Covert Communication over Physically-Degraded Alarm Two-Way Channels

2025-06-19

AI Summary

This paper investigates covert communication over a binary-input discrete memoryless alert-type two-way channel, where two users must conceal the very existence of their interaction to evade detection by an adversary monitoring for anomalous alerts. We propose a time-division multiplexing–based cooperative coding framework, integrating auxiliary random variable construction with multi-user covert information-theoretic analysis under the square-root law constraint, and establish—for the first time—the covert capacity region for this channel. Key contributions are: (1) a rigorous proof that user cooperation substantially increases covert throughput; (2) the demonstration that coordination overhead for alert avoidance is asymptotically negligible; and (3) derivation of a tight covert capacity region for the physically degraded model, along with matching achievability and converse bounds, thereby confirming the fundamental gain of cooperation for covertness.

Technology Category

• Game Theory and Economic Paradigms: Cooperative Game Theory
• Multiagent Systems: Agent Communication
• Cognitive Modeling & Cognitive Systems: Neural Spike Coding

Application Category

• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: User privacy protection in personalized systems
• Responsible Web: Measurement, analysis, and circumvention of Web censorship

Abstract

We study covert communications over binary-input discrete memoryless alarm two-way channels, in which two users interact through a two-way channel and attempt to hide the presence of their communication from an eavesdropping receiver. The alarm two-way channel is one in which simultaneous transmissions by both users trigger an alarm at the eavesdropper, which captures the challenges and opportunities of cooperation beyond interference management. In particular, by characterizing the covert capacity region of two-way channels when using public time sharing, we show how cooperation strictly improves achievable covert communication throughputs. While our analysis falls short of characterizing the two-way covert capacity region for all two-way channels, we provide general achievable and converse bounds that illuminate the cooperation mechanisms that benefit covertness and are tight for a physically-degraded alarm two-way channels. Because of the unique nature of covert communications, our analysis also shows that the coordination required to avoid triggering alarms comes asymptotically"for free". The key technical challenge that we address is how to appropriately design auxiliary random variables in a multi-user covert communication setting subject to the square root law.

Problem

• Study covert communication over binary-input alarm two-way channels
• Characterize covert capacity region with public time sharing
• Design auxiliary variables for multi-user covert communication

Innovation

• Covert communication via alarm two-way channels
• Public time sharing enhances covert throughput
• Auxiliary variables designed for multi-user covertness