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Research Team for Physical Analysis

Nowadays the importance of the physical analysis on the security cannot be overemphasized too much. There, however, exist still ¡¡few organizations to investigate such an aspect of the security even in the world. The existence of the team, therefore, is considered to be a characteristic of our research center.

The goal of the team is summarized as follows: To provide information on the security that is guaranteed by the law of physics, to clarify relationship between notions of theoretical security and actual security technologies, to propose novel security technologies with a long-range plan. To achieve the goals, we are conducting the following researches.

1. Strength Evaluation and Implementation of Tamper-proof Module

A several researches are being conducted on hardware and physical security technology. As a study of side channel attack against cryptography technology product, we are analyzing INSTAC boards. We plan to provide valuable information to our society through activities like CRYPTREC and ISO. We are trying to construct a theory unifying various scattered arguments on the tamperproof technology. The notion of randomness of data will play an important role in the research.

2. Quantum Information Security

In the middle of 80¡Çs, C-H.Bennett and G.Brassard proposed a quantum key distribution (QKD) protocol which essentially uses the quantum theory. The BB84 protocol was proved to be unconditionally secure, and thus is expected as a promising candidate for next generation security technology. We are investigating its theoretical basis, techniques for its implementation and its strength evaluation.

As the theoretical basis, we found a novel information-disturbance theorem to explain the reason why the BB84 protocol is unconditionally secure. The theorem, in addition, can be regarded as an information theoretical version of the uncertainty relation. We are trying to apply the theorem to other protocols. In the implementation of the QKD protocol, it is important to reconcile the information between a sender and a receiver and to reduce the information possessed by eavesdroppers. Error correction and privacy amplification are employed to achieve them. For realization of a QKD system, to find efficient methods for them is crucial. From such a view point, we constructed a new CSS code by using LDPC codes. Our new code is expected to make the QKD system more practical.

While the evaluation of the existing protocols is indispensable, it in general is a hard problem since no standard methods have been established in a field of the quantum security. We analyzed in detail the Y-00 protocol which had been proposed as a secure protocol. We found that it has no advantage over classical stream cipher.