# Smart Contracts

> Senddy's on-chain contracts — pool, verifiers, and yield strategies.

Source: https://www.senddy.com/docs/technical/smart-contracts
Last modified: 2026-08-01T23:49:54.000Z

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## Overview

Senddy's smart contracts are deployed on Base (Coinbase's Layer 2). The system is centered around a single pool contract that manages all deposits, shields, spends, and withdrawals.

## Core Contracts

### Pool Contract

The main contract. All user funds are held here.

**Key capabilities:**

- Deposit USDC into the pool (public)
- Batch multiple deposits in a single transaction
- Gasless deposits using Permit2 or EIP-3009 authorization
- Shield a deposit into private notes using an attestation
- Combined deposit + shield in one transaction
- Execute private spends (transfers between users)
- Execute spends with a public withdrawal
- Accrue yield from the strategy
- Screen deposits against the [Chainalysis sanctions oracle](https://go.chainalysis.com/chainalysis-oracle-docs.html) — OFAC-sanctioned addresses are blocked at the contract level

**State:**

- Known Merkle tip ring (`currentRoot` + recent roots) — the full commitment tree is maintained in the attestor enclave; the pool checks membership via `isKnownRoot`
- Nullifier accumulator (tracks spent notes)
- Deposit registry (pending deposits)
- Asset configuration and strategy addresses
- Attestor address (authorized proof verifier)

### Verifier Contracts

Senddy uses dedicated verifier contracts for each proof type:

- **Shield Verifier** — Verifies zero-knowledge proofs for shield operations, generated from the Noir shield circuit using the UltraHonk proving system
- **Spend Verifier** — Verifies zero-knowledge proofs for spend operations
- **Association Verifier** — Verifies association proofs that link funds to approved deposit sources, enabling compliance without breaking privacy

### Yield Strategy

The pool deploys funds to trusted DeFi lending protocols for yield generation. The strategy contract manages deposits, withdrawals, and yield reporting back to the pool.

The pool supports a modular strategy interface, allowing multiple yield strategies to be used in the future.

## Security

- Contracts are upgradeable with access-controlled owner functions (production should place ownership behind a timelock or multisig)
- Spends require a known Merkle tip (`isKnownRoot`) bound in the attestor EIP-712 digest
- Audited by independent security researchers; open findings tracked internally
- Bug bounty program for responsible disclosure