Public discussion strategies for secret key generation from sampled IR-UWB channel responses

Abstract

The generation of symmetric keys using physical layer measurements (e.g. received signal strength, channel responses etc.) is based on the reciprocity property of wireless channels. However, noise or other transmission artifacts can degrade the link reciprocity and lead to bit mismatching between legitimate users. One of the challenges of this new key management paradigm is to obtain as many identical bits as possible, while guaranteeing good secrecy of the public exchanges that allow the bit correction. Previous studies have provided a proof of concept for exploiting oversampled ultra wideband signals to generate secret keys with practical lengths. In order to improve the security of such schemes with respect to a nearby passive attacker with correlated channel observations, we propose public discussion alternatives including one strategy based on the signal time of flight (ToF). We show that these alternatives can reduce the advantage that such an attacker can have in terms of bit agreement between the legitimate keys and his guess.