We examine security of a protocol on cryptographic key distribution via classical noise proposed by Yuen and Kim (Phys. Lett. A 241 135 (1998)). Theoretical and experimental analysis in terms of the secure key distribution rate shows that secure key distribution is possible even if the eavesdropper could receive more photons than the legitimate receiver, as long as the signal-to-noise-ratio (SNR) of the receiver is better than -9dB of the eavesdropper's SNR. Secure key distribution was demonstrated at the maximum rate of 0.04 bit per sender's bit and transmission rate of 2 Mb/s in the experiment employing conventional fiber optics. The present protocol has advantages of the efficient key distribution and the simple implementation over other quantum key distribution protocols. However, careful design and management are necessary to keep the security of the crypto-system.
We examine security of a protocol on cryptographic key distribution via classical noise proposed by Yuen and Kim (Phys. Lett. A 241 135 (1998)). Theoretical and experimental analysis in terms of the secure key distribution rate shows that secure key distribution is possible even if the eavesdropper could receive more photons than the legitimate receiver, as long as the signal-to-noise-ratio (SNR) of the receiver is better than -9dB of the eavesdropper's SNR. Secure key distribution was demonstrated at the maximum rate of 0.04 bit per sender's bit and transmission rate of 2 Mb/s in the experiment employing conventional fiber optics. The present protocol has advantages of the efficient key distribution and the simple implementation over other quantum key distribution protocols. However, careful design and management are necessary to keep the security of the crypto-system.
We examine security of a protocol on cryptographic key distribution viaclassical noise proposed by Yuen and Kim (Phys. Lett. A 241 135 (1998)).Theoretical and experimental analysis in terms of the secure key distributionrate shows that secure key distribution is possible even if the eavesdroppercould receive more photons than the legitimate receiver, as long as thesignal-to-noise-ratio (SNR) of the receiver is better than -9dB of theeavesdropper's SNR. Secure key distribution was demonstrated at the maximumrate of 0.04 bit per sender's bit and transmission rate of 2 Mb/s in theexperiment employing conventional fiber optics. The present protocol hasadvantages of the efficient key distribution and the simple implementation overother quantum key distribution protocols. However, careful design andmanagement are necessary to keep the security of the crypto-system.
Abstract Cryptography is a scientific method that is used to transmit secret information. In contrast, quantum cryptography depends on physical laws to encrypt information; when the quantum computer appeared, the classic encryption method becomes inefficient. The quantum method is commonly used to distribute keys, a process called as quantum key distribution (QKD). In this paper, we consider the efficiency of the quantum method compared to classical methods. Also, we discuss the security of QKD against several attacks and provide security analysis based on probabilistic models. Additionally, the paper explains how to encrypt random numbers into a sequence of photons using a QKD system for the distribution of a key. This research demonstrates the efficiency and security of QKD in sending and distributing keys between communication parties. Thus, both the sender and the receiver would be able to obtain a security key using the quantum method rather than classical methods.
In fiber-optic communication networks, research on data security at lower layers of the protocol stack and in particular at the physical layer by means of information-theoretic concepts is only in the beginning. Nevertheless, it has recently attracted quite some attention as it holds the promise of providing unconditional, perfect security without the need for secret key exchanges. In this paper, we analyze some important constraints that such concepts put on a potential implementation of physical-layer security. We review the fundamentals of physical-layer security on the basis of the commonly used AWGN wiretap channel model. For such channel model we summarize the security metrics which are typically used in information theory and in particular recall that, for secure communication over the AWGN channel, the legitimate receiver needs an SNR advantage over the eavesdropper. Next, we relate the information theoretic metrics to physically measurable quantities in optical communications engineering, namely optical signal-to-noise ratio (OSNR) and bit-error ratio (BER), and translate the information-theoretic wiretap scenario to a simple real-world point-to-point optical transmission link in which part of the light is wiretapped using a bend coupler. We investigate the achievable OSNR advantage under realistic assumptions for fiber loss, tap ratio, and noise budget and find that secure transmission is limited to a distance of a few tens of kilometers in this case. The maximum secure transmission distance decreases with an increasing tap ratio chosen by the eavesdropper. This can be only counteracted by monitoring the link loss towards the legitimate receiver which would force the eavesdropper to choose small tap ratios in order to remain undetected. In an outlook towards further research directions we identify information-theoretic approaches which could potentially allow to realize physical-layer security in more generalized scenarios or over longer distances.
Quantum cryptography was designed to provide a new approach to the problem of distributing keys for private-key cryptography. The principal idea is that security can be ensured by exploiting the laws of quantum physics and, in particular, by the fact that any attempt to measure a quantum state will change it uncontrollably. This change can be detected by the legitimate users of the communication channel and so reveal to them the presence of an eavesdropper. In this paper I explain (briefly) how quantum key distribution works and some of the progress that has been made towards making this a viable technology. With the principles of quantum communication and quantum key distribution firmly established, it is perhaps time to consider how efficient it can be made. It is interesting to ask, in particular, how many bits of information might reasonably be encoded securely on each photon. The use of photons entangled in their time of arrival might make it possible to achieve data rates in excess of 10 bits per photon.
The quantum key distribution (QKD) system can provide the absolutely secure communication for distant users [C. H. Bennett and G. Brassard, Proc. of the IEEE Int. Conf. on Computers, Systems, and Signal Processing, pp. 175–179, 1984]. But it requires single photon sources, highly sensitive detectors, and newly constructed quantum channel between the legitimate users. On the other hand, classical (or quantum) noise based key distribution system is one of the candidates to realize the key distribution system with today’s technology [U. M. Maurer, IEEE Trans. Inform. Theory, 39, No.3, pp.733–742, 1993, H. P. Yuen and A. M. Kim, Phys. Lett. A, 241, pp.135–138, 1998]. In such a system, the independence of the noise between a legitimate receiver and an eavesdropper is presupposed. For long haul distant communication, however, amplification of the carrier is indispensable. This amplification process generates correlated fluctuations between them.We analyze how much correlation occurs when a coherent state is amplified and split. Then, the influence on the security level is shown in contrast to the non correlated case.