Snippet

Preventing Timing Attacks with crypto.timingSafeEqual in Node.js

Standard string comparisons using '===' terminate early on the first mismatched byte, creating timing side-channels that attackers can exploit to forge signatures byte-by-byte. The crypto.timingSafeEqual function executes comparison operations in constant time regardless of byte alignment, ensuring secret tokens and HMAC digests remain secure.

snippet.js

javascript

import crypto from 'node:crypto';
 
export function verifySignature(payload, signature, secret) {
  const hmac = crypto.createHmac('sha256', secret).update(payload).digest();
  const expectedSig = Buffer.from(signature, 'hex');
  if (hmac.length !== expectedSig.length) return false;
  return crypto.timingSafeEqual(hmac, expectedSig);
}

nodejs

Breakdown

import crypto from 'node:crypto';

Imports the native Node.js cryptography module.

const hmac = crypto.createHmac('sha256', secret).update(payload).digest();

Computes a SHA-256 HMAC digest from the input payload.

if (hmac.length !== expectedSig.length) return false;

Ensures buffers match in byte length before constant-time comparison.

return crypto.timingSafeEqual(hmac, expectedSig);

Compares byte arrays in constant time to prevent side-channel timing attacks.

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Preventing Timing Attacks with crypto.timingSafeEqual in Node.js

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