In this paper, we investigate the application of Reed-Muller (RM) codes for Physical-layer security in a real world wiretap channel scenario. Utilizing software-defined radios (SDRs) in a real indoor environment, we implement a coset coding scheme that leverages the hierarchical structure of RM codes to secure data transmission. The generator matrix of the RM code is used to partition codewords into cosets in the usual way, where each message corresponds to a unique coset, and auxiliary bits select specific codewords within each coset. This approach enables the legitimate receiver (Bob) can decode the transmitted message with minimal information leakage to eavesdropper (Eve) thus protecting the confidentiality of the communication with the help of coset structure. Mutual information neural estimation (MINE) is used to quantify information leakage and validate the effectiveness of the scheme. Experimental results indicate that RM codes can achieve robust security even in practical environments affected by real-world channel impairments. These findings demonstrate the potential of RM codes as an efficient solution for physical-layer security, particularly for applications that require low latency and short blocklengths.
In this paper, we investigate the application of Reed-Muller (RM) codes for Physical-layer security in a real world wiretap channel scenario. Utilizing software-defined radios (SDRs) in a real indoor environment, we implement a coset coding scheme that leverages the hierarchical structure of RM codes to secure data transmission. The generator matrix of the RM code is used to partition codewords into cosets in the usual way, where each message corresponds to a unique coset, and auxiliary bits select specific codewords within each coset. This approach enables the legitimate receiver (Bob) can decode the transmitted message with minimal information leakage to eavesdropper (Eve) thus protecting the confidentiality of the communication with the help of coset structure. Mutual information neural estimation (MINE) is used to quantify information leakage and validate the effectiveness of the scheme. Experimental results indicate that RM codes can achieve robust security even in practical environments affected by real-world channel impairments. These findings demonstrate the potential of RM codes as an efficient solution for physical-layer security, particularly for applications that require low latency and short blocklengths.
Physical-layer security uses the noise already present in the channel to keep a message secret without making any assumption about the eavesdropper's computing power. In Wyner's wiretap channel model, coset coding uses randomness to map the message to many codewords and protects against information leakage from an active eavesdropper. The secrecy provided by such codes is measured by their equivocation, which is the eavesdropper's remaining uncertainty about the message after she observes her channel. So computing equivocation is an important aspect of analyzing the wiretap channel model. Many channels of practical interest have no closed-form expression for equivocation, and exact calculation has been limited to a few specific channels. This dissertation studies the equivocation analysis of coset codes along two complementary directions. When a channel offers no closed-form solution, we estimate the information leakage with a neural network called the mutual information neural estimator (MINE). And for a discrete memoryless channel, we derive a general framework for the exact equivocation. The first study builds coset codes from short Reed-Muller codes and tests them over the air in a real indoor environment with software-defined radios. In this study, the secrecy is estimated using MINE, and short coset codes are shown to provide a secrecy advantage. The second study proposes a low-density parity-check (LDPC) code that injects artificial noise by flipping a chosen set of coded bits over a Gaussian wiretap channel. The third study moves from estimation to exact analysis. It examines coset coding over the Ghost Modulation wiretap channel, which is modeled as an asymmetric binary crossover erasure channel (ABCEC). Then it derives exact expressions for both the equivocation and the secrecy capacity. The final study generalizes the exact analysis to any discrete memoryless channel and verifies the framework against well-studied channels. Finally, it applies the developed framework to the asymmetric Z-channel with an efficient formulation that greatly reduces the computational cost.
Practical codes for the Gaussian wiretap channel are designed aiming at satisfying information-theoretic metrics to ensure security against a passive eavesdropper (Eve). Specifically, a design criterion is introduced for the coset coding scheme in order to satisfy a strong secrecy condition described with the mutual information between the secret message and Eve's observation. In addition, mutual information neural estimation (MINE) powered from deep learning tools is applied in order to directly compute the information-theoretic security constraint, and verify the proposed solutions. It is shown that finite-length coset codes can indeed ensure secure transmission from an information-theoretic perspective.
This paper applies channel sounding measurements to enable physical-layer security coding. The channel measurements were acquired in an indoor environment and used to assess the secrecy capacity as a function of physical location. A variety of Reed-Muller wiretap codes were applied to the channel measurements to determine the most effective code for the environment. The results suggest that deploying physical-layer security coding is a three-point design process, where channel sounding data guides 1) the physical placement of the antennas, 2) the power settings of the transmitter, and 3) the selection of wiretap coding.
