Cannot authenticate NTAG213

Question

I am using an ACR122U NFC reader to password protect an NTAG213 NFC label. I think I have managed to set the password correctly, but I cannot authenticate and change the label afterward. My code for authenticating looks like this:

#include <winscard.h>
#include <iostream>
#pragma comment(lib, "winscard.lib")

const char *ReaderName = "ACS ACR122 0";
unsigned Password = 0x12345678;

int main()
{
  //Establish context
  SCARDCONTEXT              hContext;
  DWORD SCard_Status1 = SCardEstablishContext(SCARD_SCOPE_USER, NULL, NULL, &hContext);
  if(SCard_Status1 != SCARD_S_SUCCESS)
    return 1;

  //connect to the card
  SCARDHANDLE   hCardHandle;
  DWORD Protocol;
  DWORD SCard_Status2 = SCardConnect(hContext, ReaderName, SCARD_SHARE_SHARED, SCARD_PROTOCOL_T1, &hCardHandle, &Protocol);
  if(SCard_Status2 != SCARD_S_SUCCESS)
  {
    SCardReleaseContext(hContext);
    return 1;
  }

  SCARD_IO_REQUEST Request;
  Request.dwProtocol = Protocol;
  Request.cbPciLength = sizeof(SCARD_IO_REQUEST);
  BYTE TxData[] =
  {
    0xFF, //CLA
    0x00, //INS
    0x00, //P1
    0x00, //P2
    0x08, //LC
    0xD4,
    0x40,
    0x01,
    0x1B, //PWD_AUTH (See data sheet)
    Password,
    Password >> 8,
    Password >> 16,
    Password >> 24,
  };

  BYTE RxData[254];
  unsigned long RxLength = sizeof(RxData);
  DWORD SCard_Status3 = SCardTransmit(hCardHandle, &Request, TxData, sizeof(TxData), NULL, RxData, &RxLength);
  std::cout << "SCard_Status = " << SCard_Status3 << std::endl;
  std::cout << "RxLength = " << RxLength << std::endl;

  SCardDisconnect(hCardHandle, SCARD_EJECT_CARD);
  SCardReleaseContext(hContext);
  return 0;
}

This should send the PWD_AUTH command to the NTAG213 with the Pwd. I expected to receive an error if the password is wrong or two bytes with the PACK if the password is correct. But SCard_Status is SCARD_S_SUCCESS and RxLength is 0 afterwards. And if I try to write to the label I get an error.

I am having trouble finding any examples showing how to do this. Can anyone see what I am doing wrong?

Answer 1

I am going to answer this myself. I managed to make it work by changing TxData to this:

BYTE TxData[] =
{
  0xFF, //CLA
  0x00, //INS
  0x00, //P1
  0x00, //P2
  0x07, //LC
  0xD4, 0x42, //InCommunicateThru
  0x1B, //PWD_AUTH (See data sheet)
  Password,
  Password >> 8,
  Password >> 16,
  Password >> 24,
};

I found the command InCommunicateThru (D4 42) as a replacement for InDataExchange (D4 40) in the data sheet for the PN532, which is the NFC processor inside the ACR122U.