Placeholder verifier

Placeholder proof system and its associated verifier offer an efficient solution for zero-knowledge proof verification.

Whether you are building complex decentralized applications or need to verify the correctness of computations in a trustless manner, Placeholder provides flexibility and modularity to meet your specific requirements.

This documentation serves as a guide to help you make the most of this powerful tool.

What is Placeholder

Placeholder proof system is a cutting-edge proof system with IVC (Incrementally Verifiable Computations) and custom gates.

It's built to enable zero-knowledge functionality and secure interactions on the Ethereum blockchain and other blockchain networks.

Placeholder serves a zero-knowledge succinct non-interactive argument of knowledge (zkSNARK) based on PlonK-style arithmetization.

Its modularity allows configuring and adapting it for various use cases, each with distinct security requirements.

For technical details and implementation insights, you can explore the source code in Crypto3's GitHub repository.

What is Placeholder verifier

Placeholder verifier is an essential component that enables the in-EVM verification of zero-knowledge proofs generated using the Placeholder proof system.

It's a smart contract application that can be deployed on different Ethereum networks, including local, test, and main networks.

Currently, it's deployed on the Sepolia network (contract).

You can check the full code and tests on GitHub.

Installing verifier as a dependency

The verifier is published as an npm package, so you can easily add it as a dependency for your project.

Open a terminal and run the following command from your project's home:

npm install @nilfoundation/evm-placeholder-verification@1.1.1

Alternatively, you can manually add it to your project's package.json file by including the following line:

"@nilfoundation/evm-placeholder-verification": "1.1.1"

On-chain verification

For on-chain verification of zero-knowledge proofs via Placeholder verifier import the verifier contract in your Solidity code as shown below:

import '@nilfoundation/evm-placeholder-verification/contracts/verifier.sol';

To use the verifier contract, you're going to need the following parameters:

• address for the deployed verifier contracts;
• address for the deployed gate arguments.

For examples of contracts that utilize the verifier, you can refer to the following repositories:

Basic example of a verifier;

Mina state verification.

Contract Addresses

PlaceholderVerifier

Network	Address
Sepolia	0x489dbc0762b3d9bd9843db11eecd2a177d84ba2b

UnifiedAdditionVerifier

UnifiedAdditionVerifier is a part of Proof Market's Endpoint.

Network	Address
Sepolia	0xc6E7A6Dcad73D499520DDdf5d9b56E0E18DD9bAd

Building from sources

You can follow these steps if you prefer to build the verifier from sources.

1. Clone the project from GitHub:

git clone git@github.com:NilFoundation/evm-placeholder-verification.git

2. Navigate to the evm-placeholder-verification directory:

cd evm-placeholder-verification

3. Install the necessary dependency packages:

npm i

4. Run the following command in your terminal to compile the verifier's contracts:

npx hardhat compile

5. The tests for this application are located in the test directory. You can execute tests using the following commands:

npx hardhat test # Execute tests
REPORT_GAS=true npx hardhat test # Test with gas reporting

Deploying the verifier

Local network

First, launch a Hardhat node using the following command:

npx hardhat node

Keep the terminal open and the network running for the subsequent deployment steps.

To deploy to a test environment (Ganache, for example), run the following command in another terminal window:

npx hardhat deploy --network localhost

By default, Hardhat reuses old deployments. Add the --reset flag to force a fresh deployment.

Live networks

For deployments to live Ethereum networks like Sepolia, follow the Hardhat's deployment guide for specific instructions.

Local verification of zkLLVM circuit compiler output

You can use Placeholder verifier for local verification of zero-knowledge proofs generated by the zkLLVM compiler. This is a powerful feature that allows you to validate proofs without relying on external parties.

1. Follow the steps from Building from sources section.

2. Use the zkLLVM compiler to prepare circuits as instantiated contracts that can be deployed to a blockchain.

3. Once you get zkLLVM output, create a circuit directory under contracts/zkllvm for your output. That directory should contain the following files:

• proof.bin — Placeholder proof file
• circuit_params.json — parameters file
• public_input.json — file with public input
• linked_libs_list.json — list of external libraries to be deployed for gate argument computation
• gate_argument.sol, gate0.sol, ... gateN.sol — Solidity files with gate argument computation

4. With all these files in place, you can deploy the verifier application and start verifying proofs. You only need to deploy the verifier once, and then you can verify as many proofs as you need.

To deploy the verifier contracts, run:

npx hardhat deploy

Assuming you've placed your zkLLVM output files in a directory like contracts/zkllvm/circuit-name, you can verify the proofs with this command:

npx hardhat verify-circuit-proof --test circuit-name

To verify all circuits from the contracts/zkllvm directory, run:

npx hardhat verify-circuit-proof-all