Scantegrity

Scantegrity is a security enhancement for optical scan voting systems, providing such systems with end-to-end (E2E) verifiability of election results. It uses privacy-preserving confirmation codes to allow a voter to prove to themselves that their ballot is included unmodified in the final tally. Scantegrity II prints the confirmation codes in invisible ink to improve usability and dispute resolution. As the system relies on cryptographic techniques, the ability to validate an election outcome is both software independent as well as independent of faults in the physical chain-of-custody of the paper ballots. The system was developed by a team of researchers including cryptographers David Chaum and Ron Rivest.

End-to-end Verification as an Add-on

Optical scan voting systems produce an electronic tally, while maintaining the original paper ballots which can be rescanned or manually hand-counted to provide an ostensibly corroborative tally. However, the correctness of each of these tallies requires the voter to either trust that the software is error-free and has not been hacked, or that the physical chain-of-custody of the ballots has not been broken at any point. [Citation
last =Rowell
first =Laurie
title =Down for the Count
newspaper =ACM NetWorker Magazine
date =March 2008
url =http://mags.acm.org/networker/200803/
issue =12:1
pages =17-23] Other E2E voting systems such as Punchscan and ThreeBallot, address these issues but require existing polling place equipment and procedures to be greatly altered or replaced. [Citation
last =Hunter
first =Adam
title =Click Here For President: The Future of Voting in America
newspaper =MSN Tech & Gadgets
date =2008
url =http://tech.msn.com/news/article.aspx?cp-documentid=9168472] In contrast, Scantegrity is an add-on mean to be used in conjunction with existing optical scan equipment, thereby requiring fewer hardware and software and procedural modifications. [cite journal
last =Chaum
first =David
authorlink =David_Chaum
coauthors =Aleks Essex, Richard T. Carback III, Jeremy Clark, Stefan Popoveniuc, Alan T. Sherman, Poorvi Vora
title =Scantegrity: End-to-End Voter Verifiable Optical-Scan Voting
journal =IEEE Security & Privacy
date =May/June 2008
url =http://scantegrity.org/papers/scantegrityIEEESP.pdf
issue =6:3
pages =40-46] For all other voters, the ballot marking procedure is essentially identical to conventional optical scan paper-ballots. Similarly, the underlying system still produces both an electronic tally as well as a human readable through which manual recounts can still be conducted.

Voter Experience

The Scantegrity II voting procedure is similar to that of a traditional optical scan voting system, except that each voting response location contains a random confirmation code printed in invisible ink. [cite journal
last =Chaum
first =David
authorlink =David_Chaum
coauthors =Richard Carback, Jeremy Clark, Aleksander Essex, Stefan Popoveniuc, Ronald L. Rivest, Peter Y. A. Ryan, Emily Shen, Alan T. Sherman
title =Scantegrity II: End-to-End Verifiability for Optical Scan Election Systems using Invisible Ink Confirmation Codes
journal =Proceedings of USENIX/ACCURATE EVT
date =2008
url =http://www.usenix.org/event/evt08/tech/full_papers/chaum/chaum.pdf] The voter marks the location using a specially provided "decoder" pen, which activates the invisible ink causing it to darken, revealing a confirmation code. [Citation
last =Lafsky
first =Melissa
title =Protecting Your Vote With Invisible Ink
newspaper =Discover Magazine
date =October 2008
url =http://discovermagazine.com/2008/oct/04-protecting-your-vote-with-invisible-ink]

Voters wishing the verify that their vote is unmodified may write down the confirmation codes for each race on a detachable chit that contains the ballot's serial number. [Citation
last =Mahoney
first =Matt
title =Flawless Vote Counts: Cryptography lets voters confirm that their ballots were tallied correctly
newspaper =Technology Review
date =September/October 2008
url =http://www.technologyreview.com/Infotech/21225/?a=f]

The voter can simply ignore the code and continue to mark and cast their ballot as normal. Those voters choosing to do so may write down the confirmation codes for each race on a detachable chit that contains the ballot's serial number. The confirmation codes are randomly assigned to the ballots, allowing voters to freely share their codes while keeping their votes secret. The codes are also pre-committed to by a committee of mutually-distrustful entities (such as representatives of each political party) so that the confirmation codes cannot be changed or misprinted without detection. Voters may request additional ballots to audit—they ensure the ballots are properly printed by revealing all the codes and comparing these to the codes committed to.

