zk402-core

Core types and traits for the zk402 zero-knowledge payment scheme.

Overview

This crate defines the foundational types, traits, and wire format for the zk402 payment protocol. It provides the abstraction boundaries that allow different proof systems, verifying key registries, and scheme implementations to be swapped without affecting other components.

Key Features

Zero dependencies on cryptographic libraries - All proving backends are swappable
Wire format types - Matching the x402 specification
ProofSystem trait - Abstract interface for proof generation and verification
VerifyingKeyRegistry trait - Pluggable trust model for circuit verification keys
Scheme trait - Standard interface for facilitator implementations

Types

Wire Format Types

PaymentRequirements - Payment terms from the payee
PaymentPayload - Complete payment data from the payer
PublicInputs - Public inputs to the zero-knowledge proof
ZkExtra - ZK-specific metadata

Response Types

VerifyResponse - Result of proof verification
SettleResponse - Result of on-chain settlement

Usage

Add this to your Cargo.toml:

[dependencies]
zk402-core = "0.1.0"

Example of using the core types:

use zk402_core::{PaymentRequirements, PublicInputs, ProofSystem};

// Define your proof system implementation
struct MyProofSystem;

impl ProofSystem for MyProofSystem {
    type ProvingKey = MyProvingKey;
    type VerifyingKey = MyVerifyingKey;

    fn prove(
        pk: &Self::ProvingKey,
        witness: &Witness,
        public_inputs: &PublicInputs,
    ) -> Result<Vec<u8>, ProofSystemError> {
        // Your proving logic
    }

    fn verify(
        vk: &Self::VerifyingKey,
        proof: &[u8],
        public_inputs: &PublicInputs,
    ) -> Result<bool, ProofSystemError> {
        // Your verification logic
    }
}

Architecture

The zk402-core crate is intentionally minimal and has no cryptographic dependencies. This design allows:

Proof system flexibility - Swap between Groth16, Halo2, or other systems
Trust model flexibility - Use static configs, on-chain registries, or custom solutions
Implementation flexibility - Build facilitators, provers, or custom clients

Related Crates

zk402-groth16 - Groth16 proof system implementation
zk402-prover - Client-side proof generation
zk402-facilitator - Facilitator verify/settle implementation
zk402-wasm - WebAssembly bindings for browser clients

License

Licensed under either of:

Apache License, Version 2.0 (LICENSE-APACHE)
MIT License (LICENSE-MIT)

at your option.

zk402-core 0.1.1