# A Survey on Secure WiFi Sensing Technology: Attacks and Defenses
## 1 Introduction  
Over the decades, IoT-related technologies have gone through rapid development [1, 2, 3, 4, 5, 6, 7, 8, 9], and the physical world and the information world are now tightly connected. In particular, wireless sensing, one of the key enabling technologies of IoT, revolutionizes the traditional sensing paradigm with the advantages of its non-intrusiveness, ubiquity, and ease of deployment with wireless sensors and signals [10, 11, 12, 13, 14]. This flexibility makes wireless sensing an invaluable tool in various applications, such as health monitoring [15, 16, 17], location-based services [18, 19, 20, 21], intelligent transportation [22, 23, 24], and so on [25, 26, 27]. Existing efforts in wireless sensing exploit diverse wireless signals, such as radio-frequency identification (RFID) [28, 29, 30, 31, 32], acoustic [33, 34, 35, 36, 37], WiFi [15, 16, 17, 18, 17], mmWave [39, 26, 30, 31, 32, 33, 34, 18, 35, 36, 37] signals, etc. Among these different sensing technologies, WiFi-based technologies are the most commonly used because WiFi networks are already widespread in homes, offices, and public spaces, making WiFi sensing highly accessible. Its widespread availability eliminates the need to deploy additional sensing infrastructure, significantly reducing costs. Most current WiFi-based sensing methods perform sensing tasks either by exploiting the received signal strength indicator (RSSI) to measure and analyze the power level of the received WiFi signal [44] or by using channel state information (CSI) to find fine-grained information in the amplitude and phase ofsubcarrier signals [7; 45; 46; 47]. Moreover, recent advancements in WiFi-based integrated sensing and communication (ISAC) [48; 49] have significantly enhanced the potential for future applications of WiFi sensing. These developments can enable more sophisticated and accurate sensing capabilities by combining the strengths of both WiFi-based sensing and communication technologies. However, the ease of access and ubiquity of WiFi signals and access points (APs) have raised significant security concerns and threats [50; 51; 52]. WiFi networks are pervasive in both public and private spaces, making them an attractive target for malicious attackers. The sophisticated nature of WiFi sensing technologies, which allows for detailed environmental and user data collection, exacerbates these concerns. Unlike traditional WiFi usage, which primarily focuses on data transmission, WiFi sensing can capture sensitive information such as user movements, locations, and even breathing patterns [15; 16; 17; 53]. This capability, while beneficial for legitimate applications, opens the door to various security vulnerabilities. There are two main security threats identified by existing works targeting WiFi sensing. One method is the active attack, where attackers can access WiFi networks from a distance to tamper with WiFi devices and signals, thereby manipulating the sensing results [54; 51]. Another method is the passive attack, where attackers receive and analyze WiFi signals to eavesdrop on legitimate users' private sensing results, such as tracking when a person is home and monitoring their daily routines [50; 55]. In response to these security threats, several effective countermeasures have been proposed to protect legitimate users and sensing targets. On one hand, some methods adopt active defense, where users manipulate WiFi signals to mislead attackers, causing them to obtain incorrect sensing results [56; 57]. On the other hand, some other methods perform passive defense, where a third party protects the users' sensing results or alerts users to the risk of their sensing data being leaked [58; 59]. Although it is possible to create a more secure environment for WiFi sensing by employing existing defense strategies, secure WiFi sensing still faces unique technical challenges in preserving WiFi communication links and being transparent to legitimate users.