ZK Payroll Contracts

Privacy-first payroll smart contracts for Stellar/Soroban using zero-knowledge proofs.

Overview

ZK Payroll Contracts enable companies to process payroll on-chain while keeping salary amounts private. Using Stellar's Protocol X-Ray ZK primitives (BN254, Poseidon), employers can prove payments were made without revealing exact amounts.

Features

• Private Salary Commitments — Salary amounts stored as ZK commitments
• Proof-Based Payments — Verify payments without exposing values
• Batch Payroll — Process multiple employees in single transaction
• Compliance Ready — Selective disclosure for audits via view keys
• On-Chain Verification — Groth16 proof verification on Soroban

Architecture

┌─────────────────────────────────────────────────────────┐
│                    ZK Payroll System                    │
├─────────────────────────────────────────────────────────┤
│                                                         │
│  ┌─────────────┐    ┌─────────────┐    ┌─────────────┐ │
│  │   Payroll   │    │   Salary    │    │    Proof    │ │
│  │  Registry   │───▶│ Commitment  │───▶│  Verifier   │ │
│  └─────────────┘    └─────────────┘    └─────────────┘ │
│         │                  │                  │        │
│         ▼                  ▼                  ▼        │
│  ┌─────────────┐    ┌─────────────┐    ┌─────────────┐ │
│  │  Employee   │    │   Payment   │    │   Audit     │ │
│  │  Registry   │    │   Executor  │    │   Module    │ │
│  └─────────────┘    └─────────────┘    └─────────────┘ │
│                                                         │
└─────────────────────────────────────────────────────────┘

Contracts

Contract	Description
payroll_registry	Company registration, employee management
salary_commitment	ZK commitment storage and updates
proof_verifier	Groth16 proof verification using BN254
payment_executor	Private payment execution
audit_module	Selective disclosure for compliance

Prerequisites

Tool	Minimum Version	Purpose
Rust	1.74+	Contract development and testing
Soroban CLI	v21+	Contract deployment
Stellar CLI	v21+	Network interaction
Node.js	18+	Required by snarkjs and circom WASM output
Circom	2.1+	ZK circuit compilation

Installation

# Clone the repository
git clone https://github.com/zkpayroll/zk-payroll-contracts.git
cd zk-payroll-contracts

# Install dependencies
cargo build

# Run tests
cargo test

Quick Start

1. Build Contracts

stellar contract build

2. Deploy to Testnet

# Deploy payroll registry
stellar contract deploy \
  --wasm target/wasm32-unknown-unknown/release/payroll_registry.wasm \
  --network testnet \
  --source alice

3. Initialize Company

// Register a company
payroll_registry.register_company(
    company_id,
    admin_address,
    treasury_address
);

Usage

Register Employee with Private Salary

// Create salary commitment (off-chain)
let commitment = poseidon_hash(salary_amount, blinding_factor);

// Register employee with commitment
payroll_registry.add_employee(
    company_id,
    employee_address,
    salary_commitment
);

Process Private Payroll

// Generate proof (off-chain)
let proof = generate_payment_proof(
    salary_amount,
    blinding_factor,
    recipient
);

// Execute payment with proof
payment_executor.process_payment(
    company_id,
    employee_address,
    proof
);

Compliance Audit

// Generate view key for auditor
let view_key = audit_module.generate_view_key(
    company_id,
    auditor_address,
    time_range
);

// Auditor verifies with selective disclosure
audit_module.verify_with_view_key(view_key, proof);

Project Structure

zk-payroll-contracts/
├── contracts/
│   ├── payroll_registry/
│   │   ├── src/
│   │   │   ├── lib.rs
│   │   │   ├── company.rs
│   │   │   └── employee.rs
│   │   └── Cargo.toml
│   ├── salary_commitment/
│   │   ├── src/
│   │   │   ├── lib.rs
│   │   │   └── commitment.rs
│   │   └── Cargo.toml
│   ├── proof_verifier/
│   │   ├── src/
│   │   │   ├── lib.rs
│   │   │   ├── groth16.rs
│   │   │   └── bn254.rs
│   │   └── Cargo.toml
│   ├── payment_executor/
│   │   └── ...
│   └── audit_module/
│       └── ...
├── circuits/
│   ├── payment.circom
│   └── range_proof.circom
├── scripts/
│   ├── deploy.sh
│   └── generate_proof.sh
├── tests/
│   └── integration_tests.rs
├── Cargo.toml
└── README.md

Cryptographic Primitives

This project leverages Stellar's Protocol X-Ray (Protocol 25) primitives:

• BN254 — Elliptic curve for Groth16 proof verification
• Poseidon — ZK-friendly hash function for commitments
• Groth16 — Succinct proof system for payment verification

Security

• All salary amounts are stored as Poseidon hash commitments
• Payments verified via Groth16 proofs without revealing amounts
• View keys enable selective disclosure for compliance
• No salary data exposed on public ledger

Roadmap

• Core contract architecture
• Payroll registry implementation
• Salary commitment contract
• Groth16 verifier integration
• Payment executor
• Audit module with view keys
• Batch payment optimization
• Multi-currency support

Contributing

We welcome contributions! Please see CONTRIBUTING.md for guidelines.

Good First Issues

Check out issues labeled good-first-issue and stellar-wave for contribution opportunities.

License

MIT License — see LICENSE for details.

Acknowledgments

• Stellar Development Foundation — Protocol X-Ray ZK primitives
• Nethermind — ZK tooling collaboration