In a court case currently going on here in the United States including a Colorado woman who's hard drive may well include incriminating evidence against her, it's been ruled that her encrypted password on said hard drive must be bypassed by her, and is not protected under the Fifth Amendment. Before this case, a distinction had been drawn in cases which included such situations, the difference being clear between forcing a person to reveal their password and forcing a defendant to decrypt encrypted data without revealing their password. Revealing the password has up until now been ruled as forcing the defendant to reveal the contents of their mind, this bringing up some Fifth Amendment issues - that's no longer the case according to Judge Robert Blackburn.
What Blackburn is saying here is that forcing a defendant to decrypt a laptop so its contents can be inspected is essentially the same as producing any other bit of evidence. If a law enforcement agent has a warrant, they can force you to open up your trunk, your home, and of course your person - and now your hard drive as well. In this particular case, the defendant was also recorded speaking about how she owned the laptop and that it contained incriminating evidence, so that's not doing her any favors either.
So know this, folks who do things so illegal they'll certainly be caught eventually: your hard drive passwords will not save you. Should you get in trouble with the cops for digital crimes, you've got only one course of action available to you: trash it all. Smash your computer into little bits and destroy everything. But then there's another factor in play: willful destruction of evidence. Instead just play it safe and don't do anything illegal ever - sound good?