# On a Study of Mechanisms for End-to-End Verifiable Online Voting (StuVe)

Veronique Cortier, Alexandre Debant, Ralf Küsters, Florian Moser, Johannes

Müller, Melanie Volkamer

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Veronique Cortier, Alexandre Debant, Ralf Küsters, Florian Moser, Johannes Müller, et al.. On a Study of Mechanisms for End-to-End Verifiable Online Voting (StuVe). Vote-ID 2025 - 10th International Joint Conference on Electronic Voting, Oct 2025, Nancy, France. hal-05240529

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# On a Study of Mechanisms for End-to-End Verifiable Online Voting (StuVe)

Veronique Cortier ◎1, Alexandre Debant ◎1, Ralf Küsters ◎2, Florian Moser ◎1, Johannes Müller ◎3, and Melanie Volkamer ◎4

**Abstract:** The German Federal Office for Information Security published a study on end-to-end verifiable online voting mechanisms. We aim to make this study more visible to the E-Vote-ID community (which includes academia, regulatory bodies and vendors). The study describes the core idea of the selected mechanisms and evaluates them using an interdisciplinary approach that considers secrecy, end-to-end verifiability, usability, and practicality. We find that the selection of mechanisms represents the state of the art in internet voting systems well, and that the evaluation clearly showcases the fundamental properties of each mechanism. However, we note that the evaluations are conducted on a per-mechanism basis, whereas real-world systems are composed of multiple.

**Keywords:** Internet Voting, Security, Usability, Practicality, Mechanisms, Evaluation

## 1 Introduction

Developing and implementing legal frameworks for end-to-end verifiable online voting is a pressing and challenging task for responsible regulatory institutions. Creating a reasonable framework requires a deep understanding of the technical possibilities, limitations, and pitfalls of secure online voting, as well as of the state of the art of deployed voting systems.

The *Bundesamt für Sicherheit in der Informationstechnik (BSI)*, as the Federal Agency for Information Security, is the regulatory body for online election systems in Germany, both for political and non-political elections. As part of these efforts, the BSI published in 2024 a *Study of Mechanisms for End-to-End Verifiable Online Voting (StuVe)* [Mo24]. The target of the study is to identify usable and practical mechanisms to implement the fundamental election principles [Bu23].

We believe that the results and insights from the StuVe study are valuable for many different stakeholders (e.g., other regulators, online voting vendors, or researchers). Hence, in addition

<footnote n="1">1 Université de Lorraine, CNRS, Inria, LORIA, F-54000 Nancy, France, veronique.cortier@inria.fr, https://orcid.org/0009-0003-1651-3927; alexandre.debant@inria.fr, https://orcid.org/0000-0001-5610-1765; florian.moser@inria.fr, https://orcid.org/0000-0003-2268-2367</footnote>

<footnote n="2">2 Institute of Information Security, University of Stuttgart, Germany, ralf.kuesters@sec.uni-stuttgart.de, https://orcid.org/0000-0002-9071-9312</footnote>

<footnote n="3">3 Germany, jomueller@posteo.de, https://orcid.org/0000-0003-2134-3099</footnote>

<footnote n="4">4 KASTEL Security Research Labs, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany, melanie.volkamer@kit.edu, https://orcid.org/0000-0003-2674-4043</footnote>
to making this study more visible to the E-Vote-ID community, we provide an overview of
its content, and highlight where the study is strong, but also its limitations.

## 2 The study

The main contributions of the study are evaluation criteria for verifiable internet voting mechanisms, a detailed description of some of the widely used mechanisms, and an evaluation of these mechanisms. We summarize here these contributions and then directly discuss their strong points and their limitations.

We highlight that the study provides its own summary and interpretation of its results in the executive summary and key findings, which notably do not contradict our analysis here. Additionally, the study contains remarks by the authors, which invite the reader to reflect on the approach taken. We recommend to directly consult the study for these more nuanced discussions [Mo24], while we aim here for a more concise overview of the study and discussion of its results.

The study was commissioned as a public tender at the end of 2023. The tender prescribed expertise in market analysis, cryptoanalysis and online elections [Bu23]. The final study was published in mid-2024. Its authors include established researchers in internet voting from Germany and France, with expertise in information security, cryptography and usability.

### 2.1 Evaluation criteria

Followed by a discussion of how the election principles are applied to internet voting, the technical aspects are chosen to be covered using the following criteria:

* *Secrecy*. Decomposed into three aspects — *vote privacy*, *everlasting privacy*, and *vote-buying resistance* — the evaluation rates better if it protects against stronger adversaries. Vote privacy is seen as a more fundamental secrecy property than the other two, and is therefore weighted stronger.

* *End-to-end verifiability*. The evaluation is based on the trust assumptions in the various components required for independent verification of the correctness of the election result. The weaker the necessary assumptions, the better the evaluation.

* *Usability*. The evaluation models *efficiency* (number of relevant steps to execute it) and *effectiveness* (number of all steps that are considered difficult or otherwise problematic to execute for the user). The overall evaluation requires both dimensions to perform well for a good score.

* *Practicality*. The evaluation considers *implementability* (difficulty of development) and *efficiency* (computational and communication costs). The overall evaluation weights implementability stronger, as mistakes may lead to security problems.
Discussion

✓ The evaluation considers different perspectives, including across research domains often considered separately.

