An Epistemic Approach to Coercion-Resistance for Electronic Voting Protocols

TL;DR

This paper introduces a new, simple epistemic definition of coercion resistance for electronic voting protocols, enabling clearer analysis and application to existing systems like Civitas.

Contribution

It proposes a novel, intuitive symbolic definition of coercion resistance based on epistemic logic, applicable across various protocols without specific adversary models.

Findings

Applied the new definition to three voting protocols.

Provided the first rigorous analysis of Civitas's coercion resistance.

Identified conditions under which protocols are coercion resistant or not.

Abstract

Coercion resistance is an important and one of the most intricate security requirements of electronic voting protocols. Several definitions of coercion resistance have been proposed in the literature, including definitions based on symbolic models. However, existing definitions in such models are rather restricted in their scope and quite complex. In this paper, we therefore propose a new definition of coercion resistance in a symbolic setting, based on an epistemic approach. Our definition is relatively simple and intuitive. It allows for a fine-grained formulation of coercion resistance and can be stated independently of a specific, symbolic protocol and adversary model. As a proof of concept, we apply our definition to three voting protocols. In particular, we carry out the first rigorous analysis of the recently proposed Civitas system. We precisely identify those conditions under which this system guarantees coercion resistance or fails to be coercion resistant. We also analyze protocols proposed by Lee et al. and Okamoto.