Android Question NFC Questions

[bartj]

I have several NFC related questions. I am a beginner user.

Have successfully loaded and run the NFC Advanced demo program using version 10.0 of B4A which uses version 2.01 of the NFC library. Yea! Am able to read/write Ndef mifare ultra-light and 1k classic.

It took me a while to figure out that in order for Ndef to work the card needed to be formatted for Ndef. I used a NXP play-store app to accomplish formatting.

1) It appears that I can only store ASCII data with Ndef. Is this correct?

2) In an effort to read/write at a lower level, I find that if I change the tech from:
"android.nfc.tech.Ndef"
to:
"android.nfc.tech.MifareClassic"
(using a Ndef formatted card)

I am then able to use the following from post 105409 with no compile errors or exceptions.

Note that the passed bytes are not likely to be correct. I changed them from the example.

' example in post 105409 is talking to a non mifare card
    TagTech.RunAsync("TT", "transceive", Array(Array As Byte(0x30, 0x00, 0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5,0)), 0)
    Wait For TT_RunAsync (Flag As Int, Success As Boolean, Result As Object)
    Log("Exception Check: " & LastException)
    If Success Then
        Dim rawId() As Byte = Result
        Dim bc As ByteConverter
        Log("Info: " & (bc.HexFromBytes(rawId)))
    End If

This code returns:
Info: B200000000007F078840000000000000

The middle bytes show the permissions for sector 1. See the end of this message for a screen shot from a play-store app showing sector data.

Looking at the mifate classic 1k data sheet, I see that the read command is "0x30", followed by a 1 byte address followed by a CRC. If I am reading the data sheet correctly it appears that there are 3 stages of both read and writes (termed authentication) that need to be successfully competed before I can actually access that card data.

https://www.nxp.com/docs/en/data-sheet/MF1S50YYX_V1.pdf

So my first question in that area is: Does the NFC library, when talking to Ndef cards, handle the authentication "behind the scenes", or is Ndef setup in such a way that authentication is not required (such as setting up the permissions so this is not required)?

Its likely that I will want to implement authentication in the long term. Can anyone recommend a good, concise reference for implementing authentication on Mifare classic(EV-1) 1k cards? There is an overwhelming amount of information out there. Or, has someone in the community developed code to support authentication of mifare classic 1k cards?

Thanks!

 

[Erel]

It appears that I can only store ASCII data with Ndef. Is this correct?

No. I'm not sure what you mean with ASCII data however you can write any data you like.

There is no authentication in NDEF tags but you can encrypt the data before you write it. Search for B4XEncryption.

 

[bartj]

Thanks for the response!

I ask my question about "ASCII data only" for Ndef because I see that the last byte of any Ndef record is defined to be 0xFE. Although in the Ndef "header" there is a length parameter, I am going to assume that I can have any number of occurrences of 0xFE in the payload without it causing framing errors.