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Senddy – Private, Interest‑Bearing Stablecoin Rails

Overview

Senddy is a privacy-preserving payment layer for stablecoins that also earns yield. Users deposit USDC (or other tokens) and mint private “share notes”, and spend/withdraw privately. The system requires no gas from the native chain it is deployed on and ties fees into the circuits for relayers and paymasters, making transaction graphing very difficult. Senddy will be connected to payment processors for smooth checkout flows and have a debit/credit card integrated into the network, creating a private venmo with interest and privacy benefits.

Short pitch: Private stablecoin transfers with auto‑yield, gasless onboarding, and a fast wallet UX - a fully private venmo.

Drawing

Simple system diagram of a user depositing $20 into the system and a user withdrawing $5 out of the system

Senddy in private beta
Senddy in private beta

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1) High‑Level Overview

  • Goals

    • Private transfers of stablecoins with strong unlinkability.

    • Yield by default—deposits are routed into a strategy, and holders accrue via a per‑asset index.

    • Cross chain

    • Smooth UX: AA smart wallets (Privy + ZeroDev Kernel), a custom verifying paymaster (Pimlico bundler) to cover gas in USDC verified through the circuits, and background indexing for fast wallet loads, leveraging latest and greatest zk-tech such as tachyon (credits to the zcash team).

    • Multi‑asset support—the pool can be extended beyond USDC with per‑token accounting and asset binding in commitments.

  • Core Components

    • Circuits: shield and spend_anchor (multi‑input spends).

    • Pool Contract (Upgradeable): per‑token accounting; incremental Poseidon Merkle tree; deposit escrow; nullifier controls; fee accrual.

    • SDK: proving helpers, UTXO selection, Permit2 flows, AA kernel execution encoders, memo encoding/decoding, payment-link client.

    • Paymaster: ERC‑4337 v0.7 verifying paymaster that validates fee quotes and ensures the spend includes a USDC fee paid directly to the paymaster.

    • Subgraph + (optional) Supabase indexer: stream commitments/nullifiers and build a fast local wallet view.

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Roadmap (abridged)

  • Multi-asset UX enhancements and strategy adapters.

  • Wallet integrations leveraging AA + Paymaster.

  • Advanced scanning and memo recovery tooling.

  • Formal verification and audits.

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Credits

  • Poseidon hash and Merkle tooling based on established ZK libraries.

  • Contracts leverage OpenZeppelin and AA libraries.

  • Circuits compiled with snarkjs; proving artifacts structured for browser usage.

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