SENS is envisioned as a way for devices capable of sending and receiving wireless data to use Wi-Fi signal interference differences to measure the range, velocity, direction, motion, presence, and proximity of people and objects.
It may come as no surprise that the security and privacy considerations of Wi-Fi-based sensing have not received much attention. As Restuccia warns in his paper, "As yet, research and development efforts have been focused on improving the classification accuracy of the phenomena being monitored, with little regard to S&P [security and privacy] issues. While this could be acceptable from a research perspective, we point out that to allow widespread adoption of 802.11bf, ordinary people need to trust its underlying technologies. Therefore, S&P guarantees must be provided to the end users."
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Networking researchers have known for years that Wi-Fi signals can be used for gathering data about nearby people and objects. But to date, such efforts, like trying to capture gesture input via Wi-Fi, have been the province of research projects.Since 2020, however, the IEEE 802.11bf Task Group has been meeting and exchanging notes about how to modify the IEEE 802.11 standards at both the Medium Access Control (MAC) and Physical Layer (PHY) to support Wi-Fi sensing across existing systems, including 802.11ad, 802.11ay, 802.11n, 802.11ac, 802.11ax and 802.11be.
Restuccia argues the IEEE's standardization effort, in conjunction with the many SENS systems that are apparently being developed, "will create the 'perfect storm' for the introduction into the market of groundbreaking applications that we cannot even imagine today."
We can, however, imagine some of the potential harms."Indeed, it has been shown that SENS-based classifiers can infer privacy-critical information such as keyboard typing, gesture recognition and activity tracking," Restuccia explains. "Given the broadcast nature of the wireless channel, a malicious eavesdropper could easily 'listen' to CSI [Channel State Information] reports and track the user’s activity without authorization."
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And worse still, he argues, such tracking can be done surreptitiously because Wi-Fi signals can penetrate walls, don't require light, and don't offer any visible indicator of their presence.
Restuccia suggests there needs to be a way to opt-out of SENS-based surveillance; a more privacy-friendly stance would be to opt-in, but there's not much precedent for seeking permission in the technology industry.
There's still much work to be done to resolve interference issues, some of which may arise as a result of having to share the spectrum with other wireless technologies, and to figure out the optimal tradeoff in terms of allocating spectrum to SENS versus having SENS piggyback on existing data packets.
With any luck, the security and privacy risks will get additional attention too. ®