The Fifth Amendment in the Digital Age (ZDNet - Identity Matters Blog)
Basically, if the password is a physical thing she has, than the Fifth Amendment does not protect it. But if the password is deemed to be something the defendant knows, it is protected.As the post points out, biometric technologies complicate this further.
To illustrate the principle, the Supreme Court has previously explained that a witness might be “forced to surrender a key to a strongbox containing incriminating documents,” but not “compelled to reveal the combination to a wall safe.”
The Fifth Amendment guaranty that "No person shall... be compelled in any criminal case to be a witness against himself," applies (outside the military) to those who have already been indicted by a grand jury, are standing trial, and are being asked to assist in their prosecution. The example above doesn't seem to prevent the police from hiring a locksmith to open the wall safe; it merely prevents the police from compelling the accused to help them.
The Fourth Amendment is much more relevant to privacy in the ordinary sense.
The Fourth Amendment guarantees that:
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
"Warrantless mobile device searches" (Google search) are a much hotter digital age privacy issue and it's the Fourth Amendment that seems to apply to those searches, though not necessarily to this case as I'm pretty sure they have a warrant for the laptop.
UPDATE: The attorney for the defense, having lost on the Fifth Amendment is appealing the Fifth Amendment ruling and seeking refuge in the Fourth Amendment.
Woman who pleaded Fifth in password case now citing Fourth
He said the Fourth Amendment is a better argument “for us and for the public in general.”
Fricosu’s case drew interest from civil rights groups who argued that current law needs to evolve to meet the nuances of the digital age. The prosecution, however, argued that hiding behind a password and encrypted data would make prosecution impossible in the future.
Dubois says the Fourth Amendment argument ties into the Fifth Amendment, which is also “about due process of law and fundamental fairness. ”
The court rejected the Fifth Amendment argument that focused on the password, an identity management technology, saying that the password is more akin to a physical key than a safe's combination (see above). The defense appeal of this judgement keeps the identity management issues in this case alive. The Fourth Amendment question seems to focus on the contents of the laptop and not access to them.
Still, it seems like this case has a long way to run.