Researchers from the Karlsruhe Institute of Technology (KIT) have warned about a new kind of surveillance technology that can turn WiFi routers into invisible tracking tools capable of identifying people even if they are not carrying a smartphone or any connected device.
“This technology turns every router into a potential means for surveillance,” Julian Todt, one of the authors of the study, warned. “If you regularly pass by a café that operates a WiFi network, you could be identified there without noticing it and be recognized later – for example by public authorities or companies.”
How does the attack work?
The researchers explained that the attack, called BFId, uses Beamforming Feedback Information (BFI), a feature introduced in WiFi 5 to help routers receive feedback signals from connected devices.
However, since these feedback signals are continuously transmitted in an unencrypted format, any standard WiFi device within range can passively record them.
Researchers say these signals can then be analysed using machine learning models to create “radio images” of people moving within the network’s range. They warn that these radio-based patterns are detailed enough to identify individuals based on how their bodies affect surrounding WiFi signals.
“By observing the propagation of radio waves, we can create an image of the surroundings and of persons who are present,” Thorsten Strufe explained. “This works similar to a normal camera, the difference being that in our case, radio waves instead of light waves are used for the recognition.”
As part of the study, the researchers tested the technology on 197 participants and claimed that it was able to infer the identity of individuals with 99.5% accuracy, regardless of viewing angle or walking style.
However, in order to actually link identified people with their real world identity, the attackers would still need some additional data. The attacker could potentially combine the WiFi-based tracking data with previously collected device or smartphone information in order to find the name and other details of the tracked person.
The researchers also warned that simply turning off your smartphone may not protect you from being tracked. As long as the WiFi devices in the surrounding are communicating with the network, the radio waves will continue to map the environment and bounce off anyone who walks into the room.
The paper warns that the biggest danger lies in how invisible this type of surveillance could become. Unlike CCTV cameras or facial-recognition systems, which are easy to spot, WiFi networks are already deeply embedded in homes, offices, cafés, airports and public spaces.
The researchers say this could eventually create what they describe as a “nearly comprehensive surveillance infrastructure” operating quietly in the background without raising suspicion.
They say that this technology has a potential for mass abuse by authoritarian regimes. Strufe noted that this makes the technology particularly critical for dissidents or protesters who intentionally leave their smart devices at home to avoid digital tracking.
The researchers are now calling for protective measures and privacy safeguards to be included in the EEE 802.11bf WiFi standard.
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