VoteAgain: A scalable coercion-resistant voting system

TL;DR

VoteAgain introduces a scalable, coercion-resistant voting system utilizing revoting and a novel ballot padding mechanism, enabling large-scale elections with strong privacy and verifiability guarantees.

Contribution

It presents the first scalable revoting scheme with coercion resistance that handles millions of voters efficiently.

Findings

Ensures coercion resistance through a novel deterministic ballot padding.

Achieves quasilinear tallying time for large elections.

Provides provable privacy, coercion resistance, and verifiability.

Abstract

The strongest threat model for voting systems considers coercion resistance: protection against coercers that force voters to modify their votes, or to abstain. Existing remote voting systems either do not provide this property; require an expensive tallying phase; or burden users with the need to store cryptographic key material and with the responsibility to deceive their coercers. We propose VoteAgain, a scalable voting scheme that relies on the revoting paradigm to provide coercion resistance. VoteAgain uses a novel deterministic ballot padding mechanism to ensure that coercers cannot see whether a vote has been replaced. This mechanism ensures tallies take quasilinear time, making VoteAgain the first revoting scheme that can handle elections with millions of voters. We prove that VoteAgain provides ballot privacy, coercion resistance, and verifiability; and we demonstrate its scalability using a prototype implementation of all cryptographic primitives.