Many voter-verifiable, coercion-resistant schemes have been proposed, but even the most carefully designed systems necessarily leak information via the announced result. In corner cases, this may be problematic. For example, if all the votes go to one candidate then all vote privacy evaporates. The mere possibility of candidates getting no or few votes could have implications for security in practice: if a coercer demands that a voter cast a vote for such an unpopular candidate, then the voter may feel obliged to obey, even if she is confident that the voting system satisfies the standard coercion resistance definitions. With complex ballots, there may also be a danger of "Italian" style (aka "signature") attacks: the coercer demands the voter cast a ballot with a specific, identifying pattern. Here we propose an approach to tallying end-to-end verifiable schemes that avoids revealing all the votes but still achieves whatever confidence level in the announced result is desired. Now a coerced voter can claim that the required vote must be amongst those that remained shrouded. Our approach is based on the well-established notion of Risk-Limiting Audits, but here applied to the tally rather than to the audit. We show that this approach counters coercion threats arising in extreme tallies and "Italian" attacks. We illustrate our approach by applying it to the Selene scheme, and we extend the approach to Risk-Limiting Verification, where not all vote trackers are revealed, thereby enhancing the coercion mitigation properties of Selene.
@cite_7: There are many advantages to voting schemes in which voters rank all candidates in order, rather than just choosing their favourite. However, these schemes inherently suffer from a coercion problem when there are many candidates, because a coercer can demand a certain permutation from a voter and then check whether that permutation appears during tallying. In this paper, we solve this problem for the popular STV system, by constructing an algorithm for the verifiable tallying of encrypted votes. Our construction improves upon existing work because it extends to multiple-seat STV and reveals less information than other schemes.
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@cite_19: This paper presents a novel unifying framework for electronic voting in the universal composability model that includes a property which is new to universal composability but well-known to voting systems: universal verifiability. Additionally, we propose three new techniques for secure electronic voting and prove their security and universal verifiability in the universal composability framework. 1. A tally-hiding voting system, in which the tally that is released consists of only the winner without the vote count. Our proposal builds on a novel solution to the millionaire problem which is of independent interest. 2. A self-tallying vote, in which the tally can be calculated by any observer as soon as the last vote has been cast — but before this happens, no information about the tally is leaked. 3. Authentication of voting credentials, which is a new approach for electronic voting systems based on anonymous credentials. In this approach, the vote authenticates the credential so that it cannot afterwards be used for any other purpose but to cast that vote. We propose a practical voting system that instantiates this high-level concept. Note. This is the extended version of the paper with the same title [33], which appeared in the USENIX Journal of Election Technology and Systems (JETS) [35]. Please cite that version instead.
@cite_13: In random sample voting, only a randomly chosen subset of all eligible voters are selected to vote. This poses new security challenges for the voting protocol used. In particular, one must ensure that the chosen voters were randomly selected while preserving their anonymity. Moreover, the small number of selected voters leaves little room for error and only a few manipulations of the votes may significantly change the outcome. We propose Alethea, the first random sample voting protocol that satisfies end-to-end verifiability and receipt-freeness. Our protocol makes explicit the distinction between human voters and their devices. This allows for more fine-grained statements about the required capabilities and trust assumptions of each agent than is possible in previous work. We define new security properties related to the randomness and anonymity of the sample group and the probability of undetected manipulations. We prove correctness of the protocol and its properties both using traditional paper and pen proofs and with tool support.
@cite_20: Recent advances in cryptography promise to let us run complex algorithms in the encrypted domain. However, these results are still mostly theoretical since the running times are still much larger than their equivalents in the plaintext domain. In this context, Majority Judgment is a recent proposal for a new voting system with several interesting practical advantages, but which implies a more involved tallying process than first-past-the-post voting. To protect voters’ privacy, such a process needs to be done by only manipulating encrypted data.
A number of papers @cite_3 @cite_19 @cite_20 @cite_7 try to achieve tally hiding, either by only calculating the winner(s), or via multi-party computation and other cryptographic means. An idea closer to RLTs is that of Random Sample Voting (RSV) by Chaum @cite_6 . A scheme that seeks to implement RSV in a fully verifiable fashion is Alethea @cite_13 . RSV typically samples a small and predetermined number of voters, regardless of the margins. In contrast, RLTs adjust the sample size to obtain the desired level of confidence in the reported outcome.