✓ The criteria are sufficiently general to apply to many more mechanisms than those considered in the study, which promises little bias.

2.2 Mechanism description

Based on a market and literature analysis,<fnref n="5" /> the study chooses eight mechanisms it considers most relevant to describe in detail:

* *Secret ballots:* Two mechanisms are studied to keep individual ballots secret: *malleable public-key encryption* and *malleable commitments*.

* *Verifiable tallying:* Two mechanisms are studied to verifiably tally ballots in a privacy-preserving way: *homomorphic aggregation* and *verifiable mixing*.

* *Authenticated communication:* It is studied how *digital signatures* may resolve disputes and distribute trust in the authentication of ballots.

* *Voting device verification:* Three mechanisms are studied that enable individual human voters to verify that their voting devices correctly processed their secret votes: *audit-or-cast*, *cast-and-audit*, and *return codes*.

Discussion

✓ The selection of mechanisms analysed in detail represents well the state-of-the-art internet voting systems.

✓ The description of mechanisms focuses on their core idea, sometimes providing variants to showcase different trade-offs.

✓ The extensive background provided as part of the work clarifies the terminology and explains the cryptographic primitives.

✗ Not all widely used mechanisms, such as bulletin boards, are analysed in detail. However, the study authors categorize and refer to many more mechanisms in chapter 4.10 [Mo24].

<footnote n="5">5 The market and literature analysis is not directly included in the study. However, a recent SoK which includes a market and literature analysis for mechanisms used for verifiable internet voting mechanisms [MKD24] acknowledges the study to have contributed.</footnote>
## 2.3 Mechanism evaluation

The evaluation is based on a detailed description of the mechanism, embedded into an idealized voting system, but without precising a concrete implementation or formalization. During the evaluation process, the authors had to close such gaps implicitly, in a way that might not necessarily transfer to real-world implementations.

The author's definition of the evaluation criteria was in part based on established work (e.g., [Co16; KV18; MKV18]), but also required some subjective choices. The evaluation of secrecy, usability, and practicality result each in a score, and as any scoring scheme, it might be influenced by the author's cultural context. The evaluation of verifiability results in a list of trust assumptions, which stays more objective, but places the burden of interpretation fully at the reader's side.

We highlight the following evaluation results:

* The secret ballots and verifiable tallying mechanisms perform well across the dimensions of privacy, verifiability and practicality.<fnref n="6" /> The authors conclude in one of their key-findings that any state-of-the-art system can be expected to employ one of these mechanisms.

* The voting device verification mechanisms have more mixed evaluation results, with some notably performing badly from the point of view of usability, or relying on (too) many assumptions for verifiability.

Discussion

✓ The evaluation provides insights into the fundamental properties of the mechanisms from different points of view. It highlights well the respective strengths and trade-offs of mechanisms and their variants.

X The evaluation does not consider full (real-word) systems, which are typically composed out of multiple mechanisms. The need to evaluate a system as a whole, which is more than just the sum of its mechanisms, is also formulated by the study authors.

## 3 Conclusion

The StuVe study describes a selection of the most important mechanisms used in verifiable internet voting with vote secrecy. The evaluation from four perspectives helps to reason about their fundamental properties. It is self-contained, and suited for all kinds of stakeholders (academic, industry, administration) as a starting point into internet voting, with many pointers toward advanced topics.

<footnote n="6">6 Usability is not evaluated for these mechanisms, as the user is not directly involved.</footnote>
However, the evaluation and notably the scores should not be simply taken at face value,
but need interpretation by the critical reader. Further, as with any study assessing the
state-of-the-art, the topic is a quickly moving target due to rapid developments both in
research and industry.

References

[Bu23] Bundesamt für Sicherheit in der Informationstechnik: Projekt 622: Studie zu Ende-zu-Ende-Verifizierbarkeitsmethoden für Online-Wahlen (StuVe), 2023, URL: https://www.evergabe-online.de/tenderdetails.html?id=534759.

[Co16] Cortier, V.; Galindo, D.; Küsters, R.; Müller, J.; Truderung, T.: SoK: Verifiability notions for e-voting protocols. In: IEEE Symposium on Security and Privacy (SP). 2016.

[KV18] Kulyk, O.; Volkamer, M.: Usability is not Enough: Lessons Learned from 'Human Factors in Security' Research for Verifiability. Cryptology ePrint Archive, 2018.

[MKD24] Moser, F.; Kirsten, M.; Dörre, F.: SoK - Mechanisms Used in Practice for Verifiable Internet Voting. In: E-Vote-ID. LNI, Gesellschaft für Informatik e.V., 2024.

[MKV18] Marky, K.; Kulyk, O.; Volkamer, M.: Comparative usability evaluation of cast-as-intended verification approaches in internet voting. In: SICHERHEIT. Gesellschaft für Informatik e.V., 2018.

[Mo24] Moser, F.; Müller, J.; Cortier, V.; Debant, A.; Gaudry, P.; Goetschmann, A.; Küsters, R.; Volkamer, M.: A Study of Mechanisms for End-to-End Verifiable Online Voting, tech. rep., Federal Office for Information Security, Germany, 2024, URL: https://www.bsi.bund.de/SharedDocs/Downloads/EN/BSI/Publications/Studies/Cryptography/End-to-End-Verifiable_Online-Voting.pdf.