Libnfc:APDU example

Short example illustrating how to exchange APDUs with a ISO14443-4 tag

It can be downloaded here as apdu_example.c.

apdu_example.c

#include <stdlib.h>
#include <string.h>
#include <nfc/nfc.h>

To send APDUs, we'll use a little helper function with some debugging prints of exchanged APDUs:

int
CardTransmit(nfc_device *pnd, uint8_t * capdu, size_t capdulen, uint8_t * rapdu, size_t * rapdulen)
{
  int res;
  size_t  szPos;
  printf("=> ");
  for (szPos = 0; szPos < capdulen; szPos++) {
    printf("%02x ", capdu[szPos]);
  }
  printf("\n");
  if ((res = nfc_initiator_transceive_bytes(pnd, capdu, capdulen, rapdu, *rapdulen, 500)) < 0) {
    return -1;
  } else {
    *rapdulen = (size_t) res;
    printf("<= ");
    for (szPos = 0; szPos < *rapdulen; szPos++) {
      printf("%02x ", rapdu[szPos]);
    }
    printf("\n");
    return 0;
  }
}

Start of main() is very similar to quick_start_example:

int
main(int argc, const char *argv[])
{
  nfc_device *pnd;
  nfc_target nt;
  nfc_context *context;
  nfc_init(&context);
  if (context == NULL) {
    printf("Unable to init libnfc (malloc)\n");
    exit(EXIT_FAILURE);
  }
  const char *acLibnfcVersion = nfc_version();
  (void)argc;
  printf("%s uses libnfc %s\n", argv[0], acLibnfcVersion);
 
  pnd = nfc_open(context, NULL);
 
  if (pnd == NULL) {
    printf("ERROR: %s", "Unable to open NFC device.");
    exit(EXIT_FAILURE);
  }
  if (nfc_initiator_init(pnd) < 0) {
    nfc_perror(pnd, "nfc_initiator_init");
    exit(EXIT_FAILURE);
  }
 
  printf("NFC reader: %s opened\n", nfc_device_get_name(pnd));
 
  const nfc_modulation nmMifare = {
    .nmt = NMT_ISO14443A,
    .nbr = NBR_106,
  };

Smartcards need to get RATS, so make sure NP_AUTO_ISO14443_4 is set to true, which is its default value, otherwise if e.g. you were doing some MIFARE stuff before, set it explicitly:

  // nfc_set_property_bool(pnd, NP_AUTO_ISO14443_4, true);

Polling for target... indefinitely

  printf("Polling for target...\n");
  while (nfc_initiator_select_passive_target(pnd, nmMifare, NULL, 0, &nt) <= 0);
  printf("Target detected!\n");

Now we can exchange APDUs, here we're reading a NFC-Forum Type4 Tag

  uint8_t capdu[264];
  size_t capdulen;
  uint8_t rapdu[264];
  size_t rapdulen;
  // Select application
  memcpy(capdu, "\x00\xA4\x04\x00\x07\xd2\x76\x00\x00\x85\x01\x00", 12);
  capdulen=12;
  rapdulen=sizeof(rapdu);
  if (CardTransmit(pnd, capdu, capdulen, rapdu, &rapdulen) < 0)
    exit(EXIT_FAILURE);
  if (rapdulen < 2 || rapdu[rapdulen-2] != 0x90 || rapdu[rapdulen-1] != 0x00)
    exit(EXIT_FAILURE);
  printf("Application selected!\n");
 
  // Select Capability Container
  memcpy(capdu, "\x00\xa4\x00\x0c\x02\xe1\x03", 7);  
  capdulen=7;
  rapdulen=sizeof(rapdu);
  if (CardTransmit(pnd, capdu, capdulen, rapdu, &rapdulen) < 0)
    exit(EXIT_FAILURE);
  if (rapdulen < 2 || rapdu[rapdulen-2] != 0x90 || rapdu[rapdulen-1] != 0x00) {
    capdu[3]='\x00'; // Maybe an older Tag4 ?
    if (CardTransmit(pnd, capdu, capdulen, rapdu, &rapdulen) < 0)
      exit(EXIT_FAILURE);
  }
  printf("Capability Container selected!\n");
 
  // Read Capability Container
  memcpy(capdu, "\x00\xb0\x00\x00\x0f", 5);  
  capdulen=5;
  rapdulen=sizeof(rapdu);
  if (CardTransmit(pnd, capdu, capdulen, rapdu, &rapdulen) < 0)
    exit(EXIT_FAILURE);
  if (rapdulen < 2 || rapdu[rapdulen-2] != 0x90 || rapdu[rapdulen-1] != 0x00)
    exit(EXIT_FAILURE);
  printf("Capability Container header:\n");
  size_t  szPos;
  for (szPos = 0; szPos < rapdulen-2; szPos++) {
    printf("%02x ", rapdu[szPos]);
  }
  printf("\n");

We're done!

  nfc_close(pnd);
  nfc_exit(context);
  exit(EXIT_SUCCESS);
}

To compile it

It assumes libnfc is installed into the system

gcc -o apdu_example apdu_example.c -lnfc

Testing...

$ ./apdu_example 
./apdu_example uses libnfc libnfc-1.7.0-43-ga1ef329
NFC reader: SCM Micro / SCL3711-NFC&RW opened
Polling for target...
Target detected!
=> 00 a4 04 00 07 d2 76 00 00 85 01 00 
<= 90 00 
Application selected!
=> 00 a4 00 0c 02 e1 03 
<= 6a 86 
=> 00 a4 00 00 02 e1 03 
<= 90 00 
Capability Container selected!
=> 00 b0 00 00 0f 
<= 00 0f 10 00 3b 00 34 04 06 e1 04 0e e0 00 ff 90 00 
Capability Container header:
00 0f 10 00 3b 00 34 04 06 e1 04 0e e0 00 ff