Robustness of secret key agreement protocol with massive MIMO under pilot contamination attack

We consider a secret key agreement (SKA) protocol over time division duplex for a massive Multiple-Input-Multiple-Output (MIMO) system. As a security threat, we assume that a pilot contamination attack (PCA) is attempted by an eavesdropper for the purpose to gain information about the secret key. The eavesdropper controls its transmit power for the PCA in a way to maximize the amount of eavesdropping information, while hiding her presence from legitimate users. To fend off this PCA, we consider a SKA protocol working with a PCA detector. Specifically, our SKA protocol suspends the key generation process to prevent information leakage to the eavesdropper if the PCA detector declares the presence of the PCA more than a certain number of times. Taking into account the best choice of the PCA power for the eavesdropper, we analyze an achievable length of generated secret key through our SKA protocol. Simulation results show that our SKA protocol effectively suppresses the eavesdropper's PCA power by adjusting a threshold determining the suspension of the PCA, and a positive length of secret key is achievable through our SKA protocol.