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arXiv:1506.07892 · Optical Engineering

Remote key establishment by random mode mixing in multimode fibers and optical reciprocity

Yaron Bromberg, Brandon Redding, Sébastien M. Popoff, Ningbo Zhao, Guifang Li, Hui W. Cao

Published Jan 9, 2019• 40 citations
arXivHTMLPDF

Abstract

Disorder and scattering in photonic systems have long been considered a nuisance that should be circumvented. Recently, disorder has been harnessed for a rapidly growing number of applications, including imaging, sensing, and spectroscopy. The chaotic dynamics and extreme sensitivity to external perturbations make random media particularly well-suited for optical cryptography. However, using random media for distribution of secret keys between remote users still remains challenging since it requires the users have access to the same scattering sample. Here, we utilize random mode mixing in long multimode fibers to generate and distribute keys simultaneously. Fast fluctuations in fiber mode mixing provide the source of randomness for key generation, and optical reciprocity guarantees that the keys at the two ends of the fiber are identical. We experimentally demonstrate the scheme using classical light and off-the-shelf components, opening the door for a practically secure key establishment at the physical layer of fiber-optic networks.

DOI
10.1117/1.oe.58.1.016105

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Disorder and scattering in photonic systems have long been considered a nuisance that should be circumvented. Recently, disorder has been harnessed for a rapidly growing number of applications, including imaging, sensing, and spectroscopy. The chaotic dynamics and extreme sensitivity to external perturbations make random media particularly well-suited for optical cryptography. However, using random media for distribution of secret keys between remote users still remains challenging since it requires the users have access to the same scattering sample. Here, we utilize random mode mixing in long multimode fibers to generate and distribute keys simultaneously. Fast fluctuations in fiber mode mixing provide the source of randomness for key generation, and optical reciprocity guarantees that the keys at the two ends of the fiber are identical. We experimentally demonstrate the scheme using classical light and off-the-shelf components, opening the door for a practically secure key establishment at the physical layer of fiber-optic networks.
We propose a secure key generation and distribution scheme for data encryption in classical optical fiber channel. A Delay interferometer (DI) is used to track the random phase fluctuation inside fiber, while the reconfigurable lengths of polarization-maintaining (PM) fiber are set as the source of optical phase fluctuations. The output signals from DI are extracted as the secret key and shared between the two-legal transmitter and receiver. Because of the randomness of local environment and the uniqueness of fiber channel, the phase fluctuation between orthogonal polarization modes (OPMs) can be used as secure keys to enhance the level of security in physical layer. Experimentally, we realize the random key generation and distribution over 25-km standard single-mode fiber (SSMF). Moreover, the proposed key generation scheme has the advantages of low cost, compatible with current optical fiber networks and long distance transmission with optical amplifiers.
We propose and experimentally demonstrate high-speed operation of random-channel cryptography (RCC) in multimode fibers. RCC is a key generation and distribution method based on the random channel state of a multimode fiber and multi-dimension to single-dimension projection. The reciprocal intensity transmittance of the channel shared between the two legitimate users is used to generate and distribute correlated keys. In previous work, RCC's key rate-distance product was limited by the speed of light. In this work, we show that adding a fast modulator at one end of the channel decouples the key rate and distance, resulting in a significant improvement in the key rate-distance product, limited only by the fiber's modal dispersion. Error-free transmission at a key rate-distance product of 64.7 Mbps$ \times $12 km, which is seven orders of magnitude higher than the previous demonstration, was achieved. The proposed method's security arises from a fundamental asymmetry between the eavesdroppers’ and legitimate users’ measurement complexity.
The secure distribution of a secret key is the weakest point of shared-key encryption protocols. While quantum key distribution schemes could theoretically provide unconditional security, their practical implementation remains technologically challenging. Here we provide an extended analysis and present an experimental support of a concept for a classical key generation system, based on establishing laser oscillation between two parties, which is realized using standard fiber-optic components. In our Ultra-long Fiber Laser (UFL) system, each user places a randomly chosen, spectrally selective mirror at his/her end of a fiber laser, with the two-mirror choice representing a key bit. We demonstrate the ability of each user to extract the mirror choice of the other using a simple analysis of the UFL signal, while an adversary can only reconstruct a small fraction of the key. The simplicity of this system renders it a promising alternative for practical key distribution in the optical domain.
We propose and verify a scheme that leverages the reciprocity and multipath scattering effects of multimode fibers to use them as scrambling devices. Each of the legitimate users possesses a segment of multimode fiber to scramble digital signals. When the scrambled digital signals are transmitted to a remote end through the transmission link, they need to pass through the multimode fiber at the remote end for a second scrambling to ensure security. Since the scrambling effect on the signal only exists in the multimode fiber, channel interference is compensated for, significantly enhancing transmission distance while maintaining high correlation. Additionally, the device’s security stems from its intrinsic state, as devices in different locations and environments exhibit varying states. The results show that even if an eavesdropper obtains a device with similar parameters, they cannot achieve the same sequence as the legitimate end-users. Ultimately, we achieved a key distribution rate of 0.18Gbit/s0.18 \mathrm{Gbit} / \mathrm{s}0.18Gbit/s using two segments of multimode fiber to scramble signals over a 50 km single-mode fiber.
Dynamic properties of optical signals in fiber channel provide a unique, random and reciprocal source for physical-layer secure key generation and distribution (SKGD). In this paper, an inherent physical-layer SKGD scheme is proposed and demonstrated, where the random source is originated from the dynamic fluctuation of the instant state of polarization (SOP) of optical signals in fiber. Due to the channel reciprocity, highly-correlated fluctuation of Stokes parameter of SOP is shared between the legal partners, where an error-free key generation rate (KGR) of 196-bit/s is successfully demonstrated over 25-km standard single-mode fiber (SSMF). In addition, an active polarization scrambler is deployed in fiber to increase the KGR, where an error-free KGR of 200-kbit/s is achieved.