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Comment by JBiserkov | Hacker News Reader

GitHub/Google/Microsoft/Blizzard/Heroku have "recovery" or "backup" codes which you are supposed to keep in a safe place (perhaps even a physical safe) and can be used when the phone is not available(lost, locked, erased, whatever).

They are one-time only (that's why you get 10), but are not time sensitive (like those generated by app/token) so they are longer.

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Google also tells you to add a second, "backup" number for two factor auth, or even more of them. It can be a landline, or a trusted person phone.

Phone or SMS based 2FA is inherently insecure. Can be intercepted at carrier level (and it is quite cheap to do it — some political targets in Russia and Turkey were attacked this way).

Yeah but that's a different threat model than the one discussed. It will prevent 99% of attacks but someone always comes in yelling "BUT IT'S NOT PERFECT". As they say, perfect is the enemy of good.

The solution which is considered to be "almost perfect" and relied upon as that, but failing unexpectedly is arguably worse than imperfect solution with known imperfections.

The solution which is considered to be "almost perfect" and relied upon as that, but failing unexpectedly

What other failure mode is there? A solution that's considered to be actually perfect? Regardless, you have to account for Godel.

Black swans arise because when people design things that work 99.99% of the time, they tend to relax and rely on the system more than they should, and when this 0.001% event happens, they are completely unprepared.

The correct mode of operation is to always be prepared, without relying on the "perfect" system too much. If system is actually good, "chaos monkeys" may be employed to keep everybody prepared.

Why would 99% of adversaries fail to choose the attack that's known to work?

Not everyone is a nation state or has SS7 access. Intercepting SMS isn't as easy as you make it out to be.

Not everyone, but many people of varied moral qualities _do_ have access to SS7 and carrier operations, and they can be contacted and negotiated for services.

(Not end-to-end encrypted = not secure. Should be obvious these days.)

I think the SS7 vulnerability in question you're talking about is limited to the MAP portion of SS7. So for 2FA with a landline, you should be fine.

The problem is that SMS provides better recovery rates than TOTP/HOTP + backup codes, because people can go to their carrier and get a new device at the same number.

It's important to remember that availability is an important aspect of security. If you protect a user primarily concerned with mass-account takeover attacks from a low-probability threat (people intercepting their SMS channel) but introduce a high-probability threat (dropping their phone in the toilet and being locked out of their account forever) you may not have made a good security tradeoff.

As I said above, the problem with MFA is now you have one static code for every MFA account, so we are re-introducing the problem public key infrastructure would solve, which I consider is a pretty valid limitation of MFA.

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