CRT monitors generate images by focusing electron beams on a phosphorescent screen, creating a pattern of light that forms the visible display. This process involves high-frequency signals radiating from the monitor, which hackers discovered they could intercept using specialized equipment. The transition to LED displays with HDMI cables made this much more difficult, as digital signals are more complex and involve higher frequencies.
A study by a team of researchers at the Universidad de la República Montevideo in Uruguay shows that using AI it is possible to overcome these obstacles and re-eavesdrop on the signals.
Santiago Fernández, Emilio Martínez, Gabriel Varela and Pablo Musé Federico Larroca published their findings on the arXiv preprint serverwhich explains how digital signals sent through a computer’s HDMI cable can be captured and decoded to display text on a computer screen.
STORM
The investigation focused on unintended electromagnetic emissions, a phenomenon known as TEMPEST, which has historically been associated with analog video signals. Previous eavesdropping methods designed for analog signals were ineffective for digital displays, resulting in unclear images.
To address this, the researchers used a deep learning approach to map the captured electromagnetic signals back to the original image. They framed the problem as an inverse problem and trained a neural network to interpret the degraded signals. This method significantly improved the average Character Error Rate when reading text from the captured signals.
In their paper, the researchers emphasize the importance of tuning the system to specific frequencies and creating training samples without the need for an actual TEMPEST setup. While it’s highly unlikely that anyone will use this method to eavesdrop on you—it’s governments and corporations that are most at risk—there are several ways you can protect yourself. These include using shielded cables, implementing physical barriers, placing your monitor away from windows, and using signal filtering techniques.