Biblio

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.

Recent incidents have once again brought the topic of encryption to public discourse, while researchers continue to demonstrate attacks that highlight the difficulty of implementing encryption even without the presence of "backdoors". However, apart from the threat of implementation flaws in encryption libraries, another significant threat arises when web services fail to enforce ubiquitous encryption. A recent study explored this phenomenon in popular services, and demonstrated how users are exposed to cookie hijacking attacks with severe privacy implications. Many security mechanisms purport to eliminate this problem, ranging from server-controlled options such as HSTS to user-controlled options such as HTTPS Everywhere and other browser extensions. In this paper, we create a taxonomy of available mechanisms and evaluate how they perform in practice. We design an automated testing framework for these mechanisms, and evaluate them using a dataset of 30 days of HTTP requests collected from the public wireless network of our university's campus. We find that all mechanisms suffer from implementation flaws or deployment issues and argue that, as long as servers continue to not support ubiquitous encryption across their entire domain (including all subdomains), no mechanism can effectively protect users from cookie hijacking and information leakage.