As cryptocurrency systems mature beyond basic data structures, the need for standardized, secure, and efficient API interfaces becomes paramount. Phase 2 of the WIA Cryptocurrency Standard focuses on defining the API layer that enables applications, wallets, and exchanges to interact with blockchain networks in a consistent and reliable manner.

This chapter explores the comprehensive API interface specification, covering wallet operations, exchange integrations, node communications, authentication mechanisms, and rate limiting strategies. Whether you're building a mobile wallet app, integrating cryptocurrency payments into an e-commerce platform, or developing a trading platform, understanding these API patterns is essential for creating secure and scalable cryptocurrency applications.

1. API Architecture Overview

The WIA Cryptocurrency API architecture follows RESTful principles with JSON-based request/response formats, providing a clear separation between client applications and blockchain infrastructure. This design enables flexibility, scalability, and ease of integration across diverse platforms and programming languages.

Core Architecture Principles

• RESTful Design: Using standard HTTP methods (GET, POST, PUT, DELETE) for intuitive resource manipulation
• JSON Serialization: All data exchanged in human-readable JSON format for easy debugging and interoperability
• Stateless Communication: Each request contains all necessary information, enabling horizontal scaling
• Resource-Based URLs: Clear, hierarchical endpoint structure reflecting cryptocurrency domain objects
• Versioned APIs: Support for multiple API versions to maintain backward compatibility
• HTTPS Only: Mandatory encryption for all API communications to protect sensitive data

API Layer	Purpose	Primary Users	Key Features
Wallet API	User account & transaction management	Mobile apps, Web wallets	Balance queries, Send/Receive, History
Exchange API	Trading operations	Trading platforms, Bots	Order management, Market data, Trades
Node API	Blockchain interaction	Infrastructure operators	Block data, Network status, Mempool
Market Data API	Price & volume information	Analytics platforms, Dashboards	Tickers, Charts, Historical data

2. Wallet API Specification

The Wallet API provides a comprehensive interface for managing cryptocurrency accounts, enabling applications to create wallets, check balances, send and receive transactions, and query transaction history. This API is designed with security as the foremost priority, implementing multiple layers of protection for private keys and sensitive operations.

Account Management Endpoints

// Create New Wallet
POST /api/v1/wallets
Request:
{
  "currency": "BTC",
  "label": "My Bitcoin Wallet",
  "password": "securePassword123"
}

Response:
{
  "walletId": "wlt_8f3a7b2c9d1e",
  "address": "1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa",
  "publicKey": "04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f",
  "createdAt": "2025-01-15T10:30:00Z",
  "balance": "0.00000000"
}

// Get Wallet Balance
GET /api/v1/wallets/{walletId}/balance

Response:
{
  "walletId": "wlt_8f3a7b2c9d1e",
  "currency": "BTC",
  "confirmed": "1.25000000",
  "unconfirmed": "0.05000000",
  "total": "1.30000000",
  "fiatValue": {
    "USD": 58500.00,
    "EUR": 49200.00
  },
  "lastUpdated": "2025-01-15T12:45:30Z"
}

// List All Wallets
GET /api/v1/wallets?currency=BTC&limit=50&offset=0

Response:
{
  "wallets": [
    {
      "walletId": "wlt_8f3a7b2c9d1e",
      "label": "My Bitcoin Wallet",
      "address": "1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa",
      "currency": "BTC",
      "balance": "1.30000000"
    }
  ],
  "total": 1,
  "limit": 50,
  "offset": 0
}

Transaction Operations

// Send Transaction
POST /api/v1/wallets/{walletId}/send
Request:
{
  "toAddress": "3J98t1WpEZ73CNmYviecrnyiWrnqRhWNLy",
  "amount": "0.05000000",
  "fee": "0.00001000",
  "note": "Payment for services",
  "password": "securePassword123"
}

Response:
{
  "transactionId": "tx_a3f7e2b8c1d4",
  "txHash": "f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16",
  "status": "pending",
  "fromAddress": "1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa",
  "toAddress": "3J98t1WpEZ73CNmYviecrnyiWrnqRhWNLy",
  "amount": "0.05000000",
  "fee": "0.00001000",
  "confirmations": 0,
  "estimatedConfirmationTime": "2025-01-15T13:00:00Z"
}

