Multi-Terminal Communications with Confidential Messages

The authors 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 perfect 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. This approach was first introduced by Wyner in 1975 for the wiretap channel model. In this paper, we investigate the secrecy capacity region bounds for these two communication systems. The derived outer bounds have an identical mutual information expression that applies to the broadcast channel when one sender jointly encodes both messages and to the interference channel when two senders offer independent inputs to the channel. We consider a switch channel model which is a special case of the interference channel and show that the derived outer and inner bounds meet in this case. Finally, we focus on Gaussian interference channels with confidential messages and describe several transmission schemes and their achievable rate regions under the prefect secrecy requirement.