Alchemy security basics

Alchemy Security Basics

Overview

Web3 security practices for Alchemy-powered applications: API key protection, private key management, input validation, and smart contract interaction safety.

Security Checklist

Category	Requirement	Priority
API keys	Never expose in client-side code	Critical
Private keys	Use environment vars or secret manager	Critical
Addresses	Validate and checksum all inputs	High
RPC calls	Never pass user input directly to RPC	High
Webhooks	Verify HMAC signatures	High
Dependencies	Audit npm packages for supply chain	Medium

Instructions

Step 1: API Key Protection

// WRONG — API key in frontend code
// const alchemy = new Alchemy({ apiKey: 'demo123' }); // NEVER DO THIS

// RIGHT — API key in backend proxy
// src/api/proxy.ts
import express from 'express';
import { Alchemy, Network } from 'alchemy-sdk';

const app = express();
const alchemy = new Alchemy({
  apiKey: process.env.ALCHEMY_API_KEY, // Server-side only
  network: Network.ETH_MAINNET,
});

// Proxy endpoint — frontend calls this instead of Alchemy directly
app.get('/api/balance/:address', async (req, res) => {
  const { address } = req.params;
  if (!/^0x[a-fA-F0-9]{40}$/.test(address)) {
    return res.status(400).json({ error: 'Invalid address format' });
  }
  const balance = await alchemy.core.getBalance(address);
  res.json({ balance: balance.toString() });
});

// Alchemy Dashboard: restrict API key to specific domains/IPs
// Dashboard > App > Settings > Allowed Domains

Step 2: Input Validation for Blockchain Queries

// src/security/validators.ts
import { ethers } from 'ethers';

function validateAddress(input: string): string {
  if (!ethers.isAddress(input)) throw new Error(`Invalid address: ${input}`);
  return ethers.getAddress(input); // Returns checksummed address
}

function validateBlockNumber(input: string | number): string {
  if (input === 'latest' || input === 'pending' || input === 'earliest') return input;
  const num = typeof input === 'string' ? parseInt(input) : input;
  if (isNaN(num) || num < 0) throw new Error(`Invalid block number: ${input}`);
  return `0x${num.toString(16)}`;
}

function validateTokenId(input: string): string {
  if (!/^\d+$/.test(input) && !input.startsWith('0x')) {
    throw new Error(`Invalid token ID: ${input}`);
  }
  return input;
}

export { validateAddress, validateBlockNumber, validateTokenId };

Step 3: Private Key Safety

// src/security/wallet-safety.ts
// NEVER:
// - Hardcode private keys in source code
// - Log private keys or mnemonic phrases
// - Store private keys in .env files committed to git
// - Accept private keys from user input in a web app

// Safe wallet setup for server-side operations
import { ethers } from 'ethers';
import { Alchemy, Network } from 'alchemy-sdk';

async function createSafeWallet() {
  const alchemy = new Alchemy({
    apiKey: process.env.ALCHEMY_API_KEY,
    network: Network.ETH_SEPOLIA,
  });

  const provider = await alchemy.config.getProvider();

  // Load private key from secret manager (GCP example)
  const { SecretManagerServiceClient } = await import('@google-cloud/secret-manager');
  const client = new SecretManagerServiceClient();
  const [version] = await client.accessSecretVersion({
    name: `projects/${process.env.GCP_PROJECT}/secrets/deployer-private-key/versions/latest`,
  });
  const privateKey = version.payload?.data?.toString() || '';

  const wallet = new ethers.Wallet(privateKey, provider);
  return wallet;
}

Step 4: Webhook Signature Verification

// src/security/webhook-verify.ts
import crypto from 'crypto';

function verifyAlchemyWebhookSignature(
  body: string,
  signature: string,
  signingKey: string,
): boolean {
  const hmac = crypto.createHmac('sha256', signingKey);
  hmac.update(body, 'utf8');
  const expectedSig = hmac.digest('hex');
  return crypto.timingSafeEqual(
    Buffer.from(signature),
    Buffer.from(expectedSig),
  );
}

Output

• API key proxy pattern (never expose to client)
• Input validation for addresses, blocks, and token IDs
• Private key loaded from secret manager
• Webhook HMAC signature verification

Resources

• Alchemy Security Best Practices
• Ethers.js Security
• Web3 Security Checklist

Next Steps

For production deployment, see alchemy-prod-checklist.