NTAG 424 no login possible after key 0 change

[MPucci]

Hi all,

i'm facing a strange behaviour that i can't solve. I completed all my steps to configure a #NTAG424 for a security platform: everything is ok BUT one last thing

I had to change all the 5 keys and started with this "loop" for 4 to 0:

Login with key 0

Change key X

I'm aware that changing K0 is different from K4-1 and the response is 91-00 so seems everything is correct.

Now the problem: i can login with all the kyes 4-1 but with K0 i get a 91-AE in login part 2.

I suppose that the encryption is wrong so the key is different from what i think, but i checked a lot of time the code and is ok. I only changet the cryptogram calculation as per data sheet and AN12196. 

Any hint?

Thank

[KellyLi]

Hello @MPucci 

Thanks for contacting us and based on your issue description, it's recommended that you try the steps of chapter 6.16.2 of AN12196. For example:

1. Authentication by keyNo 0x00

2. input the New key 

3. execute ChangeKey command

4. double check using the new key to authenticate NTAG424.

BR

Kelly

[MPucci]

Some more info: i know is not correct but i use the same RndA in all login before change the keys. I can't identify the root of the issue, but if i use 5 different RndA in login, no problems with keys (even K0), if i use the same RndA in login, K0 is corrupted.

So for now the problem is solved, without knowing the cause.