Daylight free-space quantum key distribution

While quantum key distribution is possible with today\´s technology, the security of systems built with today\´s components is a difficult question. Real systems might have subtle weaknesses, so called "side-channels", which allow an eavesdropper to gain information about the key without direct polarization measurements. Other degrees of freedom of the photons might carry information which is correlated to their polarization. In this paper the author investigated the possible side-channels and show, by evaluating the amount of information leakage, that this weakness can be overcome by suitable countermeasures.