[Gibbon1]

I saw an NFC chip that has 512 bytes of eeprom. Talks to a micro via I2C and has an interrupt that can be used to wake it up.

I think it's a M24LR04E.

Costs like $0.50.

I think these could be useful for devices where you have a limited amount of data you want to read or transfer. Like why have bluetooth and all the crap that entails when all you want to do is configure a device once.

Advantage of a separate IC is you can use it with whatever microcontroller development stack you have working.

[crote]

The problem is that it is simply a dual-interface EEPROM. It only holds data, it doesn't process it. Great for something like a device whose configuration you can update via NFC tap (think e-paper display), not so great if you want to do a whole challenge-response dance between microcontroller and NFC smartphone.

[hlandau]

See comment below.

More generally what I'm seeking is something in the card form factor which is suitable to store cryptographic secrets (i.e., a smartcard).

Separate IC is a disadvantage here since it creates a vulnerable security boundary and makes it infeasible to integrate the chip into a thin card.