A Unique ID for ESP32

I’ve recently been looking for a unique id for my ESP32 development. I’m not alone.

The solution is to use the MAC address. I’m not going to go into details on why, but espressif is guaranteeing their chips have unique MAC addresses. Sources: 1, 2, 3.

But what actually comes out of the APIs and how do you rely on this?

Here are the outputs of a quick test program which I am using for reference.

Getting Mac Address. esp_efuse with uint64: 158581228646888
 as hex: 91CD31E8
Getting Mac Address. esp_efuse with uint8[6]: 2324920514558144
 as hex: E8 31 CD 91 3A 90
Getting Mac Address. esp_efuse with uint8[8]: 232492051455814400
 as hex: E8 31 CD 91 3A 90 0 0
Getting Mac Address. ESP libary: CHIP MAC: 158581228646888
 as hex: 91CD31E8
Getting Mac Address. WiFi Library: E8:31:CD:91:3A:90

And here is the program for reference:

  Serial.print("Getting Mac Address. esp_efuse with uint64: ");
  uint64_t raw_esp_efuse_int64 = 0LL;
  esp_efuse_mac_get_default((uint8_t*)(&raw_esp_efuse_int64));
  Serial.println(String(raw_esp_efuse_int64));
  Serial.printf(" as hex: %X\n", raw_esp_efuse_int64);

  Serial.print("Getting Mac Address. esp_efuse with uint8[6]: ");
  uint8_t raw_esp_efuse_int_arr_6[6];
  esp_efuse_mac_get_default(raw_esp_efuse_int_arr_6);
  for (int i = 0; i < 6; i++) {
    Serial.print(String(raw_esp_efuse_int_arr_6[i]));
  }
  Serial.println("");
  Serial.printf(" as hex: %X %X %X %X %X %X\n", raw_esp_efuse_int_arr_6[0], raw_esp_efuse_int_arr_6[1],
                raw_esp_efuse_int_arr_6[2], raw_esp_efuse_int_arr_6[3], raw_esp_efuse_int_arr_6[4],
                raw_esp_efuse_int_arr_6[5]);

  Serial.print("Getting Mac Address. esp_efuse with uint8[8]: ");
  uint8_t raw_esp_efuse_int_arr_8[8];
  esp_efuse_mac_get_default(raw_esp_efuse_int_arr_8);
  for (int i = 0; i < 8; i++) {
    Serial.print(String(raw_esp_efuse_int_arr_8[i]));
  }
  Serial.println("");
  Serial.printf(" as hex: %X %X %X %X %X %X %X %X\n", raw_esp_efuse_int_arr_8[0], raw_esp_efuse_int_arr_8[1],
                raw_esp_efuse_int_arr_8[2], raw_esp_efuse_int_arr_8[3], raw_esp_efuse_int_arr_8[4],
                raw_esp_efuse_int_arr_8[5], raw_esp_efuse_int_arr_8[6], raw_esp_efuse_int_arr_8[7]);

  Serial.print("Getting Mac Address. ESP libary: ");
  uint64_t lib_esp_efuse = ESP.getEfuseMac();
  Serial.printf("CHIP MAC: %lld\n", lib_esp_efuse);
  Serial.println("");
  Serial.printf(" as hex: %X\n", lib_esp_efuse);

  Serial.print("Getting Mac Address. WiFi Library: ");
  Serial.println(WiFi.macAddress());

Conclusion

I plan to use WiFi.macAddress() if I am using Arduino, or I would use the esp_efuse_mac_get_default with an array of 6. This will be unique enough for my purposes, built only on espressif.

If I were building a much larger system and much more paranoid, I might prefix (or postfix) with something like my device version. (Where a device version is just a number I assign while compiling my firmware that would only increment with runs of the hardware. Maybe stored in NVM.)