Malicious Relay Detection and Legitimate Channel Recovery.

Full-duplex devices can compromise the integrity of wireless channel measurements through signal relaying and several attacks have been proposed based on this vulnerability. Existing source authentication methods relying on previously-collected signatures face significant challenges in detecting these attacks because a relay attacker can gradually inject the channels so that the manipulated channels will fall within the tolerance range of the authentication methods and are mistaken as new signatures. In this paper, we propose RelayShield, a system for detecting malicious relays and recovering the legitimate transmitter-receiver channels from the manipulated channels. RelayShield requires only one channel measurement at the receiver. It analyzes signal path information resolved from input channels to detect relays and recover channels. RelayShield achieves over 95% detection accuracy with channels collected in two typical indoor environments. The recovered channels can support a wide range of applications, including secret generation protocols and sensing systems.