Reading and writing Mifare Classic 1K RFID on Nexus-S

I'd like to be able to write and read strings from a Mifare 1K RFID. I successfully read and wrote to the tag I have using the NXP TagWriter App. I then tried the code here, but was able to get anything meaningful out of it. It wouldn't even authenticate until I changed

auth = mfc.authenticateSectorWithKeyA(0, MifareClassic.KEY_DEFAULT);

TO

auth = mfc.authenticateSectorWithKeyA(0, MifareClassic.KEY_MIFARE_APPLICATION_DIRECTORY);

But only got this as output:

BLOCK 0: 298091JFIS8903JF0SDF093
BLOCK 1: 298091JFIS8903JF0SDF093

Not sure what to make of it and what the process of reading and writing to the card would be. Any examples or di开发者_如何学运维rections would be very helpful!

Have you tried the code above on a blank Mifare 1K Classic tag?

Just removing one variable. It could be that the NXP TagWriter App changes the authentication key on its first write, preventing other programs from writing to it.