Nikolay Valentinovich Repnitskiy built a covert unidirectional network using two Dell SK-8115 keyboards. He stripped both down to their controller PCBs, soldered photoresistors onto the matrix pins of one, and aligned them with the Num Lock and Caps Lock LEDs of the other. One PC flashes its keyboard LEDs in a controlled pattern, triggering keypresses on the target machine without any conventional network connection.
The attack vector is narrow but real. The receiving machine registers light pulses as keystrokes, allowing an attacker to type arbitrary data onto an airgapped system, including executable code. Repnitskiy demonstrates this by delivering a small bootstrap program that, once running, makes subsequent data exfiltration substantially easier. The full project is documented on GitHub under the name 'unidirectional-network'.
Hackaday covered an earlier iteration of this technique in March 2024. What makes the current version worth reading in full is the mechanical specificity: how the PCBs are positioned, which matrix pins are modified, and how the LED timing is structured to encode usable data. The attack surface here is not theoretical.
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