Quantum key distribution networks (QKDNs) offer a promising platform for information-theoretically secure (IT-secure) communication between two or more nodes, representing an increasingly practical communication platform. Despite their promise, these systems continue to encounter significant challenges due to their restricted key-generation rate. Therefore, the efficient and effective utilization of key resources is pivotal to enhancing IT-secure communication. In this study, we propose an in-network coded–cache–aware multipath-transport mechanism called CodCam-TP that exploits information-centric networking (ICN) technologies. CodCam-TP facilitates efficient and effective IT-secure communication through in-network coding and caching, multicast, and multipath communication. Furthermore, by exploiting the pull-based hop-by-hop communication model, CodCam-TP leverages an in-band network telemetry technique to select a path based on the forwarding capacity of each available path, thus improving throughput. Additionally, we conduct several performance evaluations for CodCam-TP using Cefore, an open-source software for driving ICN-based communication, demonstrating improved secure-key-utilization efficiency and data-delivery effectiveness compared with those realized by an existing scheme.

The coding problem for wiretap channels (WTCs) with causal and/or non-causal channel state information (CSI) available at the encoder (Alice) and/or the decoder (Bob) is studied, particularly focusing on achievable secret-message secret-key (SM-SK) rate pairs under the semantic security criterion. One of our main results is summarized as Theorem 3 on causal inner bounds for SM-SK rate pairs, which follows immediately by leveraging the unified seminal theorem for WTCs with non-causal CSI at Alice that has been recently established by Bunin et al.. The only thing to do here is just to re-interpret the latter non-causal scheme in a causal manner by restricting the range of auxiliary random variables appearing in non-causal encoding to a subclass of auxiliary random variables for the causal encoder. This technique is referred to as “plugging.” Then, we are able to dispense with the block-Markov encoding scheme used in the previous works by Chia and El Gamal, Fujita, and Han and Sasaki and then extend all the known results on achievable rates. The other main results include the exact SM-SK capacity region for WTCs with non-causal CSI at “both” Alice and Bob (Theorem 2), a “tighter” causal SM-SK outer bound for state-reproducing coding schemes with CSI at Alice (Proposition 4), and the exact SM-SK capacity region for degraded WTCs with causal/non-causal CSI at both Alice and Bob (Theorem 4).

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 (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 (Theorems 2, 4, and 5).

The coding problem for wiretap channels with causal state information available at the encoder is studied. In particular, we address the wiretap channel only with one-time state information (instead of the usual causal state information up to present) in the sense that the one-time encoder uses only the current state information Sk at each time k to establish the secrecy capacity formula under the δ-strong secrecy criterion. The coding problem for wiretap channels with one-time channel state information available at the encoder under cost constraints is also studied and lower bounds on the “δ-strong” secrecy capacity given cost are also demonstrated.

The amount of digital data that requires long-term protection of integrity, authenticity, and confidentiality grows rapidly. Examples include electronic health records, genome data, and tax data. In this paper we present the secure storage system LINCOS, which provides protection of integrity, authenticity, and confidentiality in the long-term, i.e., for an indefinite time period. It is the first such system. It uses the long-term integrity scheme COPRIS, which is also presented here and is the first such scheme that does not leak any information about the protected data. COPRIS uses information-theoretic hiding commitments for confidentiality-preserving integrity and authenticity protection. LINCOS uses proactive secret sharing for confidential storage of secret data. We also present implementations of COPRIS and LINCOS. A special feature of our LINCOS implementation is the use of quantum key distribution and one-time pad encryption for information-theoretic private channels within the proactive secret sharing protocol. The technological platform for this is the Tokyo QKD Network, which is one of worlds most advanced networks of its kind. Our experimental evaluation establishes the feasibility of LINCOS and shows that in view of the expected progress in quantum communication technology, LINCOS is a promising solution for protecting very sensitive data in the cloud.

The wiretap channel has been devised and studied first by Wyner, and subsequently extended to the case with nondegraded general wiretap channels by Csiszár and Körner. Focusing mainly on the stationary memoryless channel with cost constraint, we newly introduce the notion of reliability and secrecy functions as a fundamental tool to analyze and/or design the performance of an efficient wiretap channel system, including binary symmetric wiretap channels, Poisson wiretap channels, and Gaussian wiretap channels. Compact formulas for those functions are explicitly given for stationary memoryless wiretap channels. It is also demonstrated that, based on such a pair of reliability and secrecy functions, we can control the tradeoff between reliability and secrecy (usually conflicting), both with exponentially decreasing rates as block length \(n\) becomes large. Four ways to do so are given on the basis of rate shifting, rate exchange, concatenation, and change of cost constraint. In addition, the notion of the \(\delta \) secrecy capacity is defined and shown to attain the strongest secrecy standard among others. The maximized versus averaged secrecy measures is also discussed.

We numerically evaluate the wavelength division multiplexing (WDM) data transmission of coherent phase-shift keying (PSK) and quadrature amplitude modulation (QAM) signals in optical fiber communication and deep-space communication channels with conventional homodyne-based(dyne-type) detections and various quantum detection strategies. We show the quantitative gap between these detection strategies and especially in the quantum-limited region where the quantum noise seriously limits the transmission rate. For an extremely weak signal input power, there is a crucial gap between the capacity limit and the transmission rates of the WDM system with dyne-type detections. We show that this gap is filled by applying a collective square root detection (SRD) only for each channel, not necessary for quantum collective decoding among WDM channels.

We analyze the performance of the error probability and the mutual information for quadrature amplitude modulation (QAM) and phase-shift keying systems based on quantum detection theory. It is shown that the quantum receiver called square root measurement gives about 5.7 dB improvement in power in comparison with the classical one. Furthermore, we show that the quantum QAM system can achieve the same reliability as the conventional intensity modulation-direct detection (IM-DD) system with almost equal power, compressing the required bandwidth, while the reliability is degraded in general.