Pilot Contamination for Active Eavesdropping

Existing studies on physical layer security often assume the availability of perfect channel state information (CSI) and overlook the importance of channel training needed for obtaining the CSI. In this letter, we discuss how an active eavesdropper can attack the training phase in wireless communication to improve its eavesdropping performance. We derive a new security attack from the pilot contamination phenomenon, which targets at systems using reverse training to obtain the CSI at the transmitter for precoder design. This attack changes the precoder used by the legitimate transmitter in a controlled manner to strengthen the signal reception at the eavesdropper during data transmission. Furthermore, we discuss an efficient use of the transmission energy of an advanced full-duplex eavesdropper to simultaneously achieve a satisfactory eavesdropping performance whilst degrading the detection performance of the legitimate receiver.