Unequal Cover: Measuring Privacy Disparities in Proxy Infrastructure

Abstract

Privacy-focused proxy systems (e.g., multi-party relays, VPNs, etc.) are now standard Internet infrastructure, yet little is known about potential disparities in the privacy they provide across different populations. In this work, we investigate disparities in proxy crowd sizes, measuring how mappings between users and infrastructure can produce unequal geolocation anonymity across communities. We combine infrastructure deployment data with demographic information and apply our framework to Apple's iCloud Private Relay, analyzing 83,609 U.S. census tracts, and find significant disparities: rural users receive crowd sizes over 9× smaller than urban users, and income moderately correlates with privacy outcomes in rural areas (r=0.39) while showing negligible correlation in cities. We then explore, through simulation, strategies for improving privacy equity, demonstrating that operators can enhance privacy for the worst-protected populations by up to 2.5× using simple consolidation strategies while introducing manageable potential geolocation error.