Wireless secret key sharing based on the use of a Variable-Directional Antenna over multipath channels

It has been proposed recently an approach to generate secret key exploiting reactance-domain scalar response of multipath fading channel. However, the security of the shared key has not been adequately investigated. In this paper we propose a mathematical model of the key distribution protocol based on the use of a Variable-Directional Antenna (VDA) acting on multipath wireless channels. The security of the key distribution protocol (KDP) is estimated in terms of Shannon´s information leaking to an eavesdropper. Statistical properties of VDA are investigated by simulation that results in an opportunity to calculate the security of the KDP depending on the mutual locations of the legal user and the eavesdropper. Antenna diversity is considered as a measure to enhance a level of the KDP security.