---
name: nodejs-keccak256-774c9a8f1e0c
description: 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.
origin: ecc direct-port adaptation
version: "1.0.0"
---

# 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.

```javascript
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

```typescript
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

```typescript
import { keccak256, toBytes } from 'viem';

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

### web3.js

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

### Common patterns

```typescript
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

```typescript
import { keccak256 } from 'ethers';

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

### Audit your codebase

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

## Rule

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


---
Source attribution: mturac
Original project: https://github.com/mturac/everything-openai-codex/blob/b5057da5f42ed6b12cd3a59e89af0ccd12cff7c2/skills/nodejs-keccak256/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 Mehmet Turac

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.


## Additional upstream notices

nodejs-keccak256-774c9a8f1e0c/DAVEAI-UPSTREAM-NOTICE.md

# Notices and Acknowledgements

Everything OpenAI Codex is a Codex-focused adaptation inspired by the public
[`affaan-m/everything-claude-code`](https://github.com/affaan-m/everything-claude-code)
project.

Respect to Affaan Mustafa and the contributors to that project for making the
multi-harness agent operating-system pattern visible in the open.

This repository adapts the public idea and workflow surface for OpenAI Codex:
names, defaults, install targets, docs, validators, and cross-harness guidance
are maintained here for the Codex-oriented project.


# Mega AI Hub resource metadata

Creator / publisher: mturac
Original project: https://github.com/mturac/everything-openai-codex/blob/b5057da5f42ed6b12cd3a59e89af0ccd12cff7c2/skills/nodejs-keccak256/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Backend Developer, ML / AI Engineer, Product Manager
Specialties: API, Backend, Cross Platform
Tools: Ethers, Viem, Web3.Js
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: fd0302fca0b50d285d625121dbcac88a76c395e424cbd0063a8506153ca49485