// Get Transaction History
GET /api/v1/wallets/{walletId}/transactions?limit=20&offset=0

Response:
{
  "transactions": [
    {
      "transactionId": "tx_a3f7e2b8c1d4",
      "type": "send",
      "amount": "0.05000000",
      "address": "3J98t1WpEZ73CNmYviecrnyiWrnqRhWNLy",
      "confirmations": 3,
      "timestamp": "2025-01-15T12:30:00Z",
      "status": "confirmed"
    }
  ],
  "total": 15,
  "limit": 20,
  "offset": 0
}

3. Exchange API Interface

Exchange APIs enable trading operations across cryptocurrency markets, providing access to order books, market data, and trading functionality. These APIs must handle high-frequency requests while maintaining data consistency and security.

Market Data Endpoints

// Get Market Ticker
GET /api/v1/markets/BTC-USD/ticker

Response:
{
  "symbol": "BTC-USD",
  "lastPrice": "45000.00",
  "bidPrice": "44995.00",
  "askPrice": "45005.00",
  "volume24h": "1250.50000000",
  "high24h": "45800.00",
  "low24h": "44200.00",
  "priceChange24h": "+2.5",
  "timestamp": "2025-01-15T12:45:00Z"
}

// Get Order Book
GET /api/v1/markets/BTC-USD/orderbook?depth=20

Response:
{
  "symbol": "BTC-USD",
  "bids": [
    ["44995.00", "0.50000000"],
    ["44990.00", "1.25000000"],
    ["44985.00", "0.75000000"]
  ],
  "asks": [
    ["45005.00", "0.45000000"],
    ["45010.00", "1.10000000"],
    ["45015.00", "0.80000000"]
  ],
  "timestamp": "2025-01-15T12:45:00Z",
  "sequenceId": 1234567890
}

Trading Operations

Order Type	Description	Use Case	Parameters
Market Order	Execute immediately at best price	Quick entry/exit	symbol, side, quantity
Limit Order	Execute at specified price or better	Price control	symbol, side, price, quantity
Stop-Loss	Trigger at specified price	Risk management	symbol, side, stopPrice, quantity
Stop-Limit	Limit order after stop triggered	Controlled exit	symbol, side, stopPrice, limitPrice, quantity

// Place Limit Order
POST /api/v1/orders
Request:
{
  "symbol": "BTC-USD",
  "type": "limit",
  "side": "buy",
  "price": "44500.00",
  "quantity": "0.10000000",
  "timeInForce": "GTC"
}

Response:
{
  "orderId": "ord_7b3e9f2a8c1d",
  "symbol": "BTC-USD",
  "type": "limit",
  "side": "buy",
  "price": "44500.00",
  "quantity": "0.10000000",
  "status": "open",
  "filled": "0.00000000",
  "remaining": "0.10000000",
  "createdAt": "2025-01-15T12:50:00Z"
}

// Cancel Order
DELETE /api/v1/orders/{orderId}

Response:
{
  "orderId": "ord_7b3e9f2a8c1d",
  "status": "cancelled",
  "cancelledAt": "2025-01-15T13:00:00Z"
}

4. Node API Communication

Node APIs provide direct access to blockchain infrastructure, allowing developers to query block data, submit transactions to the network, and monitor network health. These APIs are essential for building blockchain explorers, validators, and custom infrastructure tools.

Blockchain Query Endpoints

// Get Block by Height
GET /api/v1/blocks/750000

Response:
{
  "height": 750000,
  "hash": "00000000000000000003dc5b1b70d6b00e2a87e1b6e0c5c5c0a2e4e0a5c1b0e3",
  "previousHash": "00000000000000000001a8f7b9c3d5e2f0a8b6c4d2e0f8a6b4c2d0e8f6a4b2c",
  "merkleRoot": "a7b3c2d1e0f9a8b7c6d5e4f3a2b1c0d9e8f7a6b5c4d3e2f1a0b9c8d7e6f5a4b",
  "timestamp": "2025-01-15T12:00:00Z",
  "difficulty": 23137439666472.00,
  "nonce": 2758542859,
  "transactions": 2543,
  "size": 1245678,
  "confirmations": 125
}

