Play with ZK on the XRPL EVM Sidechain ✨

With just two lines of code, it is possible to easily generate and verify a ZK proof on the XRPL EVM Sidechain!✨

In this example, we will generate a zk proof (SNARK) and verify it on-chain on the XRPL EVM Sidechain using a Circom circuit representing the multiplication of two integers a and b such as a x b = c.
We want to prove to the verifier that for a given result c, we know the integers a and b without revealing them.
This tutorial uses hardhat-circom, a Hardhat plugin integrating Circom and SnarkJS into Hardhat's build process.

Install

npm i

Configure

1. Add and populate .env with DEV_PRIVATE_KEY=your_DEV_priv_key.
2. Fund your account with XRP on Devnet using this faucet: https://bridge.xrplevm.org/.
3. You can configure hardhat.config.ts and circuits.config.json as you like.

Powers of Tau

You must provide a Powers of Tau from a Phase 1 ceremony. We recommend using one of the .ptau files from the Hermez Protocol's ceremony, available from their Dropbox folder.

These are all named powersOfTau28_hez_final_*.ptau where the * is some number. This number indicates the number of constraints (2^x) that can exist in your circuits.

Nb: I have already included in the repository, within the circuit folder, a .ptau file for a constraint count of up to (2^15).

Circuits and Proof

Circuits are located within the circuits folder. Each circuit will have its own sub-folder with the actual .circom file, which represents the circuit, and an input.json file containing the circuit's inputs (what you want to prove).

Compile

Run: npx hardhat circom --verbose
This will generate the out folder with multiplier.zkey, multiplier.vkey, multiplier.r1cs, and circuit.wasm, as well as the Solidity verifier MultiplierVerifier.sol under the contracts folder.

Deploy Contract - Generate and Verify proof

Run: npx hardhat run scripts/deploy_generate_verify.ts --network XRPL_EVM_Sidechain_Devnet
This script does four things:

1. Deploys the MultiplierVerifier.sol contract.
2. Generates a proof from circuit intermediaries with generateProof() in generate.ts.
3. Generates calldata with generateCallData() in generate.ts.

After generating your proof, you will see a proof.json file in the circuit's out folder. This is actually the proof and contains an attribute publicSignals. For example, if you are proving that you know two numbers a and b such that a * b = c, the value c might be part of publicSignals, while a and b remain private. The verifier checks that the proof is valid for the given c without knowing a and b.

Commands

Here are some commands to generate new proofs and verify them once your circuit is generated and the verifier is deployed.

1. Generate a New Proof: Description: Generates a new proof and saves it to the proof.json file.
   Associated Script: scripts/generate.ts
   Note: Modify the value of BASE_PATH according to the circuit you want to use.
   Run:npx hardhat run scripts/generate.ts --network XRPL_EVM_Sidechain_Devnet

2. Verify an Existing Proof: Description: Verify an existing proof by interacting with the deployed contract.
   Associated Script: scripts/verify.ts
   Note: Modify the value of BASE_PATH according to the circuit you want to use, and update the value of VERIFIER_CONTRACT_ADDRESS with the address of your deployed contract on-chain.
   Command:npx hardhat run scripts/verify.ts --network XRPL_EVM_Sidechain_Devnet

Play arround

• Try modifying the inputs and generating a new proof, then verify it with the same verifier. What happens? Expected Outcome: The proof remains valid and the verifier accepts it because the circuit is the same!

• Try modifying your proof in the proof.json file by changing the value of publicSignals, and then verify it. What happens? Expected Outcome: The proof is no longer valid! The new value of publicSignals, which represents the public statement, does not satisfy the relation defined in your circuit.

Verify the Contract

1. Run npx hardhat flatten contracts/MultiplierVerifier.sol > Flattened.sol.
2. Go to https://explorer.xrplevm.org/ and verify your deployed contract using Flattened.sol.

Documentation

• XRPL EVM Sidechain documentation: https://opensource.ripple.com/docs/evm-sidechain/intro-to-evm-sidechain/
• SnarkJS: https://github.com/iden3/snarkjs
• Based on tutorials from https://github.com/projectsophon/hardhat-circom & https://github.com/gmchad/zardkat.

Troubleshooting

You may encounter errors during deployment (solidity compiler version: * contracts/MultiplierVerifier.sol (^0.6.11)) of the contract related to the automatically generated verifier contract. Simply modify the Solidity version in the contract file to match the one specified in your Hardhat configuration file.

More XRPL EVM Sidechain Tutorials

Repo	Link
Deploy your first Solidity contract on the XRPL EVM Sidechain using Hardhat 👷	GitHub Repository
Next.js x Rainbowkit Wallet configured for the XRPL EVM Sidechain 🌈	GitHub Repository

Additional Resources

Resources	Link
Docs	https://docs.xrplevm.org/docs/evm-sidechain/intro-to-evm-sidechain/
Bridge & Faucet	https://bridge.xrplevm.org/
MetaMask	https://metamask.io/
Solidity	https://docs.soliditylang.org/en/v0.8.26/
Hardhat	https://hardhat.org/
Remix IDE	https://remix.ethereum.org/
Grants	https://xrplgrants.org/
Accelerator	https://xrplaccelerator.org/