Implications of Coding Layers on Physical-Layer Security: A Secrecy Benefit Approach

In this work, we consider the pros and cons of using various layers of keyless coding toachieve secure and reliable communication over the Gaussian wiretap channel. We define a newapproach to information theoretic security, called practical secrecy and the secrecy benefit, to be usedover real-world channels and finite blocklength instantiations of coding layers, and use this newapproach to show the fundamental reliability and security implications of several coding mechanismsthat have traditionally been used for physical-layer security. We perform a systematic/structuredanalysis of the effect of error-control coding, scrambling, interleaving, and coset coding, as codinglayers of a secrecy system. Using this new approach, scrambling and interleaving are shown to be ofno effect in increasing information theoretic security, even when measuring the effect at the output ofthe eavesdropper’s decoder. Error control coding is shown to present a trade-off between secrecyand reliability that is dictated by the chosen code and the signal-to-noise ratios at the legitimate andeavesdropping receivers. Finally, the benefits of secrecy coding are highlighted, and it is shown howone can shape the secrecy benefit according to system specifications using combinations of differentlayers of coding to achieve both reliable and secure throughput.