Private P2P Bridge – Universal L2 Privacy for P2P Trading

Aztec
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Grant Proposal: Private P2P Bridge – Universal L2 Privacy for P2P Trading

Title: Private P2P Bridge

Summary

We propose a bridge that connects any L2 (demoed with Base) to Aztec’s testnet, adding privacy to our multi-chain P2P trading app. Merchants list ads across L2s, with consumers buying via smart contract escrow and bridges like Across. This relayer-based bridge locks USDC on Base with a taker-generated secret hash, mints zk-USDC on Aztec for private execution, and releases USDC to Arbitrum using partial notes.

Demo: A merchant on Base privately sells USDC to an Arbitrum buyer, with gas sponsored via an FPC using deposit tokens. The UI simplifies trade initiation, leveraging Aztec’s global privacy set. This extends privacy universally, unifying Ethereum without liquidity splits.

Start and End Date

  • Start: April 1, 2025
  • MVP on Aztec Testnet: June 30, 2025

About Us

Our team built a P2P trading app supporting multiple L2s (e.g., Base, Arbitrum), processing over 10k transactions over 18 months. With expertise in smart contract development, blockchain architecture, and UX, we’re set to integrate Aztec’s privacy tech universally.

Our vision: Make private P2P trading the L2 standard, contributing bridge contracts and tutorials to Aztec’s ecosystem.

Contact:
contact@iexchange.global

Links:

Details

  • Cross-Chain App: Demo a private USDC trade (Base → Aztec → Arbitrum).
  • Bridge Type: Relayer-based (trusted initially), chosen for MVP speed.
    • Trust Assumption: Relayer honesty, with a roadmap to ZK proofs (RIP-7755).
  • Design:
    • USDC locks on Base with Pedersen secretHash (taker-generated).
    • Relayer mints zk-USDC on Aztec, private escrow settles.
    • Partial notes enable private withdrawal to Arbitrum with secretHash2.
    • FPC sponsors gas using USDC deposit.
    • Relayer pre-funds Arbitrum USDC payouts, bridging via Across or another protocol if liquidity is low.
  • Technical Hurdles: Noir learning, Pedersen hash UI integration, relayer security, FPC setup.
  • User Flow:
    1. Merchant lists USDC ad on Base.
    2. Buyer on Arbitrum accepts, provides secretHash.
    3. Funds bridge to Aztec.
    4. Private escrow hides amounts.
    5. FPC deducts gas from USDC deposit, pays sequencer.
    6. Relayer bridges to Arbitrum with secretHash2.
    7. Taker claims with pre-image.
    8. UI shows status.
  • Standout: Sample Noir escrow with partial notes; UI mockup for multi-L2 trade tracking.

Grant Milestones and Roadmap

  1. April 15: Bridge design, relayer setup, Noir/Pedersen basics (Sandbox).
  2. May 15: Bridge + escrow coded, partial notes tested locally.
  3. June 15: UI + FPC integration, edge case handling.
  4. June 30: MVP on Aztec testnet (Base → Aztec → Arbitrum USDC trade).
  5. August 2025: Upgrade relayer bridge to a ZK-proof model.
  6. December 2025: Mainnet launch with full multi-L2 support.
  7. Long-Term: Extend to private stablecoin swaps across all L2s.

Grant Amount Requested & Budget Rationale

We request $50,000 to develop, deploy, and test an MVP enabling confidential P2P USDC trades between Aztec and Base testnets. The funding will support:

  • Smart contract development, including bridge and FPC contracts.
  • Relayer setup and infrastructure for reliable private trade execution.
  • UI development for trade submission and status tracking.
  • Testing and debugging for security and correctness pre-deployment.

Additional Considerations

Edge Cases:

  • Cancellations: 24-hour timeout for reclaiming stalled trades.
  • Re-orgs: Mitigated by relayer node pre-confirmations (~1-min normal, ~20-min rare).
  • Relayer Failure: Partial note-based refunds after 24h, UI updates users on delays.

UX Optimizations:

  • One-tx bridging using EIP-7702 where possible.
  • Minimal Latency (~1-min expected, relayer-dependent).
  • Intuitive UI – Multi-L2 tracking for trade execution.
1 Like
2

Thanks for your proposal. Some questions:

  1. Does this mean a user would instantly bridge from base to aztec to arbitrum (effectively bridging from base to arbitrum)? If so, it doesn’t really add any privacy as on public chains I see: 100 USDC from base to a bridge, and within 3-4 mins see the exact same 100 usdc out and probably to the same address..
  • Relayer mints zk-USDC on Aztec, private escrow settles.
  1. Can you mention a bit more on the private escrow part? How would you build it?
  • Partial notes enable private withdrawal to Arbitrum with secretHash2.
  1. Don’t need either actually! The user is simply consuming their token notes and then enqueuing a public call here.
1 Like