The physical-layer security of a quantum-noise randomized cipher (QNRC) system is, for the first time, quantitatively evaluated with secrecy capacity employed as the performance metric. Considering quantum noise as a channel advantage for legitimate parties over eavesdroppers, the specific wire-tap models for both channels of the key and data are built with channel outputs yielded by quantum heterodyne measurement; the general expressions of secrecy capacities for both channels are derived, where the matching codes are proved to be uniformly distributed. The maximal achievable secrecy rate of the system is proposed, under which secrecy of both the key and data is guaranteed. The influences of various system parameters on secrecy capacities are assessed in detail. The results indicate that QNRC combined with proper channel codes is a promising framework of secure communication for long distance with high speed, which can be orders of magnitude higher than the perfect secrecy rates of other encryption systems. Even if the eavesdropper intercepts more signal power than the legitimate receiver, secure communication (up to Gb/s) can still be achievable. Moreover, the secrecy of running key is found to be the main constraint to the systemic maximal secrecy rate.
The physical-layer security of a quantum-noise randomized cipher (QNRC) system is, for the first time, quantitatively evaluated with secrecy capacity employed as the performance metric. Considering quantum noise as a channel advantage for legitimate parties over eavesdroppers, the specific wire-tap models for both channels of the key and data are built with channel outputs yielded by quantum heterodyne measurement; the general expressions of secrecy capacities for both channels are derived, where the matching codes are proved to be uniformly distributed. The maximal achievable secrecy rate of the system is proposed, under which secrecy of both the key and data is guaranteed. The influences of various system parameters on secrecy capacities are assessed in detail. The results indicate that QNRC combined with proper channel codes is a promising framework of secure communication for long distance with high speed, which can be orders of magnitude higher than the perfect secrecy rates of other encryption systems. Even if the eavesdropper intercepts more signal power than the legitimate receiver, secure communication (up to Gb/s) can still be achievable. Moreover, the secrecy of running key is found to be the main constraint to the systemic maximal secrecy rate.
Applying the quadrature amplitude modulation (QAM) format, quantum-noise randomized cipher (QNRC) systems hide the signal states in quantum phase noise and amplitude noise to prevent eavesdropping. In this paper, based on the traditional wire-tap channel model analysis method, the physical-layer security of QAM-QNRC system is investigated quantitatively under the metric of secrecy rate. The general expressions of secrecy rates of the data and key are derived separately. Furthermore, the maximum reachable secrecy rate of a QAM-QNRC system is put forward, under which the data and key are both safe in the view of mutual information evaluation. Finally, the variation trend of secrecy rate with various system parameters is discussed in detail. The simulation results show that we can obtain a higher secrecy rate by setting reasonable parameters, such as the level of ciphertext, mesoscopic signal power, and inner gain at the transmitter. Meanwhile, the security of the key is the main constraint of the maximum reachable secrecy rate.
The inherent openness of wireless medium makes information security one of the most important and difficult problems in wireless networks.Physical layer security, which achieves the information-theoretic security by exploiting the differences between the physical properties of signal channels such that a degraded signal at an eavesdropper is always ensured and thus the original data can be hardly recovered regardless of how the signal is processed at the eavesdropper, has been studied as a promising approach to providing a strong form of security.By now, many research works have been devoted to understand the fundamental performance limits of physical layer security under different wire-tap channel models.It is notable that among different wire-tap channel models, the fading channel model has been an important model to efficiently capture the basic time-varying properties of wireless channels.Available works related to physical layer security study of the fading wire-tap channel are mainly based on the assumption that the channel from a transmitter to a legitimate receiver is independent of the one from the transmitter to an eavesdropper.In practice, however, the correlation among channels from a transmitter to different receivers has been frequently observed.Therefore, understanding the performance of physical layer security under the more practical correlated fading channels is of great importance for practical applications of physical layer security in wireless networks.In this thesis, we aim to provide a comprehensive study on the fundamental performance limits of physical layer security under a fading wire-tap channel, where the channel from transmitter to legitimate receiver is correlated with the one from transmitter to eavesdropper.We start the study from the scenario when the transmission power is asymptotically infinite.In particular, we first provide an informationtheoretic formulation of secure transmission over wireless fading channels at one realization of coherence interval in the high transmission power regime and show that the secrecy capacity is limited by the channel gain ratio of the main and eavesdropper channels rather than the transmission power, which is different from the Shannon's capacity that increases with transmission power.We next characterize the asymptotic outage probability and also asymptotic outage secrecy capacity for the correlated fading wire-tap channel as the transmission power goes to infinity.We then analyze the performance of physical layer security under correlated fading wire-tap channel with a limited transmission power, a more complicate scenario compared with the one with asymptotic-infinite power.Specifically, we provide theoretical modeling for the secrecy capacity, transmission outage probability and secrecy outage probability of such systems.In particular, we first derive a simple closedform expression of secrecy capacity based on the typical Marcum Q function.This is achieved by exploring the symmetry property between the main channel and eavesdropper channel such that some complicated integration operations involved in the secrecy capacity analysis can be significantly simplified.We then derive the transmission outage probability and secrecy outage probability to depict the reliability and security performances of the concerned wire-tap channel.Finally, extensive numerical results are provided to illustrate the inherent performance tradeoffs under i I am truly and deeply indebted to so many people that there is no way to acknowledge them all, or even any of them properly.Without their support, help and encouragement, this work would not and could not haven been done.I extend my deepest gratitude to all.