In this work, we consider the pros and cons of using various layers of keyless coding to achieve secure and reliable communication over the Gaussian wiretap channel. We define a new approach to information theoretic security, called practical secrecy and the secrecy benefit, to be used over real-world channels and finite blocklength instantiations of coding layers, and use this new approach to show the fundamental reliability and security implications of several coding mechanisms that have traditionally been used for physical-layer security. We perform a systematic/structured analysis of the effect of error-control coding, scrambling, interleaving, and coset coding, as coding layers of a secrecy system. Using this new approach, scrambling and interleaving are shown to be of no effect in increasing information theoretic security, even when measuring the effect at the output of the eavesdropper's decoder. Error control coding is shown to present a trade-off between secrecy and reliability that is dictated by the chosen code and the signal-to-noise ratios at the legitimate and eavesdropping receivers. Finally, the benefits of secrecy coding are highlighted, and it is shown how one can shape the secrecy benefit according to system specifications using combinations of different layers of coding to achieve both reliable and secure throughput.
Visible light communication (VLC) can provide short-range optical wireless communication together with illumination using LED lightings. Since VLC channel is an open wireless channel, physical-layer security is desirable in order to hide secret information from unauthorized receivers, without reliance on upper-layer cryptographic techniques. In this paper, a secure coding scheme based on polar codes is proposed to simultaneously achieve physical-layer security and transmission reliability for indoor VLC systems under Wyner's wiretap model. An indoor VLC degraded wiretap channel model and an indoor VLC undegraded wiretap model are analyzed to estimate the corresponding secrecy capacity with typical indoor VLC scenarios considering the requirements of illumination and reliable transmission. Then, a physical-layer secure coding scheme and an enhanced scheme are designed to provide securely reliable communication without sacrificing the illumination functionality. Numerical results show that for VLC degraded wiretap channel, the proposed coding scheme can reduce the bit error rate (BER) of main channel to nearly 0 and increase that of wiretap channel to 0.5. Therefore, the mutual information between the sender and the eavesdropper and the BER of the legitimate receiver are both decreased to nearly 0. Both the security and reliability of VLC are guaranteed by the proposed coding scheme. And the practical secrecy rate reaches 85.96% at some positions when codeword length is 2 048 bits. Furthermore, an enhanced coding scheme with a feedback channel is proposed to handle the case that the wiretap channel is not degraded with respect to the main channel. With the feedback channel, the wiretap channel can be equivalently degraded and the security can be increased gradually with the increment of the degradation level of the wiretap channel. Meanwhile, the secrecy capacities can be asymptotically achieved for indoor VLC systems.
Secure communication under channel uncertainty is an important and challenging problem in physical-layer security and cryptography. In this dissertation, we take a \nfundamental information-theoretic view at three concrete settings and use them to shed insight into efficient secure communication techniques for different scenarios under channel uncertainty. \n \nFirst, a multi-input multi-output (MIMO) Gaussian broadcast channel with two receivers and two messages: a common message intended for both receivers (i.e., channel \nuncertainty for decoding the common message at the receivers) and a confidential message intended for one of the receivers but needing to be kept asymptotically perfectly secret from the other is considered. A matrix characterization of the secrecy capacity region is established via a channel-enhancement argument and an extremal entropy inequality previously established for characterizing the capacity region of a degraded compound MIMO Gaussian broadcast channel. \n \nSecond, a multilevel security wiretap channel where there is one possible realization for the legitimate receiver channel but multiple possible realizations for the eavesdropper channel (i.e., channel uncertainty at the eavesdropper) is considered. A coding scheme is designed such that the number of secure bits delivered to the legitimate receiver depends on the actual realization of the eavesdropper channel. More specifically, when the eavesdropper channel realization is weak, all bits delivered to the legitimate receiver need to be secure. In addition, when the eavesdropper channel realization is strong, a prescribed part of the bits needs to remain secure. We call such codes security embedding codes, referring to the fact that high-security bits are now embedded into the low-security ones. We show that the key to achieving efficient security embedding is to jointly encode the low-security and high-security bits. In particular, the low-security bits can be used as (part of) the transmitter randomness to protect the high-security ones. \n \nFinally, motivated by the recent interest in building secure, robust and efficient distributed information storage systems, the problem of secure symmetrical multilevel diversity coding (S-SMDC) is considered. This is a setting where there are channel uncertainties at both the legitimate receiver and the eavesdropper. The problem of encoding individual sources is first studied. A precise characterization of the entire admissible rate region is established via a connection to the problem of secure coding over a three-layer wiretap network and utilizing some basic polyhedral structure of the admissible rate region. Building on this result, it is then shown that the simple coding strategy of separately encoding individual sources at the encoders can achieve the minimum sum rate for the general S-SMDC problem.