b402 Protocol

The b402 Protocol is a decentralized payment standard that extends HTTP 402 (Payment Required) for autonomous AI agent transactions.

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The HTTP 402 Status Code

HTTP 402 was reserved in the original HTTP specification for future payment systems. While it remained unused for decades, the rise of AI agents and micropayments has created the perfect use case.

HTTP/1.1 402 Payment Required
X-B402-Version: 1.0.0
X-B402-Payment-Address: 0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb
X-B402-Amount: 10.5
X-B402-Token: USDT
X-B402-Chain-Id: 56

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How b402 Works

1. Service Discovery

An AI agent discovers a service it needs:

const services = await client.discover({
    capability: 'translation',
    maxPrice: '1.0',
    language: 'en-to-zh'
});

2. Payment Request

The service provider responds with a 402 status and payment details:

{
    "status": 402,
    "payment_id": "pay_abc123",
    "amount": "0.5",
    "currency": "USDT",
    "recipient": "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb",
    "expires_at": "2024-01-15T10:30:00Z"
}

3. Payment Execution

The client agent executes the payment via smart contract:

const payment = await client.payment.create({
    paymentId: 'pay_abc123',
    amount: '0.5',
    currency: 'USDT',
    recipient: '0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb'
});

4. Service Delivery

Once payment is confirmed, the service is delivered:

// Service provider verifies payment
const verified = await verifyPayment('pay_abc123');

if (verified) {
    // Deliver the service
    return translateText(input);
}

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Key Features

Autonomous Operation

AI agents can complete entire transactions without human intervention:

• Discover services

• Negotiate prices

• Execute payments

• Receive services

• Verify delivery

Trustless Settlement

Smart contracts ensure:

• Escrow: Funds are held until service delivery

• Automatic Release: Payment released upon confirmation

• Dispute Resolution: Built-in arbitration mechanism

• Refund Protection: Automatic refunds for failed services

Micropayment Native

Optimized for small transactions:

• Minimum payment: $0.0001

• Average gas cost: < $0.01

• Settlement time: ~3 seconds

• Batch processing for efficiency

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Protocol Specification

Payment Request Headers

Header	Type	Description
X-B402-Version	string	Protocol version (e.g., "1.0.0")
X-B402-Payment-Address	address	Recipient wallet address
X-B402-Amount	string	Payment amount
X-B402-Token	string	Token symbol (BNB, USDT, etc.)
X-B402-Chain-Id	number	Blockchain network ID
X-B402-Nonce	string	Unique request identifier
X-B402-Expires	timestamp	Payment expiration time
X-B402-Memo	string	Optional payment memo

Payment States

enum PaymentState {
    PENDING = 'pending',           // Payment created
    PROCESSING = 'processing',     // Transaction submitted
    CONFIRMING = 'confirming',     // Awaiting confirmations
    CONFIRMED = 'confirmed',       // Payment complete
    FAILED = 'failed',             // Payment failed
    EXPIRED = 'expired',           // Payment expired
    REFUNDED = 'refunded'          // Payment refunded
}

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Smart Contract Interface

The b402 Protocol is implemented via smart contracts on BNB Chain:

interface IB402Payment {
    // Create a payment request
    function createPayment(
        address recipient,
        uint256 amount,
        address token,
        bytes32 serviceId
    ) external returns (bytes32 paymentId);
    
    // Execute payment
    function pay(bytes32 paymentId) external payable;
    
    // Verify payment status
    function verifyPayment(bytes32 paymentId) 
        external view returns (bool);
    
    // Release escrowed funds
    function release(bytes32 paymentId) external;
    
    // Refund payment
    function refund(bytes32 paymentId) external;
    
    // Events
    event PaymentCreated(
        bytes32 indexed paymentId,
        address indexed recipient,
        uint256 amount
    );
    
    event PaymentCompleted(
        bytes32 indexed paymentId,
        address indexed payer,
        uint256 amount
    );
    
    event PaymentReleased(
        bytes32 indexed paymentId,
        address indexed recipient
    );
}

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Security Features

Anti-Replay Protection

Each payment request includes a unique nonce to prevent replay attacks:

const nonce = generateNonce(); // Cryptographically secure random value

Expiration Mechanism

Payments automatically expire if not completed within the specified timeframe:

const payment = await client.payment.create({
    amount: '10.5',
    expiresIn: 600  // 10 minutes
});

Rate Limiting

Built-in protection against spam and abuse:

• Maximum 100 requests per minute per agent

• Exponential backoff for failed attempts

• IP-based rate limiting

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Comparison with Traditional Payments

Feature	b402 Protocol	Traditional Payment
Setup Time	Instant	Days to weeks
Transaction Fee	< $0.01	2-3% + fixed fee
Settlement Time	~3 seconds	1-3 business days
Minimum Amount	$0.0001	~$0.50
Autonomous	✅ Yes	❌ No
Programmable	✅ Yes	❌ Limited
Global	✅ Yes	❌ Restricted
Trustless	✅ Yes	❌ No

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Use Cases

1. AI-to-AI Services

// Weather Agent pays Data Agent for weather data
const weather = await weatherAgent.requestService({
    provider: 'data-agent-001',
    service: 'current-weather',
    location: 'New York',
    maxPrice: '0.01'
});

2. Micropayment Streaming

// Pay per second for compute resources
const stream = await client.payment.createStream({
    recipient: 'compute-provider',
    ratePerSecond: '0.001',
    duration: 3600  // 1 hour
});

3. Pay-Per-Use APIs

// Pay only for actual API calls
const result = await client.callAPI({
    endpoint: 'https://api.example.com/translate',
    payment: {
        amount: '0.005',
        currency: 'USDT'
    }
});

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Next Steps

• Learn about the Payment Flow in detail

• Explore Smart Contracts implementation

• Try the Quick Start Guide

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_{The b402 Protocol is open source and community-driven}