HandOff

HandOff is a lightweight escrow protocol that solves the buyer-seller dilemma in peer-to-peer transactions. When buying items on Facebook Marketplace or Craigslist, buyers risk carrying cash (robbery) while sellers risk counterfeit bills. Digital payments like Venmo require personal info exchange and enable chargebacks.

HandOff enables trustless, cashless in-person deals using a simple 4-digit unlock code mechanism inspired by food delivery apps (e.g. UberEats). The seller creates an escrow specifying price and payout token. The buyer funds it via a payment link, receiving an unlock code. When they meet in person, the buyer inspects the item and verbally gives the seller the code. The seller enters it to release funds from the smart contract. If no code is entered by the time the escrow expires, funds are returned.

Built as a pnpm monorepo, HandOff pairs a React + Vite frontend (TypeScript, wagmi/viem, React Query) with Hardhat Solidity contracts (OpenZeppelin + TypeChain). Each deal deploys its own escrow contract, while a reputation contract tracks completions/volume. We integrated Dynamic.xyz for embedded wallets, Uniswap quote/swap flow so buyers can fund in various select tokens, and ENS for name resolution plus deal-{id}.hand-off.eth receipt subnames. A notable hack: the unlock flow stores only keccak256(code) on-chain and reveals the plaintext code only to the buyer, so release can happen in-person without trusting a platform.

Built on Ethereum with gas costs under $1 per transaction. Perfect for marketplace sales, event tickets, used cars, and any in-person transaction where trust is limited.