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Researchers at La Sapienza University of Rome have unveiled a groundbreaking method to track individuals using the unique "fingerprint" their bodies create when disrupting Wi-Fi signals. Dubbed WhoFi, the technique leverages subtle distortions in Wi-Fi Channel State Information (CSI)—data capturing signal amplitude and phase—to generate persistent biometric identifiers. This enables re-identification of a person as they move between different Wi-Fi networks, even without carrying a phone.

How WhoFi Works

As Wi-Fi signals propagate, they interact with physical objects, including human bodies, altering their waveform. The team’s deep neural network, built on a transformer architecture, analyzes these CSI distortions to extract person-specific patterns. Remarkably, this method operates independently of lighting conditions, penetrates walls, and avoids the privacy intrusiveness of visual surveillance.

"The core insight is that as a Wi-Fi signal propagates through an environment, its waveform is altered by the presence and physical characteristics of objects and people along its path," the researchers state in their preprint paper. "These alterations contain rich biometric information."

Implications for Privacy and Security

The technology, achieving 95.5% accuracy on the NTU-Fi dataset, surpasses earlier efforts like EyeFi (75% accuracy). While promising for applications like secure building access or elder fall detection, it also opens a Pandora’s box of surveillance risks:
- Device-Free Tracking: Individuals can be monitored without smartphones or wearables.
- Cross-Location Identification: A person observed in one Wi-Fi zone can be recognized in another.
- Stealth Operation: Functions in darkness or through obstructions where cameras fail.

The research underscores the dual-use nature of Wi-Fi Sensing—a capability formalized in the IEEE 802.11bf standard. As wireless signals evolve beyond data transmission into sensing tools, the ethical and regulatory challenges grow exponentially. While WhoFi’s creators position it as "privacy-preserving" compared to cameras, its potential for covert tracking suggests a future where anonymity in Wi-Fi-saturated environments becomes a relic of the past.

Source: The Register