Adaptive Coding for Two-Way Wiretap Channel under Strong Secrecy

This paper studies adaptive coding for the two-way wiretap channel. Especially, the strong secrecy metric is of our interest that is defined by the information leakage of transmitted messages to the eavesdropper. First, we consider an adaptive coding, the construction of which is based on running the well studied non-adaptive coding in several rounds and the dependency between the adjacent rounds of transmission is introduced by the key exchange mechanism that is embedded in the non-adaptive coding in each transmission round. As a result, we analyze the reliability and strong secrecy that are measured by the decoding error probability and information leakage, characterize them in terms of the conditional R\'enyi mutual information, and derive inner bounds on the secrecy capacity regions for the TW-WC under strong joint and individual secrecy constraints. Second, we introduce another adaptive coding method that explores the correlation among the outputs at the receivers. With this approach, we show that for the two-way wiretap channel that fulfills the conditionally independent condition, positive transmission rates can be always guaranteed even under the joint secrecy constraint.