Secret key establishment (SKE) is a method that allows two users, Alice and Bob, to obtain shared secret keys using randomness inherent in the wireless channel. Alice and Bob sample the channel many times, extract bits from those measurements and then use the bits to encrypt further communications. Even if an eavesdropper, Eve, were to overhear Alice and Bob measure the channel, she would still have no knowledge of the secret key because she does not measure the same channel as Alice and Bob. While the channel is reciprocal and random, measurements of the channel are temporally correlated and can include nonreciprocities caused by differing transceiver characteristics and the inability of Alice and Bob to measure the channel simultaneously. The dissertation aims to reduce or remove the nonidealities and noise of the reciprocal channel measurement process in order to increase secret key bit rate while maintaining an uncorrelated bit stream.;The first contribution of this dissertation addresses correlated received signal strength (RSS) measurements and differing transceiver characteristics in the context of sensor nodes. Because typical sensor nodes are constrained both by available energy and computational power, balancing the decorrelation method with node resources and changing wireless environments is also addressed. Ranking and fractional delay interpolation are used to mitigate nonreciprocities associated with differing transceiver characteristics and the inability of the two nodes to measure the channel at identical points in time.;Second, bit extraction is applied to channel impulse response (CIR) measurements. We develop a novel, inexpensive switching system that allows existing single receiver/single transmitter channel sounding equipment to make bidirectional measurements. With this system it is possible to investigate nonreciprocal interference and experimentally evaluate bit extraction for CIR that takes advantage of both the time and spatial diversity of the wireless channel.;Finally, nonuniform sampling caused by nondeterministic packet delay when sharing a wireless channel with other users is detrimental to bit extraction yet very common in practical wireless networks, especially for IEEE 802.11-based devices. Interpolation and regression are used to estimate the reciprocal fading signal given the nonuniform samples at Alice and Bob and the nonreciprocities caused by nonsimultaneous channel measurements.
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