HASHIMOTO Yasufumi

写真a

Title

Associate Professor

Researcher Number(JSPS Kakenhi)

30452733

Homepage URL

https://sites.google.com/view/yasufumihashimoto-en

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Current Affiliation Organization 【 display / non-display 】

  • Duty   University of the Ryukyus   Faculty of Science   Mathematical Sciences   Associate Professor  

  • Concurrently   University of the Ryukyus   Graduate School of Engineering and Science   Mathematical Sciences   Associate Professor  

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Academic degree 【 display / non-display 】

  • Kyushu University -  Dr. of Mathematics

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External Career 【 display / non-display 】

  • 2005.04
    -
    2007.03

    JSPS Research Fellow, DC2  

  • 2007.04
    -
    2007.07

    COE Research Fellow, Kyushu University  

  • 2007.07
    -
    2011.03

    Institute of Systems and Information Technologies/Kyushu  

  • 2009.04
    -
    2011.03

    Kyushu University  

  • 2011.04
    -
    2019.03

    Kyushu University  

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Research Interests 【 display / non-display 】

  • Trace Formula

  • Zeta functions

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Research Areas 【 display / non-display 】

  • Algebra

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Published Papers 【 display / non-display 】

  • Solving the problem of Blockwise Isomorphism of Polynomials with Circulant matrices

    Yasufumi Hashimoto

    IEICE Trans. Fundamentals ( 一般社団法人 電子情報通信学会 )  E106.A ( 3 ) 185 - 192   2023.03 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

    　View Summary

    <p>The problem of Isomorphism of Polynomials (IP problem) is known to be important to study the security of multivariate public key cryptosystems, one of the major candidates of post-quantum cryptography, against key recovery attacks. In these years, several schemes based on the IP problem itself or its generalization have been proposed. At PQCrypto 2020, Santoso introduced a generalization of the problem of Isomorphism of Polynomials, called the problem of Blockwise Isomorphism of Polynomials (BIP problem), and proposed a new Diffie-Hellman type encryption scheme based on this problem with Circulant matrices (BIPC problem). Quite recently, Ikematsu et al. proposed an attack called the linear stack attack to recover an equivalent key of Santoso's encryption scheme. While this attack reduced the security of the scheme, it does not contribute to solving the BIPC problem itself. In the present paper, we describe how to solve the BIPC problem directly by simplifying the BIPC problem due to the conjugation property of circulant matrices. In fact, we experimentally solved the BIPC problem with the parameter, which has 256 bit security by Santoso's security analysis and has 72.7bit security against the linear stack attack, by about 10 minutes.</p>

  • An improvement of algorithms to solve under-defined systems of multivariate quadratic equations

    Yasufumi Hashimoto

    JSIAM Letters ( 一般社団法人 日本応用数理学会 )  15 ( 0 ) 53 - 56   2023 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

    　View Summary

    <p>The problem of solving a system of multivariate quadratic equations over a finite field is known to be hard in general. However, there have been several algorithms of solving the system of quadratic equations efficiently when the number of variables is sufficiently larger than the number of equations (e.g., Kipnis et al., Eurocrypt 1999; Thomae and Wolf, PKC 2012; Cheng et al., PQCrypto 2014; and Furue et al., PQCrypto 2021). In the present paper, we propose a new algorithm that is available if the number of variables is smaller than that required in the previously given algorithms.</p>

  • Square integrals of the logarithmic derivatives of Selberg's zeta functions in the critical strip

    Yasufumi Hashimoto

    International Journal of Number Theory ( World Scientific Pub Co Pte Ltd )  19 ( 04 ) 747 - 756   2022.09 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

    　View Summary

    In our previous work (Y. Hashimoto, Selberg’s zeta function for the modular group in the critical strip, Math. Nachr. 294 (2021) 1899–1904, https://doi.org/10.1002/mana.202000268 ), we proposed an upper bound of the logarithmic derivative of Selberg’s zeta function for the modular group in the critical strip. This paper studies the growth of its square integral for the modular group, co-compact arithmetic groups derived from indefinite quaternion algebras and their subgroups.

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  • Key recovery attack on Hufu-UOV

    Yasufumi Hashimoto

    JSIAM Letters ( 一般社団法人 日本応用数理学会 )  14 ( 0 ) 1 - 4   2022 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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    <p> The unbalanced oil and vinegar signature scheme (UOV) is a signature scheme whose public key is a set of quadratic polynomials over a finite field. This scheme has been considered to be secure and efficient enough under suitable parameter selections. However, its key size is relatively large, and then various arrangements of UOV with smaller keys have been proposed. Hufu-UOV proposed by Tao in 2019 is one of such variants of UOV, whose keys are generated by circulant and Toeplitz matrices. In the present paper, we study the security of Hufu-UOV and propose an attack on it. </p>

  • Vulnerability of Diene-Thabet-Yusuf's cubic multivariate signature scheme

    Yasufumi Hashimoto

    Ryukyu Mathematical Journal   34   1 - 5   2021.12

    Type of publication: Research paper (scientific journal)

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Other Papers 【 display / non-display 】

  • Universality theorems of the Selberg zeta functions for arithmetic groups

    Yasufumi Hashimoto

    arXiv math     2023.05

     

    DOI

  • An elementary construction of QR-UOV

    Yasufumi Hashimoto

    Cryptology ePrint Archive   2022 ( 145 )   2022.02

     

  • On the modifier Q for multivariate signature schemes

    Yasufumi Hashimoto

    Cryptology ePrint Archive   ( 1046 )   2021.08

     

  • A note on the multivariate cryptosystem based on a linear code

    Yasufumi Hashimoto

    Cryptology ePrint Archive   ( 1396 )   2019.12

     

  • Recent developments in multivariate public key cryptosystems,

    Yasufumi Hashimoto

    MI Lecture Notes   81   187 - 205   2019.09

     

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Academic Awards 【 display / non-display 】

  • Best Paper Award of IWSEC 2021

    2021.09   IWSEC  

  • IPSJ Outstanding Paper Award

    2020.06   IPSJ  

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