How are shared the key for AES-128 ?

[Arabella Brayer]

Hello,

I'm trying to understand how works the authentication process with the MIFARE DESFire EV1 device. I have read a lot of diverse papers, but something is not clear for me.

For instance, I have read that to start a communication using AES-128, the reader send first the number of the key to use (0x00 for the master key).
The tag produce one nonce and send it encrypted (AES-128) with the selected key.
The reader receives it and decodes it with the same key.

But... How the reader can share this information with the tag ? I think that the master key and others are different for each device. So this information must be shared somewhere. There is something that I don't understand ^^ How this key can be known from the reader ?

Thanks a lot :)

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[TapLinx Support]

Hi Arabella,

The datasheet of the MIFARE DESFire EV1 explains precisely how the authentication is implemented. It is important to understand this procedure if you want to implement the software at the reader station.

Regards,
The TapLinx team

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