The remarkable thing is that modern chip-and-pin cards do support that sort of “offline” transaction, although fortunately without the carbon copy paper. Specifically, a non-networked credit card terminal can present a transaction to the chip, the chip will cryptographically sign this transaction in a unique way, and the terminal will store it for later submittal to the credit card company, when an online connection is possible.
For a typical “online” transaction when there are no connectivity issues, the third step would send the transaction immediately to the credit card company, so they can have the option of declining the charge. The cryptography is otherwise the same, and it’s why offline transactions are possible.
Some vendors like SNCF (the national rail operator) in France use offline transactions for their ticket vending machines at rural stations, where there’s no guarantee of being within mobile phone service. The card issuer also usually programs some safeguards to prevent abuse, such as X number of offline max and then an online transaction is mandatory, or a limit on the value of purchases (eg $50 max for offline). After all, there cannot be a check against one’s credit limit when offline.
In the USA, it is exceedingly rare for credit cards to be issued as chip-and-pin, and while offline transactions can be performed with chip-and-signature cards, it’s rarely enabled since most/all terminals in the USA have been online since the introduction of electronic credit card processing.
Contactless chip cards might have changed the calculus though, since there is no PIN at all for these transactions. So perhaps issuers might allow a few offline transactions when contactless.
spankmonkey@lemmy.world 2 weeks ago
The odds of the power being out are more likely than a lack of network connection in the US, we tend to have generators or other power backups for cell towers and landlines even when the power goes out.
LilB0kChoy@lemm.ee 2 weeks ago
In the US, telephone land lines actually carry their own DC electrical charge which is provided by the telephone central office and travels through copper wires to each phone.
This is why, during a power outage in the US, a land line phone will typically continue to work. The exception being if the outage is large enough to also take out the central phone office.
spankmonkey@lemmy.world 2 weeks ago
The central phone office frequently has its own backup generators or independent power supplies which is what I was referring to.
LilB0kChoy@lemm.ee 2 weeks ago
Gotcha. That makes sense why the phones always seemed to work in every power outage. I wanted to mention the 48 volts DC setup because I’m not sure if that’s common or standard outside of the US.