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private-payment

README.md

Private Payments

Status: Complete Privacy Primitive: Confidential stablecoin transfers with regulatory compliance

Overview

This PoC group demonstrates privacy-preserving institutional payment protocols. Institutions can deposit, transfer, and withdraw stablecoins without exposing amounts, counterparties, or transaction patterns to public observers, while maintaining auditability for regulators.

Two implementation approaches are provided:

Approach Description Location
Shielded Pool On-chain UTXO pool with ZK proofs (Noir/Groth16) shielded-pool/
Plasma (Intmax) Stateless ZK-rollup with off-chain transfers plasma/

Requirements

See REQUIREMENTS.md for the shared requirements both approaches implement.

Specifications

Comparison

Aspect Shielded Pool Plasma (Intmax)
Deployment Ethereum L1 L2 rollup (posts roots to L1)
State model UTXO (commitments, nullifiers) UTXO (client-side balance trees)
Privacy mechanism ZK proofs per transaction ZK proofs per transaction
Proving system Groth16 via Noir/Barretenberg Plonky2 (recursive, transparent)
Trusted setup Yes (circuit-specific) None
Operator required No, but compliance authority required Yes (block builder, validity prover)
Gas cost per transfer ~2.6M (user pays directly) Off-chain (operator posts batched roots)
Proof generation Sub-second, client-side Multi-second, mix of client-side + server-side
Regulatory access Per-note viewing keys Dual-key (viewing key for audits)
Client requirements Wallet with local proving SDK with network calls to operator services

Benchmarks

See BENCHMARK.md for gas costs, proof generation latency, and an interpretation of the results.

Quick Start

Shielded Pool

cd shielded-pool

# Install Solidity dependencies
forge soldeer install

# Build and test contracts
forge build && forge test

# Build and test circuits
nargo compile --workspace && nargo test --workspace

See shielded-pool/README.md for E2E test instructions and deployment configuration.

Plasma (Intmax)

cd plasma

# Build
cargo check

# Run integration test (requires Docker + Anvil)
cargo test --release -- --nocapture

See plasma/README.md for prerequisites and known limitations.

Known Limitations

See each approach's README for specific limitations:

References