An Epistemic Approach to Coercion-Resistance for Electronic Voting Protocols

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.Comment: An extended version of a paper from IEEE Symposium on Security and Privacy (S&P) 200

Classifying Privacy and Verifiability Requirements for Electronic Voting

Abstract: Voter privacy and verifiability are fundamental security concepts for elec-tronic voting. Existing literature on electronic voting provides many definitions and interpretations of these concepts, both informal and formal. While the informal defini-tions are often vague and imprecise, the formal definitions tend to be very complex and restricted in their scope as they are usually tailored for specific scenarios. Moreover, some of the existing interpretations are contradictory. This paper provides informal, yet precise definitions of anonymity, receipt-freeness and coercion-resistance and identifies different levels of individual and universal veri-fiability. The overarching goal of this paper is to investigate which levels are conceiv-able for implementing these requirements in e-voting systems for elections of different significance (for instance political elections vs. elections in associations).

Statistical Epistemic Logic

We introduce a modal logic for describing statistical knowledge, which we call statistical epistemic logic. We propose a Kripke model dealing with probability distributions and stochastic assignments, and show a stochastic semantics for the logic. To our knowledge, this is the first semantics for modal logic that can express the statistical knowledge dependent on non-deterministic inputs and the statistical significance of observed results. By using statistical epistemic logic, we express a notion of statistical secrecy with a confidence level. We also show that this logic is useful to formalize statistical hypothesis testing and differential privacy in a simple and abstract manner

LNCS

Composable notions of incoercibility aim to forbid a coercer from using anything beyond the coerced parties’ inputs and outputs to catch them when they try to deceive him. Existing definitions are restricted to weak coercion types, and/or are not universally composable. Furthermore, they often make too strong assumptions on the knowledge of coerced parties—e.g., they assume they known the identities and/or the strategies of other coerced parties, or those of corrupted parties— which makes them unsuitable for applications of incoercibility such as e-voting, where colluding adversarial parties may attempt to coerce honest voters, e.g., by offering them money for a promised vote, and use their own view to check that the voter keeps his end of the bargain. In this work we put forward the first universally composable notion of incoercible multi-party computation, which satisfies the above intuition and does not assume collusions among coerced parties or knowledge of the corrupted set. We define natural notions of UC incoercibility corresponding to standard coercion-types, i.e., receipt-freeness and resistance to full-active coercion. Importantly, our suggested notion has the unique property that it builds on top of the well studied UC framework by Canetti instead of modifying it. This guarantees backwards compatibility, and allows us to inherit results from the rich UC literature. We then present MPC protocols which realize our notions of UC incoercibility given access to an arguably minimal setup—namely honestly generate tamper-proof hardware performing a very simple cryptographic operation—e.g., a smart card. This is, to our knowledge, the first proposed construction of an MPC protocol (for more than two parties) that is incoercibly secure and universally composable, and therefore the first construction of a universally composable receipt-free e-voting protocol

A Formal Taxonomy of Privacy in Voting Protocols

International audiencePrivacy is one of the main issues in electronic voting. We propose a family of symbolic privacy notions that allows to assess the level of privacy ensured by a voting protocol. Our definitions are applicable to protocols featuring multiple votes per voter and special attack scenarios such as vote-copying or forced abstention. Finally we employ our definitions on several existing voting protocols to show that our model allows to compare different types of protocols based on different techniques, and is suitable for automated verification using existing tools

Expressing Receipt-Freeness and Coercion-Resistance in Logics of Strategic Ability: Preliminary Attempt

ABSTRACT Voting is a mechanism of utmost importance to social processes. In this paper, we focus on the strategic aspect of information security in voting procedures. We argue that the notions of receipt-freeness and coercion resistance are underpinned by existence (or nonexistence) of a suitable strategy for some participants of the voting process. In order to back the argument formally, we provide logical "transcriptions" of the informal intuitions behind coercion-related properties that can be found in the existing literature. The transcriptions are formulated in the modal game logic ATL * , well known in the area of multi-agent systems