RFID authentification message

Question

I am writing some code to authentificate and overwrite some data on rfid chip. I am using javax.smartcardio and the reader is ACR122U. Now if I try to send a APDU-command like: ff860000050100066100a0a1a2a3a4a5 (authentificate with standard key at sector 2) I get Error. But I am sure that I have the right key. I tested it in acr122utools. What is the problem? Please help.

Answer 1

There is a bit different way to authenticate to the card via acr122u. At first you have to load you key to the reader memory (example: ff 82 00 00 06 a0 a1 a2 a3 a4 a5). Then you have to tell, that you will authenticate with key from memory:(example ff 86 00 00 00 50 10 00 66 10). It should be done this way, because the authentication is a "challange response". Only the parts of the key will be crypted with a random number and transfered between card and reader. I think, that own implementation of challange response is not the way you would like to go.