title: Writing to a Mifare tag with Android NFC?
body: <p>I'm trying to write a simple "Hello World" string to the first block of sector 0 on a Mifare 1K tag. The tag is brand new with default configuration. The sector trailer (block 3), when read, is: <code>00 00 00 00 00 00 00 00 ff 07 80 69 ff ff ff ff ff ff ff ff</code>. Hence, the access conditions is <code>ff 07 80 69</code>, meaning I can read and write on each block with key A.</p>
  
  <p>Still, I can't manage to write anything on the tag. Here's my code:</p>
  
  <pre><code>try {
      mfc.connect();
      boolean auth = false;
  
      auth = mfc.authenticateSectorWithKeyA(0,MifareClassic.KEY_DEFAULT);
  
      if (auth) {
  
          String text = "Hello, World!";
          byte[] value  = text.getBytes();
          byte[] toWrite = new byte[MifareClassic.BLOCK_SIZE];        
  
          for (int i=0; i&lt;MifareClassic.BLOCK_SIZE; i++) {
                if (i &lt; value.length) toWrite[i] = value[i];
                else toWrite[i] = 0;
          }           
  
          mfc.writeBlock(0, toWrite);
     }    
  </code></pre>
  
  <p>I'm getting the following exception: <code>Transceived failed</code>.</p>
  
  <p>What am I doing wrong?</p>
  
  <p>Here's the stack trace:</p>
  
  <pre><code>07-09 00:19:44.836: W/System.err(13167):    at android.nfc.TransceiveResult.getResponseOrThrow(TransceiveResult.java:52)
  07-09 00:19:44.843: W/System.err(13167):    at android.nfc.tech.BasicTagTechnology.transceive(BasicTagTechnology.java:151)
  07-09 00:19:44.843: W/System.err(13167):    at android.nfc.tech.MifareClassic.writeBlock(MifareClassic.java:453)
  07-09 00:19:44.843: W/System.err(13167):    at com.example.andorid.apis.mifare.MainActivity.resolveIntent(MainActivity.java:128)
  07-09 00:19:44.843: W/System.err(13167):    at com.example.andorid.apis.mifare.MainActivity.onNewIntent(MainActivity.java:275)
  07-09 00:19:44.843: W/System.err(13167):    at android.app.Instrumentation.callActivityOnNewIntent(Instrumentation.java:1123)
  07-09 00:19:44.843: W/System.err(13167):    at android.app.ActivityThread.deliverNewIntents(ActivityThread.java:2041)
  07-09 00:19:44.843: W/System.err(13167):    at android.app.ActivityThread.performNewIntents(ActivityThread.java:2054)
  07-09 00:19:44.843: W/System.err(13167):    at android.app.ActivityThread.handleNewIntent(ActivityThread.java:2063)
  07-09 00:19:44.843: W/System.err(13167):    at android.app.ActivityThread.access$1400(ActivityThread.java:122)
  07-09 00:19:44.843: W/System.err(13167):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1193)
  07-09 00:19:44.851: W/System.err(13167):    at android.os.Handler.dispatchMessage(Handler.java:99)
  07-09 00:19:44.851: W/System.err(13167):    at android.os.Looper.loop(Looper.java:137)
  07-09 00:19:44.851: W/System.err(13167):    at android.app.ActivityThread.main(ActivityThread.java:4340)
  07-09 00:19:44.851: W/System.err(13167):    at java.lang.reflect.Method.invokeNative(Native Method)
  07-09 00:19:44.851: W/System.err(13167):    at java.lang.reflect.Method.invoke(Method.java:511)
  07-09 00:19:44.851: W/System.err(13167):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
  07-09 00:19:44.851: W/System.err(13167):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
  07-09 00:19:44.851: W/System.err(13167):    at dalvik.system.NativeStart.main(Native Method)
  </code></pre>