A Privacy-Preserved Voting Protocol

Introduction

This project implements the voting protocol described in protocol.md. There are three contracts:

• BinaryVote - implements a single vote where voters are only allowed to cast a YES or NO ballot. Note that the contract uses the P256 or Secp256r1 elliptic curve.
• VotingContract - responsible for hosting multiple votes and executing requests from users to call functions of a deployed BinaryVote contract.
• VoteCreator - responsible for creating new votes through deploying BinaryVote and registering the instance in VotingContract.

Their relationships have been illustrated by the figure below.

Pros and Cons of the Voting Protocol

Pros

• Ballot privacy - no one except the voting authority knows the ballot contents.
• Ballot verifiable
  • Voters can verify the existence of their ballots.
  • Anyone can verify the validity of a recorded ballot.
  • Recorded ballots are immutable.
• Tally results universally verifiable
  • Anyone can verify that all and only the valid ballots have been tallied.
  • Anyone can verify the correctness of the tally results.
• Voters are allowed to cast multiple times and the newer ballot will replace the previous one cast by the same voter.

Cons

• The voting authority has to be trusted to keep ballot privacy and conduct timely tallying.

Voting Process

The following is the whole voting process:

1. The voting authority creates a new vote via VoteCreator.newBinaryVote. The ID of the created vote is compted by keccak256(authority_address, deployed_contract_address).
2. The voting authority generates a key pair for the vote and register the public key via VotingContract.setAuthPubKey.
3. Voters upload their ballots via VotingContract.cast.
4. The voting authority ends the casting period via VotingContract.beginTally.
5. The voting authority off-chain computes the tally result and upload the result via VotingContract.setTallyRes.
6. The voting authority ends the tally period via VotingContract.endTally.
7. Anyone can verify the result via VotingContract.verifyTallyRes. They can also verify individual ballot via VotingContract.verifyBallot.

./test/testVotingContract.js implements the code for testing a complete voting process.

Limitations

The implementation is created as a prototype of a privacy-preserved voting system. Therefore, it does not include features such as timing control and voter registration that are commonly seen in a typical voting process. The system currently only supports the vote where voters cast YES/NO ballots.