Democracy Dies in Darkness

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How the Supreme Court could keep police from using your cellphone to spy on you

By Bruce Schneier

November 27, 2017 at 6:00 AM

The Supreme Court will consider whether police must have a warrant to track your movements by using cellphone records. (AP Photo)

The cellphones we carry with us constantly are the most perfect surveillance device ever invented, and our laws haven’t caught up to that reality. That might change soon.

This week, the Supreme Court will hear a case with profound implications on your security and privacy in the coming years. The Fourth Amendment’s prohibition of unlawful search and seizure is a vital right that protects us all from police overreach, and the way the courts interpret it is increasingly nonsensical in our computerized and networked world. The Supreme Court can either update current law to reflect the world, or it can further solidify an unnecessary and dangerous police power.

The case centers on cellphone location data and whether the police need a warrant to get it, or if they can use a simple subpoena, which is easier to obtain. Current Fourth Amendment doctrine holds that you lose all privacy protections over any data you willingly share with a third party. Your cellular provider, under this interpretation, is a third party with whom you’ve willingly shared your movements, 24 hours a day, going back months — even though you don’t really have any choice about whether to share with them. So police can request records of where you’ve been from cell carriers without any judicial oversight. The case before the court, Carpenter v. United States, could change that.

Traditionally, information that was most precious to us was physically close to us. It was on our bodies, in our homes and offices, in our cars. Because of that, the courts gave that information extra protections. Information that we stored far away from us, or gave to other people, afforded fewer protections. Police searches have been governed by the “third-party doctrine,” which explicitly says that information we share with others is not considered private.

Related: [How to keep your private conversations private for real]

The Internet has turned that thinking upside-down. Our cellphones know who we talk to and, if we’re talking via text or email, what we say. They track our location constantly, so they know where we live and work. Because they’re the first and last thing we check every day, they know when we go to sleep and when we wake up. Because everyone has one, they know whom we sleep with. And because of how those phones work, all that information is naturally shared with third parties.

More generally, all our data is literally stored on computers belonging to other people. It’s our email, text messages, photos, Google docs, and more — all in the cloud. We store it there not because it’s unimportant, but precisely because it is important. And as the Internet of Things computerizes the rest our lives, even more data will be collected by other people: data from our health trackers and medical devices, data from our home sensors and appliances, data from Internet-connected “listeners” like Alexa, Siri and your voice-activated television.

All this data will be collected and saved by third parties, sometimes for years. The result is a detailed dossier of your activities more complete than any private investigator — or police officer — could possibly collect by following you around.

The issue here is not whether the police should be allowed to use that data to help solve crimes. Of course they should. The issue is whether that information should be protected by the warrant process that requires the police to have probable cause to investigate you and get approval by a court.

Related: [Your iPhone just got less secure. Blame the FBI.]

Warrants are a security mechanism. They prevent the police from abusing their authority to investigate someone they have no reason to suspect of a crime. They prevent the police from going on “fishing expeditions.” They protect our rights and liberties, even as we willingly give up our privacy to the legitimate needs of law enforcement.

The third-party doctrine never made a lot of sense. Just because I share an intimate secret with my spouse, friend or doctor doesn’t mean that I no longer consider it private. It makes even less sense in today’s hyper-connected world. It’s long past time the Supreme Court recognized that a months’-long history of my movements is private, and my emails and other personal data deserve the same protections, whether they’re on my laptop or on Google’s servers.

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Bruce Schneier is a security technologist and a lecturer at the Kennedy School of Government at Harvard University. His latest book is "Data and Goliath: The Hidden Battles to Collect Your Data and Control Your World."

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