  In this paper, the impact of in-band full-duplex (IBFD) wireless
communications on secret key generation via physical layer channel state
information is investigated. A key generation strategy for IBFD wireless
devices to increase the rate of generated secret keys over multipath fading
channels is proposed. Conventionally, due to the half-duplex (HD) constraint on
wireless transmissions, sensing simultaneous reciprocal channel measurements is
not possible, which leads to a degraded key generation rate. However, with the
advent of IBFD wireless devices, the legitimate nodes can sense the shared
wireless link simultaneously at the possible cost of a self-interference (SI)
channel estimation and some residual self-interference (RSI). As we
demonstrate, with HD correlated observations the key rate is upper bounded by a
constant, while with IBFD the key rate is only limited by the SI cancellation
performance and is in general greater than that of its HD counterpart. Our
analysis shows that with reasonable levels of SI cancellation, in the high SNR
regime the key rate of IBFD is much higher, while in low SNRs, the HD system
performs better. Finally, the key rate loss due to the overhead imposed by the
SI channel estimation phase is discussed.
