Discussion on: Hash your passwords with scrypt using Nodejs crypto module

[Brad Dougherty]

It's probably best to use crypto.timingSafeEqual(a, b) to compare the keys in the verify function to protect against timing attacks.

[Yash]

Hey Brad, I am new to authentication, can please explain gour point?

[Brad Dougherty]

The Wikipedia article explains it pretty well: en.wikipedia.org/wiki/Timing_attack

In other words, the verify function should look something like this:

import crypto from 'crypto';
import { promisify } from 'util';

const scrypt = promisify(crypto.scrypt);

async function verify(password, hash) {
    const [salt, key] = hash.split(":")
    const keyBuffer = Buffer.from(key, 'hex')
    const derivedKey = await scrypt(password, salt, 64)
    return crypto.timingSafeEqual(keyBuffer, derivedKey)
}

The key has to be converted into a buffer because crypto.timingSafeEqual only accepts buffers for the arguments.

Doing it this way means that the comparison operation takes the same amount of time every single time.