Google Titan Security Key

If you want U2F with recovery, the Trezor from SatoshiLabs is a great option. Only issue is the cost is a bit higher than most hardware tokens.

For both cases, what you want to have is a central account that you authenticate to using the key, and that account uses OpenSocial/OAuth-like protocols to grant access to separate services.

That’s how those central teams manage to revoke keys easily.

In the original U2F spec, I think there was an "answer" to this revocation issue: "enroll a second device for every origin, and keep this one in a safe". This way you can still connect even if you lose the first one.

In practice, well, meh...

I think I'd like a version of this scheme which works a bit like email-based verification: you have a trusted provider (like an email provider today, you can self-host or use any of the many 3rd party hosts) that you use to vouch for your identity. When you want to log into a website you use a certificate authenticating you, the website checks if it's valid with your authority (similar to the current email-based verification on most websites). If you want to change your certificate for any reason you only have to do it with your authority and everything else keeps working as usual. The drawback of course is that you have a single point of failure, if the authority is compromised you're naked in the wild.

IIRC OpenID worked like that but unfortunately it never gained traction. It's a shame really.

More practically I do use a yubikey myself but mostly as a GnuPG smartcard, not for 2FA. I actually have the same key stored on multiple tokens as a backup, so if my current key breaks I just have to fetch an other one. Of course if instead I lose it or it's stolen I'll probably have to generate new keys (even though the PIN should theoretically still protect me) so the problem still exists.

See https://twofactorauth.org/ . I thought there was an ongoing effort to add backup/restore steps to this informative site.

Indeed, I was recently locked out of some of my accounts: I used some "one-shot backup codes", but some sites didn't deliver them (and so, required involvment of admin/support by mail+phone).

With yubikeys, you can effectively clone them when setting them up initially. So you carry one and keep another spare in a safe location. If your primary fails, you can buy another and promote your hot standby to primary having set the new one up to be a clone.

umm, buy two, enroll both and keep one safe somewhere?

I'm very surprised when people voice this concern. These keys cost a mere $20 or so. There's no limit to how many website you can set them up with. So $40 or even $60 is all you need to invest in.

regarding yubico: they talk open, global standards, but then say security can only be met by producing in the USA (and Sweden!).

Why should I trust USA produced products?

Meh... "open" https://www.yubico.com/2016/05/secure-hardware-vs-open-sourc...

To be fair for home usage a soft-token is just as good and you can back it up by backing up the seed.

If your phone is compromised by someone who can exploit it then your adversarial outlook is pretty dire to begin with.

Mobile phones can be hacked; if you use your Authenticator app to log into an application on your mobile phone, it's by definition no longer two-factor authentication. The basis of that is having a separate device. Having that in a key that cannot be compromised by e.g. being rootable, internet connected, etcetera is an extra layer of security.

The mobile phone is more convenient though, and I also don't know how these things work when you try and log in via a mobile device. For high security access though, like google cloud consoles and such, a policy of not allowing access via mobile phones does make sense. (also because said console is probably not very usable on mobile).

Security tokens are more secure and can't be as easily fished as phone-based 2FA solutions. It's not about using the key on a mobile phone, it's about replacing phone-based 2FA.

You're right however that their key doesn't seem to have any interface other than USB so it won't be practically usable on smartphones. Yubico has NFC tokens[1] for that use case but it doesn't seem that Google's version offers that yet.

[1] https://www.yubico.com/products/yubikey-for-mobile/

The yubikey version of this works with phones, you can plug it in if your phone has the appropriate usb port, and it theoretically supports nfc and bluetooth but those rarely seem to work for me. I'm not sure if the google version also supports the wireless protocols but I don't see why you couldn't plug it into your phone.

All answers above sounds as great explanation! I don't understand mobile 2FA as an app only but also possibility to e.g. being called by system and you have to put some PIN/key over phone.

> 2FA over mobile phone

Still vulnerable to phishing. If you include a convincing iframe, your attacker can store your TOTP, and use it from their machine.

U2F relies on the domain of the page you are currently browsing, so the code can't be used by another party on the real site.

And if you were thinking about SMS... vulnerable to any attack on the mobile network + phishing + ...

My understanding is that it's a FIDO U2F key, like the ones from Yubico.

Funny how this climbed to the top on HN, without anyone knowing what this is exactly.