Bulletin Boards in Voting Systems: Modelling and Measuring Privacy

Transparency is crucial to ensuring fair, honest elections. Transparency is achieved by making information (e.g. election result) public. In e-voting literature, this publication is often described in terms of a bulletin board. While privacy of voting systems has been actively studied in recent years, resulting in various analysis frameworks, to date there has not been an explicit modelling of bulletin board in any such framework. Privacy implications of bulletin boards are thus understudied. In this paper, we extend the semantics of the framework of Jonker, Mauw and Pang to model a bulletin board and capture coercion-resistance. The usage of the extended framework is illustrated by an application to the Pret a Voter voting system. Moreover, we present an information-theoretical measure of privacy loss in elections.