// Get Transaction Details
GET /api/v1/transactions/{txHash}

Response:
{
  "txHash": "f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16",
  "blockHeight": 749875,
  "confirmations": 125,
  "timestamp": "2025-01-15T11:30:00Z",
  "inputs": [
    {
      "address": "1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa",
      "value": "0.06000000"
    }
  ],
  "outputs": [
    {
      "address": "3J98t1WpEZ73CNmYviecrnyiWrnqRhWNLy",
      "value": "0.05000000"
    },
    {
      "address": "1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa",
      "value": "0.00999000"
    }
  ],
  "fee": "0.00001000",
  "size": 225
}

Network Status Monitoring

// Get Network Info
GET /api/v1/network/info

Response:
{
  "network": "mainnet",
  "version": "23.0.0",
  "protocolVersion": 70016,
  "blocks": 750125,
  "connections": 8,
  "difficulty": 23137439666472.00,
  "hashrate": "180.5 EH/s",
  "mempool": {
    "size": 15234,
    "bytes": 45678901,
    "usage": 85234567
  },
  "warnings": []
}

// Get Mempool Transactions
GET /api/v1/mempool?limit=50

Response:
{
  "transactions": [
    {
      "txHash": "a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b",
      "size": 225,
      "fee": "0.00002500",
      "feeRate": "11.11",
      "firstSeen": "2025-01-15T12:45:00Z"
    }
  ],
  "total": 15234
}

5. Authentication Mechanisms

Securing API access is critical in cryptocurrency systems where unauthorized access can lead to financial loss. The WIA standard supports multiple authentication methods, each appropriate for different use cases and security requirements.

API Key Authentication

API keys provide a simple yet effective authentication method for server-to-server communication and automated systems. Each API key consists of a public identifier and a private secret that must be kept secure.

// API Key Generation
POST /api/v1/auth/keys
Request:
{
  "name": "Trading Bot Key",
  "permissions": ["read", "trade"],
  "ipWhitelist": ["203.0.113.0/24"]
}

Response:
{
  "keyId": "key_9a8b7c6d5e4f",
  "apiKey": "wia_pk_REPLACE_WITH_YOUR_API_KEY_PLACEHOLDER",
  "apiSecret": "wia_sk_REPLACE_WITH_YOUR_API_KEY_PLACEHOLDER",
  "permissions": ["read", "trade"],
  "createdAt": "2025-01-15T13:00:00Z",
  "expiresAt": "2026-01-15T13:00:00Z"
}

// Using API Key in Requests
GET /api/v1/wallets
Headers:
  X-API-Key: wia_pk_REPLACE_WITH_YOUR_API_KEY_PLACEHOLDER
  X-API-Signature: sha256_hmac(request_data, api_secret)
  X-API-Timestamp: 1642251600000

OAuth 2.0 Integration

OAuth 2.0 provides delegated authorization, allowing third-party applications to access user resources without exposing credentials. This is the preferred method for web and mobile applications where users need to grant limited access to their accounts.

OAuth Flow	Use Case	Security Level	Token Lifetime
Authorization Code	Web applications	High	Access: 1h, Refresh: 90d
PKCE	Mobile/SPA apps	High	Access: 1h, Refresh: 90d
Client Credentials	Server-to-server	Medium	Access: 24h
Refresh Token	Token renewal	High	90 days

6. Rate Limiting Strategies

Rate limiting protects API infrastructure from abuse and ensures fair resource allocation among users. The WIA standard implements tiered rate limiting based on account type, endpoint sensitivity, and authentication method.

Rate Limit Tiers

Account Tier	Requests/Minute	Requests/Hour	Burst Limit	WebSocket Connections
Anonymous	10	100	20	1
Free Tier	60	1,000	100	5
Pro Tier	300	10,000	500	25
Enterprise	1,000	100,000	2,000	100

Rate Limit Headers

// Response Headers for Rate Limiting
HTTP/1.1 200 OK
X-RateLimit-Limit: 300
X-RateLimit-Remaining: 245
X-RateLimit-Reset: 1642252200
X-RateLimit-Window: 60
Retry-After: 45

// Rate Limit Exceeded Response
HTTP/1.1 429 Too Many Requests
{
  "error": "rate_limit_exceeded",
  "message": "API rate limit exceeded",
  "limit": 300,
  "remaining": 0,
  "resetAt": "2025-01-15T13:10:00Z",
  "retryAfter": 45
}

7. WebSocket Real-Time APIs

For applications requiring real-time updates—such as trading platforms displaying live price feeds or wallets showing instant transaction confirmations—WebSocket connections provide efficient, low-latency bidirectional communication.

