Node.js Keccak-256

Ethereum uses Keccak-256, not the NIST-standardized SHA3 variant exposed by Node's crypto.createHash('sha3-256').

When to Use

• Computing Ethereum function selectors or event topics
• Building EIP-712, signature, Merkle, or storage-slot helpers in JS/TS
• Reviewing any code that hashes Ethereum data with Node crypto directly

How It Works

The two algorithms produce different outputs for the same input, and Node will not warn you.

import crypto from 'crypto';
import { keccak256, toUtf8Bytes } from 'ethers';

const data = 'hello';
const nistSha3 = crypto.createHash('sha3-256').update(data).digest('hex');
const keccak = keccak256(toUtf8Bytes(data)).slice(2);

console.log(nistSha3 === keccak); // false

Examples

ethers v6

import { keccak256, toUtf8Bytes, solidityPackedKeccak256, id } from 'ethers';

const hash = keccak256(new Uint8Array([0x01, 0x02]));
const hash2 = keccak256(toUtf8Bytes('hello'));
const topic = id('Transfer(address,address,uint256)');
const packed = solidityPackedKeccak256(
  ['address', 'uint256'],
  ['0x742d35Cc6634C0532925a3b8D4C9B569890FaC1c', 100n],
);

viem

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