Prying into Private Spaces Using Mobile Device Motion Sensors

Human made structures are designed in a predictable manner, conforming to the expectations of those who use them. These underlying patterns lend themselves to repetition in the way people get between different locations. We investigated the feasibility of an attacker using motion sensor data against their target, with the objective of predicting where they move and what activities they engaged in. In this work, we show that the gyroscope and accelerometer can be used to drive a privacy attack that stealthily maps out a user's private space with high accuracy. In particular, we show that a mobile app with access to this data can leverage it to analyze a user's step execution dynamics, turn operations, and general body movement activities and then methodically combine this information to map out paths and landmarks in protected spaces, such as houses. Using a dataset of 26 users who executed a number of activities and a combination of classification, regression, and distance matching techniques, we show this privacy attack to generate maps whose Normalized Hausdorff Distance from the ground-truth is as low as 0.1159.