"Riana Pfefferkorn, a cryptography fellow at the Stanford Center for Internet and Society, said that she's not sure there would be a good legal defense to a judicial order such as this one.
"I don't find this warrant legally problematic under the Fifth Amendment, but it does serve as a wake-up call to folks who may not have been aware of the important legal consequences that hang on which option they pick to protect their phones," she e-mailed. "To be sure, it's troubling to think that the police could end up using against you a choice you made for the sake of convenience and to make it harder for someone to snoop into your phone without your knowledge. But I don't think it runs counter to the Fifth Amendment."
However, Pfefferkorn added that while she doesn’t currently own a smartphone with Touch ID, she didn’t enable it on her previous phone "for precisely this reason: the legal protection against being compelled to unlock your phone is lesser with fingerprint-unlocking than with entering a passphrase. (Not that I expect to get arrested!)""