Taichi Isogai

Development of battery aggregation technology for smart grid

With the increasing implementation of Renewable Energy (RE) sources to the power grid, in the near future power grid will face problems such as power quality disturbances, lack of balancing capability for grid operation, and such. To face this challenge, creation of a Virtual Power Plant (VPP) by an aggregation of various Distributed Energy Resource (DER) are often reported and discussed as a solution. However, VPP created by battery aggregation is seldom discussed. This paper discusses the method and result of demonstrating VPP by battery aggregation and application to Load Frequency Control (LFC), Peak Shift (PS), and Reserve Margin (RM) functions.

Factor-4 and 6 (de)compression for values of pairings using trace maps

The security of pairing-based cryptosystems relies on the hardness of the discrete logarithm problems in elliptic curves and in finite fields related to the curves, namely, their embedding fields. Public keys and ciphertexts in the pairing-based cryptosystems are composed of points on the curves or values of pairings. Although the values of the pairings belong to the embedding fields, the representation of the field is inefficient in size because the size of the embedding fields is usually larger than the size of the elliptic curves. We show factor-4 and 6 compression and decompression for the values of the pairings with the supersingular elliptic curves of embedding degrees 4 and 6, respectively. For compression, we use the fact that the values of the pairings belong to algebraic tori that are multiplicative subgroups of the embedding fields. The algebraic tori can be expressed by the affine representation or the trace representation. Although the affine representation allows decompression maps, decompression maps for the trace representation has not been known. In this paper, we propose a trace representation with decompression maps for the characteristics 2 and 3. We first construct efficient decompression maps for trace maps by adding extra information to the trace representation. Our decompressible trace representation with additional information is as efficient as the affine representation is in terms of the costs of compression, decompression and exponentiation, and the size.

Generating Parameters for Algebraic Torus-Based Cryptosystems

Algebraic torus-based cryptosystems are public key cryptosystems based on the discrete logarithm problem, and have compact expressions compared with those of finite field-based cryptosystems. In this paper, we propose parameter selection criteria for the algebraic torus-based cryptosystems from the viewpoints of security and efficiency. The criteria include the following conditions: consistent resistance to attacks on algebraic tori and their embedding fields, and a large degree of freedom to select parameters suitable for each implementation. An extension degree and a characteristic size of a finite field on which the algebraic tori are defined are adjustable. We also provide examples of parameters satisfying the criteria.