Wireless Secret Key Generation Exploiting the Reactance-Domain Scalar Response of Multipath Fading Channels: RSSI Interleaving Scheme

Abstract

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 IEEE802.15.4/ZigBee T M 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.

Adaptive wireless channel probing for shared key generation

“…There has been an increasing interest in exploiting the randomness and reciprocity of the wireless channel to generate shared keys between two parties [2]- [5], [10]- [16]. Early research in this area focused on theoretical analysis [13]- [15], while most recent works are more interested in practical implementations of the key generation schemes using offthe-shelf wireless devices [2]- [4].…”

The generation of shared cryptographic keys through channel impulse response estimation at 60 GHz.

“…That is, each node without knowledge of the state of the other node can introduce pseudorandom reciprocal variations in the carrier of transmitted signal over any domain. Such a capability has been demonstrated in a system that varies antenna gain over time [11], [12]. Note that the variations must be independent as it is a tenet in cryptography that an adversary is presumed to be in possession of the encryption algorithm and that security rests solely on the secret key.…”

“…The ability of an eavesdropper to deduce the shared cryptographic key has been analyzed in several prior works [11], [12], [13], [14], [15], [20], however the effect of an interferer has not yet been considered. In the following section, the effects of a narrow-band FM transmitter and a low-power, broadband jammer on the performance of the key-generation system are discussed.…”

“…Note that the variations must be independent as it is a tenet in cryptography that an adversary is presumed to be in possession of the encryption algorithm and that security rests solely on the secret key. Thus it is not sufficient for two nodes to reorder data using a shared function, such as interleaving [11], [12], as this algorithm is considered to be known. A summary of pseudorandom metric variations over domains is shown in Table 2.…”

“…In [10], threshold magnitude carrier variations in time and frequency are measured. In [11] and [12], threshold magnitude-only signal-strength variation is measured in time with pseudorandom variation added via switched parasitic antenna elements [13], [17]. In [14], an ultra-wideband pulse is used to measure the channel impulse response in time.…”