With the advent of quantum key distribution (QKD) systems, perfect (i.e. information-theoretic) security can now be achieved for distribution of a cryptographic key. QKD systems and similar protocols use classical error-correcting codes for both error correction (for the honest parties to correct errors) and privacy amplification (to make an eavesdropper fully ignorant). From a coding perspective, a good model for such a setting is the wire tap channel system introduced by Wyner in 1975. In this paper, we study fundamental limits and coding methods for wire tap channel systems. We provide a novel proof for the secrecy capacity theorem for wire tap channels and show how capacity achieving codes can be used to achieve the secrecy capacity for any wiretap channel. We also consider binary erasure channel and binary symmetric channel special cases for the wiretap channel system and propose specific practical codes. In some cases our designs achieve the secrecy capacity and in others the codes provide complete security at rates below secrecy capacity in some specific cases.
In physical-layer security, communication secrecy is commonly achieved by providing the legitimate receiver a physical-layer advantage over the eavesdropper or, equivalently, by making the eavesdropper's channel more degraded than the legitimate receiver's, a setting traditionally known as the degraded wiretap channel. There may be situations, however, where such advantages cannot be guaranteed. One example is the wireless channel where the legitimate receiver's channel may be more degraded than the eavesdropper's owing to a deep fade (outage), additive interference at the edge of a network cell, etc. To our knowledge, such scenarios have not been remedied in the related literature. Thus, we propose in this work the first physical-layer security scheme that achieves communication in a setting where the eavesdropper has the physical-layer advantage over the legitimate receiver, a scenario that we call the reversely-degraded wiretap channel. Precisely, we show that by constraining the transmitter's input to be discrete uniformly distributed (such as an on-off keying modulation) and by using nonlinear threshold-based signal detection, the legitimate receiver is guaranteed to have a positive secrecy capacity even though the eavesdropper has a better signal-to-noise ratio (SNR). The former requirement on the input distribution is to limit the capacity gains of the eavesdropper at high SNR. The latter requirement allows the communication channel to exhibit supra-threshold stochastic resonance, a phenomenon whereby noise improves signal detection and increases the mutual information. A numerical example is provided to confirm our claims.
Quantum-noise randomized cipher (QNRC) is an anti-interception communication technology, which can realize high-speed encryption for data stream in true randomness. In this paper, the characteristics of the phase shift keying (PSK) and quadrature phase shift keying(QPSK) QNRC systems are verified by the simulation system with digital coherent demodulation. The decryption process of the QNRC coherent system is carried out in the optical domain for the first time. Specifically, at the quadrature coupler, the modulated local light is coupled with the received encrypted optical signal. The multi-symbol phase estimation(MSPE) module is employed to eliminate the influence of the phase deviation on the signal decision. Finally, error-free secure transmission is realized at 2.5Gsymbol/s over 500km optically amplified links. We reveal the new fact that the mesoscopic power of QPSK-QNRC system is higher than that of PSK-QNRC system.
With the advent of quantum key distribution (QKD) systems, perfect (i.e. information-theoretic) security can now be achieved for distribution of a cryptographic key. QKD systems and similar protocols use classical errorcorrecting codes for both error correction (for the honest p arties to correct errors) and privacy amplification (to make an eavesdropper fully ignorant). From a coding perspective, a good model for such a setting is the wire tap channel introduced by Wyner in 1975. In this paper, we study fundamental limits and coding methods for wire tap channels. We provide a novel proof for the secrecy capacity theorem for wire tap channels and show how capacity achieving codes can be used to achieve the secrecy capacity for any wiretap channel. We also consider binary erasure channel and binary symmetric channel special cases for the wiretap channel and propose specific practical codes. In some cases our designs achieve the secrecy capacity and in others the codes provide complete security at rates below secrecy capacity in some specific cases.