Techu: Open and Privacy-Preserving Crowdsourced GPS for the Masses.

The proliferation of mobile devices, equipped with numerous sensors and Internet connectivity, has laid the foundation for the emergence of a diverse set of crowdsourcing services. By leveraging the multitude, geographical dispersion, and technical abilities of smartphones, these services tackle challenging tasks by harnessing the power of the crowd. One such service, Crowd GPS, has gained traction in the industry and research community alike, materializing as a class of systems that track lost objects or individuals (e.g., children or elders). While these systems can have significant impact, they suffer from major privacy threats. In this paper, we highlight the inherent risks to users from the centralized designs adopted by such services and demonstrate how adversaries can trivially misuse one of the most popular crowd GPS services to track their users. As an alternative, we present Techu, a privacy-preserving crowd GPS service for tracking Bluetooth tags. Our architecture follows a hybrid decentralized approach, where an untrusted server acts as a bulletin board that collects reports of tags observed by the crowd, while observers store the location information locally and only disclose it upon proof of ownership of the tag. Techu does not require user authentication, allowing users to remain anonymous. As no user authentication is required and cloud messaging queues are leveraged for communication between users, users remain anonymous. Our security analysis highlights the privacy offered by Techu, and details how our design prevents adversaries from tracking or identifying users. Finally, our experimental evaluation demonstrates that Techu has negligible impact on power consumption, and achieves superior effectiveness to previously proposed systems while offering stronger privacy guarantees.