> ... so that might not actually work if the site you are authenticating against is well-implemented I'm using it on several sites and already did swap / reini

> ... so that might not actually work if the site you are authenticating against is well-implemented I'm using it on several sites and already did swap / reinitialize my U2F devices... It works, including on GMail. As I understand it the most recent Webauthn is going to be supported by Ledger soon. I don't think they're non-compliant or badly implemented websites: although I'm not sure what the specs say. I do personally love that I can back up my "seed" and know that by going to pick my safe at the bank I'll always be able to reinitialize an U2F device and I'll also really love that it displays "Google" on the Ledger Nano S's tiny screen. Pricey little thing to use as "only" an U2F device: about 60 USD but I like it a lot. > (Unless the Nano S also lets you back up the counter value) Late reply but... As I understand it as long as the counter is monotonic it'll always work. What Ledger does (and apparently the Trezor too from reading this thread, another device with an HSM) is, upon initializing the U2F app the first time on your hardware device, is to set the counter to the current timestamp. So basically: once you use another device to log in, then you cannot use the old one, unless you reinitialize it (and then it's the other you cannot use, unless you reinitialize it etc.). These devices do not have a clock, which is why it works that way (in the case of the Ledger Nano S / Ledger Nano X at least).