Hi, my name is Manuel and I am software engineer. Recently I bought some of your NTAG 424 DNA, that I want to use for a product authenticity solution.
I read through some documents but mainly the following two:
I bought a Identiv u Trust 3700 F CL reader that is connected to my MacBook Pro and i am running the NXP TagXplorer.
Using this as an example URL, where I have 3 custom params at the end, "n", "t", "p":
I activated "ADD TAG UID", "ADD INTERACTION COUNTER" and "ENABLE SUN MESSAGE". I also set the calculated offset Index at 33 which is right after the questionmark in the URL (i hope this is correct?!)
after writing this information to the tag i am going to NTAG 424 DNA Secruity settings where i hit "Authenticate First"
(for this first try i dont want to change any of the default keys on the chip, that would be my next step once i get this simple example working)
After being successfully authenticated
I am going to the "File Management" options and set the following data:
When i go now to NDEF Operations and click on READ NDEF button, it will give me for example this URI here:
if i click the Read from Tag button again it gives me:
which gives me the same uid, but an incremented counter and a new cmac which i guess is correct.
I guess I also need to know the key that was used to encrypt it also on the backend, correct?
I guess in this default case the key is just 16bits of zero like this 0000000000000000, correct?
But how exactly would this calculation now work? I cant figure it out with the two documents above.
Can you please give me a step by step example for this cmac calculation on my backend with my values given here?
Thanks for your help in advance.