A secret key exchange scheme for near field communication

We consider the secret key generation (SKG) problem for short-range communication (SRC) systems. Specifically, we focus on the problem that secret key generation schemes relying on the entropy of the channel are not suitable for SRC systems, which are characterized by the absence of fading. To mitigate this problem, we introduce the concept of geometric secrecy and propose a new phase-based SKG which relies only on the reciprocity of the channel in order to securely generate mutual secret keys in the presence of an eavesdropper. The method is validated via a theoretical analysis which shows that for the signal-to-noise ratio (SNR) ranges typical of SRC systems, an efficient secret key generation can be achieved.