Scaling private proximity testing protocols for geofenced information exchange: A metropolitan-wide case study

Abstract

Private Proximity Testing (PPT) protocols allow two entities to exchange location-and-time-specific information without any tangible breach of privacy between the two or any third-party intermediary such as a server or a service provider. Numerous PPT protocols have been proposed, however, to our knowledge, experimentation relies on simulations and algorithmic complexity analysis, without tests on large-scale scenarios and actual information exchange over wide metropolitan areas. In this paper, we implement and evaluate a novel PPT geofencing algorithm based on RSA factorization. The prototype used in this work was built in Android and Kotlin, initially funded by Google Digital News Initiative Innovation Fund (digitalnewsinitiative.com). We utilize WoM to implement and test a geofenced PPT protocol using prime factorization over a wide area while users move around different municipalities and (i) present findings concerning efficiency and feasibility of prime factorization PPT implementations over large geographical distributions in terms of energy and data needs, (ii) evaluate complementary technologies needed for such private distribution of location-and-time-specific information like geospatial fences and fragmentation and (iii) consider numerous legal considerations under the EU legal context.