Information-theoretically Secret Key Generation for Fading Wireless Channels

TL;DR

This paper presents practical secret key generation protocols leveraging the unique, time-varying wireless channel characteristics, validated through experiments, achieving reliable key rates in WiFi environments.

Contribution

It introduces two novel secret key generation schemes based on channel fading properties, including a level crossing method and a distribution-agnostic approach, validated through real-world experiments.

Findings

Achieved secret key rates of about 10 bits/second in WiFi channels.

Demonstrated the effectiveness of level crossing and distribution-agnostic methods.

Validated protocols through experimental implementation on a 802.11a platform.

Abstract

The multipath-rich wireless environment associated with typical wireless usage scenarios is characterized by a fading channel response that is time-varying, location-sensitive, and uniquely shared by a given transmitter-receiver pair. The complexity associated with a richly scattering environment implies that the short-term fading process is inherently hard to predict and best modeled stochastically, with rapid decorrelation properties in space, time and frequency. In this paper, we demonstrate how the channel state between a wireless transmitter and receiver can be used as the basis for building practical secret key generation protocols between two entities. We begin by presenting a scheme based on level crossings of the fading process, which is well-suited for the Rayleigh and Rician fading models associated with a richly scattering environment. Our level crossing algorithm is simple, and incorporates a self-authenticating mechanism to prevent adversarial manipulation of message exchanges during the protocol. Since the level crossing algorithm is best suited for fading processes that exhibit symmetry in their underlying distribution, we present a second and more powerful approach that is suited for more general channel state distributions. This second approach is motivated by observations from quantizing jointly Gaussian processes, but exploits empirical measurements to set quantization boundaries and a heuristic log likelihood ratio estimate to achieve an improved secret key generation rate. We validate both proposed protocols through experimentations using a customized 802.11a platform, and show for the typical WiFi channel that reliable secret key establishment can be accomplished at rates on the order of 10 bits/second.