Node.js Keccak-256

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

Scope: Ethereum hashing only — function selectors, event topics, EIP-712, Merkle proofs, storage slots, address derivation.

MUST NOT: Rewrite Node createHash('sha256') used for JWT tokens, OAuth PKCE, API keys, or other app secrets. Keccak is not SHA-256.

Prefer: keccak256 from viem when viem is already a project dependency. Use ethers only when the app already depends on it.

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

import { keccak256, toBytes } from 'viem';

const hash = keccak256(toBytes('hello'));

web3.js

const hash = web3.utils.keccak256('hello');
const packed = web3.utils.soliditySha3(
  { type: 'address', value: '0x742d35Cc6634C0532925a3b8D4C9B569890FaC1c' },
  { type: 'uint256', value: '100' },
);

Common patterns

import { id, keccak256, AbiCoder } from 'ethers';

const selector = id('transfer(address,uint256)').slice(0, 10);
const typeHash = keccak256(toUtf8Bytes('Transfer(address from,address to,uint256 value)'));

function getMappingSlot(key: string, mappingSlot: number): string {
  return keccak256(
    AbiCoder.defaultAbiCoder().encode(['address', 'uint256'], [key, mappingSlot]),
  );
}

Address from public key

import { keccak256 } from 'ethers';

function pubkeyToAddress(pubkeyBytes: Uint8Array): string {
  const hash = keccak256(pubkeyBytes.slice(1));
  return '0x' + hash.slice(-40);
}

Audit your codebase

grep -rn "createHash.*sha3" --include="*.ts" --include="*.js" --exclude-dir=node_modules .
grep -rn "keccak256" --include="*.ts" --include="*.js" . | grep -v node_modules

Interactions

• Complements viem-v2 for EVM client and keccak256 helpers
• Non-EVM address validation → solana-v1

Rule

For Ethereum contexts, never use crypto.createHash('sha3-256'). Use Keccak-aware helpers from ethers, viem, web3, or another explicit Keccak implementation.