Experimental assessment of secret key generation using parasitic reconfigurable aperture antennas

The potential of automatically generating secret keys by randomly changing the state of a reconfigurable antenna is investigated through direct measurement. Measurements are performed with a 5×5 parasitic reconfigurable aperture (RECAP) antenna at 2.54 GHz in an indoor laboratory environment, illustrating that keys can be generated with physical-layer reciprocal channel key generation (RCKG) even in static or line-of-sight (LOS) conditions. Details of the parasitic array, varactor-diode reconfigurable elements, and network-analyzer based measurement setup are presented. Analysis of the data shows that secure key bits is lower when an eavesdropper is in the LOS path between legitimate nodes as opposed to a direction perpendicular to that path. It is also illustrated that the statistics of fading induced with the reconfigurable array are not strictly Gaussian for LOS channels. Encouragingly, measurements show that around 80% of generated key bits are secure even in the worst case conditions.