[Bartek Grzeczko]

Hi, thanks for the answer but the problem is that I get the exception earlier than you. I get the exception when connecting not when authenticating with the obsolete key:
"I first authenticate with the default key FFFFFFFFFFFF to sector 0. Next I change the sector trailer with only the key A value changed to A1AAAABBBBBB. Then I start a new session and " now the exception is thrown while trying to connect:

Caused by: java.io.IOException
at android.nfc.tech.BasicTagTechnology.connect(BasicTagTechnology.java:104)
at android.nfc.tech.MifareClassic.connect(MifareClassic.java:73)
at com.nxp.nfclib.classic.ˋ.connect (:40)

I change the sector trailer with:

value =  new byte[]{

    (byte) 0xA1, (byte) 0xAA, (byte) 0xAA,

    (byte) 0xBB, (byte) 0xBB, (byte) 0xBB,

    (byte) 0xFF, (byte) 0x07, (byte) 0x80, (byte) 0x69,

    (byte) 0xFF, (byte) 0xFF, (byte) 0xFF,

    (byte) 0xFF, (byte) 0xFF, (byte) 0xFF};



mifareClassicEv1.writeBlock(3,  value)

Which seems to be the exactly same thing as you did, but when I start the new session it will throw mentioned exception while connecting (on this line:
mifareClassicEv1.getReader().connect()
)

Thanks

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[Bartek Grzeczko]

What I found out is that if I do NOT change key (sector trailer) of the sector 0 it works perfectly fine for all other sectors (from 1 to 15).
Is there anything special about sector 0 (except for the fact that block 0 contains manufacturer data) that 'destroys' the tag when you change the sector trailer 0 to the following value:

new byte[]{

    (byte) 0xA1, (byte) 0xAA, (byte) 0xAA,

    (byte) 0xBB, (byte) 0xBB, (byte) 0xBB,



    (byte) 0xFF, (byte) 0x07, (byte) 0x80, (byte) 0x69,



    (byte) 0xFF, (byte) 0xFF, (byte) 0xFF,

    (byte) 0xFF, (byte) 0xFF, (byte) 0xFF};

By 'destroys' I mean that the next attempt to call mifareClassicEv1.getReader().connect() throws exception mentioned in previous post.
Thanks for help

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