Analysis of Secret Key Robustness in Indoor Radio Channel Measurements

In the recent years, a set of works have addressed inherent characteristics of the fading propagation channel in an information-theoretic framework oriented towards security. In particular, for cryptographic purposes, secure key bits can be extracted from reciprocal radio channels, seen as a shared source of randomness between any two entities. In this paper we intend to assess the impact of true radio channel features on the security performance, by quantizing the complex channel coefficients into discrete key bits. To this end, indoor channel measurements were performed and investigated in different scenarios, e.g. LOS/NLOS condition, narrowband (NB) as well as wide band (WB) targeting OFDM systems. Secret key robustness is firstly studied for the legitimate terminals in terms of key bit disagreement ratio and key randomness, and secondly by considering an eavesdropper in a wide set of positions around these terminals and by evaluating the difference between the generated keys. A simplified channel model is also analyzed in comparison with the measured channels, as regards the characteristics of generated key bits.