Sidechains ZK

Zero knowledge cryptography code and JNI bindings for sidechains, implementing SNARK-based Ad-hoc Threshold MultiSignatures (ATMS).

Overview

This repository contains a proof-of-concept implementation of a Halo2 circuit that provides a proof that there exists t valid signatures of some subset of a given set of public keys. This is the first effort of implementing a SNARK-based Ad-hoc Threshold Multi Signature scheme.

The implementation leverages SNARK-friendly cryptographic primitives:

Zero Knowledge Proving System: Halo2 with KZG commitments
Parent Curve: BLS12-381 (compatible with Cardano Plutus)
Embedded Curve: JubJub curve (defined over BLS12-381 scalar field)
Digital Signature: Schnorr signatures over JubJub curve
Hash Function: Rescue hash for SNARK-friendly operations

⚠️ Important Disclaimer & Acceptance of Risk

This is a proof-of-concept implementation that has not undergone security auditing. This code is provided "as is" for research and educational purposes only. It has not been subjected to a formal security review or audit and may contain vulnerabilities. Do not use this code in production systems or any environment where security is critical without conducting your own thorough security assessment. By using this code, you acknowledge and accept all associated risks, and our company disclaims any liability for damages or losses.

Repository Structure

📁 `prover/` - Core SNARK Implementation

The ATMS circuit implementation using Halo2 with KZG commitments.

Key Features:

Circuit implementation for Ad-hoc Threshold Multi-Signatures
Elliptic curve operations over JubJub curve
Schnorr signature verification within SNARK circuits
Rescue hash function integration
C API bindings for interoperability

Structure:

src/signatures/ - Schnorr and ATMS signature implementations
src/ecc/ - Elliptic curve operations and Halo2 chips
src/rescue/ - Rescue hash function modules
src/c_api.rs - C API bindings
docs/ - Comprehensive cryptographic documentation

📁 `eddsa/` - EdDSA Signature Implementation

Standalone EdDSA signature implementation over the JubJub curve.

Key Features:

EdDSA signature generation and verification
JubJub curve operations
Poseidon hash integration
Cryptographic primitives for signature schemes

API:

sign(msg: &Vec<u8>, prv_key: Scalar) -> EdDsaSignature
verify(sig: EdDsaSignature, pub_key: SubgroupPoint, msg: &Vec<u8>) -> Result<(), ()>

📁 `jubjub/` - JNI Bindings (Scala/Java)

Scala/Java bindings for native cryptographic operations, enabling integration with JVM-based applications.

Structure:

jubjub-native/ - Rust native library with JNI bindings
jubjub-bindings/ - Scala wrapper around native functions

API:

derivePublicKey(privateKey: Bytes): Bytes
sign(data: Bytes, key: Bytes): Bytes
verify(data: Bytes, signature: Bytes, publicKey: Bytes): Boolean
createATMSProof(data: Bytes, signatures: Array[Bytes], keys: Array[Bytes]): Bytes

Building

Prerequisites

Rust (with nightly toolchain for cbindgen)
Scala 2.13.10
SBT 1.8.2+
Java 17+

Building Rust Components

# Build the main prover library
cd prover
cargo build --release

# Build EdDSA component
cd eddsa
cargo build --release

# Build native JNI library
cd jubjub/jubjub-native/src/native
cargo build --release

Generate C Headers

# Install cbindgen
cargo install cbindgen

# Generate header file from prover directory
cd prover
rustup run nightly cbindgen ./ --config cbindgen.toml --crate atms-halo2 --output target/include/atms_halo2.h

Building Scala/Java Components

cd jubjub
sbt compile

Testing

Rust Tests

# Run tests for prover
cd prover && cargo test

# Run tests for eddsa
cd eddsa && cargo test

# Run benchmarks
cd prover && cargo bench

Scala Tests

cd jubjub
sbt test
sbt IntegrationTest/test

Cryptographic Background

Ad-hoc Threshold Multi-Signatures (ATMS)

ATMS is a multisignature scheme that allows key-pair owners to create a threshold signature without complex distributed key generation (ad-hoc) or interactive signature procedures. The original paper "Proof-of-Stake Sidechains" by Gazi, Kiayias, and Zindros proposes three construction methods:

Trivial ATMS: Simple aggregation with individual verification
Pairing-based ATMS: Efficient but requires full participation
SNARK-based ATMS: Most efficient signatures, verifier independent of participation

This implementation focuses on SNARK-based ATMS for optimal efficiency and scalability.

Documentation

Comprehensive documentation is available in the prover/docs/ directory:

Introduction - Overview and roadmap
ECC Preliminaries - Elliptic curve cryptography
Schnorr Signatures - Signature scheme details
ATMS Implementation - Threshold signature construction
Rescue Hash - Hash function specification
Flow - Operational workflow
Primitives - Cryptographic primitive relationships

License

Licensed under the Apache License, Version 2.0 (the "License"). You may not use this repository except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an " AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License

input-output-hk/sidechains-zk