ZK as a service

This repository contains example code for using ZK-as-a-service as a second layer for an existing EVM app that can display the result of a secret vote.

An overview of how PBC can be used as a second layer solution can be found here.

Try it out

If you wish to try out a live demo of this example code, each contract has been deployed to the PBC testnet and the Ethereum Goerli testnet

This page describes how to run the example.

How to deploy

Having run the example you may wish to try to deploy these contracts yourself.

If you have made any modifications to the code, make sure that you understand how data is moved from PBC to Ethereum to ensure that it can still happen in a secure manner.

If you wish to know more, you can read details on how it works here.

More information on how to deploy the solution can be found here.

Prerequisites

To be able to compile the PBC smart contract you must have the partisia-contract compiler installed. See the documentation for a guide on how to install the compiler.

To compile and deploy the solidity contract you must have node.js installed.

To make the deployment configuration available for the deployment scripts, create a .env file in the ./public-voting directory, using the following template.

GOERLI_API_URL = "<ENDPOINT_TO_GOERLI_TESTNET>"
GOERLI_PRIVATE_KEY = "<GOERLI_TESTNET_PRIVATE_KEY>"
GOERLI_CONTRACT_ADDRESS = "<ADDRESS_OF_THE_CONTRACT_ON_GOERLI>"
ETHERSCAN_API_KEY = "<API_KEY_TO_ETHERSCAN>"
PBC_CONTRACT_ADDRESS = "<ADDRESS_OF_THE_CONTRACT_ON_PBC_TESTNET>"
ZK_NODE_PUBLIC_KEY_1 = "<1ST_BASE64_ENCODED_PUBLIC_KEY_FOUND_IN_ZK_STATE>"
ZK_NODE_PUBLIC_KEY_2 = "<2ND_BASE64_ENCODED_PUBLIC_KEY_FOUND_IN_ZK_STATE>"
ZK_NODE_PUBLIC_KEY_3 = "<3RD_BASE64_ENCODED_PUBLIC_KEY_FOUND_IN_ZK_STATE>"
ZK_NODE_PUBLIC_KEY_4 = "<4TH_BASE64_ENCODED_PUBLIC_KEY_FOUND_IN_ZK_STATE>"

Build and deploy PBC private smart contract

From working directory ./.

1. Build the PBC contract using the command

   cargo partisia-contract build --release

   The outputs are located at ./target/wasm32-unknown-unknown/release/private_voting.{abi, zkwa}.
2. Deploy PBC contract on PBC testnet.
3. Copy the address of the deployed contract and paste it into the PBC_CONTRACT_ADDRESS field in the .env file.
4. Copy each of the public keys of the ZK nodes in order and paste them into the ZK_NODE_PUBLIC_KEY_1, ZK_NODE_PUBLIC_KEY_2, ZK_NODE_PUBLIC_KEY_3 and ZK_NODE_PUBLIC_KEY_4 fields in the .env file in order.

Deploy solidity contract

From working directory ./public-voting.

1. Fill in the GOERLI_API_URL and GOERLI_PRIVATE_KEY fields in the .env file.
2. In the hardhat.config.js file, uncomment the lines

   defaultNetwork: "goerli",
   

   and

   goerli: {
     url: GOERLI_API_URL,
     accounts: [`0x${GOERLI_PRIVATE_KEY}`],
   },
   

   to enable the Goerli network when running hardhat scripts.
3. Run the commands

   npm install
   npx hardhat run scripts/deploy.js --network goerli

Verifying the contract on goerli.etherscan.io makes it possible to interact with the contract on goerli.etherscan.io.

1. Fill in the GOERLI_CONTRACT_ADDRESS and ETHERSCAN_API_KEY fields in the .env file.
2. Run the command

   npx hardhat run scripts/verify.js --network goerli

Helper scripts

The ./public-voting/scripts directory contains several scripts to help with deploying the solidity contract to Ethereum.

deploy.js

This script help with deploying the PublicVoting.sol contract, using the hardhat runtime.

To work correctly, it expects that the environment variables GOERLI_API_URL, GOERLI_PRIVATE_KEY, PBC_CONTRACT_ADDRESS, ZK_NODE_PUBLIC_KEY_1, ZK_NODE_PUBLIC_KEY_2, ZK_NODE_PUBLIC_KEY_3, and ZK_NODE_PUBLIC_KEY_4 are set. See above for details.

Given the environment variables, the script formats them to form valid constructor arguments before deploying.

The deploy.js script can be run with the command:

npx hardhat run scripts/deploy.js --network goerli

verify.js

This script can be used to verify a deployed contract on the goerli.etherscan.io block explorer.

Verifying contract provides etherscan with an ABI for the contract, making it possible to display the contract state and to interact with the contract via the etherscan UI.

For the script to work it expects the same environment variables as the deploy.js script. Additionally, the variables GOERLI_CONTRACT_ADDRESS and ETHERSCAN_API_KEY must also be available.

The script formats the input from the deploy.js script, which is needed when verifying.

The script can be run with the command

npx hardhat run scripts/verify.js --network goerli

pbc.js

This script can convert a public key, provided by a computation node on PBC, to an Ethereum address.

It is used by the deploy.js and verify.js scripts to format the constructor arguments. It can also be used from the command line, to manually verify that the addresses on Ethereum are correctly derived from a public key from PBC.

Given a public key from PBC A/J83e6pRe9ARxCJNrUxu2iVfh3HTKk4CEYyZFxWn4NG, the script can be run with the command

npx run-func scripts/pbc.js testKey "A9SqNrfygSuXOLNsdy4Gx8d0kSV5S/ET7GCnTVz90FQ7"

Deriving from:    A9SqNrfygSuXOLNsdy4Gx8d0kSV5S/ET7GCnTVz90FQ7
EC point:         d4aa36b7f2812b9738b36c772e06c7c7749125794bf113ec60a74d5cfdd0543bab6ac00abfa468e83e14ea45541e7d3c479c9af4b8d7a83ce8300a88fc20043d
Ethereum Address: b6e8E2BD838518F6Ac146fa6f7271c023723C0d0