crypto.ts20 lines · main

1	import { timingSafeEqual } from 'node:crypto';
2
3	/**
4	* Constant-time equality check for shared secrets and HMAC outputs.
5	*
6	* Why: comparing tokens with `===` runs in time proportional to the shared
7	* prefix length, which leaks byte-by-byte info to a remote attacker who
8	* can measure response latency. `timingSafeEqual` runs in time
9	* proportional to length only, regardless of content.
10	*
11	* Length-mismatch is checked up front and bails fast — for fixed-length
12	* secrets (the runtime shared secret is `>= 32` chars, HMAC outputs are
13	* fixed by digest size) the length itself is not the secret. For
14	* variable-length inputs you control, pad both sides to the same length
15	* before calling.
16	*/
17	export function constantTimeEqual(a: string, b: string): boolean {
18	if (a.length !== b.length) return false;
19	return timingSafeEqual(Buffer.from(a), Buffer.from(b));
20	}