racerboy (imported) wrote: Mon May 23, 2022 2:43 pm
In some cases, when a website wants your cell phone or number it's not so much to track you but for "two factor authentication."
[rant mode on]
Sorry to burst your bubble, but phone number or text messages is NOT a two-factor authentication and should not be used as such.
First - it is controlled by corporate entity (or state) - thus can't be used as trusted authenticator.
Second - sim cards are trivially reissued to third party via minimal social engineering (more than enough cases of that happened in Russia, probably not much better in other countries).
Third - again, at this point - text messages are trivially interceptable by thirdparty (google SS7, and well:
https://www.theguardian.com/technology/ ... exts-calls ). The protocols which run our phone network are... legacy of 80-90s and are not encrypted or authenticated. There are countermeasures to that, but the problem is basically unfixable at this point. Entry barrier for that is pretty low too, you do not need to be nation-state for that.
If you must use 2FA - use proper hardware token or some authenticator solution (TOTP is the protocol you are looking for, it is standard, and requires nothing more than shared secret and same time on both ends - authenticator and server). Doesn't even need internet connection for that.
[/end of rant]
PS. If you ever followed the history of use 'phone number as identity' - it all tracks back first to 'to prevent spam' (which is a lie, phone numbers are cheap, and it does not prevent them). But worse - it ends up as easily trackable identity - email can be had for free, but phone number is usually tied to you and some sort of ID