, the solution is hidden volumes. If the government can't prove you have an encrypted disk, they can't compel you to reveal its contents.