Halo2 Starter

This repo will help you start building ZK circuits with Halo2 (we'll be using the PSE fork).

Tip

If you’re a beginner and trying to learn the basics of developing with Halo2, check out my beginner tutorial where I’ll teach you how to rewrite TornadoCash with Halo2 > https://github.com/teddav/tornado-halo2

Prerequisite

You need to have Rust installed

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

KZG SRS

You're going to need the result of a "Powers of Tau" ceremony. You can download such a file from https://github.com/han0110/halo2-kzg-srs
Copy the file to proof/ptau directory (I already pre-downloaded the hermez-raw-15 for you).

wget -P ./proof/ptau https://trusted-setup-halo2kzg.s3.eu-central-1.amazonaws.com/hermez-raw-15

Write circuits

You can write your circuits in the circuits directory. You'll find there my "DummyCircuit" example.

MockProver

Halo2 provides a MockProver to quickly test our circuits. You can find a simple test in circuits/tests/prove.rs.
Run with

cargo test prove_mock

Real prover

Running a real prover/verifier is a bit more complex. You will find examples on how to do that in proof/examples.
When calling generate_params() you can specify a Powers of Tau file, or just generate a proof with random SRS (only for testing!).

You can find the entire flow (generate + verify proof) in proof/tests/prove.rs. Run it:

cargo test generate_verify_proof

Notice how a proof generated this way would be worthless: because the KZG parameters are generated during the test and not through a trusted setup.

Generate proof

cargo run --example generate_proof
cargo run --example verify_proof
cargo run --example generate_verifier_solidity

The generated proof (and parameters) will be saved in the output directory

Contracts

In contracts you can find everything you need to run your on-chain tests.
Once you've generated the Verifier contracts, copy them to contracts/src and then run the test_Verify test (in contracts/test/MyContract.t.sol)

forge test --mt test_Verify

Extra features

Graph

https://zcash.github.io/halo2/user/dev-tools.html

Instance columns have a white background.
Advice columns have a red background.
Fixed columns have a blue background.

You can generate the graph for your circuit by running

cargo test generate_graph

Cheat the verifier

I added a special feature just for you: the ability to modify the proof manually and check if verification still passes. This can be useful to check if your circuit is not under-constrained.

You'll find an example on how to do that in circuits/testts/cheater.rs, which you can run with

cargo test cheater

teddav/halo2-starter