Masahito Gotaishi

Proposal of a signature scheme based on STS trapdoor

A New digital signature scheme based on Stepwise Triangular Scheme (STS) is proposed. The proposed trapdoor has resolved the vulnerability of STS and secure against both Grobner Bases and Rank Attacks. In addition, as a basic trapdoor, it is more efficient than the existing systems. With the efficient implementation, the Multivariate Public Key Cryptosystems (MPKC) signature public key has the signature longer than the message by less than 25 %, for example.

Privacy Preserving Data Processing with Collaboration of Homomorphic Cryptosystems

We propose a privacy-preserving data processing system using homomorphic cryptosystem. Proposed system consists of several functionalities corresponding to addition and multiplication of plaintexts encrypted in ciphertexts. Using these functionalities repeatedly, any multivariate polynomial evaluation of secret inputs can be achieved. We clarify the role and the function of each organization participating in the process — custodians of personal data, processing center of cryptographic function, and computing center. The cooperation of several entities makes arbitrary times of the calculations, which is a requirement of fully homomorphic encryption, more efficient. We give security proofs of the scheme and show the result of implementation of the scheme.

Privacy Preserving Data Processing

A data processing functions are expected as a key-issue of knowledge-intensive service functions in the Cloud computing environment. Cloud computing is a technology that evolved from technologies of the field of virtual machine and distributed computing. However, these unique technologies brings unique privacy and security problems concerns for customers and service providers due to involvement of expertise (such as knowledge, experience, idea, etc.) in data to be processed. We propose the cryptographic protocols preserving the privacy of users and confidentiality of the problem solving servers.

Advanced Concept of Information Security Comprehensive Science

I nformation security and ethics as bases of our life are becoming in-creasingly important in the new information society which we have never experienced before. In this paper, we present an advanced con-cept of information security in terms of comprehensive science. Free-dom, Security and Privacy are the three key values of information soci-ety. These three values are liable to conflict with each other and among them, sometimes three contradictions arises. We use the concept of “Aufheben,” (sublate), a technical term of philosophy, to cope with it. S. Tsujii introduced a new concept of information security as the com-prehensive science in 1993. Moreover, we have endeavored to evaluate the effectiveness of the concept by establishing the “MELT UP Forum.” The MELT UP Forum aims to foster, to identify and to extend a core or comprehensive science that deals with Management, Ethics, Law, and Technology across a wide spectrum of endeavors.

Privacy Preserving Problem Solving Scheme

A natural language-based problem solving schemes are expected as a key-issue of knowledge-intensive service functions in the Cloud computing environment. In the meanwhile, the privacy preserving issues are crucial due to involvement of expertise (such as knowledge, experience, idea, etc.) in the problems and its solution. We propose the cryptographic protocols preserving the privacy of users and confidentiality of the problem solving servers.

Secure Problems Solving Scheme

We propose the concept of service functions and features in knowledge society, including the problem, solutions and semantic themes, the private information retrieval theme, the privacy preserving data processing, and the new public key cryptosystem in which the problems of human-machine interaction, privacy preserving are resolved.

Improvement of the Low Rank Attack

Time complexity of Low Rank Attack is lower than originally estimated. Now the algorithm is improved and the time complexity is computed as O(Ln³ + mn⁴), outperforming the original Low Rank Attack with the complexity O(Ln³ q^r +mn⁴).