* Future Perspective

We aim to develop new methods for signal transmission and generation which exploit randomly fluctuating phenomena. One promising application is secure key sharing using correlated randomness. Secure key sharing technology enables two users to share common secret information even if no secret information is available for them in advance. To this goal, we have proposed the use of randomly fluctuating phenomena in optical devices to generate correlated randomness. The proposed secure key sharing scheme in principle can achieve a high security level. Another promising application area is random number generation for data security. We have developed a compact optical device which can generate absolutely unpredictable random numbers much faster than existing technologies. These applications are expected to become key technologies in future communication networks.

* Secure Keys from Correlated Randomness

We are developing a new method of generating secret keys for communication. This method allows users to communicate securely even if they do not have any initial secret information. It makes use of correlated randomness, generated by intrinsically unpredictable physical phenomena. The method is based on mathematical analysis of the optimal properties of correlated randomness for strong security against attacks by eavesdropping. Sources of correlated randomness are developed using fluctuating signals in high-speed semiconductor lasers with correlations controlled by driving with common broadband random light signals. A compact laser module for correlated randomness is being developed, based on integrated optical circuit technology. We are also developing protocols which allow users to efficiently process correlated random signals to generate secret keys.

* Fast physical random number generation

Absolutely unpredictable random number sequences are essential for data security. For example, they are used for encryption, password generation, and the segmentation processing of secret data in secret sharing schemes. So there is a demand for a compact device that rapidly generates unpredictable random numbers on the basis of a physical phenomenon. We are developing a random signal generator module, based on the phenomenon in which the intensity of light from a laser varies randomly over time at high speed. We are using the most advanced integrated optical circuit technology and high-frequency packaging technology to achieve a fast and compact random signal generator module. Digitizing the random output signal of the module can produce an unpredictable sequence of random numbers at high speed. The current module has achieved random number generation at 2.08 Gbit/s.