  In this paper, we investigate the problem of secure broadcasting over
block-fading channels with limited channel knowledge at the transmitter. More
particularly, we analyze the effect of having imperfect channel state
information (CSI) via a finite rate feedback on the throughput of a broadcast
channel where the transmission is intended for multiple legitimate receivers in
the presence of an eavesdropper. First, we partially characterize the ergodic
secrecy capacity of the system when the source broadcasts the same information
to all the receivers, i.e., common message transmission. Then, we look at the
independent messages case, where the transmitter broadcasts multiple
independent messages to the legitimate receivers. For this case, we present
lower and upper bounds on the ergodic secrecy sum-capacity. In both scenarios,
we show that the proposed lower and upper bounds coincide asymptotically as the
capacity of the feedback links becomes large, hence, fully characterizing the
secrecy capacity in this case.
