Secure Joint Source-Channel Coding of Multimodal Semantic Sources

Abstract

We study the problem of secure joint source-channel coding for multimodal semantic sources transmitted over noisy wiretap channels. The source model consists of $m$ modalities (e.g., image, audio, and sensor data), all represented as random variables. The encoder observes independent and identically distributed samples of an arbitrary non-empty subset of modalities, which are encoded, using wiretap coding with a help of a secret key shared with the legitimate receiver, and transmitted over a discrete memoryless wiretap channel. The legitimate receiver reconstructs all modalities. We extend the rate-distortion-perception characterisation to semantic unimodal and multimodal sources. We establish outer and inner bounds on the tradeoff between transmission rate, key rate, fidelity, and secrecy under per-modality distortion and perception constraints, and per-subset equivocation constraint. The bounds coincide for the less noisy wiretap channels. Our results show that the fundamental limit for secrecy consists of three operationally distinct components: the level of compression of each subset of modalities, the secret key rate, and the statistics of the wiretap channel.