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1. The Secrecy Capacity of Cost-constrained Wiretap Channels

   https://doi.org/10.1109/TIT.2020.3039916  

   Sreekumar, Sreejith; Bunin, Alexander; Goldfeld, Ziv; Permuter, Haim (January 2022, IEEE transactions on information theory)

   In many information-theoretic channel coding problems, adding an input cost constraint to the operational setup amounts to restricting the optimization domain in the capacity formula. This paper shows that, in contrast to common belief, such a simple modification does not hold for the cost-constrained (CC) wiretap channel (WTC). The secrecy-capacity of the discrete memoryless (DM) WTC without cost constraints is described by a single auxiliary random variable. For the CC DM-WTC, however, we show that two auxiliaries are necessary to achieve capacity. Specifically, we first derive the secrecy-capacity formula, proving the direct part via superposition coding. Then, we provide an example of a CC DM-WTC whose secrecy-capacity cannot be achieved using a single auxiliary. This establishes the fundamental role of superposition coding over CC WTCs. 

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2. Soft-covering via Constant-composition Superposition codes

   https://doi.org/10.1109/ISIT45174.2021.9518258  

   Sreekumar, Sreejith; Goldfeld, Ziv (January 2021, Proceedings of the IEEE International Symposium on Information Theory (ISIT))

   We consider the problem of soft-covering with constant composition superposition codes and characterize the optimal soft-covering exponent. A double-exponential concentration bound for deviation of the exponent from its mean is also established. We demonstrate an application of the result to achieving the secrecy-capacity region of a broadcast channel with confidential messages under a per-codeword cost constraint. This generalizes the recent characterization of the wiretap channel secrecy-capacity under an average cost constraint, highlighting the potential utility of the superposition soft-covering result to the analysis of coding problems. 

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3. Secure computation of linear functions over linear discrete multiple-access wiretap channels

   https://doi.org/10.1109/ACSSC.2016.7869665  

   Goldenbaum, Mario; Boche, Holger; Poor, H. Vincent (November 2016, Proceedings of the 50th Annual Asilomar Conference on Signals, Systems, and Computers)

   In this paper, a joint source-channel coding approach is taken to the problem of securely computing a function of distributed sources over a multiple-access wiretap channel that is linear with respect to a finite field. It is shown that if the joint source distribution fulfills certain conditions and the function to be computed matches the linear structure of the channel, secrecy comes for free in the sense that the fundamental limit (i.e., the secrecy computation-capacity) is achieved without the need for stochastic encoding. Furthermore, the legitimate receiver does not need any advantage over the eavesdropper, which is in stark contrast to standard physical-layer security results. 

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4. Physical Layer Security: Channel Sounding Results for the Multi-Antenna Wiretap Channel

   https://doi.org/10.3390/e25101397  

   Harman, Daniel; Knapp, Karl; Sweat, Tyler; Lundrigan, Philip; Rice, Michael; Harrison, Willie (October 2023, Entropy)

   Many physical-layer security works in the literature rely on purely theoretical work or simulated results to establish the value of physical-layer security in securing communications. We consider the secrecy capacity of a wireless Gaussian wiretap channel using channel sounding measurements to analyze the potential for secure communication in a real-world scenario. A multi-input, multi-output, multi-eavesdropper (MIMOME) system is deployed using orthogonal frequency division multiplexing (OFDM) over an 802.11n wireless network. Channel state information (CSI) measurements were taken in an indoor environment to analyze time-varying scenarios and spatial variations. It is shown that secrecy capacity is highly affected by environmental changes, such as foot traffic, network congestion, and propagation characteristics of the physical environment. We also present a numerical method for calculating MIMOME secrecy capacity in general and comment on the use of OFDM with regard to calculating secrecy capacity. 

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5. On the Duality Between the BSC and Quantum PSC

   https://doi.org/10.1109/ISIT45174.2021.9518034  

   Rengaswamy, Narayanan; Pfister, Henry D. (July 2021, 2021 IEEE International Symposium on Information Theory (ISIT))

   null (Ed.)

   In 2018, Renes [IEEE Trans. Inf. Theory, vol. 64, no. 1, pp. 577-592 (2018)] developed a general theory of channel duality for classical-input quantum-output channels. His result shows that a number of well-known duality results for linear codes on the binary erasure channel can be extended to general classical channels at the expense of using dual problems which are intrinsically quantum mechanical. One special case of this duality is a connection between coding for error correction on the quantum pure-state channel (PSC) and coding for wiretap secrecy on the classical binary symmetric channel (BSC). Similarly, coding for error correction on the BSC is related to wire-tap secrecy on the PSC. While this result has important implications for classical coding, the machinery behind the general duality result is rather challenging for researchers without a strong background in quantum information theory. In this work, we leverage prior results for linear codes on PSCs to give an alternate derivation of the aforementioned special case by computing closed-form expressions for the performance metrics. The noted prior results include the optimality of square-root measurement for linear codes on the PSC and the Fourier duality of linear codes. 

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