nodejs-keccak256

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SKILL.md

Prevent Ethereum hashing bugs in JavaScript and TypeScript. Node's sha3-256 is NIST SHA3, not Ethereum Keccak-256, and silently breaks selectors, signatures, storage slots, and address derivation. Use when hashing for Ethereum in JavaScript or TypeScript, or when a selector, signature, storage slot, or derived address is wrong.

npx skills add affaan-m/ecc --skill nodejs-keccak256

Documentation

SKILL.mdView source

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'

Examples

ethers v6

viem

web3.js

Common patterns

Address from public key

Audit your codebase

Rule

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

npx skills add affaan-m/ecc --skill nodejs-keccak256

Documentation

SKILL.md

nodejs-keccak256 | SkillBundle

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],
);

import { keccak256, toBytes } from 'viem';
 
const hash = keccak256(toBytes('hello'));

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

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]),
  );
}

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

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