hexnumber-formattinguniqueidentifierrfidserial-number

# RFID algorithm to get card ID

I receive bytes from an RFID reader when presenting a card, but I'm unable to figure out how to derive the card ID from these bytes.

For example, I have a card that has these numbers printed on it: 0007625328 116,23152. I would expect that this is the ID of that card, right?

For this card, I get the following bytes from the reader (in hexadecimal representation): <42><09><01><74><00><74><5A><70>.

Solution

• The decimal number 0007625328 translates to `0x00745A70` in hexadecimal representation.

The number 116,23152 is actually a different representation of that same value (0007625328):

• 116 in decimal is `0x74` in hexadecimal.
• 23152 in decimal is `0x5A70` in hexadecimal.
• Combined, this also gives `0x00745A70`.

So the value that you receive (`42 09 01 74 00 74 5A 70`) seems to be the concatenation of some form of prefix value (`0x42090174`) and the printed card serial number (`0x00745A70`).