DESFire authentication with AES

Question

If I do an authentication to a DESFire card using AES, do I need to do the key diversification? If so, is there some code example of how to do the diversification?

Answer 1

No, you don't have to use a diversified key. You can just as well use the same key(s) for all your DESFire cards. However, it is advisable to use a diversified key in order to prevent attacks on the whole system if an attacker discovers the key(s) for one card.

With regard to key diversification functions, I suggest that you take a look at NXP's application note on Symmetric key diversifications.