Researchers eavesdrop on smartphone finger taps

have been experimenting with a novel way to eavesdrop on what you’re typing on your smartphone: They listen to the interaction between your fingers and the screen.

In a paper called Hearing your touch: A new acoustic side channel on smartphones, academics at the University of Cambridge claim to

The first acoustic side channel attack that recovers what users type on the virtual keyboard of their touch-screen smartphone or tablet.

In tests, they showed moderate success guessing what users entered into the software-based keyboard devices.

According to the researchers’ paper, when users tap out numbers and letters on a smartphone’s virtual keyboard, it generates a sound wave that travels both on the surface of the screen and in the air. The location of the user’s finger on the screen distorts the wave, and the microphone on the mobile device picks up this distortion, enabling an algorithm to “hear” what the user typed.

To make it work, the researchers use machine learning (a form of artificial intelligence) to train their algorithm using around 21 hours of audio recordings of finger taps.

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