Noisy Carrier Modulation for HF RFID

Radio-frequency tokens are vulnerable to eavesdropping. Several schemes have been proposed that use additional devices to generate cover noise, or bit collisions, in order to protect communication between a reader and a token. I discuss the practical weaknesses in current bit-blocking schemes and propose an alternative implementation where the tokens modulate their reply onto a noisy carrier provided by the reader. I believe that this modification resolves some weaknesses of bit-blocking protocols and is also easier to implement as it does not require additional blocking devices. This method can also be used to simply add noise to the backward communication channel in order to complicate the recovery of eavesdropped data.