Recent developments in the field of space-division multiplexing (SDM) for fiber-optic communication systems suggest that the spatial diversity offered by SDM can be used not only to increase system capacity, but also to achieve provable security against physical layer attacks. We examine the information-theoretic security of SDM with a focus on frequency-selective and rapidly-varying frequency-flat channels. We analytically evaluate the outage-free secrecy capacity - the maximal data rate that guarantees perfect security within a class of channel realizations. Using analysis and simulations, we evaluate the impact of key system parameters on the secrecy capacity of SDM systems. Our results show that, with a proper code design that balances the trade-off between data rate and confidentiality, we can take full advantage of SDM to offer a secure information rate that could be orders of magnitude higher than what can be achieved through quantum key distribution (QKD).
Recent developments in the field of space-division multiplexing (SDM) for fiber-optic communication systems suggest that the spatial diversity offered by SDM can be used not only to increase system capacity, but also to achieve provable security against physical layer attacks. We examine the information-theoretic security of SDM with a focus on frequency-selective and rapidly-varying frequency-flat channels. We analytically evaluate the outage-free secrecy capacity - the maximal data rate that guarantees perfect security within a class of channel realizations. Using analysis and simulations, we evaluate the impact of key system parameters on the secrecy capacity of SDM systems. Our results show that, with a proper code design that balances the trade-off between data rate and confidentiality, we can take full advantage of SDM to offer a secure information rate that could be orders of magnitude higher than what can be achieved through quantum key distribution (QKD).
Space-division multiplexed (SDM) fiber optic transmission systems can not only increase system capacity, but also achieve physical-layer security against fiber tapping attacks. In this paper, we examine the information-theoretic security of optical multiple-input-multiple-output (MIMO) SDM by evaluating the tradeoff between the achievable information rate and the confidentiality for different channel dynamics. In particular, we provide problem formulations for secure communication over these channels and study three types of secrecy capacities: 1) guaranteed capacity; 2) outage capacity; and 3) average capacity, each serving as a performance metric for a coding strategy tailored to a specific type of MIMO-SDM channel. We also assess the impact of key system parameters, such as the number of modes, the mode-dependent loss (MDL), and the signal-to-noise ratio (SNR), on the various secrecy capacities. Our results indicate that, with a proper design of channel codes that balance information rate and security, an SDM system has the potential of offering confidential data transmission at a rate that could be orders of magnitude higher than what can be achieved through other means of encryption. Moreover, we show that MDL, unavoidably induced by fiber tapping, can allow information-theoretic security even if the SNR of the eavesdropper's receiver is better than that of the legitimate receiver.
Recent developments in the field of space-division multiplexing (SDM) for fiber-optic communication systems suggest that the spatial diversity offered by SDMcan be used not only to increase system capacity, but also to achieve provable security against physical layer attacks. In this work, we outline some of the mathematical framework necessary to assess the security benefits of the SDM. We substantiate our conjecture that allocating the maximal allowable power to each mode is optimal in terms of physical layer security. Further more, we expand the scope of our security analyses to include distortion as a quantitative metric for secrecy and study how the rate of reliable communication between the legitimate transmitter-receiver pair can be chosen to maximize reconstruction (decoding) errors of the eavesdropper.
In this paper, we examine the information-theoretic security of multiple-input-multiple-output space-division multiplexed (MIMO-SDM) fiber-optic communication systems in the presence of multiple eavesdroppers. In particular, we analyze the achievable secrecy rate for the two special cases that reflect different capabilities of the eavesdroppers: independent eavesdroppers who do not share received information and colluding (cooperating) eavesdroppers who can combine and jointly process the received signals. Our results show that MIMO-SDM systems are robust against multiple independent tapping attacks, in the sense that the average achievable secrecy rate is strictly positive even with an infinite number of eavesdroppers. Though extremely difficult to implement in practice, if all the eavesdroppers could cooperate coherently, the average secrecy rate decreases quickly with the number of eavesdroppers. As such, to counter the colluding eavesdroppers, a combination of much higher SNR for the legitimate receiver and higher mode-dependent loss (MDL) for the eavesdroppers is needed.
