Zero Knowledge Proof Voting Contract

Even or Odd voting smart contract using Zero Knowledge Proof(zkSNARKs) on Ethereum. Zero Knowledge Proof allows you to vote with privacy.

The number you used for voting is hidden; Only the result is verified by zkSNARKs and stored on the blockchain.

demo_vote.mp4

Example of transaction result: https://ropsten.etherscan.io/tx/0x9447fd2e774b7a9bc465806d69539b53b8bc0d388edaa1eea2a76590f608fa29

Try it out

https://zkp-vote-tomoima525.vercel.app/

Make sure that you are connected to Ropsten network and have some ether in your account

How does this work?

Zokrates is used for Zero Knowledge Proof. Here's the steps:

1. Compute witness by calculating Even or Odd using a program compiled with zokrates-js.
2. Using witness and the proving.key provided by the verifier(in this project, proving.key is in https://github.com/tomoima525/zkp-toy/blob/main/public/proving.key), we generate proof and inputs
3. Submit tranactions to the blockchain. After the zkSNARKs-powered smart contract verifies your proof and inputs, it will update the stored result.

The figure below illustrates the flow

Run locally

We use hardhat for deployment and testing

• Run yarn install
• Start the local node

  $ npx hardhat node
  

• Deploy the smart contract to your local network

  $ npx hardhat run --network localhost scripts/deploy.ts
  ...
  VoteEvenOrOdd deployed to: 0x5FbDB2315678afecb367f032d93F642f64180aa3
  

• Create .env.local file under the root of the project and copy the deployed address

  NEXT_PUBLIC_VOTE_ADDRESS_LOCAL=0x5FbDB2315678afecb367f032d93F642f64180aa3
  

• Start the frontend

  $ yarn run dev
  

Running test

$ npx hardhat test

Setup your own proving.key

You can provide your own proving.key by running Zokrates locally. You also need to generate one when you change your program code

• You need Docker!! E.g. https://docs.docker.com/desktop/mac/install/
• After installing Docker, run the command below to start zokrates with the root directory set to the contracts repository

  $ docker run -v <path for circuits locally>:/home/zokrates/code -ti zokrates/zokrates /bin/bash
  

  e.g.

  $ docker run -v ~/workspace/solidity/zkp-toy/contracts/:/home/zokrates/code -ti zokrates/zokrates /bin/bash
  

• Run the command below to generate the proving.key and the verification.key

  $ zokrates setup
  

• Upload proving.key somewhere accessible
• Update the download link at https://github.com/tomoima525/zkp-toy/blob/main/src/pages/index.tsx#L175

  const res = await fetch("https://your-public.site/proving.key");