Reading NFC UID from android phone with PN532 and ArduinoMega

Question

I am trying to use the PN532 to read my NFC UID from phone(Samsung Galaxy S10), but i receive just 08 and another 3 digits of random values.I read that a value that start with 08 is a RID(Random ID). Is there any possible way to read just a unique value, or use the PN532 to read something that is unique from my phones NFC? I want to use that value to compare it with a constant in my code and send an impulse to a relay to open a door. This code is from da Adafruit_PN532 library.

#include <Wire.h>
#include <SPI.h>
#include <Adafruit_PN532.h>

#define PN532_IRQ   (2)
#define PN532_RESET (3)  // Not connected by default on the NFC Shield

// Or use this line for a breakout or shield with an I2C connection:
Adafruit_PN532 nfc(PN532_IRQ, PN532_RESET);

void setup(void) {
  Serial.begin(115200);
  Serial.println("Hello!");

  nfc.begin();

  uint32_t versiondata = nfc.getFirmwareVersion();
  if (! versiondata) {
    Serial.print("Didn't find PN53x board");
    while (1); // halt
  }

  Serial.print("Found chip PN5"); Serial.println((versiondata >> 24) & 0xFF, HEX);
  Serial.print("Firmware ver. "); Serial.print((versiondata >> 16) & 0xFF, DEC);
  Serial.print('.'); Serial.println((versiondata >> 8) & 0xFF, DEC);

  // configure board to read RFID tags
  nfc.SAMConfig();

  Serial.println("Waiting for an ISO14443A Card ...");
}


void loop(void) {
  uint8_t success;
  uint8_t uid[] = { 0, 0, 0, 0, 0, 0, 0 };  // Buffer to store the returned UID
  uint8_t uidLength;                        // Length of the UID (4 or 7 bytes depending on ISO14443A card type)

  // Wait for an ISO14443A type cards (Mifare, etc.).  When one is found
  // 'uid' will be populated with the UID, and uidLength will indicate
  // if the uid is 4 bytes (Mifare Classic) or 7 bytes (Mifare Ultralight)
  success = nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, uid, &uidLength);

  if (success) {
    // Display some basic information about the card
    Serial.println("Found an ISO14443A card");
    Serial.print("  UID Length: "); Serial.print(uidLength, DEC); Serial.println(" bytes");
    Serial.print("  UID Value: ");
    nfc.PrintHex(uid, uidLength);

    if (uidLength == 4) {
      // We probably have a Mifare Classic card ...
      uint32_t cardid = uid[0];
      cardid <<= 8;
      cardid |= uid[1];
      cardid <<= 8;
      cardid |= uid[2];
      cardid <<= 8;
      cardid |= uid[3];
      Serial.print("Seems to be a Mifare Classic card #");
      Serial.println(cardid);
    }
    delay(2000);
  }
}

Answer 1

Do not use the NFC UID for any security purpose, as you can see a phone does give a random one for privacy purposes.

The NFC UID is designed only to help reading hardware deal with handling sending data to the right card when multiple different Tags are in range. There is no guarantee that the UID is actually Unique and that it cannot duplicated (even with Tag that are supposed to have it programmed at the factory you can buy clones from China where they can be programmed by the end user).

It is better to use cryptographic methods with data stored on a tag or emulated Tag if using a phone to provide uniqueness to use a Tag for anything with security implications.