Wiretap Channels With Causal State Information: Strong Secrecy

• Published in: IEEE transactions on information theory Vol. 65; no. 10; pp. 6750 - 6765
• Main Authors: Han, Te Sun, Sasaki, Masahide
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; causal coding; Channel coding; Channel state information; Channels; Ciphers; Coders; Coding; Communication channels; Cryptography; Decoding; Electronic surveillance; Encryption; Lower bounds; Optical wavelength conversion; Random variables; secrecy capacity; secret key agreement; strong secrecy; Theorems; Wiretap channel; Wiretapping
• ISSN: 0018-9448; 1557-9654; 1557-9654
• DOI: 10.1109/TIT.2019.2925611

The coding problem for wiretap channels with causal channel state information available at the encoder and/or the decoder is studied under the strong secrecy criterion. This problem consists of two aspects: one is due to wiretap channel coding and the other is due to one-time pad cipher based on the secret key agreement between Alice and Bob using the channel state information. These two aspects are closely related to each other and give rise to an intriguing tradeoff between exploiting the state to boost secret-message rates versus extracting cryptographic key to improve secrecy capabilities. This issue has yet to be understood how to optimally reconcile the two. We newly devised the "iterative" forward-backward coding scheme, combining wiretap channel coding and secret-key-agreement-based one-time pad cipher. We then established reasonable lower bounds of the secrecy capacity for wiretap channels with causal channel state information available only at the encoder (<xref ref-type="theorem" rid="theorem1">Theorem 1 ), which can be easily extended to general cases with various kinds of correlated channel state information at the encoder (Alice), decoder (Bob), and wiretapper (Eve). In particular, for degraded wiretap channels, we give the secret-message (secret-key) capacity bounds (<xref ref-type="theorem" rid="theorem2">Theorems 2 , <xref ref-type="theorem" rid="theorem4">4 , and <xref ref-type="theorem" rid="theorem5">5 ).