On Wednesday, the first commercial communication network using quantum cryptography was demonstrated. The encryption offered with this form of communication is said to be unbreakable, which is achieved by the generation and distribution of keys by means of quantum cryptographic technologies. This novel form of secure communication could find many applications, such as those required by financial institutions or government agencies.

According to Bristol University, the network uses both standard optical fiber and line-of-sight to connect five subsidiaries of Siemens located in Austria. In total there are six nodes and eight intermediary links, ranging from 6 km to 82 km in distance, and there are six different quantum cryptographic technologies used for the key generation. Bristol University, along with partners from 12 European countries, have worked towards making the project a reality since April 2004.

A demonstration of this network-wide key generation and distribution took place at the Siemens Forum in Vienna, along with presentations of practical uses for the network and keys. One practical use that was presented was a secure voice-over-ip telephone application, secured by a “one-time-pad-encryption.” Another example was a video-conferencing application that was protected by symmetrical AES-encryption with frequent key changes.

Also demonstrated at the Siemens Forum was a low-cost key distributor, which has the potential to bring a quantum cryptographic network to consumers. Members of Bristol University have developed a low cost line-of-sight quantum cryptography system, which can apparently be used in daylight conditions. Such a system could allow online consumer transactions to be protected by a PIN, which would be encoded by the use of secret bits shared with the bank. So far high performance, stable and mobile quantum cryptographic devices have been produced that can fit inside boxes 19-inches in size and that are able to interoperate over standardized interfaces.

Although point-to-point quantum cryptographic solutions already exist commercially and are suitable for certain applications, they are still faced with particular limits. One such limit is that there is a maximum allowable distance between sender and receiver over a fiber optic cable, due to an increased loss of photons in the cable over increased cable length. Another limit includes the possible interruption of the communication due to the optical fiber being cut or due to interference in line-of-sight applications. A network on the other hand can extend the communication range indefinitely by bridging connections, as well as offering alternative paths for communication if one connection is disrupted. Lastly, a network could allow for simultaneous connections, increasing communication speed and versatility.