ZK Payment Negotiator

Identity-aware payments, privacy-first.

Jay Yu, Sophia Dew, Mahi Jariwala, Bek Hamit

An AI-powered payment system where your identity determines your price — but your identity stays private.

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Overview

ZK Payment Negotiator combines zero-knowledge proofs with the HTTP 402 payment protocol to enable privacy-preserving, identity-aware pricing.

Users authenticate with Google and receive a zero-knowledge proof verifying their email domain (e.g., @stanford.edu, @enterprise.com) without exposing their actual email. This cryptographic proof feeds into an AI negotiation agent that dynamically prices content based on verified organizational affiliation: students get discounts, enterprises pay premium rates, partners unlock special deals.

When a price is agreed, payment settles instantly via the x402 protocol using USDC on Base.

The server knows what you are, never who you are.

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How It Works

1. Authenticate — Sign in with Google via Privy. An embedded wallet is created for you.

2. Generate ZK Proof — A zero-knowledge proof binds your wallet to your email domain without revealing your identity.

3. Negotiate — Chat with the AI agent to request premium content. Your verified domain determines your price tier.

4. Pay & Access — Accept the offer, pay with USDC via x402, and unlock your content. Transaction settles on-chain.

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Tech Stack

• Frontend: Next.js, React, TypeScript
• Backend: Express.js, MongoDB Atlas
• Authentication: Privy (Google OAuth + embedded wallets)
• ZK Proofs: Circom, snarkjs, Groth16
• Payments: x402 protocol, USDC on Base Sepolia
• AI: Claude (Anthropic) with tool use for agentic negotiation

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Setup

Prerequisites

• Node.js 18+
• pnpm (npm install -g pnpm)
• Privy account (https://dashboard.privy.io)

1. Configure Privy

1. Create an app at https://dashboard.privy.io
2. Enable Google OAuth in Login Methods
3. Add http://localhost:3000 to Allowed Origins
4. Copy your App ID

2. Set Environment Variables

cp frontend/.env.example frontend/.env.local
cp backend/.env.example backend/.env
# Edit both files with your API keys

3. Run the Project

make          # Install deps and start

4. (Optional) Enable Real ZK Proofs

To generate cryptographically valid proofs that can be verified on-chain:

# Install circom first
brew install circom    # macOS
# Or: https://docs.circom.io/getting-started/installation/

# Build circuits
make circom

After running make circom, the app automatically detects the circuit files and generates real proofs.

5. Stop Services

make stop

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ZK Proof Modes

Mock Mode (Default)

• No circom required
• Generates proof structure with random values
• Public signals use real Poseidon hashes
• Good for development and testing UI

Real Mode (Optional)

• Requires circom installed
• Run make circom to compile circuits
• Generates cryptographically valid Groth16 proofs
• Proofs can be verified on-chain

The app automatically detects which mode to use based on whether circuit files exist in frontend/public/zk/.

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Project Structure

x402-zkid/
├── Makefile              # Build orchestration
├── package.json          # Root package
├── circuits/             # ZK circuits (optional)
│   ├── jwt_domain_verifier.circom
│   └── build.js          # Circuit compiler
├── frontend/             # Next.js app
│   ├── app/
│   │   ├── page.tsx      # Main page
│   │   ├── layout.tsx    # Root layout
│   │   └── globals.css   # Styles
│   ├── lib/
│   │   ├── zkproof.ts    # Dual-mode proof generation
│   │   ├── api.ts        # Backend API client
│   │   └── x402client.ts # x402 payment client
│   └── components/
│       └── Providers.tsx # Privy wrapper
└── backend/              # Express.js API
    └── src/
        ├── index.ts      # Server entry
        ├── agent/        # AI negotiation agent
        └── x402/         # Payment handling

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Public Signals

The ZK proof exposes three public signals:

• domainHash: Poseidon hash of the email domain
• nullifier: Unique identifier (domain + secret)
• walletBinding: Hash binding wallet to domain

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Ports

• Frontend: http://localhost:3000
• Backend: http://localhost:3001

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License

MIT