What are Timing Attacks, and why should crypto.timingSafeEqual be used to compare sensitive tokens?

Short answer

These attacks measure the server's response time in nanoseconds to infer how many characters matched before failure; timingSafeEqual prevents this by comparing bytes in constant time.

Explanation

Ordinary comparisons such as === compare strings character by character and stop at the first difference (Short-circuiting). This lets an attacker make many attempts and accurately guess encryption keys and Webhook signatures. crypto.timingSafeEqual compares two Buffer objects in constant time regardless of where the first match or difference occurs.

Code example

import crypto from "node:crypto";
const isMatch = crypto.timingSafeEqual(
  Buffer.from(signatureA, "utf8"),
  Buffer.from(signatureB, "utf8")
);

Common mistakes

• Comparing Webhook signatures (such as Stripe or GitHub) with the ordinary === equality operator.

Follow-up questions

• How do you protect a Node.js project from Supply Chain Attacks in the npm ecosystem?

Sources

• Node.js docs — crypto.timingSafeEqual()