They could have licensed the IP from the same company.

Possibly so. It just means that based on the report's findings, even if you'd decided to play it safe and buy exclusively from NXP directly (the creators of this ecosystem and owners of the MIFARE trademark), it looks like you could still end up with backdoored hardware.

Sorry if I was being unclear with my compound snark, but using a MIFARE Classic of any provenance would be a firing offense for the CISO of my daydream company.

Indeed. Alas (or fortunately depending which colour team you work on), fully broken Mifare Classic is still all over the place, and likewise the "hardened" variant broken in this paper :(

What's a good alternative? How more expensive is it?

MIFARE DESFire is an option. In a genral public reseller, I found 100 DESFire cards sold for 146€ (tax excluded), while 100 of the equivalent versions as MIFARE Classic are sold for 109€ (tax excluded). This is a differnce of 37 cents by card, MIFARE Classic are about 25% less expensive than MIFARE DESFire. I guess the difference increase with the quantity you buy at once.

NXP would probably want to steer you away from mifare classic in the first place, wouldn't they?

Maybe for greenfield deployment… but there’s all the existing infrastructure to support.

I still see classic being installed for door/gate systems in American apartments that are under active construction in 2024. Presumably that’s because resellers either don’t know better or they just have a massive inventory.

I still see new apartment buildings with Sentex or Linear call boxes with the factory master passwords. I don't think these guys are crack security experts.

They found the exact same backdoor key present on old NXP and Infineon cards produced as early as 1996. See p.11:

> But, quite surprisingly, some other cards, aside from the Fudan ones, accept the same backdoor authentication commands using the same key as for the FM11RF08!

> ...

> - Infineon SLE66R35 possibly produced at least during a period 1996-20136 ;

> - NXP MF1ICS5003 produced at least between 1998 and 2000 ;

> - NXP MF1ICS5004 produced at least in 2001.

> ...

> Additionally, what are we to make of the fact that old NXP and Infineon cards share the very same backdoor key?

I think it's more likely those NXP/Infineon parts are counterfeits. Look at A.12, there are early cards that don't NACK $F000 but claim to be NXP or Infineon, behavior counter to legit parts. It looks like the Chinese copies started to chameleon that behavior later as well.

... or used the IP without licensing.