Facilitator Service

Backend service for verifying FHE payments.

Production Service

A hosted facilitator is available for immediate use:

https://zama-facilitator.ultravioletadao.xyz

Hosted by Ultravioleta DAO. Supports Sepolia testnet.

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Overview

The facilitator is a Hono-based API that:

• Extracts transfer events from blockchain
• Decrypts amounts using FHE relayer
• Validates payment requirements

Project Structure

x402-facilitator/
├── src/
│   ├── index.ts           # Server entry point
│   ├── routes/
│   │   ├── health.ts      # Health check
│   │   └── verify.ts      # Payment verification
│   ├── services/
│   │   └── verification.ts # Core logic
│   ├── types/
│   │   └── index.ts       # Zod schemas
│   └── utils/
│       └── config.ts      # Configuration
└── package.json

Running

Development

cd packages/x402-facilitator
pnpm dev

Production

pnpm build
pnpm start

Endpoints

GET /

Service information.

{
  "name": "X402 FHE Facilitator",
  "version": "1.0.0",
  "endpoints": {
    "health": "GET /health",
    "verify": "POST /verify"
  }
}

GET /health

Health check.

{
  "status": "ok",
  "service": "x402-facilitator",
  "version": "1.0.0",
  "networks": ["fhevm-local", "sepolia"]
}

POST /verify

Verify FHE payment. See API Reference.

Verification Process

1. Parse Request: Validate with Zod schemas
2. Get Transaction: Fetch receipt from blockchain
3. Extract Event: Find ConfidentialTransfer log
4. Verify Recipient: Match transfer destination
5. Verify Sender: Match decryption signature user
6. Decrypt Amount: Use FHE relayer SDK
7. Compare Amount: Check against requirements

Dependencies

Package	Purpose
hono	Web framework
ethers	Blockchain interaction
@zama-fhe/relayer-sdk	FHE decryption
zod	Schema validation

Error Handling

Status	Meaning
200	Payment valid
400	Invalid payment
500	Server error