Review of free-space quantum key distribution

Quantum key distribution is a method of distributing cryptographic key securely over a distance. No other method of key distribution has been proven secure. Today trusted couriers are used to distribute keys for cryptography with the highest security level. However, the use of couriers for key distribution is impractical in many cases. Therefore, quantum key distribution may be of interest for many civilian and military cryptographic applications. This report presents the concept of quantum key distribution in general and free-space applications in specific. The presentation includes a background and the principle of the general method. Furthermore, the last year´s experimental realisations of free-space quantum key distribution systems are reviewed and some military applications are presented. Finally, some recommendation of further work is suggested.