CODEWITHSUNDEEP
androidauthenticationnfcmifarendef
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Reputation: 1304

Write to NTAG216 after authenticating?

I am authenticating my tag using this piece of code

nfcA.connect();
byte[] authResponse = nfcA.transceive(new byte[]{
                (byte)0x1b,
                pwd[0], pwd[1], pwd[2], pwd[3]
        });
nfcA.close();

I checked the result of authResponse and it is equal to my pack. After authenticating, I write NDEF contents using the writeNdefMessage() method of the Ndef class, but I was not able to write.

This is where I found the way to authenticate the tag.

This is my approach:

However, I get a java.io.IOException whenever I'm calling writeNdefMessage().

Upvotes: 4

Views: 1012

Answers (1)

Michael Roland
Michael Roland

Reputation: 40821

The reason why you can't write is because you lose authentication state again before actually writing to the tag. With most devices (though some exceptions to this exist!), calling tag.connect()/tag.close() will cause the tag to be re-activated and, consequently, to lose its authentication state. Thus, you need to authenticate and write within the same connection.

As you can't send low-level commands through the Ndef abstraction, this means that you have to do all the writing with low-level commands. I.e. you have to re-implement the NDEF abstraction layer for that particular tag type (the NFC Forum Type 2 Tag Operation specification in your case) yourself and write the NDEF message page-by-page.

As NTAG216 should be discovered as MifareUltralight, the easiest way would be to use a MifareUltralight connection. You coud then

  1. do the authentication:

    mfu.transceive(new byte[]{ (byte)0x1b, pwd[0], pwd[1], pwd[2], pwd[3] });

  2. write the tag page-by-page (you probably need to write pages 4 and onwards which contain the NDEF message wrapped in a TLV structure with the tag 0x03, you might also need to write page 3 if you need to make any changes to the capability container):

    mfu.write(pageNumber, data)

    where data is the four byte data value that should be written to page pageNumber.

Upvotes: 1

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