On the one hand, Quantum key distribution (QKD) offers unparalleled security relying on the principles of quantum mechanics. On the other hand, space division multiplexing (SDM) is recognized as the route toward a capacity upgrade for current core optical communication networks and will progressively permeate into shorter-reach networks. Incorporating QKD into classical networks, with SDM being one of its components, will enhance data communication security. Understanding the security implications of implementing QKD over SDM is crucial for the practical deployment of quantum-secure communication technologies, especially in scenarios where high data capacity and multiplexing techniques are essential. In this paper, we study a QKD eavesdropping use case where connectivity is provided via SDM fibers. Specifically, we discuss the detector blinding attack (DBA) concerning inter-core crosstalk in an entanglement based QKD system. Additionally, we analyze the blinding power of DBA over quasi-homogeneous and heterogeneous seven-core fiber scenarios. Furthermore, the potential countermeasures to mitigate the impact of such attacks are discussed.
In this paper, we examine the information-theoretic security of multiple-input-multiple-output space-division multiplexed (MIMO-SDM) fiber-optic communication systems in the presence of multiple eavesdroppers. In particular, we analyze the achievable secrecy rate for the two special cases that reflect different capabilities of the eavesdroppers: independent eavesdroppers who do not share received information and colluding (cooperating) eavesdroppers who can combine and jointly process the received signals. Our results show that MIMO-SDM systems are robust against multiple independent tapping attacks, in the sense that the average achievable secrecy rate is strictly positive even with an infinite number of eavesdroppers. Though extremely difficult to implement in practice, if all the eavesdroppers could cooperate coherently, the average secrecy rate decreases quickly with the number of eavesdroppers. As such, to counter the colluding eavesdroppers, a combination of much higher SNR for the legitimate receiver and higher mode-dependent loss (MDL) for the eavesdroppers is needed.
Free-space optical (FSO) communication provides a promising alternative solution to the traditional radio frequency (RF) communications. Compared to the RF technology, there are many advantages of FSO communications, such as ultra-high bandwidth, license-free spectrum, low inter-channel interference, and energy-efficient transmission. The potential applications for FSO communication include the last-one-mile access link from the fiber-based backbone network, low earth orbit (LEO) satellite communications, high-altitude base station platforms or vehicles, deep-space communications, and in-building automation connections. As the FSO technology becomes mature and increasingly involved, the security and reliability requirements of such applications also become crucial. Regarding the security issues, although the FSO communication is inherently more secure than the RF counterpart due to high directivity of its line-of-sight (LOS) link, it can still suffer from optical wire-tapping attack. There are many different application schemes that an eavesdropper can still probe the FSO link. Traditionally, to protect the communication, many works have been done on encryption layer and upper network layer, such as computationally intensive cryptographic algorithms and message exchanging protocols. In recent years, physical-layer security (PLS) has been getting more attentions as it provides an extra layer of security against eavesdropping. The PLS schemes, in general can be categorized into two main categories: classical PLS and quantum key distribution (QKD) protocols. The classical PLS is based on the information theoretic security analysis, while the QKD security is guaranteed by the quantum mechanics laws. Both techniques have been studied for FSO channels. In the first half of this dissertation, we study the PLS in a LOS FSO channel using orbital angular momentum (OAM) multiplexing and show that higher secrecy capacity can be achieved using OAM multiplexing technology in the presence of atmospheric turbulence effects. Then, we proposed an adaptation scheme for QKD system over FSO channel with different QKD protocols, i.e. BB84 and decoy state protocols. By adapting the source brightness based on the channel condition, we optimized the secret key rate (SKR) of the QKD system. Furthermore, we proposed a multiple spatial modes-based QKD system with backpropagation method to increase the total SKR through parallel channels. Regarding the reliability of an optical communication system as well as information reconciliation for both PLS and QKD schemes, the forward error correction (FEC) becomes an essential technique to enable high-speed transmission. The FEC with low-density parity-check (LDPC) codes has been studied for decades from LDPC block codes to the most recent spatially-coupled (SC) LDPC codes. For FSO communications, due to the time-varying nature of FSO channels, the capability of rate adaptation is important to achieve a consistent reliable transmission. In the second half of this dissertation, we proposed unified FPGA-based architecture to implement both quasi-cyclic (QC) LDPC codes and SC-LDPC codes with rate adaptation capability. The performance is verified through FPGA emulation to show good error floor properties. To further validate the rate adaptation capability, we have built a spatial light modulator (SLM)-based FSO channel emulator to test the adaptive coding scheme. Furthermore, we have conducted a fiber-based experiment with our rate adaptative coding scheme to show that the proposed adaptive coding scheme can be also used in dynamic fiber-based networks.