An AI system called DeepTempest can clean up images and text reconstructed from the radio waves leaking out of an HDMI cable, cutting errors by more than 60% against the previous best attack.
It builds on TempestSDR, software that works with an antenna and a HackRF radio (a general-purpose radio receiver) to pick up the electromagnetic field an HDMI cable gives off and redraw the image on another screen. In a video posted to X on November 8, a laptop rebuilds what is playing on a monitor beside it. Quality depends on shielding, distance and interference, and the raw picture is imperfect but recognizable. DeepTempest, developed by Federico Larroca at the University of the Republic in Montevideo, Uruguay, adds AI to make that output easier to read.
The two headline numbers measure different things. When the reconstructed text was run through optical character recognition (OCR), software that turns pictures of text into characters, roughly 30% of characters were wrong. The 60% figure compares that error rate with the previous state-of-the-art attack, so it describes how much better DeepTempest is, not a second error rate. A 30% miss rate sounds bad, but human readers can still follow text with that many errors.
Eavesdropping on electronic leakage is old. Tempest is an NSA codename for spying via electromagnetic leakage and for the defenses against it: distance, shielding, filtering and masking, which also cover sound and vibration, such as logging keystrokes through a phone's motion sensor. The field traces back to Second World War teleprinters whose electromagnetic spikes could be intercepted to capture text, and the shielding advice from their supplier, Bell System, still holds. In 2001, Tempest for Eliza made a monitor broadcast music to a radio. What is new here is the AI.
The practical threat looks narrow. The demo works with the target cable close enough that you could see the display yourself. A van across the street would pick up little, even from a poorly shielded cable, unless the scanner were seriously powerful.
The defensive advice is unchanged: avoid cheap cables. Pricier ones include electromagnetic shielding, a feature once sold as protecting audio and video fidelity from interference coming in. For anyone with a reason to worry about snoops, the more relevant direction is signal going out.