Comment by jqpabc123
2 days ago
In TOTP, time exists independent of both client and server and as you point out, is no secret to either.
In HOTP, the secret counter is not independent and must remain synchronized between client and server.
A counter that can be synchronized on demand is kinda superfluous --- not really secret and not terribly relevant either. All else being equal, an attacker can sync up just as easily as a legitimate client so why bother with the counter?
I expect HOTP exists somewhere out there in the real world but I have yet to encounter it. Every 2FA I have actual experience with has been TOTP.
> A counter that can be synchronized on demand is kinda superfluous --- not really secret and not terribly relevant either. All else being equal, an attacker can sync up just as easily as a legitimate client so why bother with the counter?
A unique counter for each authorization attempt ensures the resulting key is different for each attempt, which makes replay attacks not possible. I agree if you sync the counter two ways, it is better to use a "nonce", a totally random secret each time.