In collaboration with Princeton University

Semantically-Secured Message-Key Trade-off over Wiretap Channels with Random Parameters

A. Bunin, Z. Goldfeld, H. H. Permuter, S. Shamai, P. Cuff and P. Piantanida

In Proceedings of the 2nd Workshop on Communication Security affiliated with EUROCRYPT, Paris, France, April 2017

We study the trade-off between secret message (SM) and secret key (SK) rates, simultaneously achievable over
a state-dependent (SD) wiretap channel (WTC) with non-causal channel state information (CSI) at the encoder. This
model subsumes other instances of CSI availability as special cases, and calls for efficient utilization of the state
sequence for both reliability and security purposes. An inner bound on the semantic-security (SS) SM-SK capacity
region is derived based on a superposition coding scheme inspired by a past work of the authors. The region is
shown to attain capacity for a certain class of SD-WTCs. SS is established by virtue of two versions of the strong
soft-covering lemma. The derived region yields an improvement upon the previously best known SM-SK trade-off
result reported by Prabhakaran et al., and, to the best of our knowledge, upon all other existing lower bounds for
either SM or SK for this setup, even if the semantic security requirement is relaxed to weak secrecy. It is demonstrated
that our region can be strictly larger than those reported in the preceding works.