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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Journal Articles

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

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

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

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

5. Hiroki Okada, Ken Umeno. “Randomness Evaluation With the Discrete Fourier Transform Test Based on Exact Analysis of the Reference Distribution”. 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. 岡田 大樹，高木 剛．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． ISEC 3月研究会 2026年 

2. 岡田 大樹，高木 剛．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． ISEC 5月研究会 2025年 

3. 岡田 大樹，高木 剛．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．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. 中村 徹，岡田 大樹，福島 和英，磯原 隆将．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．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. 岡田 大樹，Benjamin R. Curtis，清本 晋作，Carlos Cid．TFHE における Integer-wise 型一般化 Bootstrapping．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. 岡田 大樹，高安 敦，福島 和英，清本 晋作，高木 剛．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．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. 岡田 大樹，梅野 健．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．信学技報, vol. 115, no. 178, CCS2015-42, pp. 73–78, 2015 年 8 月. 

8. 岡田 大樹，梅野 健．カオス的ユニタリ変換を用いた乱数検定．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

External Reviewer

• CRYPTO, Asiacrypt, PQCrypto,  IEEE Transaction on Information Forensics and Security, IEICE Trans. Fundamentals, etc.

Local Organizing Committee

• Secretary, IWSEC 2025

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)