Keita Ishizuka
石塚 慶太
Research Associate at Mitsubishi Electric Corporation, Information Technology R&D Center. Ph.D. in Information Science from Tohoku University (2024).
I work on algebraic coding theory with applications to post-quantum cryptography and combinatorial designs. My research bridges pure mathematical structures such as error-correcting codes, Hadamard matrices, and graph invariants with their applications to cryptography, quantum error correction, and computational complexity.
Research Interests
My research focuses on coding theory. Traditionally, error-correcting codes are technology that enables reliable communication over a noisy channel. They are now also tied to other mathematical objects in combinatorics, and they have various applications to cryptography and to quantum error correction.
Read more about my researchPublications
My name is highlighted in bold. Refereed venues are listed separately from preprints, posters and non-refereed presentations; items are numbered within each category.
Journal Articles
8Refereed journal articles.
Constructions of self-orthogonal and LCD subspace codes
Dean Crnković, Keita Ishizuka, Hadi Kharaghani, Sho Suda, Andrea Švob
Discrete Mathematics , 349(6) , pp. 115066 (2026)
Characterizations of the minimum weights of LCD codes of large dimensions
Makoto Araya, Masaaki Harada, Keita Ishizuka, Yuto Tanaka
IEEE Transactions on Information Theory , 70(12) , pp. 8758-8769 (2024)
Ternary Extremal Four-Negacirculant Self-Dual Codes
Masaaki Harada, Keita Ishizuka, Hadi Kharaghani
Graphs and Combinatorics , 40(3) , Art. 59 (2024)
Hadamard matrices of order 36 formed by codewords in some ternary self-dual codes
Masaaki Harada, Keita Ishizuka
Discrete Mathematics , 347(1) , pp. 113661 (2024)
Construction of quaternary Hermitian LCD codes
Keita Ishizuka
Cryptography and Communications , 15(2) , pp. 455-467 (2023)
Construction for both self-dual codes and LCD codes
Keita Ishizuka, Ken Saito
Advances in Mathematics of Communications , 17(1) , pp. 139-151 (2023)
On the existence of quaternary Hermitian LCD codes with Hermitian dual distance 1
Keita Ishizuka, Ken Saito
Discrete Mathematics , 345(2) , pp. 112702 (2022)
Classification of optimal quaternary Hermitian LCD codes of dimension 2
Keita Ishizuka
Journal of Algebra Combinatorics Discrete Structures and Applications , 7(3) , pp. 229-236 (2020)
Refereed Conference Proceedings
2Full-paper peer review with archival proceedings.
Bilinear Hulls for Support Splitting: Characterization, Optimization, and Applications
Yusuke Aikawa, Keita Ishizuka, Tomoki Moriya
SAC 2026 (Selected Areas in Cryptography), Springer LNCS post-proceedings (2026) to appear
Uniform Sampling of Self-Orthogonal Codes via Orthogonal Group Actions
Keita Ishizuka
IEEE Information Theory Workshop (ITW) 2026, Tempe (2026) to appear
Posters and Extended Abstracts
2Reviewed for presentation, without full-paper peer review.
Exactly Uniform Sampling of Entanglement-Assisted Quantum Codes with a Prescribed Number of Ebits
Keita Ishizuka
QIP 2027 (30th Conference on Quantum Information Processing), Singapore (2027) to appear
Poster: Reducing Hull Dimensions for Efficient Permutation Recovery in Code-Based Cryptography
Keita Ishizuka
Proceedings of the 2025 ACM SIGSAC Conference on Computer and Communications Security (CCS 2025) , pp. 4812-4814 (2025)
Preprints
7Publicly available on arXiv; not yet accepted.
Almost All Vectorial Functions Have Trivial Extended-Affine Stabilizers
Keita Ishizuka
(2026) under review
The Closure of LCD-to-GI Reductions via Generalized Inner Products
Keita Ishizuka
(2026) under review
Caps and LCD Codes with Large Dimensions
Keita Ishizuka, Yuhi Kamio
(2026) under review
Uniform Sampling of Linear Codes with Prescribed Hull Dimension
Keita Ishizuka
(2026)
Enumeration and Monotonicity of Linear Codes with Prescribed Hull Dimensions
Stefka Bouyuklieva, Iliya Bouyukliev, Keita Ishizuka, Ferruh Özbudak
(2026) under review
Classification of binary, ternary and quaternary Hermitian LCD codes
Keita Ishizuka
(2026) under review
Binary LCD Codes and Their Graph Representations
Keita Ishizuka
(2024) under review
Contributed Talks
9Presentations at meetings with no archival refereed paper.
