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 ultra-long fiber laser. This new concept is supported by experimental results showing how the radio-frequency 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.
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Funding: French National Research Agency (grants LABEX SIGMALIM and ANR 08-JCJC-0122 PARADHOQS); European Research Council (project ULTRALASER); Leverhulme Trust (grant RPG-278); Spanish MICINN project TEC2011-27314 (RAMAS); and XLIM Institute (grant VIP2013).
- fiber lasers
- fiber optics communications
- optical security