Rust Circuit Compiler (RCC)

A proof-of-concept zk circuit building and witness generation library.

Why another circuit builder?

RCC has two main differentiating factors from existing zk circuit libraries.

1. Separation of circuit building and witness generation. In RCC, circuit builders do not compute witnesses, instead, they generate rust code which is then compiled into the witness generator (similar to Circom). This makes witness generation very efficient.
2. Abstraction via traits. High-level circuits can be built generically over traits, which enables circuit re-use. Backends can implement these traits in the most efficient manner available to the backend, such via custom and lookup gates.

FAQ

• Q: I'm building a new zk proving backend in rust, why should I integrate with RCC?
• A:
  1. Implementing an RCC circuit builder means that your backend get access to high-level circuit functionalities, for free.
  2. RCC provide a way for your circuit builder to build a very efficient witness generator.

RCC vs. ...

We take heavy inspirations and lessons from Circom and other rust-based circuit building libraries, including:

• Arkworks R1CS builder
• ECLAIR / OpenZL
• halo2-lib by Axiom
• halo2-wrong by PSE
• Plonky2
• Boojum

The main difference between RCC and other circuit builders in Rust:

• RCC works like Circom, where witness generation code is generated during circuit building. This enables parallelism for witness generation.
• RCC focuses on ergonomics of circuit writing (see traits) and provides command-line tools to work with circuits (TODO).

The main difference between RCC and Circom:

• Witness generator in RCC is not restricted to field operations and can be arbitrary rust code.
• RCC is not tied to a particular proving backend. It is relatively easy to write a new proving backend for RCC. RCC also aims to support all style of proof systems, from R1CS, Plonkish, to layered arithmetic circuits (e.g. GKR).

Compilation Pipeline

The high-level flow is as follows:

                                       ┌────────────────┐
                                   ┌──►│ circuit_config │
                                   │   └────────────────┘
                                   │
                                   │
┌─────────────┐ rustc ┌──────────┐ │   ┌────────────────┐ rustc   ┌──────────┐    ┌───────────┐
│ circuit.rs  ├───────┤  binary  ├─┴──►│ runtime_lib.rs ├────────►│ runtime  ├───►│ witnesses │
└─────────────┘       └──────────┘     └────────────────┘         └─────▲────┘    └───────────┘
                                                                        │
                                                                        │
                                                                        │
                                                                  ┌─────┴────┐
                                                                  │  input   │
                                                                  └──────────┘

Example circuits

Example circuits and instructions to compile them can be found in circuit-examples.

License & Contribution

Licensed under either of the following licenses, at your option.

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.