Secure array synthesis for encryption key establishment in multipath channels

This paper explores optimal array beamforming for establishing secret encryption keys through bidirectional channel estimation in multipath propagation environments. The problem is cast as a convex optimization of the average secure key rate achieved in the presence of a passive eavesdropper, and the optimization is performed using semi-definite programming. Representative results demonstrate that, compared to a conventional but suboptimal beamforming solution, the optimal solution achieves significantly higher key establishment performance, with the relative performance improvement increasing with the transmit correlation.