ARQ-based key scheduling algorithm over correlated erasure channels

This paper focuses on the problem of sharing secret keys using the Automatic Repeat reQuest (ARQ) protocol. We first model the forward and feedback channels as erasure channels for both legitimate receiver (Bob) and an eavesdropper (Eve). In prior works, wiretap channel is modeled as statistically independent packet erasure channels for Bob and Eve. In this paper, we go beyond the state-of-the-art by addressing correlated erasure events across the wiretap channel. The created randomness is shared between two legitimate parties through ARQ transmission that will be mapped into a destination set using the first order digital filter with feedback. Then, we characterize Eve´s information loss about this shared destination set, due to inevitable transmission errors that will be manipulated by privacy amplification to generate a series of secret keys about which Eve´s knowledge remains negligible. We define two metrics to measure secrecy enhancement: outage probability and secret key rate. The resulting secrecy improvement is presented as a function of the correlation coefficients and the erasure probabilities for both channels. It is shown that secrecy improvement is achievable even when Eve has a better channel than the legitimate receiver, and her channel condition is unknown.