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arXiv:quant-ph/0210089

Secure communication using coherent states

Geraldo A. Barbosa, Eric Corndorf, Prem Kumar, Horace P. Yuen, Giacomo Mauro D’Ariano, Matteo G. A. Paris, Paolo Perinotti

Published Oct 11, 2002• 8 citations
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Abstract

We demonstrate that secure communication using coherent states is possible. The optimal eavesdropping strategy for an M-ry ciphering scheme shows that the minimum probability of error in a measurement for bit determination can be made arbitrarily close to the pure guessing value P_e=1/2. This ciphering scheme can be optically amplified without degrading the security level. New avenues are open to secure communications at high speeds in fiber-optic or free-space channels.

DOI
10.48550/arxiv.quant-ph/0210089

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We demonstrate that secure communication using coherent states is possible. The optimal eavesdropping strategy for an M-ry ciphering scheme shows that the minimum probability of error in a measurement for bit determination can be made arbitrarily close to the pure guessing value P_e=1/2. This ciphering scheme can be optically amplified without degrading the security level. New avenues are open to secure communications at high speeds in fiber-optic or free-space channels.
This work shows how two parties A and B can securely share unlimited sequences of random bits at optical speeds. A and B possess true-random physical sources and exchange random bits by using a random sequence received to cipher the following one to be sent. A starting shared secret key is used and the method can be described as a one-time-pad unlimited extender. It is demonstrated that the minimum probability of error in signal determination by the eavesdropper can be set arbitrarily close to the pure guessing level. Being based on the M-ry encryption protocol this method also allows for optical amplification without security degradation, offering practical advantages over the Bennett-Brassard 1984 protocol for key distribution.
The cryptographic communication has a lot of important applications, particularly in the magnificent prospects of private communication. As one knows, the security of cryptographic channel depends crucially on the secrecy of the key. The Vernam cipher is the only cipher system which has guaranteed security. In that system the key must be as long as the message and most be used only once. Quantum cryptography is a method whereby key secrecy can be guaranteed by a physical law. So it is impossible, even in principle, to eavesdrop on such channels. Quantum cryptography has been developed in recent years. Up to now, many schemes of quantum cryptography have been proposed. Now one of the main problems in this field is how to increase transmission distance. In order to use quantum nature of light, up to now proposed schemes all use very dim light pulses. The average photon number is about 0.1. Because of the loss of the optical fiber, it is difficult for the quantum cryptography based on one photon level or on dim light to realize quantum key-distribution over long distance. A quantum key distribution based on coherent state is introduced in this paper. Here we discuss the feasibility and security of this scheme.
We demonstrate high-speed (250 Mbps) data encryption over 25 km of telecommunication fiber by use of coherent states. For the parameter values used in the experiment, the demonstration is secure against individual ciphertext-only eavesdropping attacks near the transmitter with ideal detection equipment. Whereas other quantum-cryptographic schemes require the use of fragile quantum states and ultrasensitive detection equipment, our protocol is loss tolerant, uses off-the-shelf components, and is optically amplifiable.
We demonstrate high-speed (0.25Gbps) data encryption over 50km of telecom fiber using coherent states of light. For the parameter values used in the experiment, the demonstration is secure against individual ciphertext-only eavesdropping attacks near the transmitter with ideal detection equipment. While other quantum cryptographic schemes require the use of fragile quantum states and ultra-sensitive detection equipment, our protocol is loss tolerant, uses off-the-shelf components, and is optically amplifiable.
Continuous-variable quantum secure communication encoded by Gaussian mapping offers high-capacity and high transmission rates. For the theoretically secure encryption scheme of a 1-time pad, a highly reliable coherent-state quantum secure communication system has been established, and its security has been quantitatively evaluated using Wyner’s wiretap channel theory. We also propose an information reconstruction scheme based on multidimensional rotation to extract secret messages at low-to-medium signal-to-noise ratios. Meanwhile, to address the unbalanced optical path, we design a self-balanced homodyne detector based on a programmable gain amplifier, achieving an electronic noise variance of 1.624 × 10 − 7 V 2 and a bandwidth of 715 MHz. In 10-km optical fiber transmission, the system successfully achieved secure transmission of the dichroic image, processed 1,536 information blocks, each containing 2 10 continuous variables, with a block error rate of approximately 8.78 × 10 − 5 , and ultimately achieved the secrecy capacity of 2.44 × 10 5 bits per second.