Hiroki Okada
(岡田 大樹)
✉️ ir-okada [at] kddi.com

Education and Affiliations

2007-2010 Osaka Ibaraki  High School
2010-2014 Kyoto University, Undergraduate School of Informatics and Mathematical Science
2014-2016 Kyoto University, Department of Applied Mathematics and Physics, Graduate School of Informatics

2016-present KDDI Corporation

2017-present KDDI Research, Inc. Information Security Laboratory
2023-present Ph.D: The University of Tokyo, Graduate School of Information Science and Technology, Mathematical Cryptography Laboratory

Preprints

1. Hiroki Okada, Rachel Player, Simon Pohmann. “Fheanor: a new, modular FHE library for designing and optimising schemes." ePrint 2025/864

International Conference

1. "Threshold FHE with Short Decryption Shares without a Semi-trusted Server"
   Hiroki Okada, Tsuyoshi Takagi
   to appear at ACISP 2026

2. "Efficient Homomorphic String Search via TFHE"
   Shintaro Narisada, Hiroki Okada, Takashi Nishide, Kazuhide Fukushima
   to appear at ACISP 2026 (Industry Track)

3. "Low Communication Threshold FHE from Standard (Module-)LWE"
   Hiroki Okada, Tsuyoshi Takagi
   Asiacrypt 2025

4. "Refined Analysis of the Concrete Hardness of the Quasi-Cyclic Syndrome Decoding"
   Shintaro Narisada, Hiroki Okada, Yusuke Aikawa, Kazuhide Fukushima
   IWSEC2025

5. "On Algebraic Homomorphic Encryption and its Applications to Doubly-Efficient PIR"
   Hiroki Okada, Rachel Player, Simon Pohmann, Christian Weinert
   Eurocrypt 2025

6. “Gram Root Decomposition over the Polynomial Ring: Application to Sphericalization of Discrete Gaussian”
   Hiroki Okada, Tsuyoshi Takagi
   ICISSP 2025

7. "Towards Practical Doubly-Efficient Private Information Retrieval"
   Hiroki Okada, Rachel Player, Simon Pohmann, Christian Weinert
   FC 2024

8. "Time-Memory Trade-off Algorithms for Homomorphically Evaluating Look-up Table in TFHE"
   Shintaro Narisada, Hiroki Okada, Kazuhide Fukushima, Takashi Nishide
   WAHC 2024

9. "Solving McEliece-1409 in One Day—Cryptanalysis with the Improved BJMM Algorithm"
   Shintaro Narisada, Shusaku Uemura, Hiroki Okada, Hiroki Furue, Yusuke Aikawa, Kazuhide Fukushima
   ISC2024

10. “Homomorphic Polynomial Evaluation Using Galois Structure and Applications to BFV Bootstrapping”
    Hiroki Okada, Rachel Player, Simon Pohmann
    Asiacrypt 2023

11. “Achieving Private Verification in Multi-Stakeholder Environment and Application to Stable Matching”
    Toru Nakamura, Hiroki Okada, Kazuhide Fukushima, Takamasa Isohara
    ICEIS 2023

12. "GPU Acceleration of High-Precision Homomorphic Computation Utilizing Redundant Representation"
    Shintaro Narisada, Hiroki Okada, Kazuhide Fukushima, Shinsaku Kiyomoto, Takashi Nishide
    WAHC 2023

13. “SoK: Towards CCA Secure Fully Homomorphic Encryption”
    Hiroki Okada, Kazuhide Fukushima
    SECRYPT 2023

14. “Spherical Gaussian Leftover Hash Lemma via the Rényi Divergence”
    Hiroki Okada, Kazuhide Fukushima, Shinsaku Kiyomoto, Tsuyoshi Takagi
    ACNS 2023

15. “Revisiting the DFT Test in the NIST SP 800-22 Randomness Test Suite”
    Hiroki Okada, Kazuhide Fukushima
    ICISSP 2023

16. “Side-channel Analysis and Countermeasure for Implementation of Lattice-based Signature”
    Kazuhide Fukushima, Hiroki Okada, Sofiane Takarabt, Amina Korchi, Meziane Hamoud, Khaled Karray, Youssef Souissy, Sylvain Guilley
    SECRYPT 2022

17. “A Comparison of GKE Protocols based on SIDH”
    Hiroki Okada, Shinsaku Kiyomoto, Carlos Cid
    SECRYPT 2021

18. “A Compact Digital Signature Scheme Based on the Module-LWR Problem”
    Hiroki Okada, Atsushi Takayasu, Kazuhide Fukushima, Shinsaku Kiyomoto, Tsuyoshi Takagi
    ICICS 2020

19. “Integerwise Functional Bootstrapping on TFHE”
    Hiroki Okada, Shinsaku Kiyomoto, Carlos Cid
    ISC 2020

20. “Linear Depth Integer-Wise Homomorphic Division”
    Hiroki Okada, Carlos Cid, Seira Hidano, Shinsaku Kiyomoto
    WISTP 2018

21. “On the Complexity of the LWR-Solving BKW Algorithm”
    Hiroki Okada, Atsushi Takayasu, Kazuhide Fukushima, Shinsaku Kiyomoto, Tsuyoshi Takagi
    ICISC 2018

22. “Brain Electrical Capacitance Volume Tomography Signals Analysis with Moving Maximum Lyapunov Exponents”
    Hiroki Okada, Ken Umeno, Dwi Handoko, Muhammad Fathul Ihsan, Rizky Maharani, Panji Nursetia, Habib Rosyad, Warsito Purwo Taruno
    Advanced Science, Engineering and Medicine 7.10 (2015)

