How can I enable the proximity check of my NTAG 424 DNA?

[Begai123]

I bought a couple of NTAG 424 DNA tags recently for a personal project. Their purpose is to store a link to my website. I chose this type of NFC tag because I read online they have the ability to somehow tell if the user is physically near the tag or not. My problem is that I can't seem to enable that proximity check. Can anyone point me to some documentation or tutorials? My search in the web and ChatGPT proved unfruitful.

[Fabian_R]

Hello this is Fabian,

Thank you very much for the interest in our products.

Unfortunately, the NTAG 424 does NOT have a Proximity check feature. This feature is quite restricted and, some of our MIFARE DESFire cards (EV2, EV3).

Still, in order to gain access to the use of this feature it is required to sign an NDA with us.

[Begai123]

9.3 "The Secure Dynamic Messaging (SDM) allows for confidential and integrity protected
data exchange, without requiring a preceding authentication. NT4H2421Tx supports
SDM for reading from one of the StandardData files on the PICC. Secure Dynamic
Messaging allows adding security to the data read, while still being able to access it with
standard NDEF readers. The typical use case is an NDEF holding a URI and some meta-
data, where SDM allows this meta-data to be communicated confidentiality and integrity
protected toward a backend server".
The way I understand this is: on each scan of the tag, a secure message is added to the url, different on each scan (dynamic). Then won't this mean that for a person to access the link stored on the tag, they have to be physically close to the tag? Or does the NTAG 424 DNA not support this?

[Fabian_R]

Hello,

This is correct, in order to read the Tag it is required to be close to the tag to scan it. The NDEF read will contain the encoded message that needs to be decrypted by the back end server.

The difference is that Proximity Check is a protective feature implemented to avoid a relay attack. The NTAG 424 does not have this protective feature. It just allows anyone to read the NDEF but, if your reader application isn't built to send the encrypted data to the server you will just end-up with a gibberish NDEF message.

Is possible that the misunderstanding was because of the use Proximity Check, it is the actual name of the MIFARE's feature.