Nodejs Keccak256

If you're building Ethereum tooling in JavaScript or TypeScript, you've probably already shipped this bug. Node's `crypto.createHash('sha3-256')` implements NIST SHA3, not the Keccak-256 variant Ethereum actually uses, and the outputs are silently different. This skill teaches Claude to catch the distinction and use the right helpers from ethers, viem, or web3.js when computing function selectors, event topics, storage slots, or deriving addresses from public keys. It includes grep commands to audit your codebase and side-by-side examples showing why `nistSha3 === keccak` returns false. Small footgun, massive consequences if you get it wrong.

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last updated: Jul 14, 2026

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Install

$ npx -y skills add affaan-m/everything-claude-code --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],
);