NTAG 424 encrypted file data

[MPucci]

Hello community,

talking about NTAG424 and SDMENCFileData: is it possible to add to static file data a random padding? The goal is to have at any NDEF reading a different value, because even if the mirror is crypted, is always the same.

Thanks

Mario

[MPucci · Accepted solution]

Hi Fabian,

my fault. I discovered that my enc data was just an encryption of static file without the algorithm inside ntag. Maybe i messed up the offsets that prevents the algorithm to work properly.

Thanks

[Fabian_R]

No problem. I'm glad you were able to identify the root cause.

[Fabian_R]

Hello, my name is Fabian, I've been assigned to support your case.
Thank you for your interest in our products.
SDMENCFileData is already an encrypted file, its structure and format are defined by some proprietary security mechanisms. For this reason, the encryption protocol used typically includes padding schemes, these are implemented in order to meet specific block sizes.
Unfortunately, since there are some proprietary implementations, we cannot share any specifics regarding this procedure.

[MPucci]

Thanks Fabian,

i've all the info necessary to decrypt it from the NDEF message. My problem is different if i understood correctly the documentation: take for example page 13 of AN12196. The StaticFileData is 7878787878787878778.... and the corresponding SDMENCFileData is 94592FDE69FA06E8E3B6CA686A22842B. This value of SDMENCFile data is fixed, i mean is always the same at every read of NDEF. This can lead a malicoius to think that in this position there is a static data, even if encrypted. I'd like to change the SDMENCFiledata at every read with "Static data + random data". From my algorithm, once decripted i know where is the static and where is the random.