title: Mifare Change KEY A and B
body: <p>I have an ACR122U Contactless NFC reader. I bought a lot of blank RFID Mifare 4k tags. Their default Authentication KEY A and KEY B is FF FF FF FF FF FF.</p>
  
  <p>Now I want to change them to something else. I'm using APDU structure. I'm sending commands like this and it works well:</p>
  
  <pre><code>byte[] baData = { 0x01, 0x00, (byte)i, 0x60, 0x00 };
  APDUCommand apdux3 = new APDUCommand((byte)0xFF, (byte)0x86, (byte)0x00, (byte)0x00, baData, 0x05);
  </code></pre>
  
  <p>It works well. I don't know what this interface and model means, but using this type and structure, I want to change KEY A and KEY B.</p>
  
  <p>Please help me. I can't find any document.</p>
  
  <p>Regards</p>