Securing massive MIMO at the physical layer

We consider a single-cell downlink massive MIMO system in the presence of an adversary capable of jamming and eavesdropping. We show that, classical attacks of eavesdropping and data jamming can be simultaneously rendered useless. Specifically, we show that, the secure degrees of freedom (DoF) attained in the presence of classical attacks is as same as the maximum DoF attained under no attack. We propose a novel beamforming strategy that establishes information theoretic security without need to Wyner encoding. We next introduce a new attack strategy that involves jamming pilot signals and eavesdropping in succession. We show that under such an attack, the maximum secure DoF is equal to zero. Furthermore, the maximum achievable rates of users vanish even in the asymptotic regime in number of base station (BS) antennas. We develop counter strategies for this new attack in which we use secret key to encrypt the pilot sequence. We show that hiding the training signal assignments from the adversary enables the users to achieve a secure DoF, identical to the one achieved under no attack.