Public Evidence from Secret Ballots

Elections seem simple---aren't they just counting? But they have a unique, challenging combination of security and privacy requirements. The stakes are high; the context is adversarial; the electorate needs to be convinced that the results are correct; and the secrecy of the ballot must be ensured. And they have practical constraints: time is of the essence, and voting systems need to be affordable and maintainable, and usable by voters, election officials, and pollworkers. It is thus not surprising that voting is a rich research area spanning theory, applied cryptography, practical systems analysis, usable security, and statistics. Election integrity involves two key concepts: convincing evidence that outcomes are correct and privacy, which amounts to convincing assurance that there is no evidence about how any given person voted. These are obviously in tension. We examine how current systems walk this tightrope.Comment: To appear in E-Vote-Id '1

A two authorities electronic vote scheme

[EN] In this paper we propose a new electronic multi-authority voting system based on blind signatures. We focus on the open problem of the efficiency of electronic voting systems. Most of the proposed systems rely on complex architectures or expensive proofs, in this work we aim to reduce the time-complexity of the voting process, both for the voter and the authorities involved. Our system is focused on simplicity and it is based on the assumption of two unrelated entities. This simplicity makes our approach scalable and flexible to multiple kinds of elections. We propose a method that limits the number of authorities to only 2 of them; we reduce the overall number of modular operations; and, propose a method which cut downs the interactions needed to cast a vote. The result is a voting protocol whose complexity scales linearly with the number of votes.Larriba-Flor, AM.; Sempere Luna, JM.; López Rodríguez, D. (2020). A two authorities electronic vote scheme. Computers & Security. 97:1-12. https://doi.org/10.1016/j.cose.2020.101940S11297Bloom, B. H. (1970). Space/time trade-offs in hash coding with allowable errors. Communications of the ACM, 13(7), 422-426. doi:10.1145/362686.362692Brams S., Fishburn P.C.. 2007. Approval voting Springer ScienceCarroll, T. E., & Grosu, D. (2009). A secure and anonymous voter-controlled election scheme. Journal of Network and Computer Applications, 32(3), 599-606. doi:10.1016/j.jnca.2008.07.010Chaum, D. L. (1981). Untraceable electronic mail, return addresses, and digital pseudonyms. Communications of the ACM, 24(2), 84-90. doi:10.1145/358549.358563Cramer, R., Gennaro, R., & Schoenmakers, B. (1997). A secure and optimally efficient multi-authority election scheme. European Transactions on Telecommunications, 8(5), 481-490. doi:10.1002/ett.4460080506Desmedt, Y. G. (2010). Threshold cryptography. European Transactions on Telecommunications, 5(4), 449-458. doi:10.1002/ett.4460050407Elgamal, T. (1985). A public key cryptosystem and a signature scheme based on discrete logarithms. IEEE Transactions on Information Theory, 31(4), 469-472. doi:10.1109/tit.1985.1057074Juang, W.-S. (2002). A Verifiable Multi-Authority Secret Election Allowing Abstention from Voting. The Computer Journal, 45(6), 672-682. doi:10.1093/comjnl/45.6.672Menezes A., van Oorschot P.C., Vanstone S.A.. 1996. Handbook of Applied Cryptography.Parhami, B. (1994). Voting algorithms. IEEE Transactions on Reliability, 43(4), 617-629. doi:10.1109/24.370218Rabin, M. O. (1980). Probabilistic Algorithms in Finite Fields. SIAM Journal on Computing, 9(2), 273-280. doi:10.1137/0209024Rabin, M. O. (1983). Transaction protection by beacons. Journal of Computer and System Sciences, 27(2), 256-267. doi:10.1016/0022-0000(83)90042-9Salazar, J. L., Piles, J. J., Ruiz-Mas, J., & Moreno-Jiménez, J. M. (2010). Security approaches in e-cognocracy. Computer Standards & Interfaces, 32(5-6), 256-265. doi:10.1016/j.csi.2010.01.004Nguyen, T. A. T., & Dang, T. K. (2013). Enhanced security in internet voting protocol using blind signature and dynamic ballots. Electronic Commerce Research, 13(3), 257-272. doi:10.1007/s10660-013-9120-5Wu, Z.-Y., Wu, J.-C., Lin, S.-C., & Wang, C. (2014). An electronic voting mechanism for fighting bribery and coercion. Journal of Network and Computer Applications, 40, 139-150. doi:10.1016/j.jnca.2013.09.011Yang, X., Yi, X., Nepal, S., Kelarev, A., & Han, F. (2018). A Secure Verifiable Ranked Choice Online Voting System Based on Homomorphic Encryption. IEEE Access, 6, 20506-20519. doi:10.1109/access.2018.2817518Yi, X., & Okamoto, E. (2013). Practical Internet voting system. Journal of Network and Computer Applications, 36(1), 378-387. doi:10.1016/j.jnca.2012.05.00

