Generating random uint256 numbers in JS

Question

I need to generate a uint256 random number offchain (in a Node.js client). Since BN doesn't have a random() function, what's the best way to do so?

Answer 1

You can use Node.js' crypto.randomBytes to generate a cryptographically secure random number:

import { randomBytes } from 'crypto';
import BN from 'bn.js';

const value = randomBytes(32); // 32 bytes = 256 bits

// Value as native bigint
const bigInt = BigInt(`0x${value.toString('hex')}`);

// Value as BN.js number
const bn = new BN(value.toString('hex'), 16);

Answer 2

If you have web3 you can use randomHex from web3-utils.

web3.utils.randomHex(32)
> "0xa5b9d60f32436310afebcfda832817a68921beb782fabf7915cc0460b443116a"