  We investigate the effects of an additional relay node on the secrecy of
broadcast channels by considering the model of relay broadcast channels with
confidential messages. We show that this additional relay node can increase the
achievable secrecy rate region of the broadcast channels with confidential
messages. More specifically, first, we investigate the discrete memoryless
relay broadcast channels with two confidential messages and one common message.
Three inner bounds (with respect to decode-forward, generalized noise-forward
and compress-forward strategies) and an outer bound on the
capacity-equivocation region are provided. Second, we investigate the discrete
memoryless relay broadcast channels with two confidential messages. Inner and
outer bounds on the capacity-equivocation region are provided. Finally, we
investigate the discrete memoryless relay broadcast channels with one
confidential message and one common message. Inner and outer bounds on the
capacity-equivocation region are provided, and the results are further
explained via a Gaussian example. Compared with Csiszar-Korner's work on
broadcast channels with confidential messages (BCC), we find that with the help
of the relay node, the secrecy capacity region of the Gaussian BCC is enhanced.
