Certification Codes for Maliciousness Detection in Physical-layer Network Coding

The problem of two sources wanting to share information through a potentially untrustworthy relay node is considered. The two sources transmit symbols simultaneously, and the relay node employs Physical-layer Network Coding (PNC) to forward information back to the two sources in order to increase throughput. In such a system using PNC, the relay node can easily fool the source nodes by manipulating the PNC output symbols. To enable relay maliciousness detection, a class of variable-rate codes, called certification codes, is introduced. In a certification code, redundancy is added to the source message to act as a certificate, allowing a node to determine if the relay is behaving in a malicious manner. A simple binary certification code is designed and analyzed to demonstrate the proposed approach.