Matters of Coercion-Resistance in Cryptographic Voting Schemes

This work addresses coercion-resistance in cryptographic voting schemes. It focuses on three particularly challenging cases: write-in candidates, internet elections and delegated voting. Furthermore, this work presents a taxonomy for analyzing and comparing a huge variety of voting schemes, and presents practical experiences with the voting scheme Bingo Voting

Design and cryptographic security analysis of e-voting protocols

Electronic voting (e-voting) systems are used in numerous countries for political elections, but also for less critical elections within clubs and associations, and hence affect the lives of millions of people. It is therefore important to ensure that single voters' choices remain private, and to be able to verify that an election result coincides with the voters' intention. Unfortunately, for most e-voting systems employed in real elections, these fundamental security and privacy properties cannot be guaranteed, so that in particular the legitimacy of such political elections is challenged. This demonstrates the importance of employing e-voting systems that are rootedly designed to guarantee the required security. However, it turned out to be highly challenging to construct secure yet practical e-voting systems since one always has to find a balance between the (possibly conflicting) requirements of the given kind of election. In the first two chapters of the thesis' main part, we present two practical e-voting systems which are both meant for low-risk and non-political elections, e.g., within clubs or associations. We have implemented both systems to demonstrate their practicability. The first system, called sElect, is designed to be as simple as possible while still guaranteeing a good level of security. The second system, called Ordinos, provides a superior level of privacy as it only reveals the most necessary information about the election outcome, e.g., solely the winner's name but nothing else. We will rigorously analyze the security of sElect and Ordinos. To do this, we formally define the required security properties and then mathematically prove that sElect and Ordinos achieve them. In the third chapter of the thesis' main part, we provide substantial work on the fundamental notion of verifiability of e-voting systems. We analyze and compare all formal verifiability definitions from the literature regarding how meaningful, expressive, or general they are

Election Security Is Harder Than You Think

Recent years have seen the rise of nation-state interference in elections across the globe, making the ever-present need for more secure elections all the more dire. While certain common-sense approaches have been a typical response in the past, e.g. ``don't connect voting machines to the Internet'' and ``use a voting system with a paper trail'', known-good solutions to improving election security have languished in relative obscurity for decades. These techniques are only now finally being implemented at scale, and that implementation has brought the intricacies of sophisticated approaches to election security into full relief. This dissertation argues that while approaches to improve election security like paper ballots and post-election audits seem straightforward, in reality there are significant practical barriers to sufficient implementation. Overcoming these barriers is a necessary condition for an election to be secure, and while doing so is possible, it requires significant refinement of existing techniques. In order to better understand how election security technology can be improved, I first develop what it means for an election to be secure. I then delve into experimental results regarding voter-verified paper, discussing the challenges presented by paper ballots as well as some strategies to improve the security they can deliver. I examine the post-election audit ecosystem and propose a manifest improvement to audit workload analysis through parallelization. Finally, I show that even when all of these conditions are met (as in a vote-by-mail scenario), there are still wrinkles that must be addressed for an election to be truly secure.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163272/1/matber_1.pd

