Random Numbers for Quantum Key Distribution

Quantum key distribution (QKD) has seen an important development for the last ten years. Nowadays, different companies offer commercial solutions and key exchanges at pulse rates of up to 1 GHz and over distances of up to 200 km have been demonstrated in research labs. However, the generation of random bit strings has often been neglected and it remains a technical problem, as physical random number generators have still insufficient bit rates for high speed QKD. In this talk, after an introduction in QKD, a state of the art prototype developed at the University of Geneva was presented. This prototype allows generating keys at high rates over up to 200 km of optical fiber. However, due to the lack of high rate physical random generators, random bits at a rate of 350 MHz are produced by a pseudo random number generator seeded by random bits originating from a quantum random number generator (4 MHz, id Quantique). It was show how an eavesdropper could attack a QKD system based on pseudo random numbers. Finally, different possibilities to increase the rates of quantum random number generators was discussed.