On the trade-off between rate and reliability for secret key generation in wireless channels

Wireless propagation channels can be used to obtain secret keys to enhance security. By exploiting the reciprocity of the channel between legitimate users and its independence of an eavesdropper's channel, it can be quantised to produce a string of bits. The quality of these bits can be enhanced by using guard bands when quantising, which means that some samples are not used due to their poor quality. Although this increases the probability that the legitimate users produce the same bits, it also reduces the number of generated bits. We derive the optimal trade-off between these contrasting quantities, first for a single sample and then extended to a frequency-selective channel. The results are presented for both software simulations and hardware evaluations.