  Secure communication with feedback is studied. An achievability scheme in
which the backward channel is used to generate a shared secret key is proposed.
The scenario of binary symmetric forward and backward channels is considered,
and a combination of the proposed scheme and Maurer's coding scheme is shown to
achieve improved secrecy rates. The scenario of a Gaussian channel with perfect
output feedback is also analyzed and the Schalkwijk-Kailath coding scheme is
shown to achieve the secrecy capacity for this channel.
