Paper 2023/1102

Coercion Mitigation for Voting Systems with Trackers: A Selene Case Study

Abstract

An interesting approach to achieving verifiability in voting systems is to make use of tracking numbers. This gives voters a simple way of verifying that their ballot was counted: they can simply look up their ballot/tracker pair on a public bulletin board. It is crucial to understand how trackers affect other security properties, in particular privacy. However, existing privacy definitions are not designed to accommodate tracker-based voting systems. Furthermore, the addition of trackers increases the threat of coercion. There does however exist techniques to mitigate the coercion threat. While the term coercion mitigation has been used in the literature when describing voting systems such as Selene, no formal definition of coercion mitigation seems to exist. In this paper we formally define what coercion mitigation means for tracker-based voting systems. We model Selene in our framework and we prove that Selene provides coercion mitigation, in addition to privacy and verifiability.