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.

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

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

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

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

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
  

$ npx hardhat test

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");