The eleventh circuit court has ruled that defendants cannot be forced to decrypt the contents of their hard drives, as this is in violation of the 5th amendment.

First, the decryption and production of the hard drives would require the use of the contents of Doe’s mind and could not be fairly characterized as a physical act that would be nontestimonial in nature. We conclude that the decryption and production would be tantamount to testimony by Doe of his knowledge of the existence and location of potentially incriminating files; of his possession, control, and access to the encrypted portions of the drives; and of his capability to decrypt the files.
http://volokh.com/2012/02/23/elevent...pted-computer/

Very cool.