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Compilation Artifacts and Serialization

This document provides an in-depth explanation of the primary compilation artifacts - the layered circuit and the input solver, as well as their respective serialization formats.

Layered Circuit​

The layered circuit is a crucial component that represents the final structure of the compiled circuit. It is used by both the prover and verifier during the zero-knowledge proof process.

Format Specification​

The layered circuits are structured according to the definitions provided in layered/circuit.go.

Overview​

The entire circuit is known as RootCircuit, while individual layers are referred to as Circuit.

A RootCircuit consists of multiple layers, each containing 2n2^n gates. A Circuit encapsulates the interconnections of gates between two successive layers.

Circuits can recursively include other circuits as sub-circuits.

The identifier for a Circuit corresponds to its position within the RootCircuit.Circuits array.

The RootCircuit.Layers array holds the identifiers for each layer's Circuit.

Distinct Representations​

A gate is considered random if its Coef is equivalent to RootCircuit.Field.

Serialization Process​

At its core, uint64 types are serialized in little-endian format, while big.Int types are serialized as 1/4/32-byte little-endian sequences depending on the particular field.

The serialization of an array begins with a uint64 that denotes its length, followed by the serialized representation of its elements.

A unique identifier, the magic number 3770719418566461763 (b'CIRCUIT4'), is prefixed to the serialized RootCircuit data stream to ensure data integrity.

Refer Go implementation and Rust implementation for details.

Input Solver​

The input solver (irwg.RootCircuit), or witness solver, is an intermediary form of the circuit that facilitates witness generation.

Refer Go implementation, Rust implementation for circuit and Rust implementation for instruction for details.

Witness Serialization​

The witness, an array of big.Int, serves as the input for the layered circuit. It is also defined in ir/input_solver.go.

One witness file contains one or multiple witnesses, stored in a compact form.

Refer Go implementation for details.