Secrecy when the eavesdropper controls its channel states

This work investigates providing information theoretically secure communication in a scenario where the eavesdropper is more powerful as compared to models considered to date. Specifically, we consider the setting where the eavesdropper, based on signals it received in the past, modifies its channel state in order to benefit its reception of the legitimate parties´ messages. Natural to this setting is that the legitimate parties do not have any knowledge of the eavesdropper´s channel state. In this setting, we study the Gaussian two-way wiretap channel, namely two legitimate nodes connected by a bi-directional link in the presence of an eavesdropper that receives the superposition of signals from both nodes. We show that a positive secrecy rate in the sense of strong secrecy is achievable even under these assumptions. The secrecy rate obtained scales with transmit power. The achievable strategy involves cooperative jamming pointing out to its robustness to the adaptive nature of the eavesdropper channel.