Roger Schlafly sez: + [quotes from] + DOE v. United States, 487 U.S. 201; 108 S. Ct. 2341 (1988) + ... + I conclude that in a criminal case, all of the supreme court + justices agree that a criminal defendant cannot be forced to + reveal the combination to a wall safe, or any other information in + his mind, by the Fifth Amendment. Except that the Fifth Amendment is not limited to "criminal cases" in the way one might ordinarily understand that phrase. One may assert the Fifth Amendment in a civil case, in an administrative proceeding, at a legislative hearing, or, indeed, in the absence of any formal proceeding. See _Kastigar_. (I posted a summary of Doe II just the other day. Did it not reach the list?) Also, "any other information" is a little too broad. You can be forced to reveal "pedigree" information such as name and DOB. See _Penna. v. Muniz_ (1990). Asking an apparently drunk driver the date of his sixth birthday (as part of a DWI test) is, however, an effort to elicit Fifth Amendment "testimony"; given the added factors of potential incrimination and compulsion (implicit in custodial interrogation sans Miranda warnings), the privilege may be validly exercised in response to such a question. See ibid. The much more interesting question, from a legal perspective, is what happens if your key/password/passphrase is written/stored on physical media.