Wiretap channel with rate-limited feedback

This paper studies the problem of secure communication over a degraded wiretap channel p(y, z|x) = p(y|x)p(z|y) with secure feedback link of rate R_f, where X is the channel input, and Y and Z are channel outputs observed by the legitimate receiver and the wiretapper respectively. The secrecy capacity is characterized as C_s{R_f) = maxmin{I(X; Y), I(X; Y|Z) + R_f}. p(x)equation. A capacity-achieving coding scheme is presented, in which the receiver securely feeds back fresh randomness with rate R_f, independent of the received channel output. The transmitter then uses the shared randomness as a secret key on top of Wynerpsilas coding scheme for wiretap channel without feedback. Hence, when the receiver has a means of interacting with the transmitter, he should allocate all resources to convey a new key rather than sending back the channel output. For the converse, a recursive argument is used to obtain the single-letter characterization.