[MIFARE DESFIRE EV1] How to update IV in AES(read/write).

[byungil byungil]

Hello I'm studying AES on DESFire.

I have some questions.

I don't know how to update IV in step 15 of specification document AN0945 page 60.

Concretley, I want to Updated IV in step 15 how I know IV backward 8bytes.

Please Somebody help me.

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[Benjamin Benjamin]

1

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[mifaresdk]

Hi,

the example explains an AES authentication in detail. The IV vector is used in block ciphers to chain blocks together. The first block uses usually a random or a “well known” value. In the case of the DESFire authentication the IV is for the first block 00…00. But for the second block you do not use 00..00 again! You use the output of the previous block for the IV vector of the next block. In this way all blocks are “chained”.

Please visit:
https://en.wikipedia.org/wiki/Initialization_vector

and:

https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation

Kind regards,
The MIFARE Team

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[Author]

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