Secret Key Agreement for Massive MIMO Systems with Two-Way Training under Pilot Contamination Attack

This work presents a secret key agreement (SKA) protocol for a multiuser time-division duplex cellular system under an active eavesdropping called pilot contamination attack (PCA) when the base station (BS) is equipped with a large antenna array. In particular, we study how to incorporate twoway training, i.e. conducting training processes in both the uplink and down-link transmissions, into the SKA protocol for the purpose of strengthening the protocol against the PCA and/or improving secret key generation efficiency. It will be shown that the two-way training provides the SKA protocol with a considerable enhencement of estimation for eavesdropper´s channel. Secrecy performances of the proposed SKA protocol is quantitatively analyzed in terms of secrecy outage probability and average secret key rate, which shows that the two-way training improves the security performances especially in fast fading environments.