End-to-End Verifiability for Ranking-based E-Voting Systems

There are many different systems for conducting and deciding the result of an election or referendum. One of the more popular electoral systems is the plurality system: the candidate with the most votes wins the election. We use the term "First Past the Post" (FPTP) to refer to a plurality system which elects a single member or party. FPTP is often criticized for producing results which are unrepresentative of the votes cast by its participants; large parties are often over-represented whilst smaller parties are often under-represented. Ranked voting systems exist to provide a fairer and more representative result compared to plurality systems. The Condorcet method is one ranked voting system which uses pairwise comparisons between all choices to declare a winner, however circular ambiguities may result in no winner. Another example of a ranked voting system is Single Transferable Vote (STV), which aims to achieve representation by allowing voters to rank their choices directly. STV elects multiple winners, so if a voter's first choice does not win under STV, then their vote is applied to their next highest ranked choice. This process repeats until all choices are exhausted.

Whilst we may decide between many different voting systems, there are few ways to cast votes within these systems. The traditional method involves voting in person at a local polling station. It is often the case that a person cannot visit their local polling station to cast their vote for many reasons: a person may live too far away from their polling station, a person's working hours may clash with those of the polling station and individuals with disabilities may find it difficult to reach their polling station. Some voting systems allow remote voting in the form of posted ballots; however, these often require registering for a postal vote some months in advance of an election and postal delays may delay the vote. This motivates the need for a secure, remote electronic voting (e-voting) system usable in the case where local voting is impossible. These remote voting systems should be End-to-End (E2E) verifiable and have no tallying authority, allowing voters to verify that their votes were casted as intended and to verify that every vote was tallied correctly to produce the result of the election, without the need to trust a potentially corrupt authority.

E2E verifiable voting systems without tallying authorities have been proposed for FPTP (such as DRE-ip), however there is a lack of such protocols for ranking based systems including Condorcet and STV. The aims of this project are to: 1. Explore E2E verifiability without tallying authorities for the Condorcet method; 2. Extend the exploration for STV; 3. Contribute to ongoing trials for e-voting.