Quantum Cryptography: Encrypting with Light

Data transmission that is absolutely impervious to interception has now come a step closer: several partners recently demonstrated the first quantum cryptography network in the world as part of the research project SECOQC. The network combines seven high-security links on the basis of quantum cryptography, which is impervious to physical attack, and connects various Siemens locations in Austria. The company also worked on the integration of the system and developed solutions for administering and monitoring the network. Siemens is also participating in the development of a quantum cryptography chip.

Quantum cryptography operates with photons, the carriers of light. Because of the special features of quantum physics, the researchers involved, among them the famous scientist Anton Zeilinger, can use the photons to generate identical keys between two partners for secure transmission of data. Since any measurement of a photon leaves clear traces, an eavesdropper would be detected immediately. This results from a fundamental principle of the complex world of quantum mechanics according to which a measured value is changed by the measurement itself.

In practice, the data transmission requires a quantum cryptography network. Without the network, the distances between the partners are limited, because photons cannot be transmitted arbitrarily far. The network passes the keys onward – in the experiment in Vienna, at any rate, it conveyed them over 85 kilometers. The scientists carried out a telephone conversation over the network, and the data was sent via optical fibers – after having been encrypted securely with quantum cryptography.

The fiber-optic network was supplied by Siemens. The developers of Siemens IT Solutions and Services provided for the system integration and the requirements analysis in collaboration with the Austrian Research Center. In this context, Siemens first analyzed possible system architectures, identified and defined interfaces, and attended to the integration of quantum cryptography distribution systems. The company has been looking at quantum cryptography for a number of years now. In the framework of this research, the chip was developed together with the Austrian Research Center and the University of Graz. With quantum cryptography, entities such as companies or banks could encrypt their communications.