Fifty Shades of Ballot Privacy: Privacy against a Malicious Board

Véronique Cortier (1, 2) , Joseph Lallemand (2, 1, 3) , Bogdan Warinschi (4)

1 LORIA - Laboratoire Lorrain de Recherche en Informatique et ses Applications
2 PESTO - Proof techniques for security protocols
3 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]
4 University of Bristol [Bristol]

We propose a framework for the analysis of electronic voting schemes in the presence of malicious bulletin boards. We identify a spectrum of notions where the adversary is allowed to tamper with the bulletin board in ways that reflect practical deployment and usage considerations. To clarify the security guarantees provided by the different notions we establish a relation with simulation-based security with respect to a family of ideal functionalities. The ideal functionalities make clear the set of authorised attacker capabilities which makes it easier to understand and compare the associated levels of security. We then leverage this relation to show that each distinct level of ballot privacy entails some distinct form of individual verifiability. As an application, we study three protocols of the literature (Helios, Belenios, and Civitas) and identify the different levels of privacy they offer.

Domaines: Cryptographie et sécurité [cs.CR]

Véronique Cortier, Joseph Lallemand, Bogdan Warinschi. Fifty Shades of Ballot Privacy: Privacy against a Malicious Board. CSF 2020 - 33rd IEEE Computer Security Foundations Symposium, Jun 2020, Boston / Virtual, United States. ⟨hal-02969613⟩