When Edward Snowden met with reporters in a Hong Kong hotel room to spill the NSA’s secrets, he famously asked them to put their phones in the refrigerator to block any radio signals that might be used to silently activate the devices’ microphones or cameras. So it’s fitting that a little over three years later, he has returned to that same smartphone radio surveillance problem.

Edward Snowden iPhone Case
Image credit: Pub Pub

Mr. Snowden co-designed the device with Andrew “Bunnie“ Huang, a well-known hardware hacker who holds a PhD in electrical engineering from MIT. Together, the pair presented the mockup of the iPhone case via video link during an event at MIT’s Media Lab in Cambridge, Massachusetts, earlier this year.

The primary reason behind the case-like device, according to Snowden and Huang, is to constantly check whether your smartphone’s radio is actively transmitting. According to the designers, this is an infinitely more trustworthy method of knowing a phone’s radios are off compared to using “airplane mode,” which has been shown to be both hacked and spoofed in the past.

Edward Snowden’s iPhone case alerts users when the phone’s radios are broadcasting

Snowden and Huang hope to create a device which offers strong privacy guarantees to smartphone owners who have a need to shield their devices from government-funded adversaries with advanced hacking and surveillance capabilities. An example of someone who might find use in the device would be a reporter trying to carry their devices into hostile foreign countries without constantly revealing their location.

“Unfortunately, journalists can be betrayed by their own tools. Their smartphones, and essential tool for communicating with sources and the outside world – as well as for taking photos and authoring articles – are also the perfect tracking device,” Huang and Snowden mentioned in a paper released in concomitance with the presentation.

“One good journalist in the right place at the right time can change history,” Edward Snowden told the MIT Media Lab during the presentation. “This makes them a target, and increasingly tools of their trade are being used against them.”

“They’re overseas, in Syria or Iraq, and those [governments] have exploits that cause their phones to do things they don’t expect them to do,” Huang said. “You can think your phone’s radios are off, and not telling your location to anyone, but actually still be at risk.”

Edward Snowden iPhone Case
Image credit: Pub Pub

The security device looks little more than a battery case for an iPhone

The initial mockup of the device, which the creators call an “introspection engine,” looks and functions like a battery case with an added display showing whether the device is not transmitting, or “dark,” or if it in fact is transmitting.

Additionally, the device would also feature an audible alarm that be set to trip in case any activity is seen on any set of radios. Edward Snowden and Huang are considering adding a “kill switch” option that would forcibly disconnect power to the phone in the case that a radio is found to be errantly transmitting.

“Our approach is: state-level adversaries are powerful, assume the phone is compromised,” said Huang. “Let’s look at hardware-related signals that are extremely difficult to fake. We want to give a you-bet-your-life assurance that the phone actually has its radios off when it says it does.”

Snowden hopes device will see worldwide supply chain eventually

The iPhone modification, at this point, is little more than a design. While the designers have tested their method of picking up the electrical signals sent to an iPhone 6’s antennae to verify that they can spot its different radio messages, they have yet to build a prototype, not to mention a product.

However, the pair released a detailed paper explaining their technique, and said that they hope to develop a prototype over the next year and eventually create a supply chain in China of modified iPhones to offer journalists and newsrooms.

The head off any potential mistrust of their Chinese manufacturers, Huang said that the device’s code and hardware design will both be fully open-source.