Techniques for protecting communication between a card reader and a contactless smartcard are disclosed. In one embodiment, a protocol transmitter includes a transmit circuit and a processor. The transmit circuit is configured to generate a blocking signal having a frequency used by the card reader to communicate with the contactless smartcard. The processor is coupled to the transmit circuit and configured to modulate the blocking signal according to a communication protocol of the contactless smartcard. A first antenna of the protocol transmitter is disposed a predetermined distance from the card reader and is coupled to the transmit circuit to radiate the blocking signal. Optionally, the processor modulates the blocking signal so as to simulate a data exchange between the card reader and the contactless smartcard.