Nodejs Keccak256

Prevents a silent footgun in Ethereum development: Node's `crypto.createHash('sha3-256')` returns NIST SHA3, not the Keccak-256 that Ethereum actually uses, and the two produce different hashes for identical inputs. This matters when you're computing function selectors, event topics, storage slots, or deriving addresses from public keys. The skill shows you the correct helpers from ethers, viem, and web3.js, plus grep commands to audit your codebase for dangerous `createHash('sha3')` calls. If you've ever wondered why your locally computed signature or selector didn't match on-chain data, this is probably why.

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last updated: Aug 21, 2026

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Install

$ npx -y skills add affaan-m/ecc --skill nodejs-keccak256 --agent claude-code

Installs into .claude/skills of the current project.

Files

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],
);