Can your mouse eavesdrop on you?

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The optical sensors in computer mice can be used for eavesdropping. We break down why this is fascinating — but still a long way from real-world practicality.
 
A recent publication by researchers at the University of California, Irvine, demonstrates a fascinating fact: optical sensors in computer mice have become so sensitive that, in addition to tracking surface movements, they can pick up even minute vibrations — for instance, those generated by a nearby conversation. The theoretical attack, dubbed “Mic-E-Mouse”, could potentially allow adversaries to listen in on discussions in “secure” rooms, provided the attacker can somehow intercept the data transmitted by the mouse. As is often the case with academic papers of this kind, the proposed method comes with quite a few limitations.

Specifics of the Mic-E-Mouse attack

Let’s be clear from the start — not just any old mouse will work for this attack. It specifically requires models with the most sensitive optical sensors. Such a sensor is essentially an extremely simplified video camera that films the surface of the desk at a resolution of 16×16 or 32×32 pixels. The mouse’s internal circuitry compares consecutive frames to determine how far and in which direction the mouse has moved. How often these snapshots are taken determines the mouse’s final resolution, expressed in dots per inch (DPI). The higher the DPI, the less the user has to move the mouse to position the cursor on the screen. There’s also a second metric: the polling rate — the frequency at which the mouse data is transmitted to the computer. A sensitive sensor in a mouse that transmits data infrequently is of no use. For the Mic-E-Mouse attack to even be feasible, the mouse needs both a high resolution (10 000DPI or more) and a high polling rate (4000Hz or more).

Why do these particular specifications matter? Human speech, which the researchers intended to eavesdrop on, is audible in a frequency range of approximately 100 to 6000Hz. Speech causes sound waves, which create vibrations on the surfaces of nearby objects. Capturing these vibrations requires an extremely precise sensor, and the data coming from it must be transmitted to the PC in the most complete form possible — with the data update frequency being most critical. According to the Nyquist–Shannon sampling theorem, an analog signal within a specific frequency range can be digitized if the sampling rate is at least twice the highest frequency of the signal. Consequently, a mouse transmitting data at 4000Hz can theoretically capture an audio frequency range up to a maximum of 2000Hz. But what kind of recording can a mouse capture anyway? Let’s take a look.

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