Two-Way Wiretap Channel under Mixed Secrecy Constraint

2026-07-22

AI Summary

This study addresses mixed-security communication over a two-way wiretap channel, where only User 1’s message is subject to a strong secrecy constraint while User 2 has no confidentiality requirement. By integrating non-adaptive coding constructions with a one-way key-exchange reduction technique, and employing a one-time pad argument together with explicit padding, the proposed approach effectively eliminates the initial rate loss typically incurred in such settings. The work establishes, for the first time, an adaptive achievable rate region under a strong mixed-secrecy criterion, guaranteeing exponentially decaying information leakage. This result not only subsumes existing weak unilateral secrecy schemes but also enables secure communication without asymptotic rate loss in the large blocklength regime.

Abstract

This paper studies the two-way wiretap channel (TW-WC) with an external eavesdropper under strong one-sided (mixed) secrecy: only User~1's message is required to be secure from the eavesdropper, while no secrecy constraint is imposed on User~2's message. Secrecy is measured by the information leakage of User~1's message to the eavesdropper. Applying a non-adaptive construction and a one-sided reduction of the key-exchange construction, we obtain exponential error and leakage bounds for every fixed number of adaptive rounds. A quantitative one-time-pad argument propagates the leakage of the key used in the next round, and an explicit padding construction removes the initialization-rate loss for all sufficiently large blocklengths. We derive the corresponding strong mixed-secrecy achievable regions. The non-adaptive construction recovers the previously reported weak one-sided single-letter inner bound under the stronger secrecy criterion. The overall adaptive achievable region includes the non-adaptive construction as a fallback and also contains a key-exchange subregion that can be strictly larger.

Problem

• two-way wiretap channel
• mixed secrecy
• eavesdropper
• information leakage
• strong secrecy

Innovation

• two-way wiretap channel
• mixed secrecy
• key-exchange construction
• exponential leakage bound
• adaptive coding