Proof of Presence — Bot-proof, privacy-preserving attendance for Web3 events

What it is:
Proof of Presence (PoP) is a privacy-preserving event attendance registry that leverages zero-knowledge proofs to verify that attendees are unique humans without revealing their identity. Attendees check in via World ID (Tier 1: Orb-verified) or Privy (Tier 2: email/phone), and their attendance is recorded anonymously on-chain using only a nullifierHash — never their wallet address or identity.
How it works:

1. Attendee submits check-in → proves uniqueness via World ID ZK proof or Privy email
2. Chainlink CRE Workflow (running in a secure enclave) receives the proof → verifies it against World ID API inside the enclave → calls recordAttendance() on the Sepolia contract via Keystone Forwarder
3. ProofOfPresence contract stores the record indexed by anonymous nullifierHash → mints a non-transferable ERC-721 Soulbound Badge(POPB)
4. CCIP automatically bridges the attendance record to Base Sepolia and Optimism Sepolia cross-chain
   Problem it solves:

• Privacy in attendance tracking: No wallet address ever stored on-chain. Events can verify attendance without exposing attendee identity.
• Sybil-resistance: World ID ZK proofs prove uniqueness without identity.
• Decentralized proof of presence: Records live on-chain across multiple blockchains via CCIP; no centralized company controls attendance data.
• Cross-chain portability: One check-in, attendance recorded on 3 chains automatically (Sepolia, Base, Optimism).
  Pitch Deck: https://docs.google.com/presentation/d/1_11vtRN-ifEk24ousRe02EeF-wnXo673/edit?usp=sharing&ouid=102851583388467822955&rtpof=true&sd=true

How is it built?
Tech Stack:

• Identity: World ID (ZK Orb proof) + Privy (email/phone fallback)
• Automation: Chainlink CRE (Confidential Runtime Environment) with Keystone Forwarder for secure off-chain→on-chain bridge
• Cross-chain: Chainlink CCIP for automatic message bridging
• Smart Contracts: Solidity 0.8.20 (ProofOfPresence + PoP_CCIP_Receiver)
• Frontend: Next.js 15, Tailwind CSS, MiniKit SDK
• Test Network: Ethereum Sepolia (primary), Base Sepolia, Optimism Sepolia
  User Flow
  Browser/World App → World ID ZK Proof
    ↓
  Next.js Frontend (/checkin, /processing, /credential, /vault)
    ↓
  Chainlink CRE Workflow (4 nodes)
   • HTTP Trigger (receives nullifierHash + proof)
   • Confidential HTTP (verifies against World ID API in TEE enclave)
   • ABI encoding (prepares attestation)
   • EVMClient.writeReport() → Keystone Forwarder
    ↓
  ProofOfPresence.sol (Sepolia)
   • onReport() (via IReceiver interface)
   • Records registry[nullifierHash][eventId]
   • Mints ERC-721 SBT badge
   • Sends CCIP messages
    ↓
  PoP_CCIP_Receiver.sol (Base + Optimism)
   • _ccipReceive() mirrors records

Key Contracts Deployed:

• ProofOfPresence (Sepolia): 0xbA985984B1319451968f42281b1a92Ca709cF820
• PoP_CCIP_Receiver (Base Sepolia): 0x508eC020139E6fcdA3878B18898F0E372D906b1a
• PoP_CCIP_Receiver (Optimism Sepolia): 0xd01fac0953530D7833bA8eB0cc3CcCa2433BCD0b