NFCのトピックRe: Ntag424 dna

Ntag424 dna

Cihan29 — Thu, 06 Feb 2025 03:28:35 GMT

Hello, I need to get information about Ntag424 dna SUN features.firstly I need to explain that I want to use these nfc tags to make unique and safe url's , so whenever someone scan(they will scan only with phone) them their url must be change (something like dynamic value)actually I have couple of questions whose answers will explain everything.I want to ask some of my questions based on scenarios;

1- Is it possible for the URL in a card that I wrote a URL on using Sun features to change every time it is read? (For example, I scanned the card with my phone using a mobile application used to control the URL and saw the URL, will I see a different URL than the first URL I saw when I scan it the second time)

2-I want my encrypted URLs to be resolved on my web server, but will the phones transmit this encrypted URL to the browser because I can only decrypt this data on my server if I receive it from the browser?

3-Which nfc reader/writer and software should I choose for Ntag 424 dna tags that I want to write with using SUN features?

4-(this question is valid even if the answer to the first questions is negative) What can I do to make my url change the Ntag424 tag itself every time it is read? (for example the first url is https://www.nxp.com/auth?c=8F3D1A2B&mac=5A6C7D8E9F012345
and after scanning it became https://www.nxp.com/auth?c=9B5E3F4C&mac=7D8E9F0123456A6C)

Re: Ntag424 dna

Daniel_Gutierrez — Mon, 10 Feb 2025 20:29:13 GMT

Hello @Cihan29, Good Day!

Thank you very much for your interest in our products.

Regarding the SUN/SDM feature of the NTAG 424, you will find that it offers a protected data exchange between the tag and the NFC Reader Device, and what happens is that it mirrors stored values from the NTAG memory onto the NDEF message which can be an URL. Some of these mirrored values include for example the tag's UID, an NFC tap counter and a unique authentication code (CMAC/MAC) for each tap and are attached as ASCII encoded text at the end of the URL. With this in mind, it makes sense that the data attached at the end of the link examples you provide changes, because in these cases we are seeing the CMAC followed by the MAC and these are codes that will change with every tap.

Please refer to section 3 of the NTAG 424 DNA Application Note to get a deeper understanding on Secure Dynamic Messaging and find some examples of URLs with mirrored data attached.

When it comes to encrypting and decrypting the data mentioned above, you may find guidance in section 3.4.2.1 of the same document. You will find as well that you can handle the decrypting stage using a backend server, as you mentioned, one that shall know the keys used for the encryption. However, if you are trying to make the link accessible only after a successful decryption, you could consider encrypting the message as plain text and handle its decryption separately. For a detailed description of the encryption processes, please take a look at section 9.1.4 of the NTAG 424 DNA Data Sheet.

For testing purposes, you may use the PEGODA Contactless Smart Card Reader as well as software applications such as RFIDDiscover or NFC TagWriter App by NXP.

My best regards,
Daniel.

Re: Ntag424 dna

Cihan29 — Thu, 13 Feb 2025 09:03:44 GMT

Thank you mr.@Daniel_Gutierrez. Your comment really answered my questions.I really thank you again and again.