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International Conference on Transparent Optical Networks

Radio-frequency spectrum coding in ultra-long fibre laser based cryptography

Katarzyna Krupa, Alessandro Tonello, Sonia Boscolo, Alain Barthélémy, Vincent Kermène, Agnès Desfarges‐Berthelemot, Badr Mohamed Ibrahim Shalaby, Sergei K. Turitsyn, Juan Diego Ania‐Castañón

Published Jul 1, 2015• 0 citations
Publisher

Abstract

We propose a new approach for secret key exchange involving the variation of the cavity length of an ultra-long fibre laser. The scheme is based on the realisation that the free spectral range of the laser cavity can be used as an information carrier. We present a proof-of-principle demonstration of this new concept using a 50-km-long fibre laser to link two users, both of whom can randomly add an extra 1-km-long fibre segment.

DOI
10.1109/icton.2015.7193390

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We propose a new approach for secret key exchange involving the variation of the cavity length of an ultra-long fibre laser. The scheme is based on the realisation that the free spectral range of the laser cavity can be used as an information carrier. We present a proof-of-principle demonstration of this new concept using a 50-km-long fibre laser to link two users, both of whom can randomly add an extra 1-km-long fibre segment.
Abstract We propose a new approach to the generation of an alphabet for secret key exchange relying on small variations in the cavity length of an ultralong fiber laser. This new concept is supported by experimental results showing how the radiofrequency spectrum of the laser can be exploited as a carrier to exchange information. The test bench for our proof of principle is a 50-km-long fiber laser linking two users, Alice and Bob, where each user can randomly add an extra 1-km-long segment of fiber. The choice of laser length is driven by two independent random binary values, which makes such length become itself a random variable. The security of key exchange is ensured whenever the two independent random choices lead to the same laser length and, hence, to the same free spectral range.
Abstract In traditional communication systems the transmission medium is considered as a given characteristic of the channel, which does not depend on the properties of the transmitter and the receiver. Recent experimental demonstrations of the feasibility of extending the laser cavity over the whole communication link connecting the two parties, forming an ultra‐long fiber laser (UFL), have raised groundbreaking possibilities in communication and particularly in secure communications. Here, a 500 km long secure key distribution link based on Raman gain UFL is demonstrated. An error‐free distribution of a random key with an average rate of 100 bps between the users is demonstrated and the key is shown to be unrecoverable to an eavesdropper employing either time or frequency domain passive attacks.
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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.
Coding data bits in the phase or polarisation state of light allows us to exploit the wave particle duality for novel communication protocols. Using this principle the first practical quantum communication systems have been built. These are the fibre and free-space quantum cryptography apparatus used for secure exchange of keys. To date free space key exchange has aimed at long range with 144km range achieved and future experiments aiming to extend this range to 1000km exchanging keys with low earth orbit satellites. At the other end of the spectrum we are developing low cost hand held systems. These systems could be an effective way for the user to generate a store of secrets shared with a central repository. These secrets can then be used up to protect a wide variety of sensitive classical communications. Examples include on-line PIN protection for consumer transactions and password protection in secure access schemes.