Multi-terminal networks with an untrusted relay

This paper investigates the impact of cooperation with an untrusted relay in multi-source multi-destination networks. The set up considered is one where the relay is the only means of communications due to the absence of direct links between the sources and the destinations. Since the relay is untrusted, all messages from the sources need to be kept secret from the relay. Furthermore, the destinations are assumed to have different levels of security clearance, i.e., some private messages should only be decoded by their intended receiver and should be kept secret from other destinations. An achievable secure rate region is found by using random binning at the sources, cooperative jamming from the destinations, and compress-and-forward at the relay. Additionally, a genie aided outer bound on the secure rate region is derived. Comparison of inner and outer bounds are provided.