🛡️ ShieldRoll: Privacy-Preserving Global Payroll on Stellar

A privacy-preserving payroll distribution system powered by Stellar, Soroban, and Zero-Knowledge Proofs (Groth16). This system allows employers to deposit bulk sums of USDC and distribute them to employees without revealing individual salaries or linking withdrawals to the source deposit.

🚀 Overview

In a traditional transparent blockchain, payroll distributions reveal sensitive employee salary data. This project solves that by using Circom circuits to generate ZK-SNARKs that prove:

1. Summation Integrity: The sum of all private salaries equals the public bulk deposit.
2. Commitment Authenticity: Each salary is correctly hashed and included in a Merkle Tree root.
3. Double-Spend Protection: Each "note" can only be withdrawn once via a cryptographic Nullifier.

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🏗️ Core Components

1. ZK Circuits (/circuits)

• payroll.circom: The "Employer" circuit. It proves that a list of private salaries ${s_1, s_2, ..., s_n}$ sums up to a public $Total$ and generates a Merkle root of commitments.
• withdraw.circom: The "Employee" circuit. It proves that the user knows the preimage of a commitment in the tree and generates a unique nullifier to claim their USDC.

2. Soroban Smart Contract (/contract)

• BN254 Optimization: Leveraging Stellar Protocol 25's native pairing_check host functions for gas-efficient proof verification.
• Nullifier Set: An on-chain registry that prevents any note from being double-claimed.
• Stellar Asset Integration: Fully compatible with USDC and other SEP-24/SAC tokens.

3. Client-Side Proof Generator (/client)

• CSV Processing: Automatically parses employee records.
• Poseidon Hashing: Generates ZK-friendly commitments.
• Proof Generation: Uses SnarkJS to generate Groth16 proofs for the Stellar network.

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🛠️ Getting Started

Prerequisites

• Circom 2.0
• Stellar CLI
• Node.js & TypeScript

Installation

git clone <this-repo>
cd stellar-privacy-payroll
npm install

Circuit Compilation & Setup

# Compile the summation circuit
circom circuits/payroll.circom --wasm --r1cs -o ./build

# Run trusted setup (Powers of Tau) - simplification
snarkjs groth16 setup build/payroll.r1cs ptau/powersOfTau28_hez_final_15.ptau payroll_final.zkey

Running the Payroll

1. Fill client/salaries.csv with 100 employee salaries.
2. Run npx ts-node client/proof_gen.ts to generate the bulk deposit proof.
3. Submit the proof and the root to the Soroban contract via deposit.
4. Employees can then use their individual secrets to withdraw privately.

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🔐 Security & Privacy

• Anonymity Set: Withdrawals are 1-of-100 anonymous within the Merkle root.
• Resistance: Proofs are bound to the recipient address to prevent front-running/hijacking.
• Integrity: Mathematical constraints ensure the employer cannot deposit less than the promised salaries.

📜 License

MIT