I see the advice not to use SMS for 2FA comes up a lot on HN, and understand the reasons why that is true. But I find that recommendation comes up short. What are the alternatives, and how can they be widely deployed for little cost?
The point is to prove that you have possession of both knowledge and a physical token (hence two factor). And while sms to phone makes it seem like you are proving possession of the phone, you’re actually proving that you have the phone that texts will route to. That last bit is movable and subject to shockingly little security, hence the issue.