CrowdNotifier: Decentralized Privacy-Preserving Presence Tracing

Authors: Wouter Lueks (EPFL), Seda Gürses (TU Delft), Michael Veale (UCL), Edouard Bugnion (EPFL), Marcel Salathé (EPFL), Kenneth G. Paterson (ETH Zürich), Carmela Troncoso (EPFL)

Volume: 2021
Issue: 4
Pages: 350–368

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Abstract: There is growing evidence that SARS-CoV-2 can be transmitted beyond close proximity contacts, in particular in closed and crowded environments with insufficient ventilation. To help mitigation efforts, contact tracers need a way to notify those who were present in such environments at the same time as infected individuals. Neither traditional human-based contact tracing powered by handwritten or electronic lists, nor Bluetooth-enabled proximity tracing can handle this problem efficiently. In this paper, we propose CrowdNotifier, a protocol that can complement manual contact tracing by efficiently notifying visitors of venues and events with SARS-CoV-2-positive attendees. We prove that CrowdNotifier provides strong privacy and abuseresistance, and show that it can scale to handle notification at a national scale.

Keywords: Presence tracing, proximity tracing, privacypreserving protocols

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