  In this paper we study the problem of half-duplex active eavesdropping in
fast fading channels. The active eavesdropper is a more powerful adversary than
the classical eavesdropper. It can choose between two functional modes:
eavesdropping the transmission between the legitimate parties (Ex mode), and
jamming it (Jx mode) -- the active eavesdropper cannot function in full duplex
mode. We consider a conservative scenario, when the active eavesdropper can
choose its strategy based on the legitimate transmitter-receiver pair's
strategy -- and thus the transmitter and legitimate receiver have to plan for
the worst. We show that conventional physical-layer secrecy approaches perform
poorly (if at all), and we introduce a novel encoding scheme, based on very
limited and unsecured feedback -- the Block-Markov Wyner (BMW) encoding scheme
-- which outperforms any schemes currently available.
