Book review: Applied cryptography: Protocols, algorithms, and source code in C

There have been intensive research efforts in the last two decades or so to design and deploy electronic voting (e-voting) protocols/systems which allow voters and/or external auditors to check that the votes were counted correctly. This security property, which not least was motivated by numerous problems in even national elections, is called verifiability. It is meant to defend against voting devices and servers that have programming errors or are outright malicious. In order to properly evaluate and analyze e-voting protocols w.r.t.~verifiability, one fundamental challenge has been to formally capture the meaning of this security property. While the first formal definitions of verifiability were devised in the late 1980s already, new verifiability definitions are still being proposed. The definitions differ in various aspects, including the classes of protocols they capture and even their formulations of the very core of the meaning of verifiability. This is an unsatisfying state of affairs, leaving the research on the verifiability of e-voting protocols in a fuzzy state. In this paper, we review all formal definitions of verifiability proposed in the literature and cast them in a framework proposed by Kuesters, Truderung, and Vogt (the KTV framework), yielding a uniform treatment of verifiability. This enables us to provide a detailed comparison of the various definitions of verifiability from the literature. We thoroughly discuss advantages and disadvantages, and point to limitations and problems. Finally, from these discussions and based on the KTV framework, we distill a general definition of verifiability, which can be instantiated in various ways, and provide precise guidelines for its instantiation. The concepts for verifiability we develop should be widely applicable also beyond the framework used here. Altogether, our work offers a well-founded reference point for future research on the verifiability of e-voting systems.

/pdf/sok-verifiability-notions-for-e-voting-protocols-hlydbs7y2d.pdf

SoK: Verifiability Notions for E-Voting Protocols

Elections seem simple—aren’t they just about 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. They also have practical constraints: time is of the essence, and voting systems need to be affordable and maintainable, as well as 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.

Public Evidence from Secret Ballots

We present the electronic voting protocol Belenios together with its associated voting platform. Belenios guarantees vote privacy and full verifiability, even against a compromised voting server. While the core of the voting protocol was already described and formally proved secure, we detail here the complete voting system from the setup to the tally and the recovery procedures.

https://hal.inria.fr/hal-02066930/document

Belenios: a simple private and verifiable electronic voting system

Modern remote electronic voting systems, such as the prominent Helios system, are designed to provide vote privacy and verifiability, where, roughly speaking, the latter means that voters can make sure that their votes were actually counted. In this paper, we propose a new practical voting system called sElect (secure/simple elections). This system, which we implemented as a platform independent web-based application, is meant for low-risk elections and is designed to be particularly simple and lightweight in terms of its structure, the cryptography it uses, and the user experience. One of the unique features of sElect is that it supports fully automated verification, which does not require any user interaction and is triggered as soon as a voter looks at the election result. Despite its simplicity, we prove that this system provides a good level of privacy, verifiability, and accountability for low-risk elections.

sElect: A Lightweight Verifiable Remote 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.

Ordinos: A Verifiable Tally-Hiding E-Voting System

Mix nets are often used to provide privacy in modern security protocols, through shuffling. Some of the most important applications, such as secure electronic voting, require mix nets that are verifiable. In the literature, numerous techniques have been proposed to make mix nets verifiable. Some of them have also been employed for securing real political elections.

/pdf/a-verifiable-and-practical-lattice-based-decryption-mix-net-2bkecjc212.pdf

A Verifiable and Practical Lattice-Based Decryption Mix Net with External Auditing

Since David Chaum introduced the idea of mix nets 40 years ago, they have become widely used building blocks for privacy-preserving protocols. Several important applications, such as secure e-voting, require that the employed mix net be verifiable. In the literature, numerous techniques have been proposed to make mix nets verifiable. Some of them have also been employed in politically binding elections. Verifiable mix nets differ in many aspects, including their precise verifiability levels, possible trust assumptions, and required cryptographic primitives; unfortunately, these differences are often opaque, making comparison painful. To shed light on this intransparent state of affairs, we provide the following contributions. For each verifiability technique proposed to date, we first precisely describe how the underlying basic mix net is to be extended and which (additional) cryptographic primitives are required, and then study its verifiability level, including possible trust assumptions, within one generic and expressive verifiability framework. Based on our uniform treatment, we are able to transparently compare all known verifiability techniques for mix nets, including their advantages and limitations. Altogether, our work offers a detailed and expressive reference point for the design, employment, and comparison of verifiable mix nets.

/pdf/sok-techniques-for-verifiable-mix-nets-t9pfcm3iu3.pdf

Johannes Müller

Papers

SoK: Verifiability Notions for E-Voting Protocols

sElect: A Lightweight Verifiable Remote Voting System

Ordinos: A Verifiable Tally-Hiding E-Voting System

A Verifiable and Practical Lattice-Based Decryption Mix Net with External Auditing

SoK: Techniques for Verifiable Mix Nets