// WebSocket Connection
ws://api.wiacrypto.com/v1/stream

// Subscribe to Price Updates
{
  "action": "subscribe",
  "channels": ["ticker.BTC-USD", "ticker.ETH-USD"]
}

// Receive Price Updates
{
  "channel": "ticker.BTC-USD",
  "data": {
    "symbol": "BTC-USD",
    "price": "45125.50",
    "volume": "1250.75",
    "timestamp": "2025-01-15T13:15:30.500Z"
  }
}

// Subscribe to Transaction Confirmations
{
  "action": "subscribe",
  "channels": ["tx.1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa"]
}

// Receive Confirmation Updates
{
  "channel": "tx.1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa",
  "data": {
    "txHash": "f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16",
    "confirmations": 3,
    "blockHeight": 749875,
    "timestamp": "2025-01-15T13:15:35.000Z"
  }
}

8. Error Handling and Response Codes

Consistent error handling helps developers quickly diagnose and resolve issues. The WIA API standard uses HTTP status codes combined with detailed error messages in JSON format.

HTTP Code	Error Type	Description	Action
400	Bad Request	Invalid parameters or malformed request	Check request format and parameters
401	Unauthorized	Missing or invalid authentication	Provide valid API key or OAuth token
403	Forbidden	Insufficient permissions	Request higher permissions or use different account
404	Not Found	Resource doesn't exist	Verify resource ID or endpoint
429	Rate Limited	Too many requests	Wait and retry, upgrade tier
500	Server Error	Internal server error	Retry with exponential backoff
503	Service Unavailable	Temporary service disruption	Check status page, retry later

// Error Response Format
{
  "error": {
    "code": "insufficient_balance",
    "message": "Wallet balance insufficient for transaction",
    "details": {
      "required": "0.05001000",
      "available": "0.03000000",
      "currency": "BTC"
    },
    "requestId": "req_a1b2c3d4e5f6",
    "timestamp": "2025-01-15T13:20:00Z",
    "documentation": "https://docs.wiacrypto.com/errors/insufficient_balance"
  }
}

9. API Versioning and Deprecation

As cryptocurrency standards evolve, maintaining backward compatibility while introducing new features requires careful API versioning and deprecation policies.

Version Migration Path

// Deprecation Warning Header
HTTP/1.1 200 OK
X-API-Version: v1
X-API-Deprecated: true
X-API-Sunset: 2026-01-15T00:00:00Z
X-API-Migrate-To: /api/v2/wallets
Link: <https://docs.wiacrypto.com/migration/v1-to-v2>; rel="migration-guide"

// Version Information Endpoint
GET /api/version

Response:
{
  "current": "v2",
  "supported": ["v1", "v2"],
  "deprecated": {
    "v1": {
      "sunsetDate": "2026-01-15T00:00:00Z",
      "migrationGuide": "https://docs.wiacrypto.com/migration/v1-to-v2"
    }
  }
}

10. API Security Best Practices

Security in cryptocurrency APIs extends beyond authentication to encompass request validation, data encryption, audit logging, and protection against common attacks.

Security Checklist

• HTTPS Everywhere: Enforce TLS 1.3 for all API communications
• Input Validation: Validate and sanitize all user inputs to prevent injection attacks
• Request Signing: Use HMAC signatures to verify request integrity
• IP Whitelisting: Restrict API access to known IP addresses when possible
• Audit Logging: Log all API requests with user identity, timestamp, and action
• DDoS Protection: Implement rate limiting and traffic filtering
• Secrets Management: Never log or expose API secrets in error messages
• Two-Factor Authentication: Require 2FA for sensitive operations (withdrawals, key generation)