Sweden for example implements the public knowledge side of it, forcing identification to be reliable and 2FA.

> The link between a person and the identity number is established through the civil registry and through identity documents and secondarily through the widespread use of the number in various contacts with authorities, businesses etc. They are necessary for personal service at banks, authorities, health care and other services which use the personal identity number. Most people are familiar with their full number and those of their children without hesitation. Personal identity numbers of individuals are openly available from the Swedish tax authorities to anyone who asks (over phone, letter, over the desk, but not over the internet), according to the Swedish principle of freedom of information. Redistribution of these numbers using computers is, however, governed by the law of personal details, an implementation of the Data Protection Directive.

https://en.wikipedia.org/wiki/Personal_identity_number_(Swed...

Then 2FA through BankID, with a chain of trust started with the KYC of your bank. No SMS, "state something only you know" or similarly awful methods.

https://en.wikipedia.org/wiki/BankID

I think in most countries in Europe the national id number is enough to link taxes to specific people (identity card numbers are to most effects public), even though for official international documents you need to provide the accepted Tax Identification Number (TIN) which you can find in https://www.oecd.org/tax/automatic-exchange/crs-implementati..., but more as a convenience than anything else.

That keeping secret your SSN is a thing is something that mostly affects the US.