Halo2

Open Source

Zcash's Rust proving system implementing PLONKish arithmetization with no trusted setup, widely forked across the ZK ecosystem.

About

Halo2 is the proving system developed by the Electric Coin Company for Zcash's Orchard shielded protocol, implementing a PLONKish arithmetization with an inner-product-argument polynomial commitment that requires no trusted setup. The Privacy & Scaling Explorations (PSE) fork adds KZG commitments and underpins projects like the PSE zkEVM and Scroll. Its flexible custom-gate and lookup-table model is powerful but makes circuits hard to reason about, and under-constrained halo2 circuits are a recognized bug class targeted by tools like Quantstamp's halo2-analyzer. It is maintained in Rust by ECC with an active ecosystem of forks.