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Machine-checking multi-round proofs of shuffle: Terelius-Wikstrom and Bayer-Groth

Thomas Haines, Rajeev Goré, Mukesh Tiwari

SEC '23: Proceedings of the 32nd USENIX Conference on Security Symposium

Swansea University Author: Mukesh Tiwari

Abstract

Shuffles are used in electronic voting in much the same way physical ballot boxes are used in paper systems: (encrypted) ballots are input into the shuffle and (encrypted) ballots are output in a random order, thereby breaking the link between voter identities and ballots. To guarantee that no ballo...

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Published in: SEC '23: Proceedings of the 32nd USENIX Conference on Security Symposium
ISBN: 978-1-939133-37-3
Published: ACM 2023
Online Access: https://dl.acm.org/doi/10.5555/3620237.3620599
URI: https://cronfa.swan.ac.uk/Record/cronfa65926
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Abstract: Shuffles are used in electronic voting in much the same way physical ballot boxes are used in paper systems: (encrypted) ballots are input into the shuffle and (encrypted) ballots are output in a random order, thereby breaking the link between voter identities and ballots. To guarantee that no ballots are added, omitted or altered, zero-knowledge proofs, called proofs of shuffle, are used to provide publicly verifiable transcripts that prove that the outputs are a re-encrypted permutation of the inputs. The most prominent proofs of shuffle, in practice, are those due to Terelius and Wikström (TW), and Bayer and Groth (BG). TW is simpler whereas BG is more efficient, both in terms of bandwidth and computation. Security for the simpler (TW) proof of shuffle has already been machine-checked but several prominent vendors insist on using the more complicated BG proof of shuffle. Here, we machine-check the security of the Bayer-Groth proof of shuffle via the Coq proof-assistant. We then extract the verifier (software) required to check the transcripts produced by Bayer-Groth implementations and use it to check transcripts from the Swiss Post evoting system under development for national elections in Switzerland.
Item Description: https://dl.acm.org/doi/10.5555/3620237.3620599
College: Faculty of Science and Engineering
Funders: Wewould like to thank the shepherd and reviewers for their excellent feedback. Thomas Haines is the recipient of an Australian Research Council Australian Discovery Early Career Award (project number DE220100595). Rajeev Goré supported by FWF project P 33548 and the National Centre for Research and Development, Poland (NCBR), and the Luxembourg National Research Fund (FNR),under the PolLux/FNRCOREproject STV (POLLUX-VII/1/2019).