How should I decryp...

How should I decrypt whole content of NDEF message ?  

Posts: 1
New Member
Joined: 11 months ago


I'm looking for a way to decrypt NFC tags with full knowledge of the data.

I only need one data missing, it's the key with which the tag is encoded. Where can I find it?

I use NXP tags NTAG 424. 


I'm really at a dead end.


My URL looks like this: 



and I would like to be able to get search leads to find my URL (server side) in the form:


http://localhost/uid=0000000&ctr=000000 ...


Does anyone have any suggestions for me?


Thank you in advance,

1 Reply
Posts: 22
Joined: 1 year ago

As you are using an NTAG424 auth tag then we'll assume that you mean that you are talking about the key that's used to encrypt the Secure Unique NFC Message (SUN). The key is set on the tags during manufacture to a default but can be changed during encoding. As the default key setting will be the same on all chips, it clearly is necessary to change the key to ensure that it provides security.

How to set the key during encoding and how to use the SUN for authentication is information that is only available from NXP under a signed non-disclosure agreement. The 'short' data sheet does not provide this information. Unfortunately, because of the NDA, we cannot provide more information. 

If we misunderstood your query, please reply and we'll help the best we can !


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