Mechanism of Quantum Cryptography

Quantum cryptography, which makes eavesdropping theoretically impossible, is gathering substantial attention as a next-generation cryptography that takes the place of modern algorithm-based cryptography. Quantum cryptography communications are transmitted by assigning a digital one or zero signal to each photon, or so-called "grains of light". On the contrary, with current optical communications, digital one and zero signals are expressed through the relative strength or weakness of the light. Optical strength or weakness is made up of tens of thousands of photons carrying the same information, so, for example, it is impossible to know if a number of those photons have been intercepted (i.e., eavesdropped) during the communication. However, with quantum cryptography communications, the information carried by the photons is instantly broken if the communication is observed/eavesdropped, instantly making it possible to know if the communication has been intercepted and making it impossible for the communication to be crypto-analyzed by a third party. *

NOTE:

Quantum cryptography uses the Heisenberg Uncertainty Principle, which holds that when a phenomenon is observed its characteristics are always affected by the act of observation.

Integrated Quantum Cryptography System

Research is progressing with certain technologies applying quantum mechanics, such as quantum computers and quantum teleportation. Of these technologies, quantum cryptography is closest to practical use. Mitsubishi Electric has developed the Integrated Quantum Cryptography System, a unique approach to the level of practical use. This system encrypts and decrypts data using high-speed modern cryptography, and communicates the encryption key with absolutely secure quantum cryptography. By combining these two cryptography technologies, this novel system brings absolutely secure future technologies a step closer to practical use.

Mitsuru, Matsui

General Manager
Information Security Technology Department

I worked on the development of MISTY cryptography technology for many years, but I first became involved in development of quantum cryptography in 1999. At that time, basic experiments were being done at universities and other research institutions, but it was a rare case for a modern cryptographer to be involved in quantum cryptography. It would be no exaggeration to say that, at the time, quantum cryptography was still a dream technology, but I worked on how to make quantum cryptography a reality by utilizing technological capabilities of the time and personal experience gained through the development of modern cryptography. Together with researchers who had a background in physics, we tackled an unknown field, and in September 2000, about one year after starting, we succeeded in running a quantum cryptography communication experiment, the first of its kind in Japan.

One of the issues that we could not avoid in making quantum cryptography practical was ensuring the stability of communications over existing installed optical fiber. Unlike an experiment in an artificial environment like a laboratory, existing installed optical fiber has many factors that make communications unstable, like the fact that the fiber stretches and contracts with temperature changes. To overcome this difficulty, in 2004 we conducted a quantum cryptography field trial that involved transmitting a communication 96 kilometer distances over existing optical fiber. Also, in 2007, we also succeeded in quantum cryptography experiments using a single photon source. Quantum cryptography involves conducting communications with individual grains of light (photons), and we had formerly created single photons by attenuating laser light. Development of a quantum cryptography communication system that uses a single photon source is another major factor in the technology's practicality.