The most often used identifier of the RFID chip explained

What is the RF chip ID, UID, or NUID? Can I change it or emulate it with a NFC phone?

18. March 2021
Have you read about the RFID chip ID, UID, or NUID and are wondering what the differences are? Is it possible to emulate the RFID card ID number with a mobile phone? Are you wondering why you get different ID numbers from the same RFID card? With this article, we will help you understand the most often used RFID chip identifier.
The main part of the RFID transponder is the RFID chip. Some chips are read-only and they contain only a preprogramed chip ID code, while others contain memory that can be written and protected in addition to an ID code. There are also chips that are completely blank, and even the ID code can be programmed later on by the application. 

The chip ID code (also known as ‘chip UID, NUID,’ etc.) is 4–7 byte long
preprogramed serial number. Some chip ID codes are programmed electronically, while others are even laser engraved during the chip manufacturing and cannot be altered or changed. The UID means chip’s Unique ID. Chips with 7-byte ID usually have a UID number which means that the manufacturers have declared them Unique IDs. Chips with 4-byte ID numbers have been so widely produced and the number range doesn’t allow manufacturers to guarantee that the chips are unique, so they have a Non-Unique ID or NUID code.

We have not received an official answer from the manufacturer, but we assume that a UID code used in NXP chips NTAG213 cannot be the same in NTAG215 or NTAG216 variation or in other kinds of chips on the same frequency like the DESFire family. 
The most popular 125 kHz chips are the EM4200 and TK4100. Since they are produced buy different manufacturers, we assume that the chip IDs are not unique. You can also buy freely available 125 kHz blank cards with T5577 chips and inexpensive equipment that can be used for copying chip ID numbers. These cloned chips undermine the 125 kHz chip’s security.

To the best of our knowledge, the 13.56 MHz with a 7-byte long NUID chip number cannot be cloned. The are some special grey-market chips made in China with the possibility to program a 4-byte ID number, but chip manufacturers have improved the security and issued new generations of the most widely-used chips. 

The NFC phone cannot emulate a RFID card chip ID number. When using a NFC phone for access control or another solution, the phone has to have a special app that communicates dynamically with a reader and doesn’t just emit an ID number like the RFID transponders do. If the NFC phone can emulate the transponder chip ID number it would undermine the security of the 13.56 MHz chips like the cloners do for 125 kHz chips.

If you have a RFID transponder and you get different ID numbers on a different reader you should read the following explanation.

The RFID transponder chip ID can be read in more than 50 different ways (125 kHz reader, 13.56 MHz reader). It can be read in decimal or hexadecimal format, the sequence of read bytes can be from MSB (most significant byte) to LSB (less significant byte) or vice versa, and even the single bits can be read in multiple ways. 

Usually, low-cost RFID readers are able to read the code in a single way, while more sophisticated readers come with software tools to set the proper reading format.

For 125 kHz chips, the usual reading format is a 10-digit decimal number, but other formats are popular as well. Some MIFARE® chip readers read by default read the ID in a format 8-digit Hexadecimal (8 HEX), but we saw many applications which use the 8 HEX reverse byte format as well. NFC devices like mobile phones and tablets read the ID code in the 14 HEX Reverse byte format.

To identify an ID format, you should watch the ID code length and if there are only numbers or ASCII characters as well. 

A sample 10DEC code is 1234567890. If a reader uses an 8H-> 10D conversion, it means that the HEX code is 499602D2. This is a 4-byte code and bytes are 49-96-02-D2. 49 is MSB and D2 is LSB. If a reader would use 8 HEX Reverse Byte format, the reading would be D2-02-96-49 and if converted to Decimal it would be 3523384905.

This is just a sample how to calculate different formats, and if you need to dig deeper, we suggest to use a calculator like:

Our budget-friendly 125 kHz reader, which reads in a 10 DEC format is the R80D reader, while the more sophisticated reader with configuration tools is the Syris RD200-LF.

For 13.56 MHz chips, we offer a budget-friendly 8HEX reader R80C, a 14HEX inexpensive NFC keyboard emulating reader R80UF, and Syris readers with configurating tools RD200-M1 and RD300-H1, where the last one has a bit farther reading distances and reads very small tags as well. 

If you have any questions send an email to or call +38641 884 124 and we will be happy to help you.
< Back