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Comment by moron4hire | Hacker News Reader

SSNs are not unique.

In what sense? They're only ever assigned to a single individual, and they are not reused[1]. The number uniquely IDs the individual.

The Wikipedia article makes the same point as the parent poster: "the Social Security number has become a de facto national identification number".

[1]: https://en.wikipedia.org/wiki/Social_Security_number#Exhaust...

That's a technically accurate, but weasely answer from the SSA. Realistically, there are many loopholes and exceptions.

- People born in various New England states have social security number overlap with number ranges issued by the social security systems in Micronesia, Palau and the Marshall islands. Those territories get services from Federal programs which causes issues.

- EINs and SSNs are issued by different departments and can overlap. People in various scenarios will provide the number in the wrong context.

- Millions of people use the wrong SSN without fraudulent intent.

- People frequently and fraudulently use the SSNs of children and older people.

- Hundreds of thousands/low millions of people have multiple valid SSNs.

- 40,000 people used a real SSN included as a sample in a wallet in the 1930's.

- Some populations have a higher incidence of mistakes, fraud, multiple valid SSNs or other problems. One dataset that I was acquainted with had IIRC a 7% known exception rate for SSNs.

People from the Marshall islands can move to the US.

When they do, they need to apply for a US Social Security number.

How does someone end up with multiple valid SSNs?

They get one at a young age at and are unaware of it for various reasons.

Remember that there are 320M US citizens with all sorts of improbable stories. You have people born abroad, native americans on isolated reservations, people born at home or with irregular birth certificates, people with scummy parents committing fraud in their child's name, etc.

When New York implemented facial recognition on IDs, over 100 people were arrested for having multiple driver's licenses. Stuff happens!

They claim they're not reused, even though the current living US population is a third of the entire keyspace (320 million vs 1 billion).

That, and the keyspace is sparsely populated, since the prefix is geographically assigned.

until june 25, 2011, after which it is now random:

https://www.ssa.gov/employer/randomization.html

Just think about it for a minute. It's a nine digit number, of which only the last four are serial (the other 6 encode location and issuing date in a round about way). Our population is currently 320,000,000, meaning even if all 9-digit numbers were in play (somewhere around 350 values in the area number are not currently used), the current living population is already using 1/3 of all SSNs.

Add in the fact that some not-as-rare-as-you-would-hope people can have multiple SSNs and you just can't say for certain "this SSN means this person".

SSA may say numbers don't get reused, but that is a straight up lie and they know it. I've seen it happen in databases I've ran. Dead people occasionally get their SSN reissued.

While the SSA says that they do not reuse SSNs (which is nicely couched in the present tense in the FAQ cited by Wikipedia), there have been historic, mostly accidental, reuses in some of the geographic administration districts (the SSA only really centralized number generation in the 2011 decision to also start randomizing them), and I think far back enough now that the overlaps mostly don't matter operationally...

Off hand I don't have a source I can cite on that, only that in past job (mostly health care claims) I've been involved with some quite hard work to ensure not to build systems that use an SSN as a individual ID as much because there are some very weird edge cases out there, especially if you have old, dirty, and/or large enough datasets, as because it's not a good idea in the first place to rely just on SSNs for anything other than a Tax ID.

At least in the sense that there's no 1-1 mapping from SSNs to individuals.

http://www.witn.com/home/headlines/Duplicate__111371029.html

nitpick: based on the example you linked, you probably mean 1-1 in the opposite direction, or something like, "no well-defined function" in that direction.

But people think they and worse they are intended to be.

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