The role of channel states in secret key generation

In this work, we investigate secret key generation from channel states. We point out, by means of a packet-delay-based attack, that observing its own channel states is not the only way an adversary can learn about the channel states of the legitimate communicating parties. The attack suggests that it is not secure to transmit data via the channel whose states generate secret keys. However, not using the channel at all would result in a waste of bandwidth. Hence, we propose using this channel to transmit the bits needed to reconcile the channel state estimates at the transmitter and the receiver. This is a necessary step in secret key generation that required a separate channel in previous work. Although the scheme proposed here in effect prohibits the use of an adaptive transmitter, we show, for the Rayleigh fading channel, that a decent key rate that outperforms existing schemes is obtained. This is due to the fact that collection of the channel state information and transmission of the reconciliation bits are performed concurrently rather than via time sharing.