Section: New Results

Wi-Fi and privacy

Participants : Mathieu Cunche, Célestin Matte.

As communications-enabled devices are becoming more and more ubiquitous, it becomes easier to track the movements of individuals through the radio signals broadcasted by their devices. While there is a strong interest for physical analytics platforms to leverage this information for many purposes, this tracking also threatens the privacy of individuals. To solve this issue, we propose a privacy-preserving solution for collecting aggregate mobility patterns while at the same time satisfying the strong guarantee of ε-differential privacy. More precisely, we introduce a sanitization mechanism for efficient, privacy-preserving and non-interactive approximate distinct counting for physical analytics based on perturbed Bloom filters. We also extend and generalize previous approaches for estimating distinct count of events and joint events (i.e., intersection, and more generally tout of -n cardinalities). Finally, we experimentally evaluate our approach and compare it to previous ones on a real dataset.

Wi-Fi signals emitted by mobile smartphones can be exploited to passively track users’ mobility. Turning off the Wi-Fi interface of the device is often presented as a mean to evade those tracking systems. As a matter of fact this method is sometime suggested by the actors of the Wi-Fi tracking industry as a way to opt-out from those systems. The Android system features an option to enable or disable Wi-Fi on the device. However, disabling Wi-Fi through this option is not sufficient to prevent all Wi-Fi activity of the device. Based on measurements on a range of Android devices, we show in [18] that another option, called “Always allow scanning”, when activated, makes a device send Wi-Fi frames which can be used to track this device, even if the Wi-Fi switch is off. This option is not clearly described in all Android versions, and sometimes even not deactivatable. Besides, the Google Maps application prompts the user to activate this option.