  Wireless radio channels are known to contain information about the
surrounding propagation environment, which can be extracted using established
wireless sensing methods. Thus, today's ubiquitous wireless devices are
attractive targets for passive eavesdroppers to launch reconnaissance attacks.
In particular, by overhearing standard communication signals, eavesdroppers
obtain estimations of wireless channels which can give away sensitive
information about indoor environments. For instance, by applying simple
statistical methods, adversaries can infer human motion from wireless channel
observations, allowing to remotely monitor premises of victims. In this work,
building on the advent of intelligent reflecting surfaces (IRSs), we propose
IRShield as a novel countermeasure against adversarial wireless sensing.
IRShield is designed as a plug-and-play privacy-preserving extension to
existing wireless networks. At the core of IRShield, we design an IRS
configuration algorithm to obfuscate wireless channels. We validate the
effectiveness with extensive experimental evaluations. In a state-of-the-art
human motion detection attack using off-the-shelf Wi-Fi devices, IRShield
lowered detection rates to 5% or less.
