SenShield: Preserving User Privacy Against Passive WiFi Sensing

在过去的十年中，研究人员已经证明，WiFi信号可以用于从人体运动到情感的各种传感应用。最近，无设备WiFi传感已经获得了牵引力，因为它不需要目标携带设备。虽然没有设备，但这些解决方案在分米级跟踪用户的移动和轨迹以及识别他们的活动（例如，跑步、走路）和精细的手势（嘴唇、手指）。事实上，考虑到我们周围有大量支持WiFi的设备，WiFi传感是完成此类任务的一种方便方法。从技术角度来看，WiFi传感归结为提取人体运动对信号传播的影响，这在概念上类似于双基地雷达。最近，一些初创公司（例如，Totemic，Emerald）冒险进入这一领域，将他们的产品定位为非侵入性和隐私保护的健康监测设备，而不是视频和身体传感器。然而，该技术的成熟性、实用性以及WiFi设备的丰富性对用户隐私构成了重大风险。在最简单的形式中，窃贼可以根据居住者的数量甚至居住者的健康状况，通过监测他们的移动速度或心跳来识别空房子或对其进行分析。更重要的隐私风险是，与雷达不同，对手可以被动地利用WiFi传感技术（即，而不发射任何信号），因此未被检测到。此外，WiFi设备制造商和政府机构可能会通过不引人注意的固件操作进行大规模监控。不幸的是，即使存在这样的风险，我们也不能拒绝使用WiFi设备，因为它们已经是我们家庭和工作生活中不可或缺的一部分。虽然WiFi传感在概念上类似于雷达，但我们不能利用传统的雷达干扰技术，因为它们会干扰WiFi上的合法通信。在SenShield中，我们设计了基本的解决方案，以最大限度地减少最近出现的WiFi传感技术所带来的担忧。更具体地说，我们的目标是挫败被动WiFi传感的可能性，其中对手不发送任何信号，并试图通过窃听正在进行的合法WiFi通信来获得所有必要的信息。

Within the past decade, researchers have shown that WiFi signals can be used for a variety of sensing applications ranging from human motions to emotions. Lately, device-free WiFi sensing has gained traction since it does not require the target to carry a device. Although device-free, these solutions proved highly accurate in tracking movement and trajectory of the users on decimeter-level as well as recognizing their activities (e.g., running, walking) and fine- grained gestures (lips, fingers). Indeed, WiFi sensing is a convenient method for such tasks, given the abundance of WiFi- enabled devices around us. From a technical point of view, WiFi sensing boils down to extracting the impact of human body motion on the signal propagation, which is conceptually similar to bistatic radar. Recently, a few startups (e.g., Totemic, Emerald) ventured into this area, branding their products as non-invasive and privacy-preserving health monitoring devices, as opposed to video and on-body sensors. However, the maturity of the technology, its practicality, and the abundance of WiFi devices pose significant risks to user privacy. In its simplest form, a burglar can identify empty houses or profile them based on the number of occupants and even the health of the occupants through monitoring their moving speed or heartbeat. The more significant privacy risk is that, unlike radars, the adversary can leverage WiFi sensing techniques passively (i.e., without transmitting any signal), hence going undetected. Furthermore, WiFi device manufacturers and government agencies can potentially conduct mass surveillance with unnoticeable firmware manipulation. Unfortunately, even in the presence of such risks, we cannot defy the use of WiFi devices since they are already an integral part of our lives at home and work. Although WiFi sensing is conceptually similar to radar, we cannot leverage classic radar jamming techniques because they interfere with legitimate communication over WiFi. In SenShield, we devise fundamental solutions to minimize the concerns raised by the recent advent of WiFi sensing techniques. More specifically, we aim at thwarting passive WiFi sensing possibilities where the adversary does not transmit any signal and tries to obtain all necessary information via eavesdropping on ongoing legitimate WiFi communication.