Formal Methods for Trustworthy Voting Systems : From Trusted Components to Reliable Software

Voting is prominently an important part of democratic societies, and its outcome may have a dramatic and broad impact on societal progress. Therefore, it is paramount that such a society has extensive trust in the electoral process, such that the system’s functioning is reliable and stable with respect to the expectations within society. Yet, with or without the use of modern technology, voting is full of algorithmic and security challenges, and the failure to address these challenges in a controlled manner may produce fundamental flaws in the voting system and potentially undermine critical societal aspects. In this thesis, we argue for a development process of voting systems that is rooted in and assisted by formal methods that produce transparently checkable evidence for the guarantees that the final system should provide so that it can be deemed trustworthy. The goal of this thesis is to advance the state of the art in formal methods that allow to systematically develop trustworthy voting systems that can be provenly verified. In the literature, voting systems are modeled in the following four comparatively separable and distinguishable layers: (1) the physical layer, (2) the computational layer, (3) the election layer, and (4) the human layer. Current research usually either mostly stays within one of those layers or lacks machine-checkable evidence, and consequently, trusted and understandable criteria often lack formally proven and checkable guarantees on software-level and vice versa. The contributions in this work are formal methods that fill in the trust gap between the principal election layer and the computational layer by a reliable translation of trusted and understandable criteria into trustworthy software. Thereby, we enable that executable procedures can be formally traced back and understood by election experts without the need for inspection on code level, and trust can be preserved to the trustworthy system. The works in this thesis all contribute to this end and consist in five distinct contributions, which are the following: (I) a method for the generation of secure card-based communication schemes, (II) a method for the synthesis of reliable tallying procedures, (III) a method for the efficient verification of reliable tallying procedures, (IV) a method for the computation of dependable election margins for reliable audits, (V) a case study about the security verification of the GI voter-anonymization software. These contributions span formal methods on illustrative examples for each of the three principal components, (1) voter-ballot box communication, (2) election method, and (3) election management, between the election layer and the computational layer. Within the first component, the voter-ballot box communication channel, we build a bridge from the communication channel to the cryptography scheme by automatically generating secure card-based schemes from a small formal model with a parameterization of the desired security requirements. For the second component, the election method, we build a bridge from the election method to the tallying procedure by (1) automatically synthesizing a runnable tallying procedure from the desired requirements given as properties that capture the desired intuitions or regulations of fairness considerations, (2) automatically generating either comprehensible arguments or bounded proofs to compare tallying procedures based on user-definable fairness properties, and (3) automatically computing concrete election margins for a given tallying procedure, the collected ballots, and the computed election result, that enable efficient election audits. Finally, for the third and final component, the election management system, we perform a case study and apply state-of-the-art verification technology to a real-world e-voting system that has been used for the annual elections of the German Informatics Society (GI – “Gesellschaft für Informatik”) in 2019. The case study consists in the formal implementation-level security verification that the voter identities are securely anonymized and the voters’ passwords cannot be leaked. The presented methods assist the systematic development and verification of provenly trustworthy voting systems across traditional layers, i.e., from the election layer to the computational layer. They all pursue the goal of making voting systems trustworthy by reliable and explainable formal requirements. We evaluate the devised methods on minimal card-based protocols that compute a secure AND function for two different decks of cards, a classical knock-out tournament and several Condorcet rules, various plurality, scoring, and Condorcet rules from the literature, the Danish national parliamentary elections in 2015, and a state-of-the-art electronic voting system that is used for the German Informatics Society’s annual elections in 2019 and following

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

Analysis of Blockchain Solutions for E-Voting: A Systematic Literature Review

To this day, abstention rates continue to rise, largely due to the need to travel to vote. This is why remote e-voting will increase the turnout by allowing everyone to vote without the need to travel. It will also minimize the risks and obtain results in a faster way compared to a traditional vote with paper ballots. In fact, given the high stakes of an election, a remote e-voting solution must meet the highest standards of security, reliability, and transparency to gain the trust of citizens. In literature, several remote e-voting solutions based on blockchain technology have been proposed. Indeed, the blockchain technology is proposed today as a new technical infrastructure for several types of IT applications because it allows to remove the TTP and decentralize transactions while offering a transparent and fully protected data storage. In addition, it allows to implement in its environment the smart-contracts technology which is used to automate and execute agreements between users. In this paper, we are interested in reviewing the most revealing e-voting solutions based on blockchain technology

