Wireless secret key generation exploiting the reactance-domain scalar response of multipath fading channels : RSSI interleaving scheme

A secure communication scheme that uses the random fluctuation of the natural environment of communication channels is studied and an improved scheme for the secret key generation is proposed. We have been developing a novel secret key generation and agreement scheme that uses the fluctuation of channel characteristics with an Espar (electronically steerable parasitic array radiator) antenna. This antenna consists of a single central active element surrounded by parasitic elements loaded with variable reactors. Using an Espar antenna, we can increase the fluctuation of the channel characteristics and acquire the undulated RSSI (received signal strength indicator) profile in a short time to generate a randomized secret key. We acquire more randomized and stronger secret keys generated from the interleaved RSSI values in this scheme. As a result of experiments on the prototype system in which the IEEE 802.15.4/ZigBeetrade wireless PAN (personal area network) chip is mounted, we confirmed that the probability of success for key generation was estimated to exceed 99.998% when 128-bit secret keys are changed every two seconds and that the generated secret keys were sufficiently random to pass the FIPS (Federal Information Processing Standards) PUB 140-2 statistical test for random numbers