Plausible Deniability over Broadcast Channels

TL;DR

This paper introduces the concept of Plausible Deniability in broadcast channels, analyzing how parties can produce fake outputs that seem plausible to an eavesdropper while maintaining communication rates.

Contribution

It formalizes the notion of plausible deniability in information theory and characterizes capacity regions for different variants in broadcast channels.

Findings

Full capacity region characterized for Message and Transmitter Deniability.

Achievable rate region provided for Receiver Deniability in degraded channels.

Framework enables secure and plausible communication in eavesdropped broadcast scenarios.

Abstract

In this paper, we introduce the notion of Plausible Deniability in an information theoretic framework. We consider a scenario where an entity that eavesdrops through a broadcast channel summons one of the parties in a communication protocol to reveal their message (or signal vector). It is desirable that the summoned party have enough freedom to produce a fake output that is likely plausible given the eavesdropper's observation. We examine three variants of this problem -- Message Deniability, Transmitter Deniability, and Receiver Deniability. In the first setting, the message sender is summoned to produce the sent message. Similarly, in the second and third settings, the transmitter and the receiver are required to produce the transmitted codeword, and the received vector respectively. For each of these settings, we examine the maximum communication rate that allows a given minimum rate of plausible fake outputs. For the Message and Transmitter Deniability problems, we fully characterise the capacity region for general broadcast channels, while for the Receiver Deniability problem, we give an achievable rate region for physically degraded broadcast channels.