topic Re: Auth desfire ev3 AES key return different RandA' in Other NXP Products

Auth desfire ev3 AES key return different RandA'

amrin-hexondata — Thu, 02 May 2024 09:29:59 GMT

I'm trying to authenticate desfire ev3 with default AES (16 bytes 0) via apdu.

However I'm getting non identical RandA' after sending RandA || RandB'. You can check to see if the problem lies in my encryption. I clipped my encryption code in the photo attached.

I use key and iv of zeros for encrypt and decrypt. When auth with des/2ktdes, I follow this following step.

Send -> [0x0A, 0x00]

Respond -> [0xAF, RandB_Encrypted]

Then I decrypt RandB_Encrypted -> RandB

Rotate left by 1 byte -> RandB_rotate

Generate RandA_Encrypted

Decrypt RandA_Encrypted -> RandA

XOR RandA, RandB_rotate -> RandAB

Encrypt XOR -> RandAB_Encrypted

Concat RandA + RandAB_Encrypted -> dataToSend

Send -> [0xAF, dataToSend]

Respond -> [0x00, RandA'_Encrypted]

Then I decrypt RandA'_Encrypted -> newRandA

Rotate right by 1 byte -> newRandA_rotate

compare newRandA_rotate and RandA_Encrypted

success

However after creating application with keytype AES. I couldn't finish the authentication process. I follow the exact same steps as above, and I'm getting different RandA' at authentication part 2. Is the step for auth with AES different from des/2ktdes?

Command used for auth AES -> [0xAA, 0x00]

Thank you for your time.

Re: Auth desfire ev3 AES key return different RandA'

Fabian_R — Thu, 02 May 2024 23:09:19 GMT

Hello sir,

My apologies, there are some differences between the procedure and the one explained in our files. Unfortunately, these are secured files and, cannot be disclosed openly. It is required to sign an NDA and, request the files by yourself following this User Manual and FAQ.

Re: Auth desfire ev3 AES key return different RandA'

amrin-hexondata — Fri, 03 May 2024 01:20:30 GMT

Hi Fabian, thank you for the reply. I do have access to the secured files. I tried to follow the steps in the document, but im still not able to auth using aes.

Re: Auth desfire ev3 AES key return different RandA'

Fabian_R — Fri, 03 May 2024 22:35:20 GMT

Hello sir,

As I mentioned, the implementation of the encryption isn't correct. Our NFC Reader Library has great examples explaining these procedures with our API. I highly recommend using one of our readers to perform a correct authentication.