Source-Channel Secrecy with Causal Disclosure

TL;DR

This paper explores imperfect secrecy in communication systems by measuring the eavesdropper's distortion, analyzing the effects of causal disclosure, and comparing secret key and wiretap channel approaches for secure source transmission.

Contribution

It introduces a new distortion-based secrecy measure for systems with causal disclosure and compares wiretap channels to secret key methods, revealing new insights and challenges.

Findings

Weak secrecy provides similar eavesdropper distortion as strong secrecy.

Revealing public messages freely can be detrimental to secrecy.

Separating source and channel coding is effective for achievability.

Abstract

Imperfect secrecy in communication systems is investigated. Instead of using equivocation as a measure of secrecy, the distortion that an eavesdropper incurs in producing an estimate of the source sequence is examined. The communication system consists of a source and a broadcast (wiretap) channel, and lossless reproduction of the source sequence at the legitimate receiver is required. A key aspect of this model is that the eavesdropper's actions are allowed to depend on the past behavior of the system. Achievability results are obtained by studying the performance of source and channel coding operations separately, and then linking them together digitally. Although the problem addressed here has been solved when the secrecy resource is shared secret key, it is found that substituting secret key for a wiretap channel brings new insights and challenges: the notion of weak secrecy provides just as much distortion at the eavesdropper as strong secrecy, and revealing public messages freely is detrimental.