Relay Channels with Confidential Messages

TL;DR

This paper investigates secure communication over relay channels where the relay can also act as a wire-tapper, defining and analyzing rate regions for confidential message transmission with deterministic and stochastic encoders.

Contribution

It introduces two new rate region definitions for relay channels with confidential messages and derives bounds, showing stochastic encoding can improve security and rate.

Findings

Explicit inner and outer bounds for rate regions

Stochastic encoder enlarges the rate region

Evaluation of Gaussian relay channel with confidentiality constraints

Abstract

We consider a relay channel where a relay helps the transmission of messages from one sender to one receiver. The relay is considered not only as a sender that helps the message transmission but as a wire-tapper who can obtain some knowledge about the transmitted messages. In this paper we study the coding problem of the relay channel under the situation that some of transmitted messages are confidential to the relay. A security of such confidential messages is measured by the conditional entropy. The rate region is defined by the set of transmission rates for which messages are reliably transmitted and the security of confidential messages is larger than a prescribed level. In this paper we give two definition of the rate region. We first define the rate region in the case of deterministic encoder and call it the deterministic rate region. Next, we define the rate region in the case of stochastic encoder and call it the stochastic rate region. We derive explicit inner and outer bounds for the above two rate regions and present a class of relay channels where two bounds match. Furthermore, we show that stochastic encoder can enlarge the rate region. We also evaluate the deterministic rate region of the Gaussian relay channel with confidential messages.