More on ThreeBallot Voting

Last week I posted a short overview of Ron Rivest’s ThreeBallot voting system paper. In his weblog, Ed Felten has begun a discussion about issues related to write-in candidates.

At first, I didn’t think the issue of write-in candidates was much of a problem. An approach for write-ins would be to slightly mechanize the process. Voters would not mark pre-printed ballots. Instead, they would use an isolated ballot generating machine that would let them mark the three ballots and, optionally, add a write-in. The machine would print a three-part ballot that has all the write-in names. This machine would also perform the necessary constraint checks.

Now, this would only partially preserve the secrecy of the ballot. To vote for a write-in, one’s receipt would definitely show the candidate’s name. As long as enough voters wrote-in identical candidate names, no one would know with certainty if the voter actually voted for the write-in or not due to the way the ThreeBallot system works. HOWEVER, and this is a big “however,” this approach (having a machine print the write-in on all three ballots) can be used to prove to someone else how a voter cast their ballot. This can lead to voter coercion and vote selling. Here’s how:

  1. The voter adds a write-in candidate with a unique, silly name like Phoebe Figalilly
  2. The voter marks the three ballots to cast a vote for a candidate (which doesn’t have to be the write-in)
  3. The voter leaves with a copy of one of the ballots listing the unique write-in name
  4. By showing the receipt to a third party, the third party can review the posted list of ballots and find the three with the unique write-in name allowing them to determine how the vote was cast.

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