LocIn: Inferring Semantic Location from Spatial Maps in Mixed Reality

Mixed reality (MR) devices capture 3D spatial maps of users' surroundings to integrate virtual content into their physical environment. Existing permission models implemented in popular MR platforms allow all MR apps to access these 3D spatial maps without explicit permission. Unmonitored access of MR apps to these 3D spatial maps poses serious privacy threats to users as these maps capture detailed geometric and semantic characteristics of users' environments. In this paper, we present LOCIN, a new location inference attack that exploits these detailed characteristics embedded in 3D spatial maps to infer a user's indoor location type. LOCIN develops a multi-task approach to train an end-to-end encoder-decoder network that extracts a spatial feature representation for capturing contextual patterns of the user's environment. LOCIN leverages this representation to detect 3D objects and surfaces and integrates them into a classification network with a novel unified optimization function to predict the user's indoor location. We demonstrate LOCIN attack on spatial maps collected from three popular MR devices. We show that LOCIN infers a user's location type with an average 84.1% accuracy.