Secrecy Rate- Distortion Tradeoff for Integrated Sensing and Communication With an Untrusted Sensing Node

Integrated sensing and communication (ISAC) tech-nology combines communication and sensing functionalities through a unified signal waveform. While this integration offers potential benefits such as improved spectrum sharing and reduced processing costs, it also poses security challenges. Specifically, when the communication receiver and sensing entity operate as separate nodes, maintaining message secrecy from the sensing entity becomes crucial. To address this challenge, we propose a two-receiver state-dependent ISAC model that includes an untrusted sensing node. In this model, the ISAC transmitter aims to convey a message to the communication receiver while enabling the sensing of channel state for an untrusted sensing receiver, all while keeping the message secret from the untrusted sensing receiver. We consider the fundamental tradeoff between secure communication rate and sensing distortion within this model, which is characterized by the secrecy capacity-distortion function. To establish an inner bound on the secrecy capacity-distortion tradeoff region, we adopt an input-constrained wiretap coding approach. In addition, we present an outer bound on the tradeoff region by independently deriving the necessary conditions on the rate and on the sensing distortion. We also provide two illustrative examples that highlight the utilities of these bounds and demonstrate the superiority of the unified signal waveform over a separation-based approach via time-sharing.