This should be cause for serious concern. There's often no way to prove that someone knows a key or pass-phrase. If a personal computer I've used for years has

This should be cause for serious concern. There's often no way to prove that someone knows a key or pass-phrase. If a personal computer I've used for years has TrueCrypt at boot, perhaps a reasonable argument[1] could be made that I know the password. That's not true of a flash drive or an encrypted file on a shared computer. If someone plants a safe in my house, I may be held in contempt for a while while it's drilled open. Properly encrypted data might withstand attacks for a lifetime or more. [1] Best I can tell, it's possible for me to TrueCrypt encrypt your computer with only physical access. You wouldn't notice until next boot.