Hacker News Reader

Comment by gst | Hacker News Reader

Last time I checked (more than a year ago) most of the websites didn't care about the counter value.

(If you use a Ledger device for U2F and subsequently restore a new (or a reset) device from your private seed the counter will be reset. Trezor has the same issue but allows you to manually set the counter to work around it.)

View on HN

I haven't got any info on websites caring about the counter value. It seems.. pointless to use U2F if you just disregard the counter value. You need to extract it from the response in order to construct the binary data to verify the signature. If one disregards the counter value, they can just outright drop the whole U2F.

> If one disregards the counter value, they can just outright drop the whole U2F.

It's not pointless. Disregarding the counter only enables replay attacks, that is: the attacker must previously have captured a challenge/response. The phishing resistance is still retained because it relies on the browser passing the origin to the u2f device and the browser can't be fooled by similar URLs while a human entering a TOTO token can.

U2F isn't as trivial to implement as RFC4226 OTP. It takes effort. Implementing the counter check is trivial. Disregarding the counter and stating "that only enables replays" is absolutely unacceptable. If one is so irresponsible to the point they're enabling a replay attack - then there's no excuse and no valid argument to support the use of U2F at all. If you (not YOU, personally) can't implement the protocol fully, don't half-ass it and plant mines. That's my take on it, and anyone who implements this protocol to secure people's accounts MUST (not SHOULD) think the same. There is NO excuse for deliberate irresponsibility.

Reply on news.ycombinator.com