  We study information-theoretic security for discrete memoryless interference
and broadcast channels with independent confidential messages sent to two
receivers. Confidential messages are transmitted to their respective receivers
with information-theoretic secrecy. That is, each receiver is kept in total
ignorance with respect to the message intended for the other receiver. The
secrecy level is measured by the equivocation rate at the eavesdropping
receiver. In this paper, we present inner and outer bounds on secrecy capacity
regions for these two communication systems. The derived outer bounds have an
identical mutual information expression that applies to both channel models.
The difference is in the input distributions over which the expression is
optimized. The inner bound rate regions are achieved by random binning
techniques. For the broadcast channel, a double-binning coding scheme allows
for both joint encoding and preserving of confidentiality. Furthermore, we show
that, for a special case of the interference channel, referred to as the switch
channel, the two bound bounds meet. Finally, we describe several transmission
schemes for Gaussian interference channels and derive their achievable rate
regions while ensuring mutual information-theoretic secrecy. An encoding scheme
in which transmitters dedicate some of their power to create artificial noise
is proposed and shown to outperform both time-sharing and simple multiplexed
transmission of the confidential messages.
