[mytailorisrich]

Stored values cards were the way French public phone booths worked when they first moved away from coins in the 80s.

There were single-use chip cards that you bought and kept in your wallet. Plain eeprom.

I remember I built a reader for them as a teenager...

[lxgr]

These were storage only though, right? Such systems are trivial to compromise.

Stored-value payment cards usually contain at least a secret key and some logic that allows them to establish a secure channel to another trusted entity, such as a merchant smartcard (which can be embedded in a terminal) or a backend server (and a corresponding HSM).