Review Your Choices: When Confirmation Pages Break Ballot Secrecy in Online Elections

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Online voting systems typically display a confirmation screen allowing voters to confirm their selections before casting. This paper considers whether a network-based observer can extract information about voter selections from the length of the exchanged network data. We conducted a detailed analysis of the Simply Voting implementation, which had randomly varying lengths of exchanged data due to dynamic page content and gzip compression. We demonstrated that we could correctly guess a voter’s selection with accuracy values ranging up to 100% in some instances. Even on more complex ballots, we generally could still rule out some combinations of candidates. We conducted a coordinated disclosure with the vendor and worked with them to roll out a mitigation. To their credit, this discovery (and therefore its fix) was made possible by their willingness to provide a publicly accessible demo, which, as we will show, remains a rarity in the industry.




Brunet, J., Pananos, A. D., & Essex, A. (2022). Review Your Choices: When Confirmation Pages Break Ballot Secrecy in Online Elections. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 13553 LNCS, pp. 36–52). Springer Science and Business Media Deutschland GmbH.

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