Schneier on Security

Cell Phone Kill Switches Mandatory in California

California passed a kill-switch law, meaning that all cell phones sold in California must have the capability to be remotely turned off. It was sold as an antitheft measure. If the phone company could remotely render a cell phone inoperative, there would be less incentive to steal one.

I worry more about the side effects: once the feature is in place, it can be used by all sorts of people for all sorts of reasons.

The law raises concerns about how the switch might be used or abused, because it also provides law enforcement with the authority to use the feature to kill phones. And any feature accessible to consumers and law enforcement could be accessible to hackers, who might use it to randomly kill phones for kicks or revenge, or to perpetrators of crimes who might—depending on how the kill switch is implemented—be able to use it to prevent someone from calling for help.

“It’s great for the consumer, but it invites a lot of mischief,” says Hanni Fakhoury, staff attorney for the Electronic Frontier Foundation, which opposes the law. “You can imagine a domestic violence situation or a stalking context where someone kills [a victim’s] phone and prevents them from calling the police or reporting abuse. It will not be a surprise when you see it being used this way.”

I wrote about this in 2008, more generally:

The possibilities are endless, and very dangerous. Making this work involves building a nearly flawless hierarchical system of authority. That’s a difficult security problem even in its simplest form. Distributing that system among a variety of different devices—computers, phones, PDAs, cameras, recorders—with different firmware and manufacturers, is even more difficult. Not to mention delegating different levels of authority to various agencies, enterprises, industries and individuals, and then enforcing the necessary safeguards.

Once we go down this path—giving one device authority over other devices—the security problems start piling up. Who has the authority to limit functionality of my devices, and how do they get that authority? What prevents them from abusing that power? Do I get the ability to override their limitations? In what circumstances, and how? Can they override my override?

The law only affects California, but phone manufacturers won’t sell two different phones. So this means that all cell phones will eventually have this capability. And, of course, the procedural controls and limitations written into the California law don’t apply elsewhere

EDITED TO ADD (9/12): Users can opt out, at least for now: “The bill would authorize an authorized user to affirmatively elect to
disable or opt-out of the technological solution at any time.”

How the bill can be used to disrupt protests.

Posted on August 29, 2014 at 12:31 PM • View Comments