A Proxy Voting Scheme Ensuring Participation Privacy and Receipt-Freeness

Proxy voting is a form of voting meant to support the voters who want to delegate their voting right to a trusted entity, the so-called proxy. Depending on the form of proxy voting, the proxy is either authorized to cast a ballot for the voting option that the voter chooses, or to vote according to her own wishes, if the voter is not sure how to vote and wants to delegate the decision making in the election. While the first form of proxy voting has been applied to traditional elections in order to support the voters who are unable to physically get to a polling station, the second form has been a topic of research in Internet voting. Recently, an Internet voting scheme has been proposed, that extends the well-known Helios scheme towards the functionality of proxy voting. This scheme, however, also has the drawbacks of Helios regarding participation privacy and receipt-freeness. As such, the information whether any voter participated in the election either by casting a direct vote or delegating their vote can be deduced from the published information. The scheme furthermore allows both the voters and the proxies to create receipts that prove casting a ballot for a specific candidate, as well as allows the voters to create receipts that prove delegating to a specific proxy. In this work we use the idea of dummy ballots, proposed in another extension of Helios to extend the proxy voting scheme towards participation privacy and receipt-freeness

Ordinos: A Verifiable Tally-Hiding E-Voting System

Modern electronic voting systems (e-voting systems) are designed to provide not only vote privacy but also (end-to-end) verifiability. Several verifiable e-voting systems have been proposed in the literature, with Helios being one of the most prominent ones. Almost all such systems, however, reveal not just the voting result but also the full tally, consisting of the exact number of votes per candidate or even all single votes. There are several situations where this is undesirable. For example, in elections with only a few voters (e.g., boardroom or jury votings), revealing the complete tally leads to a low privacy level, possibly deterring voters from voting for their actual preference. In other cases, revealing the complete tally might unnecessarily embarrass some candidates. Often, the voting result merely consists of a single winner or a ranking of candidates, so revealing only this information but not the complete tally is sufficient. This property is called tally-hiding and it offers completely new options for e-voting. In this paper, we propose the first provably secure end-to-end verifiable tally-hiding e-voting system, called Ordinos. We instantiated our system with suitable cryptographic primitives, including an MPC protocol for greater-than tests, implemented the system, and evaluated its performance, demonstrating its practicality. Moreover, our work provides a deeper understanding of tally-hiding in general, in particular in how far tally-hiding affects the levels of privacy and verifiability of e-voting systems

Guess my vote : a study of opacity and information flow in voting systems

With an overall theme of information flow, this thesis has two main strands. In the first part of the thesis, I review existing information flow properties, highlighting a recent definition known as opacity [25]. Intuitively, a predicate cP is opaque if for every run in which cP is true, there exists an indistinguishable run in which it is false, where a run can be regarded as a sequence of events. Hence, the observer is never able to establish the truth of cPo The predicate cP can be defined according to requirements of the system, giving opacity a great deal of flexibility and versatility. Opacity is then studied in relation to several well-known definitions for information flow. As will be shown, several of these properties can be cast as variations of opacity, while others have a relationship by implication with the opacity property [139]. This demonstrates the flexibility of opacity, at the same time establishing its distinct character. In the second part of the thesis, I investigate information flow in voting systems. Pret a Voter [36] is the main exemplar, and is compared to other schemes in the case study. I first analyse information flow in Pret a Voter and the FOO scheme [59], concentrating on the core protocols. The aim is to investigate the security requirements of each scheme, and the extent to which they can be captured using opacity. I then discuss a systems-based analysis of Pret a Voter [163], which adapts and extends an earlier analysis of the Chaum [35] and Neff [131]' [132]' [133] schemes in [92]. Although this analysis has identified several potential vulnerabilities, it cannot be regarded as systematic, and a more rigorous approach may be necessary. It is possible that a combination of the information flow and systems- based analyses might be the answer. The analysis of coercion-resistance, which is performed on Pret a Voter and the FOO scheme, may exemplify this more systematic approach. Receipt-freeness usually means that the voter is unable to construct a proof of her vote. Coercion-resistance is a stronger property in that it accounts for the possibility of interaction between the coercer and the voter during protocol execution. It appears that the opacity property is ideally suited to expressing the requirements for coercion-resistance in each scheme. A formal definition of receipt-freeness cast as a variation of opacity is proposed [138], together with suggestions on how it might be reinforced to capture coercion-resistance. In total, the thesis demonstrates the remarkable flexibility of opacity, both in expressing differing security requirements and as a tool for security analysis. This work lays the groundwork for future enhancement of the opacity framework.EThOS - Electronic Theses Online ServiceDSTL : EPSRCGBUnited Kingdo