SUVS: Secure Unencrypted Voting Scheme

[EN] In this paper, we propose a light-weight electronic voting protocol. The approach used by our protocol to conceal the ballots does not imply encryption, and guarantees the privacy of the direction of the vote unless all the contestants (parties) agree to do so. Our method is based on the division of the ballot into different pieces of information, which separately reveal no information at all, and that can be latter aggregated to recover the original vote. We show that, despite its simplicity, this scheme is powerful, it does not sacrifice any of the security properties demanded in a formal electronic voting protocol, and, furthermore, even in post-quantum scenarios, neither the casted votes can be tampered with, nor the identity of any elector can be linked with the direction of her vote.Results related to Spanish Patent Application number P202131209.Larriba, AM.; López Rodríguez, D. (2022). SUVS: Secure Unencrypted Voting Scheme. Informatica. 33(4):749-769. https://doi.org/10.15388/22-INFOR50374976933

Electronic Voting: 6th International Joint Conference, E-Vote-ID 2021, Virtual Event, October 5–8, 2021: proceedings

This volume contains the papers presented at E-Vote-ID 2021, the Sixth International Joint Conference on Electronic Voting, held during October 5–8, 2021. Due to the extraordinary situation brought about by the COVID-19, the conference was held online for the second consecutive edition, instead of in the traditional venue in Bregenz, Austria. The E-Vote-ID conference is the result of the merger of the EVOTE and Vote-ID conferences, with first EVOTE conference taking place 17 years ago in Austria. Since that conference in 2004, over 1000 experts have attended the venue, including scholars, practitioners, authorities, electoral managers, vendors, and PhD students. The conference focuses on the most relevant debates on the development of electronic voting, from aspects relating to security and usability through to practical experiences and applications of voting systems, also including legal, social, or political aspects, amongst others, and has turned out to be an important global referent in relation to this issue

Sixth International Joint Conference on Electronic Voting E-Vote-ID 2021. 5-8 October 2021

This volume contains papers presented at E-Vote-ID 2021, the Sixth International Joint Conference on Electronic Voting, held during October 5-8, 2021. Due to the extraordinary situation provoked by Covid-19 Pandemic, the conference is held online for second consecutive edition, instead of in the traditional venue in Bregenz, Austria. E-Vote-ID Conference resulted from the merging of EVOTE and Vote-ID and counting up to 17 years since the _rst E-Vote conference in Austria. Since that conference in 2004, over 1000 experts have attended the venue, including scholars, practitioners, authorities, electoral managers, vendors, and PhD Students. The conference collected the most relevant debates on the development of Electronic Voting, from aspects relating to security and usability through to practical experiences and applications of voting systems, also including legal, social or political aspects, amongst others; turning out to be an important global referent in relation to this issue. Also, this year, the conference consisted of: · Security, Usability and Technical Issues Track · Administrative, Legal, Political and Social Issues Track · Election and Practical Experiences Track · PhD Colloquium, Poster and Demo Session on the day before the conference E-VOTE-ID 2021 received 49 submissions, being, each of them, reviewed by 3 to 5 program committee members, using a double blind review process. As a result, 27 papers were accepted for its presentation in the conference. The selected papers cover a wide range of topics connected with electronic voting, including experiences and revisions of the real uses of E-voting systems and corresponding processes in elections. We would also like to thank the German Informatics Society (Gesellschaft für Informatik) with its ECOM working group and KASTEL for their partnership over many years. Further we would like to thank the Swiss Federal Chancellery and the Regional Government of Vorarlberg for their kind support. EVote- ID 2021 conference is kindly supported through European Union's Horizon 2020 projects ECEPS (grant agreement 857622) and mGov4EU (grant agreement 959072). Special thanks go to the members of the international program committee for their hard work in reviewing, discussing, and shepherding papers. They ensured the high quality of these proceedings with their knowledge and experience

