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e QKD links which form the Tokyo QKD Network are managed and operated by NEC, Toshiba, Gakushuin University, NTT-NICT and SeQureNet [7][8][17]–[19]. e link operated by NTT-NICT uses JGN’s dark ber between Koganei and Otemachi [14]. Leaving the details of those systems to other chapters, we summarize their QKD link protocols, transmission distances and transmis-sion loss in Table 1.We constructed a system capable of safe password authentication, data transmission, data preservation and data reconstruction in line with information theory, on the distributed storage. Figure 4 shows secret sharing process-ing time in the three phases (registration, pre-computation and reconstruction). Figure 4 (a) shows the dependency of processing time on the Mersenne prime index size when the data size is 46 kilobytes, and Figure 4 (b) shows the dependency of processing time on le size when a Mersenne prime of 244497-1 is used.Note that the results shown in Fig.4 were obtained using conventional-type PCs; so, a drastic processing per-formance improvement would be expected if high-perfor-mance servers were used. However, the most signicant factor limiting the processing speed of the current system is the key-synchronization process (i.e., key-sorting process which is executed on a server) that is essential to OTP encryption using the QKD platform supplied. So, we expect that soware improvement will enable high-speed process-ing. On the other hand, we have proved by experience that our current system is capable of completing the process from registration to reconstruction of 10 M of data—oen used for mail transmission—in approximately two minutes. is is the world’s rst successful demonstration of a system capable of safe password authentication, data transmission, data preservation and data reconstruction in line with in-formation theory.4Summaryus, by combining QKD and a newly developed password-authenticated secret sharing scheme, we demon-strated, for the rst time to our best knowledge, a distrib-uted storage system with information theoretically secure data transmission, storage, and authentication in a metro-politan area network. is system uses a QKD network capable of generating information theoretically secure keys. We are currently planning to construct a system enabling safe data secrecy preservation for a very long time, by periodically updating shares stored in servers and adding long-term data leakage prevention capabilities to our sys-tem. Even if various new types of cryptographic schemes and networks systems become available, risks of eavesdrop-ping and code-breaking will always exist if they are inca-pable of ensuring safety in line with information theory. e system we developed is not technically decodable and is therefore expected to be very robust against the types of attacks anticipated in the near future. NICT is capable of quickly responding to potential decryption threats by providing safe system solutions to Japanese people. NICT is also responsible for continuously enhancing relevant technologies and preparing for future threats.Our system uses secret computation, which is essential in secret sharing. It is promising to apply the secret com-putation technology in cloud services, such as statistical data computations while protecting users’ privacy informa-tion attached to the data. NICT will continue to pursue functional enhancement in communications technology, thereby fullling our duty to oer safe information com-munications systems.AcknowledgmentsA part of this research and development was con-ducted with the support of the Innovative Research and Development Promotion Program (ImPACT) designed by the Council for Science, Technology and Innovation. We thank the sta of the organizations participating in the ImPACT project “Realization of Advanced Knowledge in-frastructure serving for connecting Quantum Articial Brains via Networks,” for their support and fruitful discus-sion.ReferenceR1P. W. Shor, “Algorithms for quantum computation: Discrete logarithms and factoring,” Proceeding of the 35th Annual Symposimu on Fundations of Computer Science, pp.12–134 (IEEE Computer Society Press, Los Alamitos, 1994).2J. Hoffstein, J. Pipher, and J. H. Silverman, “NTRU: A Ring based Public Key Cryptosystem,” ANTS-III Proceedings of the Third International Symposium on Algorithmic Number Theory, pp.267–288 (ANTS-III, London, 1998).3O. Goldreich, S. Goldwasser, and S. Halevi, “Public-Key Cryptosystems from Lattice Reduction Problems,” Proceeding of CRYPTO 1997 pp.112–131 (Springer, Heidelberg, 1997).4http://csrc.nist.gov/groups/ST/post-quantum-crypto/documents/call-for-pro-posals-draft-aug-2016.pdf5C. H. Bennett and G. Brassard, “Quantum cryptography: public-key distribution and coin tossing,” in Proceedings of the IEEE International Conference on Computers, Systems and Signal Processing (Institute of Electrical and Electronics Engineers, New York, 1984), pp.175–1796N. Gisin, G. Ribordy, W. Tittel, and H. Zbinden, “Quantum cryptography,” Rev. 28　　　Journal of the National Institute of Information and Communications Technology Vol. 64 No. 1 (2017)3 Quantum Key Distribution Network