Secure Compute-and-Forward in a Bidirectional Relay

Bidirectional relaying, where a relay helps two user nodes to exchange messages has been an active area of recent research. In the compute-and-forward strategy for bidirectional relaying, the relay computes a function of the two messages using the naturally-occurring sum of symbols simultaneously transmitted by user nodes in a Gaussian Multiple Access Channel (MAC), and the computed function value is forwarded to the user nodes in an ensuing broadcast phase. In this paper, the authors consider the Gaussian MAC in bidirectional relaying with the messages taking values in a finite Abelian group and the relay computing the sum within the group under an additional secrecy constraint for protection against a honest but curious relay.