Kryvos: Publicly Tally-Hiding Verifiable E-Voting

Elections are an important corner stone of democratic processes. In addition to publishing the final result (e.g., the overall winner), elections typically publish the full tally consisting of all (aggregated) individual votes. This causes several issues, including loss of privacy for both voters and election candidates as well as so-called Italian attacks that allow for easily coercing voters. Several e-voting systems have been proposed to address these issues by hiding (parts of) the tally. This property is called tally-hiding. Existing tally-hiding e-voting systems in the literature aim at hiding (part of) the tally from everyone, including voting authorities, while at the same time offering verifiability, an important and standard feature of modern e-voting systems which allows voters and external observers to check that the published election result indeed corresponds to how voters actually voted. In contrast, real elections often follow a different common practice for hiding the tally: the voting authorities internally compute (and learn) the full tally but publish only the final result (e.g., the winner). This practice, which we coin publicly tally-hiding, indeed solves the aforementioned issues for the public, but currently has to sacrifice verifiability due to a lack of practical systems. In this paper, we close this gap. We formalize the common notion of publicly tally-hiding and propose the first provably secure verifiable e-voting system, called Kryvos, which directly targets publicly tally-hiding elections. We instantiate our system for a wide range of both simple and complex voting methods and various result functions. We provide an extensive evaluation which shows that Kryvos is practical and able to handle a large number of candidates, complex voting methods and result functions. Altogether, Kryvos shows that the concept of publicly tally-hiding offers a new trade-off between privacy and efficiency that is different from all previous tally-hiding systems and which allows for a radically new protocol design resulting in a practical e-voting system

Secure multi party computations for electronic voting

Στην παρούσα εργασία, μελετούμε το πρόβλημα της ηλεκτρονικής ψηφοφορίας. Θεωρούμε ότι είναι έκφανση μιας γενικής διαδικασίας αποφάσεων που μπορεί να υλοποιηθεί μέσω υπολογισμών πολλαπλών οντοτήτων, οι οποίοι πρέπει να ικανοποιούν πολλές και αντικρουόμενες απαιτήσεις ασφαλείας. Έτσι μελετούμε σχετικές προσεγγίσεις οι οποίες βασιζονται σε κρυπτογραφικές τεχνικές, όπως τα ομομορφικά κρυπτοσυστήματα, τα δίκτυα μίξης και οι τυφλές υπογραφές. Αναλύουμε πώς προσφέρουν ακεραιότητα και ιδιωτικότητα (μυστικότητα) στην διαδικασία και την σχέση τους με την αποδοτικότητα. Εξετάζουμε τα είδη λειτουργιών κοινωνικής επιλογής που μπορούν να υποστηρίξουν και παρέχουμε δύο υλοποιήσεις. Επιπλέον ασχολούμαστε με την αντιμετώπιση ισχυρότερων αντιπάλων μη παρέχοντας αποδείξεις ψήφου ή προσφέροντας δυνατότητες αντίστασης στον εξαναγκασμό. Με βάση την τελευταία έννοια προτείνουμε μια τροποποίηση σε ένα ευρέως χρησιμοποιούμενο πρωτόκολλο. Τέλος μελετούμε δύο γνωστές υλοποιήσεις συστημάτων ηλεκτρονικής ψηφοφοριας το Helios και το Pret a Voter .In this thesis, we study the problem of electronic voting as a general decision making process that can be implemented using multi party computations, fulfilling strict and often conflicting security requirements. To this end, we review relevant cryptographic techniques and their combinations to form voting protocols. More specifically, we analyze schemes based on homomorphic cryptosystems, mixnets with proofs of shuffles and blind signatures. We analyze how they achieve integrity and privacy in the voting process, while keeping efficiency. We examine the types of social choice functions that can be supported by each protocol. We provide two proof of concept implementations. Moreover, we review ways to thwart stronger adversaries by adding receipt freeness and coercion resistance to voting systems. We build on the latter concept to propose a modification to a well known protocol. Finally, we study two actual e-Voting implementations namely Helios and Pret a Voter

A toolbox for verifiable tally-hiding e-voting systems

Cryptology ePrint Archive: Report 2021/491https://eprint.iacr.org/2021/491International audienceIn most verifiable electronic voting schemes, one key step is the tally phase, where the election result is computed from the encrypted ballots. A generic technique consists in first applying (verifiable) mixnets to the ballots and then revealing all the votes in the clear. This however discloses much more information than the result of the election itself (that is, the winners) and may offer the possibility to coerce voters. In this paper, we present a collection of building blocks for designing tally-hiding schemes based on multi-party computations. As an application, we propose the first tally-hiding schemes with no leakage for four important counting functions: D'Hondt, Condorcet, STV, and Majority Judgment. We also unveil unknown flaws or leakage in several previously proposed tally-hiding schemes