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Different ranges MIFARE DESFire EV1 AES Authentication With TRF7970A

Oliver Birnfeld
Prodigy 95 points
Other Parts Discussed in Thread: DLP-7970ABP

Hello,

I'm currently working on an application with Mifare DESFire EV1 AES Authentication and I used SLOA213 with the DLP-7970ABP BoosterPack as starting point. I'm wondering why anticollison and selection is working with higher distances than the AES-Authentication?

Or in in SLOA213 code: Iso14443aLayer4() is returning STATUS_SUCCESS on distances <=20mm but Aes_authenticate(...) only receives valid data on distances <=5mm. What's the reason for this? What am I missing?

Thanks and best regards,

Oliver

  • 0
    TI__Guru*** 129610 points
    Hello Oliver,

    This is typical for the DESFire cards. They are designed for security and generally in our experience have been shown to be off tuned from 13.56MHz to limit the range.

    The reason the anticollision processes but Authentication does not is because the data transferred for anticollision is minimal and can be transferred without any RF error at greater distance.

    Conversely, the AES authentication packets are far longer and more susceptible to RF transmission errors, and therefore requires being closer to the RF field to execute reliably.
  • 0 in reply to Ralph Jacobi
    Prodigy 95 points
    Hello Ralph,

    thanks for your quick reply. This confirmed my suspicion that the different data lenght is responsible. But that leads to the question if I could increase the range by detuning my reader antenna in the same direction... ;-)

    Best regards,
    Oliver
  • 0 in reply to Oliver Birnfeld
    TI__Guru*** 129610 points
    Hi Oliver,

    Definitely! :)

    Also one other aspect to keep in mind is that when you send AES encrypted data, the tag does have to de-crypt that, so it would also take more power to run the AES engines on the tag and that power is exclusively being provided from the RF field. Therefore, while you can improve the range of the tag by matching the frequency better, you still would always see the anticollision process at a further distance.