Prior work in channel based key extraction has assumed that the adversary has negligible knowledge/control of the wireless channel. Recent analysis, however, has shown that this assumption is not necessarily valid. Gaining a better understanding of the implications of this assumption is crucial as the wireless channel plays a critical role in the security of this type of key extraction system. In this paper, we discuss why we feel this assumption oversimplifies the problem and present a formal adversary model which takes into account an adversary's knowledge/control of the wireless channel. We present impossibility results learned from our formal model and discuss why previously proposed systems fail to defend against our adversary. We propose the first secret key extraction system which thwarts this adversary and give a generic implementation of our system.
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