Journal Articles

1. “Integer-Wise Functional Bootstrapping on TFHE: Applications in Secure Integer Arithmetics”
   Hiroki Okada, Shinsaku Kiyomoto, Carlos Cid
   Information 12.8 (2021)

2. “Faster Rotation-Based Gauss Sieve for Solving the SVP on General Ideal Lattices”
   S. Narisada, Hiroki Okada, Kazuhide Fukushima, Shinsaku Kiyomoto
   IEICE Trans. Fundam. Electron. Commun. Comput. Sci. E104.A.1 (2021), pp. 79–88

3. “A Compact Digital Signature Scheme Based on the Module-LWR Problem”
   Hiroki Okada, Atsushi Takayasu, Kazuhide Fukushima, Shinsaku Kiyomoto, Tsuyoshi Takagi
   IEICE Trans. Fundam. Electron. Commun. Comput. Sci. E104.A.9 (2021), pp. 1219–1234

4. “On the Complexity of the LWR-Solving BKW Algorithm”
   Hiroki Okada, Atsushi Takayasu, Kazuhide Fukushima, Shinsaku Kiyomoto, Tsuyoshi Takagi
   IEICE Trans. Fundam. Electron. Commun. Comput. Sci. E103.A.1 (2020), pp. 173–182

5. “Randomness Evaluation With the Discrete Fourier Transform Test Based on Exact Analysis of the Reference Distribution”
   Hiroki Okada, Ken Umeno
   IEEE Trans. Inf. Forensics Secur. 12.5 (2017), pp. 1218–1226

Talks

1.  FHE.org meetups  on Feb 5th, 2026: "Low Communication Threshold FHE from Standard (Module-)LWE"

Workshops in Japan

1. 信頼できるサーバが不要な低通信量しきい値完全準同型暗号
   岡田 大樹，高木 剛
   ISEC 3月研究会 2026年 

2. 標準的な(Module-)LWEに基づく低通信量なしきい値完全準同型暗号
   岡田 大樹，高木 剛
   ISEC 5月研究会 2025年 

3. 標準的な(Ring-)LWEに基づくシミュレーション安全なしきい値公開鍵暗号
   岡田 大樹，高木 剛
   2024年暗号と情報セキュリティシンポジウム (SCIS2024)，2A3-3，2024 年

4. マルチステークホルダ環境を考慮したプライバシと透明性を両立するプロトコルの考察
   中村 徹，岡田 大樹，福島 和英，磯原 隆将
   2022 年コンピュータセキュリティシンポジウム (CSS2022)，2A2-I-2， 2022 年

5. TFHE における Integer-wise 型一般化 Bootstrapping
   岡田 大樹，Benjamin R. Curtis，清本 晋作，Carlos Cid
   2020 年暗号と情報セキュリティシンポジウム (SCIS2020)，1B1-3，2020 年

6. LWR 問題解読のためのサンプル増幅法を用いたBKW アルゴリズム
   岡田 大樹，高安 敦，福島 和英，清本 晋作，高木 剛
   2017 年コンピュータセキュリティシンポジウム (CSS2017)，1E4-2，2017 年

7. 複数の系列を同時に使用する離散フーリエ変換検定法について
   岡田 大樹，梅野 健
   信学技報, vol. 115, no. 178, CCS2015-42, pp. 73–78, 2015 年 8 月

8. カオス的ユニタリ変換を用いた乱数検定
   岡田 大樹，梅野 健
   信学技報, vol. 114, no. 145, NLP2014- 42, pp. 59–64, 2014 年 7 月

Awards

1. ISEC encouragement award 2025
   for the paper : 標準的な(Module-)LWEに基づく低通信量なしきい値完全準同型暗号

2. Symposium on Cryptography and Information Security 2024 (SCIS 2024), Best Paper Award
   for the paper : 標準的な(Ring-)LWEに基づくシミュレーション安全なしきい値公開鍵暗号

3. Invited to the journal Information as a best paper from ISC 2020 and ISC 2021
   for the paper : Integerwise Functional Bootstrapping on TFHE

4. Computer Security Symposium 2017 (CSS2017), Encouraging Award
   for the paper : LWR 問題解読のためのサンプル増幅法を用いたBKW アルゴリズム

5. Complex Communication Sciences Workshop 2015, Encouraging Award
   for the paper : 複数の系列を同時に使用する離散フーリエ変換検定法について 

Activities

Program Committee

• Asiacrypt 2026

• SCIS 2020

Local Organizing Committee

• Secretary, IWSEC 2025

External Reviewer

• CRYPTO, Asiacrypt, PQCrypto, ISITA, ProvSec, SECRYPT, CSCML, ...

• DCC (Designs, Codes and Cryptography), IEEE Transaction on Information Forensics and Security, IEICE Trans. Fundamentals, ...

Technical Committee

• 2023–2026 Secretary, Technical Committee on Information Security (ISEC), IEICE

Editorial Board

• 2025-present Guest Editor of Special Section  on Cryptography and Information Security in the IEICE Trans. Fundamentals 2027

• 2025-present Associate Editor of IEICE Trans. Fundamentals

Media 

1. 2021 年 2 月 8 日，「高性能の電子署名，米標準候補上回る」日本経済新聞

Official Qualification (in Japan)

• 電気通信主任技術者 (伝送交換) (資格者証番号: AA21A01838J) 

• 第一級陸上特殊無線技士 (免許番号: ABOJ00883)