StreamPay

This project is a global, trustless payment network that combines the security of Bitcoin, the speed and stability of PayPal’s PYUSD stablecoin, and privacy-preserving identity verification via Self Protocol. It allows anyone, anywhere, to receive or send instant PYUSD payments that settle on a Bitcoin-secured layer (Citrea) with built-in off-ramps to local currencies. A borderless payment layer that fuses the stability of PayPal’s PYUSD with the security of Bitcoin and the privacy guarantees of zero-knowledge identity. It enables individuals and businesses anywhere in the world to send and receive payments instantly in a stable digital dollar, with every transaction settling trustlessly on Citrea — the first EVM-compatible ZK rollup secured by Bitcoin. A defining feature of the system is its privacy-preserving compliance. Using the Self Protocol, users can prove attributes such as age, residency or non-sanctions status without disclosing any underlying personal data. This allows merchants and regulators to meet KYC/AML requirements while keeping end-user information completely private, creating a safer and more inclusive financial rail. While off-ramps built into the backend convert PYUSD into local currencies on demand. Merchants and consumers interact with a clean web or mobile interface; under the hood, smart contracts on Citrea manage payments, escrows and identity proofs, and trigger settlement or fiat conversion events in real time. By combining Bitcoin-level security, stablecoin usability, ZK identity verification and instant off-ramps, the project establishes a new benchmark for digital payments infrastructure. It gives developers a composable open-source rail to integrate into their own apps, and gives users a trustless way to transact globally without sacrificing speed, stability or privacy.

How It Works

1. Frontend Web/App Layer A simple, user-friendly app for merchants and consumers. Users can see payment requests, pay with PYUSD, or withdraw to their bank account or preferred off-ramp.

2. Identity & Compliance via Self Protocol During onboarding, users prove attributes (e.g. country, age, “not on sanctions list”) using Self’s ZK-proof SDK. No private data is shared with the dApp — only proofs. This gives regulators and merchants confidence without breaking privacy.

3. Smart Contracts on Citrea Payment Contract: Holds PYUSD on Citrea (EVM-compatible Bitcoin rollup) and manages escrow & instant settlement between payer and payee. Identity Contract: Receives and verifies Self’s on-chain proofs, gating access to merchants who pass KYC/AML attributes without collecting their data. All contracts are open-source, deployed on Citrea testnet for hackathon judging.

4. PayPal PYUSD Integration PYUSD is the medium of exchange — stable, programmable, widely recognizable. The system uses PYUSD on supported networks for instant, low-cost transactions. It unlocks micro-transactions, subscriptions, cross-border payroll, and B2B settlements.

5. Off-Ramp Backend A backend microservice monitors contract events. When a user requests a fiat withdrawal, it triggers a pre-arranged off-ramp partner (exchange, bank API) to deliver local currency. The backend also manages KYT/AML checks, fee calculation, and ensures fast fiat delivery.

We built our payment layer as a set of smart contracts and lightweight services that sit on top of Citrea, the EVM-compatible ZK rollup secured by Bitcoin. All payments, escrows and identity checks happen on Citrea so we get Bitcoin-level security and low fees.

For the money side we integrated PayPal’s PYUSD stablecoin so every transfer uses a familiar, fully-backed digital dollar. For identity and compliance we used the Self Protocol to let users prove who they are (age, residency, non-sanctions, etc.) without handing over personal data. This makes merchants happy while still keeping end-user privacy.

We wrote the core in Solidity with a to handle off-ramps and a React front-end to make it simple for users. We also plugged in ENS-style name resolution for readable addresses and built direct hooks into partner off-ramp APIs to let people cash out instantly into local currency.

The “hacky” part is that we stitched all of these sponsor pieces together so that from the user’s view it looks like one seamless app. Under the hood PYUSD runs on Citrea, Self Protocol proofs are verified inside our contracts, and our off-ramp module listens for events and triggers fiat payouts automatically. This let us ship a working demo very quickly without reinventing the wheel.