ScatterShield: Defending Against Unauthorized WiFi Sensing with Backscatter Tags

The ubiquity of WiFi devices has created a significant opportunity for a wide range of applications utilizing WiFi-based wireless sensing. However, it also comes with the risk of privacy breaches, where eavesdroppers can infer users' locations as well as activities by passively receiving and analyzing WiFi signals. In this paper, we propose ScatterShield to defend against wireless sensing eavesdropping attacks with low-cost backscatter tags. The main idea of ScatterShield is to interfere with the channel state information, thereby obfuscating the privacy-related features carried by CSI. We address the challenge of effectively interfering with unauthorized WiFi sensing with weak backscattered signals. We analyze the impact of backscattered signals on WiFi sensing and propose a method for interference with the cooperation of multiple tags. We design the interference strategies for tag operating, enabling ScatterShield to defend against various attack methods while retaining normal WiFi communication. We implement ScatterShield on our backscatter tags and evaluate its performance extensively. The result shows that ScatterShield can reduce the detection rate of state-of-the-art motion detection methods by more than 60%.