Ryo Ohashi's homepage

Journal articles

Takara Taniguchi, Ryo Ohashi, Tsuyoshi Takagi, "Enumeration algorithm for genus-4 superspecial hyperelliptic curves with automorphism group $Q_8$", JSIAM Letters 17, 89–92, 2025.
Ryo Ohashi, Hiroshi Onuki, Momonari Kudo, Ryo Yoshizumi, Koji Nuida, "Listing superspecial curves of genus three using Richelot isogeny graph", Research in Number Theory 11, Article number: 76, 2025.
Ryo Ohashi, Momonari Kudo, Shushi Harashita, "The $a$-numbers of non-hyperelliptic curves of genus 3 with cyclic automorphism group of order 6", Acta Arithmetica 216, 227–248, 2024.
Ryo Ohashi, Momonari Kudo, "Computing superspecial hyperelliptic curves of genus 4 with automorphism group properly containing the Klein 4-group", Journal of Computational Algebra 11, 100020, 2024.
Ryo Ohashi, "On the Rosenhain forms of superspecial curves of genus two", Finite Fields and Their Applications 97, 102445, 2024.
Ryo Ohashi, Shushi Harashita, "Differential forms on the curves associated to Appell-Lauricella hypergeometric series and the Cartier operator on them", Yokohama Mathematical Journal 69, 1–32, 2023.
Ryo Ohashi, "Maximality of Ciani curves over finite fields", Finite Fields and Their Applications 83, 102089, 2022.
Ryo Ohashi, "On the maximality of hyperelliptic Howe curves of genus 3", Kodai Mathematical Journal 45, No. 2, 282–294, 2022.

Ryo Ohashi, Hiroshi Onuki, "An efficient collision attack on Castryck-Decru-Smith's hash function", PQCrypto2025, Lecture Notes in Computer Science 15578, 89–118, 2025.
Ryo Yoshizumi, Hiroshi Onuki, Ryo Ohashi, Momonari Kudo, Koji Nuida, "Efficient theta-based algorithms for computing $(\ell,\ell)$-isogenies on Kummer surfaces for arbitrary odd $\ell$", PQCrypto2025, Lecture Notes in Computer Science 15578, 3–37, 2025.
Ryo Ohashi, Momonari Kudo, Shushi Harashita, "Fast enumeration of superspecial hyperelliptic curves of genus 4 with automorphism group $V_4$", WAIFI2022, Lecture Notes in Computer Science 13638, 107–124, 2023.

Ryo Ohashi, Momonari Kudo, "On superspecial hyperelliptic curves of genus 5 whose automorphism groups contain $C_2^3$", accepted for presentation at CASC2025.

Ryo Ohashi, Hiroshi Onuki, "A collision attack on the LTZ hash function based on a conjecture on supersingular non-superspecial isogeny graphs of dimension 2", submitted.
Yuya Yamamoto, Ryo Ohashi, Shushi Harashita: "Supersingular genus-two curves of Rosenhain form and hypergeometric series", submitted.
Ryo Ohashi, "Superspecial curves of generalized Legendre form", submitted.
Takumi Ogasawara, Ryo Ohashi, Kosuke Sakata, Shushi Harashita, "Superspecial genus-4 double covers of elliptic curves", submitted (preprint: arXiv:2403.08139).

Ryo Ohashi, Hiroshi Onuki, Momonari Kudo, Ryo Yoshizumi, Koji Nuida, "Computation of the superspecial (2,2)-isogeny graph using theta functions", 数理解析研究所講究録, No. 2280, 12–22, 2024 (pdf).
Ryo Ohashi, Hiroshi Onuki, "Construction of a hash function using superspecial abelian 3-folds", 暗号と情報セキュリティシンポジウム2024予稿集, 3A3-3, 2024 (pdf).