NDSS

Et Tu Alexa? When Commodity WiFi Devices Turn into Adversarial Motion Sensors

Yanzi Zhu (UC Santa Barbara), Zhujun Xiao (University of Chicago), Yuxin Chen (University of Chicago), Zhijing Li (UC Santa Barbara), Max Liu (University of Chicago), Ben Y. Zhao (University of Chicago), Heather Zheng (University of Chicago)

Wireless devices are everywhere, constantly bombarding us with transmissions across a wide range of RF frequencies. Many of these invisible transmissions reflect off our bodies, carrying off information about our location, movement, and other physiological properties. While a boon to professionals with carefully calibrated instruments, they may also be revealing our physical
status to potential attackers nearby.

Our work demonstrates a new set of silent reconnaissance attacks that leverages the presence of commodity WiFi devices to track users inside private homes and offices, without compromising any WiFi network, data packets, or devices. We show that just by sniffing existing WiFi signals, an
adversary can accurately detect and track movements of users inside a building. This is made possible by our new signal model that links together human motion near WiFi transmitters and variance of multipath signal propagation seen by the attacker sniffer outside of the property.
These attacks are cheap, highly effective, and difficult to detect. We implement
the attack using a single commodity smartphone, and deploy it in 11 real-world offices and residential apartments, and show it is highly effective. Finally, we evaluate potential defenses, and
propose a practical and effective defense based on AP signal obfuscation.