@InProceedings{JPRS24,
   author = { Douglas W. Jones and Sunoo Park and Ronald L. Rivest and Adam Sealfon },
   title = { Scan, Shuffle, Rescan: Two-Prover Election Audits With Untrusted Scanners },
   booktitle = { Proceedings Financial Cryptography '24 },
   date = { 2024-03-07 },
   eventdate = { 2024-03-07 },
   OPTyear = { 2024 },
   OPTmonth = { March 7, },
   url = { https://fc24.ifca.ai/ },
   abstract = {
We introduce a new way to conduct election audits using
untrusted scanners.
%
\emph{Post-election audits} perform 
statistical hypothesis testing to confirm election outcomes.
However, existing approaches are costly and laborious for
close elections---often the most important cases to audit---requiring 
extensive hand inspection of ballots.
We instead propose automated consistency checks, 
augmented by manual checks of only a small number of ballots.
Our protocols scan each ballot twice,
shuffling the ballots between scans:
a ``two-scan'' approach inspired by two-prover proof systems.
We show that this gives strong statistical guarantees 
even for close elections,
provided that (1) the permutation accomplished by the shuffle
is unknown to the scanners and
(2) the scanners cannot reliably identify a particular ballot among others
cast for the same candidate.
Our techniques drastically reduce the time, expense, and labor
of auditing close elections, 
which we hope will promote wider deployment.