Mifare 1k what is the use of two keys

Question

Why are there two keys available (key A and B) for every sector in Mifare 1k smart card? I have read the documentation and I can't find any explanation on the use of two keys. Why they didn't put one 12 byte key instead of two 6 byte keys? The only logical explanation, to me, is to have one master key(A), with which you can change the other key(B), and use the other key(B) for authentication and read/write operations. So for example, one person can have the B key, and can write and read data blocks from the card, but can't change neither the A or B key, or access codes.

I'm I anywhere near?

Tnx guys

Answer 1

You are exactly right about the idea of the "master key". The details are actually exactly the opposite of what you propose: key B would normally be the master key. The access rights that can be given to the 2 keys are not symmetric: e.g. key B can have exclusive write access, while key A cannot. (See section 8.7 of the datasheet for the gory details.)