Picture this scene: A hacker takes a seat in a crowded cafe, latte in hand, and casually pulls out her laptop. With a discreet sideways glance, she eyes her target at the table next to her, blithely tapping away on a tablet. He’s not on Wi-Fi—but that doesn’t matter. Her laptop is equipped with special equipment to detect the electromagnetic disturbances emanating from the tablet screen itself. She carefully shifts her laptop on the table, it picks up and processes the signal and—voilà!—his tablet screen comes into view on hers, its images plucked out of the air.
This isn’t just spy movie gadget magic: In recent years, researchers have demonstrated this exploit, successfully decoding the leaked signals to recover an on-screen image. In a new paper, Hayashi highlights this security threat and how electronics manufacturers can take steps to secure our screens.
This hack is possible because the internals of every computing device we own give off electromagnetic radiation. It leaks from the cables and circuitry that carry the display signal from the processor to the screen, and it’s even emitted by the screen pixels themselves. These cables and circuitry become accidental antennas that transmit the display signal into our surroundings—one that a would-be hacker could tune in to.
The reproduced image isn’t always perfect and works best with mostly static images and high-contrast changes. But that’s good enough to take advantage of mobile devices, whose onscreen keys light up when they’re touched, making it possible to capture passwords and other sensitive input. The author notes that as receiver technology gets better and cheaper, the threat to our screens will only grow.
To combat these attacks, users can take some measures to shield their devices: For example, placing a see-through conductive film over the display can reduce screen leakage. But the author also says that manufacturers, which so far have been focused on protecting our data, must now also consider how to design devices with secure screens. Possible countermeasures include passive solutions like internal shielding and ensuring that components don’t act like antennas. But they may also extend to active solutions like embedding a piece of circuitry to scramble the signal. (Radio Science, doi:10.1002/2016RS006034, 2016)
—Mark Zastrow, Freelance Writer