Scantegrity II: End-to-End Verifiability for Optical Scan Election Systems using Invisible Ink Confirmation Codes

Abstract

We introduce Scantegrity II, a practical enhancement for optical scan voting systems that achieves increased election integrity through the novel use of confirmation codes printed on ballots in invisible ink. Voters mark ballots just as in conventional optical scan but using a special pen that develops the invisible ink. Verifiability of election integrity is end-to-end, allowing voters to check that their votes are correctly included (without revealing their votes) and allowing anyone to check that the tally is computed correctly from the included votes. Unlike in the original Scantegrity, dispute resolution neither relies on paper chits nor requires election officials to recover particular ballot forms. Scantegrity II works with either precinct-based or central scan systems. The basic system has been implemented in open-source Java with off-the-shelf printing equipment and has been tested in a small election. An enhancement to Scantegrity II keeps ballot identification and other unique information that is revealed to the voter in the booth from being learned by persons other than the voter. This modification achieves privacy that is essentially equivalent to that of ordinary paper ballot systems, allowing manual counting and recounting of ballots.