Change app key

[zero]

Hello,

I am trying to change an app key over a Mifare Desfire EV1 card.

So, I am authenticated using my Masterkey, then I have created an application (11 11 11) for test :

>>> cmd = 90 CA 00 00 05 11 11 11 E9 8E 00
<<< data = A5 7D B8 9C 77 A2 17 37
<<< sw = 91 00

My first question is, what is the default key for this application ? is it the Master key ?

Then I am trying to change the app key :

Let's suppose that the current app key is :

k_old = "22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22" (AES Key)

and the new key is :

k_new = "33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33"

Now I have to execute the C4 command with some cipher data as input. To calculate the cipher data I did those operations, but I am not sure about it :

data = k_new XOR k_old
c1 = crc32(data)
c2 = crc32(k_new)

then :
cipher = AES-128-CBC (Session_key, data + c1 + c2 + padding, iv=0)

then the final commande is :

90 C4 00 00 21 80 cipher


Is that correct ?
And I also have a question about how crc32 is calculated I found several algorithms on the internet, and there is no way to check if mine is correct.


Thank you :)

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