Selene: Voting with Transparent Verification and Coercion Mitigation

Jun 8, 2016 12:00 AM

Who: Peter Y A Ryan (University of Luxembourg)\
When: 14:30, June 8 \
Where: room EDIT 81033\
Title: {{ page.title }}

In conventional cryptographic E2E verification schemes, voters are provided with encrypted ballots that enable them to confirm that their vote is accurately included in the tally. Technically this is very appealing, but voters, election officials etc. need to understand some rather subtle arguments to appreciate the integrity and ballot secrecy guarantees provided by such mechanisms.

A simple way to achieve a degree of verifiability and ballot privacy is to provide each voter with a unique, private tracking number. Votes are posted on a bulletin board in the clear along with their tracking number. Thus voters can visit the WBB confirm that there is an entry with their tracking number showing the correct vote. The beauty of this approach is its simplicity and understandability. There are, however, two drawbacks: we must ensure that trackers are unique and a coercer can demand that the voter reveal her tracking number. It is interesting to note that the coercer must ask for the tracker before posting. If he asks after posting the voter has a simple strategy to fool him: just reads off a tracker number with the coercer’s required vote from the WBB.

In this talk, I describe a scheme that addresses both of these problems. The main idea is to close off the coercer’s window of opportunity by ensuring that the voters only learn their tracker numbers after votes have been posted. Notification of the trackers must provide high assurance but be deniable. The resulting scheme provides receipt-freeness but also provides a more immediately understandable form of verifiability: voters can find their vote, in the clear, in the tally identified by their secret tracker.

However, there is a sting in the tail: a coerced voter might light on the coercer’s tracker, or the coercer may simply claim that the tracker is his. I describe some elaborations of the basic scheme to counter this problem.

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