Hi folks. I understand the underlying principles of SUN/SDM, but cannot for the life of me figure out how to program the tag with nxp's tagwriter.
Firstly, the pdf that gets linked every time a question like this is asked anywhere, but doesn't really give good implementation info: https://www.nxp.com/docs/en/application-note/AN12196.pdf
I understand I need several components:
Static https://example.com/nfc?x= + &y= for example
Mirrored uid & nfc counter and cmac
Offsets that dictate where the mirrored and encrypted content is interleaved with the static content, and the length of the mirrored and encrypted content.
The tagwriter app provides two dataset types that seem appropriate, Link and Plain Text.
Link provides a custom URL option, and "configure mirroring options". Say I put in a custom url of https://example.com/nfc?x=00000000000000000000000000000000&y=0000000000000000 (or the same without the padded data, or any other variation thereof).
When I click in to configure mirroring, I can select ntag 424 dna (good) and enable SDM mirroring (also seems good) but that gives two hex fields with a couple of what look like read/write/delete hex value options. SDM meta read access right and derivation key for cmac calculation. These... don't seem like what I'm looking for.
The other type of dataset is plain text - I get the impression (even though it doesn't say anywhere) that this is where I can put NDEF commands.
From the docs it looks like I want a PICCData encrypted mirror - an encrypted combo of UID and NFCCounter with cmac appended to the end of whatever our url schema is.
How do I accomplish this?
What records should I create? Do they interact with the Link type record?
Given the example url above with padding, what's the procedure to get that working?
Thanks folks.
