What did I really vote for? On the usability of verifiable e-voting schemes

E-voting has been embraced by a number of countries, delivering benefits in terms of efficiency and accessibility. End-to-end verifiable e-voting schemes facilitate verification of the integrity of individual votes during the election process. In particular, methods for cast-as-intended verification enable voters to confirm that their cast votes have not been manipulated by the voting client. A well-known technique for effecting cast-as-intended verification is the Benaloh Challenge. The usability of this challenge is crucial because voters have to be actively engaged in the verification process. In this paper, we report on a usability evaluation of three different approaches of the Benaloh Challenge in the remote e-voting context. We performed a comparative user study with 95 participants. We conclude with a recommendation for which approaches should be provided to afford verification in real-world elections and suggest usability improvements

Efficiency Comparison of Various Approaches in E-Voting Protocols

In order to ensure the security of remote Internet voting, the systems that are currently proposed make use of complex cryptographic techniques. Since these techniques are often computationally extensive, efficiency becomes an issue. Identifying the most efficient Internet voting system is a non-trivial task -- in particular for someone who does not have a sufficient knowledge on the systems that currently exist, and on the cryptographic components that constitute those systems. Aside from these components, the efficiency of Internet voting also depends on various parameters, such as expected number of participating voters and ballot complexity. In this paper we propose a tool for evaluating the efficiency of different approaches for an input scenario, that could be of use to election organizers deciding how to implement the voting system

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

Extending the Helios Internet Voting Scheme Towards New Election Settings

Internet voting has long been a topic both of public discussion and also of scientific research. While the introduction of Internet voting may bring many advantages, it is further important to ensure an adequate level of security of the systems and underlying schemes that are used for casting and tallying the votes in order to encourage faith and acceptance for this relatively new way of voting. A number of cryptographic schemes have been proposed, that enable secure Internet voting. One of the most established and well-researched solutions is the Helios scheme, which is also implemented as an open-source system. Both its implementation and the scheme behind it has been extensively studied in the literature, and the Helios system has been used for numerous elections in practice, such as the IACR elections. However, there are election settings for which Helios is currently not appropriate, either due to infrastructure demands, required functionality for the voters or assurance of the security requirements. These kinds of election settings could benefit from the advantages that secure Internet voting provides. In this thesis we identify the election settings not currently supported by Helios, propose our extensions for each one of these settings and evaluate their security. Hence, this work describes four Internet voting schemes that are build upon Helios, with each scheme developed towards a specific setting. The first scheme presented here enables elections within the so-called boardroom voting setting. This setting is characterized by its decentralization, whereby all the tasks within the election are distributively performed by the voters themselves, without the support of a centralized infrastructure. The election in the boardroom voting setting are further conducted in an ad-hoc manner, so that limited time is available for preparation beforehand. We propose an extension of Helios that distributes the tasks of the voting system components in Helios among the voters. For this, we use cryptographic primitives such as decentralized key exchange with short authentication strings, distributed secret sharing and distributed decryption and Byzantine agreement. The second scheme extends Helios with proxy voting functionality. Proxy voting, as a newly emerged form of voting, enables the voter to delegate her voting right in the election to a trusted third-party, the so-called proxy, who is authorized to vote on the voter's behalf. This extension facilitates such delegation while assuring the security for delegating voters and for the proxies and preserves the security guarantees provided by Helios for the voters who vote directly (instead of delegating). For ensuring the security of our extension, we introduce the so-called delegation credentials that are assigned to the voters and are used to compute anonymized delegation tokens sent to the proxies to enable delegation. We further use cryptographic primitives such as proofs of knowledge and signatures of knowledge. The third scheme combines the first two settings to extend Helios towards the proxy boardroom voting setting, namely, a setting in which the elections are performed in a decentralized way as in boardroom voting, yet the voters who cannot participate in the election themselves are allowed to delegate their voting right to a trusted proxy before the election. The security of our extension is assured with threshold secret sharing and Pedersen commitments. The fourth scheme extends Helios by improving its security. As such, it introduces participation privacy, meaning that the voting system does not reveal which voters have participated in the election, while supporting verification that only the eligible voters have cast their ballots in the election. The extension furthermore introduces receipt-freeness, ensuring that the voter cannot create a receipt that proves to a third party how she voted, thus preventing vote selling. To ensure the security of the extension, a new kind of entity is introduced, the posting trustee, and a new kind of ballot, the so-called dummy ballot that is indistinguishable from a normal ballot cast by the voter, but does not modify the election result. We furthermore use disjunctive zero-knowledge proofs and proofs of signature knowledge to prove, that a sender of a particular ballot knows the private signature key of an eligible voter, or that the ballot is a dummy ballot. For each one of the extensions, the security model is provided, which describes the security requirements and the assumptions that are necessary for ensuring the security requirements (i.e. vote privacy or vote integrity), is provided. For the first three extensions, the security model is used as a base for the informal security evaluation, in which an informal argument is used to show, that the security requirements hold under the described assumptions. Conducting a formal security evaluation for these extensions is considered an important part of the future work, in which new formal definitions have to be developed. For the fourth extension, we provide a formal security analysis that relies on the formal definitions for the security requirements of vote privacy, vote integrity and eligibility, available in the literature. We furthermore introduce new formal definitions for participation privacy, receipt-freeness and fairness, which we also use for the formal proofs of our extension

People want reassurance when making privacy-related decisions — Not technicalities

Online service users sometimes need support when making privacy-related decisions. Humans make decisions either slowly, by painstakingly consulting all possible information, or quickly, by relying on cues to trigger heuristics. Human emotions elicited by the decision context affects decisions, often without the decision maker being aware of it. We wanted to determine how an information-based decision can be supported, and also to understand which cues are used by a heuristics-based approach. Our first study enhanced understanding of underlying encryption mechanisms using metaphors. Our participants objected to efforts to make them ‘technical experts’, expressing a need for reassurance instead. We fed their free-text responses into a Q-sort, to determine which cues they rely on to make heuristic-based decisions. We confirmed the desire for reassurance. Our third study elicited ‘cyber stories’: Unprompted narratives about cyber-related experiences to detect emotional undertones in this domain. Responses revealed a general negativity, which is bound to influence cybersecurity-related decisions

Extending Helios Towards Private Eligibility Verifiability

We show how to extend the Helios voting system to provide eligibility verifiability without revealing who voted which we call private eligibility verifiability. The main idea is that real votes are hidden in a crowd of null votes that are cast by others but are indistinguishable from those of the eligible voter. This extended Helios scheme also improves Helios towards receipt-freeness

Security Proofs for Participation Privacy and Stronger Verifiability for Helios

The Helios voting scheme is well studied including formal proofs for verifiability and ballot privacy, but it does not provide participation privacy (i.e. it reveals who participated in the election). Kulyk, Teague and Volkamer proposed an extension to Helios that is claimed to provide ballot privacy as well as participation privacy while providing stronger verifiability than Helios. However, the authors did not prove their claims. Our contribution is to provide a formal definition for participation privacy and to prove that their claims hold