Checking Confirmation Codes

After the election is finished, the election authority publicly posts a list of confirmation codes for the positions marked on each ballot it received. Voters who wrote down their codes can verify that the codes are correct for their ballot number and that no codes were added or removed. [Citation
last =Mahoney
first =Matt
title =Flawless Vote Counts: Cryptography lets voters confirm that their ballots were tallied correctly
newspaper =Technology Review
date =September/October 2008
url =http://www.technologyreview.com/Infotech/21225/?a=f] If the posted record is incorrect, the voter may file a dispute. Spurious disputes can be excluded from consideration by comparing the claimed codes to the set of possible codes for a given contest on a ballot—the probability of randomly guessing a code that actually appeared on the ballot is low.

Tally Verification

After the election, the trustees generate an independent tally from the voter-verifiable list of ballots and confirmation codes. Since the link between a confirmation code and the candidate voted for must remain secret, the tally is generated using an anonymity-preserving backend. Many such backends have been proposed for tallying votes, including the ones used by Punchscan and Prêt à Voter. Scantegrity currently uses a backend based on the Aperio voting system. [cite journal
last =Essex
first =Aleks
coauthors =Jeremy Clark, Carlisle Adams
title =Aperio: High Integrity Elections for Developing Countries
journal =IAVoSS Workshop On Trustworthy Elections
date =2008
url =http://www.site.uottawa.ca/~aesse083/papers/aperio-WOTE.pdf ] Steps in the tally can be recalculated by anyone to ensure its correctness. For this reason, the system is more accurately described as mathematical voting than electronic voting. The security of the system does not require any software to operate correctly, only that the mathematical operations are independently corroborated by all interested parties. [Citation
last =Lombardi
first =Rosie
title =Canadian voting machine enters American political machine
newspaper =InterGovWorld.com
date =March 27, 2008
url =http://www.intergovworld.com/article/eca959c50a01040801d1f967f0e6eacb/pg1.htm]

Further Reading

Academic Papers

* [http://www.usenix.org/event/evt08/tech/full_papers/chaum/chaum.pdf Scantegrity II: End-to-End Verifiability for Optical Scan Election Systems using Invisible Ink Confirmation Codes] . 2008.
* [http://scantegrity.org/papers/scantegrityIEEESP.pdf Scantegrity: End-to-End Voter Verifiable Optical-Scan Voting] . 2008.

Articles

* [http://discovermagazine.com/2008/oct/04-protecting-your-vote-with-invisible-ink Protecting Your Vote With Invisible Ink] (Discover Magazine).
* [http://www.technologyreview.com/Infotech/21225/?a=f Flawless Vote Counts] (Technology Review).
* [http://tech.msn.com/news/article.aspx?cp-documentid=9168472 Click Here For President: The Future of Voting in America] (MSN Tech & Gadgets).
* [http://www.npr.org/templates/story/story.php?storyId=87974935 Shift Back to Paper Ballots Sparks Disagreement] (Morning Edition).
* [http://mags.acm.org/networker/200803/ Down for the Count] (ACM netWorker).
* [http://www.intergovworld.com/article/eca959c50a01040801d1f967f0e6eacb/pg1.htm Canadian voting machine enters American political machine] (InterGovWorld).

Notes

External Links

* [http://www.scantegrity.org Scantegrity.org]
* [http://video.google.com/videoplay?docid=7963759819804190312 Scantegrity II] Video Presentation