The EU has a federated public key cryptography based identity system. The member states recognize identities issued by other member states, but there is no central system.

In any case, the private key is stored on a plastic ID, only released with a PIN, and the databases only store the corresponding public key.

A leak of a public key without the private key is harmless.

https://en.m.wikipedia.org/wiki/EIDAS

SSNs sit in a middle ground between being public and private. A large number of companies and organizations use it to both identify people and as proof of identity. Those are two separate functions.

When I go to a bank for a loan, I should give them some form of private id as proof I am who I say I am (this doesn't have to be a federally issued number).

When companies communicate about me with each other (such as running a credit check on me which is likely why T-Mobile even had SSNs) they should use my public id.

SSNs aren't a great source of identity mostly because they were never designed to be - they aren't unique, until somewhat recently they were issued in a predictable order, an individual can have their SSN changed, and since they are only 9 digits we're going to run out of them on a practical timeline, etc.

They became a defacto identifier for many institutions just because US citizens and permanent residents generally have one - but aside from convenience, they're pretty problematic compared even to something like a UUID/GUID.

If you were trying to design a true national ID number, you'd probably want to approach the problem more like a database designer would: you'd want something that had possible unique values far exceeding the reasonable number of people you expect to exist before the collapse of society, that was reasonably random and difficult to predict based on other known attributes about the person, that by spec was never shared with another person, etc.

If the US was capable of rational policy decisions, you could do any of a number of things to present a trusted representation of your identity without a “secret” 9 digit number.

We already have such a system, it’s called a passport, and it has complementary “cousins” like passport cards and nexus cards. That framework could easily be built upon, but there is a mountain of paranoia and stupid to climb first.

Instead we have the current system where fraud is endemic and where millions of people are marginalized by poor access to ID.

An SSN is a username, not a password. We need an identity system with real passwords that can be changed in the case of a breach.

One option would be to offer a national oauth-style ID verification system.

I have this same question also.