Session Key Generation SV2 Value

AMS1979 — Sat, 26 Jun 2021 10:15:54 GMT

On page 15 of https://www.nxp.com/docs/en/application-note/AN12196.pdfI'm unclear as to how the following values are generated or derived from the url, and what to do with them in the overall calculations

1. PICCDataTag [bit] - 1100 0111 (what is this)
2. Is part of the Session Key SV2 hardcoded? "3CC300010080"

let SV2 = `3CC300010080${uid}${SDMReadCtr}`;

3. PICCDataTag - UID mirroring [bit7] 1 (UID mirroring enabled)
4. PICCDataTag - SDMReadCtr mirroring [bit6] - 1 (SDMReadCtr mirroring enabled)
5. PICCDataTag - UID Length [bit3-0] - = 111b = 7d (7 byte UID)

Using your example on https://community.nxp.com/t5/NFC/Configuring-NTAG-424-DNA-with-Encrypted-Part-and-CMAC-Part/m-p/1049315?commentID=1349087#comment

I am able to validate the SDMMAC (Step6 / Step7 pg 17), with all generated URLs (https://ntag.nxp.com/424?e=EF963FF7828658A599F3041510671E88&c=94EED9EE65 337086) with [e] and [c] values, however, once I change the key, and update key also on the server. It fails to validate. I'm trying to figure out what is changing other than the key. I started with a fresh key, and it was only until I experimented with changes it no longer worked even switching back to 00000000000000000000000000000000

Any help is appreciated!

Thanks

NFCのトピックSession Key Generation SV2 Value

Session Key Generation SV2 Value