Hacker News Reader

Comment by LeoPanthera | Hacker News Reader

The key is credit card number + expiry date. Cards can share numbers as long as the expiry date is different.

No they cannot. Most customers keep the same CC # and get a new expiry and security code when renewed.

Yes you can't "share" numbers (in the sense of 2 people having the same CC number), but what you describe prevents a new number to be needed (so it is one less new number needed)

Where? This is not common practice where I live, in fact, it's the first time I've heard about it. Interesting!

Do you have a debit or credit card account that you've kept open through a few expiration dates? An old card maybe? Compare it to your current one.

It's always a new number. Shortly before the cards expire, you're issued a new one. That's how it's been for me for this whole century.

This isn’t true, the same PAN (Primary Account Number) is never issued to two different accounts. Even if you wanted to solve all the payment routing problems this could cause, it wouldn’t be possible to implement. The expiry date can change while the PAN stays the same, so you’d never be able to gurantee a unique key today stays unique in the future.

I used to work in a bank where we had to specifically implement routines for when visa reused the PANs...

There was a period between the old expiration and the new issue and not common, but it did happen from time to time.

I should have been a bit more verbose. Two accounts won’t have the same PAN at the same time.

Which is notable, but doesn't matter in the context of "running out of numbers"

Seems to matter a lot for IPv4.

Being able to recycle numbers is the difference between "this can work for a few years at full scale" and "this can work forever". IPv4 can't even reach the first level. It can't even give out one address per human.

I'm sure you've seen the idea that an upgrade to IP could have just added another octet or two and changed nothing else. It would have worked pretty well to prevent us running out of addresses, with 40 or 48 bits.

Well, 16 digit credit card numbers are a hair under 50 bits. And full-size 19 digit credit card numbers are a hair under 60 bits. That's plenty. You can give out a million of them to every person. If we couldn't reuse, they would eventually run out. Because we can, they won't run out.

For example, last time mine renewed I found out that AWS didn't record the expiry date. I only have to update the CVV.

Reply on news.ycombinator.com