Signal Processing Research Group
Research Topics
NTT Communication Science Laboratories
Media Information Laboratory
Recognition Research Group
Signal Processing Research Group
Communication environment research group
Innovative Communication Laboratory
Human and Information Science@Laboratory
Moriya Research Laboratory
NTT Science and Core Technology Laboratory Group
Nippon Telegraph and Telephone Corporation (NTT)
Research Topics
Dynamical Information Processing
Methods for Communication using Strongly Fluctuating Phenomena

The use of strong fluctuations in devices poses new possibilities of communication technology. We are exploring the possibilities by applying new methods from the fields of nonlinear dynamics and information theory to problems of signal transmission and generation in strongly fluctuating devices. In particular, we are developing a secure key sharing scheme and a fast and compact physical random number generator, based on strongly fluctuating phenomena in optical devices.

* 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.
[ Reference ]
* Future Perspective
[1] J. Muramatsu, K. Yoshimura, K. Arai, and P. Davis,
hSecret key capacity for optimally correlated sources under sampling attack,hIEEE Trans. on Information Theory 52 (2006) pp. 5140-5155.
[2] J. Muramatsu, K. Yoshimura, and P. Davis,
hInformation Theoretic Security Based on Bounded Observability,h Lecture Notes in Computer Science 5973 (2010) pp. 128-139.
[3] T. Yamamoto, I. Oowada, H. Yip, A. Uchida, S. Yoshimori, K. Yoshimura, J. Muramatsu, S. Goto, and P. Davis,
hCommon-noise-induced synchronization in semiconductor lasers,h Optics Express 15 (2007) pp. 3974-3980.
[4] I. Oowada, H. Ariizumi, M. Li, S. Yoshimori, A. Uchida, K. Yoshimura, and P. Davis,
hSynchronization by injection of common chaotic signal in semiconductor lasers with optical feedback,h Optics Express 17 (2009) pp. 10025-10034.
[5] S. Goto, P. Davis, K. Yoshimura, and A. Uchida,
hSynchronization of chaotic semiconductor lasers by optical injection with random phase modulation,h Optical and Quantum Electronics 41 (2009) pp. 137-149.
[6] K. Yoshimura and K. Arai,
hPhase reduction of stochastic limit cycle oscillators,h Phys. Rev. Lett. 101 (2008) 154101.
[7] K. Yoshimura, P. Davis, and A. Uchida,
hNonresonant entrainment of detuned oscillators induced by common external noise,h Progress of Theoretical Physics 120 (2008) pp. 621-633.
[8] K. Yoshimura, J. Muramatsu, and P. Davis, hConditions for common-noise-induced synchronization in time-delay systems,h Physica D 237 (2008) pp. 3146-3152.
* Secure Keys from Correlated Randomness
[1] A. Uchida, K. Amano, M. Inoue, K. Hirano, S. Naito, H. Someya,I. Oowada, T. Kurashige, M. Shiki, S. Yoshimori, K. Yoshimura, and P. Davis,
hFast physical random bit generation with chaotic semiconductor lasers,hNature Photonics 2 (2008) pp. 728-732.
[2] T. Honjo, A. Uchida, K. Amano, K. Hirano, H. Someya, H. Okumura,K. Yoshimura, P. Davis, and Y. Tokura,
hDifferential-phase-shift quantum key distribution experiment using fast physical random bit generator with chaotic semiconductor lasers,h Optics Express 17 (2009) pp. 9053-9061.
[3] T. Harayama, S. Sunada, K. Yoshimura, P. Davis, K. Tsuzuki, and A.Uchida,
hFast nondeterministic random-bit generator using on-chip chaos lasers,h Physical Review A 83 (2011) 031803.
[4] S. Sunada, T. Harayama, K. Arai, K. Yoshimura, P. Davis, K. Tsuzuki, and A. Uchida,
hChaos laser chips with delayed optical feedback using a passive ring waveguide,h Optics Express 19 (2011) pp. 5713-5724.
[5] S. Sunada, T. Harayama, K. Arai, K. Yoshimura, P. Davis, K. Tsuzuki, and A. Uchida,
hRandom optical pulse generation with bistable semiconductor ring lasers,h Optics Express 19 (2011) pp. 7439-7450.
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