On extended-affine symmetries of vectorial Boolean functions
Keita Ishizuka
2026 Symposium on Cryptography and Information Security (SCIS 2026) (2026)
Speeding up the support splitting algorithm using bilinear forms
Yusuke Aikawa, Keita Ishizuka, Tomoki Moriya
2026 Symposium on Cryptography and Information Security (SCIS 2026) (2026)
On largest minimum weights of binary LCD codes
Keita Ishizuka
41st Symposium on Algebraic Combinatorics (2025)
On weak keys in SPN block ciphers via the correlation matrix
Keita Ishizuka, Kosei Sakamoto, Rentaro Shiba
2025 Symposium on Cryptography and Information Security (SCIS 2025) (2025)
Orthogonal projectors of binary LCD codes
Keita Ishizuka
Finite Group Theory, Algebraic Combinatorics and Vertex Algebras (2024)
Orthogonal projectors of binary LCD codes
Keita Ishizuka
New Constructions of Expander Graphs and Their Applications 3 (2024)
Construction and characterization of LCD codes
Keita Ishizuka
39th Symposium on Algebraic Combinatorics (2023)
Construction of quaternary Hermitian LCD codes
Keita Ishizuka
Joint Research Meeting on Applied Mathematics 2022 (2022)
Classification of optimal quaternary Hermitian LCD codes of dimension 2
Keita Ishizuka
Workshop on Discrete Mathematics and Its Applications 2020 (2020)
Seminars
1Seminar and colloquium talks given at host institutions.
Linear complementary dual codes and its applications
Keita Ishizuka
Topology and Geometry Seminar, Hiroshima University (2025)
Other Publications
1Translations and non-refereed technical output.
DNA Data Storage Technology Review (Japanese translation)
Takaki Nakamura, Keita Ishizuka, Yuichi Aoki
DNA Data Storage Alliance / SNIA Japan (2026)
Grants & Funding
Competitive research funding. Role is shown in brackets.
Ongoing
Currently running.
Elucidating the Relationships between Codes, Graphs, and Hadamard Matrices
KAKENHI Fund for the Promotion of Joint International Research (Fostering Joint International Research) (JP25KK0004) [PI]
International collaboration with Prof. Hadi Kharaghani at the University of Lethbridge (Canada) to investigate deep structural connections between error-correcting codes, graph invariants, and Hadamard matrices through algebraic and computational methods.
Apr 2026 – Mar 2029
Elucidating the Relationships between Graph and Code Invariants
Grant-in-Aid for Early-Career Scientists (KAKENHI) (JP25K17290) [PI]
Developing a framework connecting graph-theoretic invariants with code-theoretic properties, enabling the use of graph isomorphism algorithms for code equivalence testing and the construction of new codes from combinatorial structures.
Apr 2025 – Mar 2028
Awarded, Starting
Selected in the public call; contract not yet concluded.
Foundations of Small-Alphabet Insertion-Deletion Correcting Codes for DNA Data Storage
ATLA Innovative Science and Technology Initiative for Security, Type C [PI]
Dec 2026 – Mar 2029
Completed
Finished projects.
Development and Security Evaluation of Post-Quantum Cryptography Using Coding Theory
Grant-in-Aid for Research Activity Start-up (KAKENHI) (JP24K23876) [PI]
Applying algebraic coding theory to analyze and improve the security of code-based post-quantum cryptographic schemes.
Jul 2024 – Mar 2026
Background
Appointments
2024 –
Research Associate
Mitsubishi Electric Corporation, Information Technology R&D Center
Post-quantum cryptography, code-based security
Research Visits
2026
University of Lethbridge
Canada
Jul – Dec 2026 · Supported by KAKENHI JP25KK0004 (own grant) · Host: Prof. Hadi Kharaghani
2023
University of Lethbridge
Canada
Sep – Nov 2023 · Tohoku University Graduate Program in Data Science (GP-DS) · Host: Prof. Hadi Kharaghani
Education
2021 – 2024
Ph.D. in Information Science
Tohoku University
2019 – 2021
M.S. in Information Science
Tohoku University
2013 – 2019
B.Eng.
Tohoku University
Service
Referee for Advances in Mathematics of Communications, Computational and Applied Mathematics, Finite Fields and Their Applications and Journal of Applied Mathematics and Computing.