This is mostly against phishing. A phisher can get users to insert a token from a USB device or a text into evil.com. But U2F uses public key crypto, so your token derived for evil.com is not the same as for github.com

This is a brilliant idea to use as a third factor. Instead of TOTP or the hardware U2F key, just create keys for all your browsers. That way, you're more protected against phishing, but still have a way to log in if you lose your keyfile.

My knee jerk reaction was 'sounds an awful lot like a cookie', but maybe that's an indicator that the problem could be slightly generalized to offering a 'secure' version of localstorage.

It's almost like a cookie, yes, in that you could say "trust this browser". However, the problem comes when you ask for the second factor for a new computer. A TOTP approach would give the second factor to the phisher, whereas U2F does not.

Come to think of it, I'm not sure that's a problem with the cookie and not with TOTP.

Ahhhh. That makes a lot more sense. Thank you.

I think the greatest practical threat to TOTP is phishing. U2F, regardless of where keys are stored, binds a keypair to an origin. Only authentication requests from `github.com` can use the `github.com` keys. For my money, any U2F implementation is a win over any TOTP.

For the uninitiated, TOTP is....?

U2F has the advantage that a server compromise won't compromise the second factor as there's no shared secret accessible to both parties.

Of course, keeping the token on the same machine that you're using for logging in is reducing the security, but then, the token is stored in the Keychain and once you're at the point where malware is so deeply hooked into the system that it has access to the system Keychain, then it can also inject itself into your browser and get a 2FA token whenever you log in.

Passwords are often already on the users phone. Such as if you use say Authy or Google Authenticator for your 2 factor, your phone if say an iPhone already stores all your passwords in your keychain which is accessible on your iPhone just like on your computer. Or if you use 1Password your passwords are accessible on your phone just like on your desktop. So still comes down to you having a strong master password for your keychain and or 1Password, etc that only you know.

If you use Authy on your phone, they have long had a chrome extension that allows you to get your codes on your computer, already for years and that works with all your existing codes rather than this which is limited to just GitHub currently it sounds.

But hopefully someone else can comment on the security improvements of Soft U2F or if its more just building a standard rather than people having to rely on Authy or such.

> But hopefully someone else can comment on the security improvements of Soft U2F or if its more just building a standard rather than people having to rely on Authy or such.

The main difference is that U2F is phishing-resistant because it binds keys to the origin. TOTP, on the other hand, can still be phished.

(I believe Authy attempted to solve some of this with their browser extension for sites that use their first-party integration, rather than just for users using Authy as a generic TOTP app. I would generally avoid their first-party integration because of their reliance on SMS.)

The improvement is accessibility. It's less secure than physical 2FA but more so than just 1FA. As the article says, "for many, the security of software-based U2F is sufficient and helps to mitigate against many common attacks such as password dumps, brute force attacks, and phishing related exploits."

It's really not that much less secure than physical 2FA: I'm willing to bet that most people just leave their hardware key in their laptop at all times. (where "most people" ends up being corporate U2F users, who are probably given YubiKey Nanos and the like)

At that point, your laptop is basically your 2nd factor - which this software is pretty similar to.

But even if you leave it in, everything is still protected in hardware, and in addition, malware can't trigger a physical presence button push...so, it is in fact significantly less secure...

> malware can't trigger a physical presence button push

It kinda can, it just needs to trigger a dialog the user thinks looks legit. Or easier, just stay resident until the next time the user pushes the button.

Don't get me wrong, U2F has benefits, but it's not invulnerable to malware designed for it. You want real system level protections to back it up and most users aren't running on operating systems that can really cash the check you're trying to write with that threat model.

on an unrelated note: can someone explain why SMS based 2FA was every considered to be a good idea? That crap drives me NUTS.

Mostly because, thus far, it has the best user setup experience (doesn't require user to download a new app and hence can often get enabled in seconds) and has the best "lost device"/"broken device" story (people tend to not have their backup codes). I think things like Soft U2F can change that equation a bit. An iCloud keychain synced 2FA credential would go a long way toward addressing some of the usability issues with traditional TOTP based 2FA.

You have to get people to buy into using 2fa. SMS and cell phones were good for that. They are not secure and are being abused now (SS7 attacks) and one day won't be used for 2fa at all, but the platform was a good start and certainly better than nothing at all. Hopefully, OATH (HOTP and TOTP) and FIDO will take over where SMS leaves off.

And the real danger of cell phones and SMS is account recovery processes that SMS a recovery code to your cell. That's way more concerning than 2fa via SMS IMO.

SMS-based 2FA also gives companies a good excuse to collect users' mobile phone numbers — particularly sites for which one might not otherwise feel compelled to provide that information.

Not saying it was a good idea for security, but that probably made it easier to justify internally.

It feels inherently insecure to blast a 2FA code across every device where you've got Hangouts installed. (And if you've got Hangouts installed on the PC where you're logging into, then it's not 2FA anymore.)

> It feels inherently insecure to blast a 2FA code across every device where you've got Hangouts installed.

I think that may be Project Fi specific. To my knowledge, Hangouts doesn't do SMS anymore except for Project Fi customers, and even prior to them forcibly removing SMS handling from Hangouts on my Samsung and telling me to find something else after an update, it never synced SMS messages it to other Hangouts instances.