Subscription3

Subscription3 is a simple way to pay subscriptions with crypto—privately and automatically. Instead of entering credit cards or PayPal, users create a private subscription UID inside the Aztec Network. Only the user and service provider can see what the subscription is for. On Ethereum, our contract holds a balance for each UID and knows only how much USD the subscription costs. When it’s time to pay, Chainlink Runtime Environment triggers a job that calls our contract, which fetches the real-time ETH/USD price from Pyth, converts the fee into ETH, and sends it to Aztec for private settlement. Anyone can top up a subscription balance, making it easy for parents, friends, or employers to contribute. Subscription3 brings privacy, decentralization, and crypto-native automation to the world of recurring payments.

Subscription3 is built by connecting four components: Ethereum, Pyth, Chainlink CRE, and the Aztec privacy network. On Ethereum, we deploy a smart contract that maintains a balance sheet for each subscription UID and stores its USD-denominated fee (2 decimals). For simplicity in this hackathon, our payment flow uses ETH only, but the contract design can easily be extended to any ERC-20 token using Pyth’s broad range of price feeds—or even multi-chain assets via Pyth’s cross-chain pricing.

When a subscription becomes due, Chainlink’s Runtime Environment executes a recurring schedule (e.g., monthly) and calls our contract’s executePayment(uid). Inside this function, we fetch a fresh ETH/USD price from Pyth using getPriceNoOlderThan, normalize the exponent, convert the USD amount into wei, and then execute the payment to the Aztec placeholder address. All sensitive subscription metadata (service provider, order ID, monthly fee) lives privately inside Aztec, while L1 only handles an opaque UID and balances. Anyone—not just the subscriber—can deposit ETH to fund a UID.

The system blends privacy (Aztec), accurate real-time pricing (Pyth), decentralized recurring automation (Chainlink CRE), and a minimal, hackathon-friendly contract/API on Ethereum. It was stitched together manually, including the exponent math for Pyth and the UID-based abstraction layer for Aztec, resulting in a fully functioning privacy-preserving recurring payment pipeline.