Stupid Simple Arduino LF RFID Tag Spoofer

Step 2 RFID background

A passive RFID tag has a coil and a chip with data on it.  An RFID reader has a coil in it that has a coil in it that creates a varying electronic field (in this case 125 KHz), which is called the carrier signal.  When the tag is close to the RFID reader then the magnetic field powers the chip on the tag, which then responds by tuning and detuning its own antenna.  This all works on the principle of inductive coupling, to learn more about his see www.rfid-handbook.de/rfid/types_of_rfid.html

125 KHz cards use manchester encoding to encode the data to send it to the reader.  Manchester encoding basically takes the XOR of the bit that needs to be transmitted and the clock value.  So if the clock value is low (0) and the value to transmit is 1 then it would be 0 XOR 1 which is 1.  This has to be done on every clock cycle.  For more information on manchester encoding see en.wikipedia.org/wiki/Manchester_code.