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. H. Okada, R. Player, S. Pohmann. “Fheanor: a new, modular FHE library for designing and optimising schemes." ePrint 2025/864

International Conference

1. H. Okada, T. Takagi. "Low Communication Threshold FHE from Standard (Module-)LWE," Asiacrypt 2025

2. S. Narisada, H. Okada, Y. Aikawa, K. Fukushima. "Refined Analysis of the Concrete Hardness of the Quasi-Cyclic Syndrome Decoding" IWSEC2025 

3. H. Okada, R. Player, S. Pohmann, C. Weinert. "On Algebraic Homomorphic Encryption and its Applications to Doubly-Efficient PIR" Eurocrypt 2025

4. H. Okada, T. Takagi. “Gram Root Decomposition over the Polynomial Ring: Application to Sphericalization of Discrete Gaussian” ICISSP 2025

5. H. Okada, R. Player, S. Pohmann, C. Weinert. "Towards Practical Doubly-Efficient Private Information Retrieval" FC 2024

6. S. Narisada, H. Okada, K. Fukushima, T. Nishide "Time-Memory Trade-off Algorithms for Homomorphically Evaluating Look-up Table in TFHE." WAHC 2024 

7. S. Narisada, S. Uemura, H. Okada, H. Furue, Y. Aikawa, K. Fukushima "Solving McEliece-1409 in One Day—Cryptanalysis with the Improved BJMM Algorithm." ISC2024

8. H. Okada, R. Player, S. Pohmann. “Homomorphic Polynomial Evaluation Using Galois Structure and Applications to BFV Bootstrapping”. Asiacrypt 2023

9. T. Nakamura, H. Okada, K. Fukushima, T. Isohara. “Achieving Private Verification in Multi-Stakeholder Environment and Application to Stable Matching”. ICEIS 2023

10. S. Narisada, H. Okada, K. Fukushima, S. Kiyomoto, T. Nishide. "GPU Acceleration of High-Precision Homomorphic Computation Utilizing Redundant Representation". WAHC 2023

11. H. Okada, K. Fukushima. “SoK: Towards CCA Secure Fully Homomorphic Encryption”. SECRYPT 2023

12. H. Okada, K. Fukushima, S. Kiyomoto, T. Takagi. “Spherical Gaussian Leftover Hash Lemma via the Rényi Divergence”. ACNS 2023

13. H. Okada, K. Fukushima. “Revisiting the DFT Test in the NIST SP 800-22 Randomness Test Suite”. ICISSP 2023

14. K. Fukushima, H. Okada, S. Takarabt, A. Korchi, M. Hamoud, K. Karray, Y. Souissy, S. Guilley. “Side-channel Analysis and Countermeasure for Implementation of Lattice-based Signature”. SECRYPT 2022

15. H. Okada, S. Kiyomoto, C. Cid. “A Comparison of GKE Protocols based on SIDH”. SECRYPT 2021

16. H. Okada, A. Takayasu, K. Fukushima, S. Kiyomoto, T. Takagi. “A Compact Digital Signature Scheme Based on the Module-LWR Problem”. ICICS 2020

17. H. Okada, S. Kiyomoto, C. Cid. “Integerwise Functional Bootstrapping on TFHE”. ISC 2020

18. H. Okada, C. Cid, S. Hidano, S. Kiyomoto. “Linear Depth Integer-Wise Homomorphic Division”. WISTP 2018

19. H. Okada, A. Takayasu, K. Fukushima, S. Kiyomoto, T. Takagi. “On the Complexity of the LWR-Solving BKW Algorithm”. ICISC 2018

20. H. Okada, K. Umeno, D. Handoko, M. F. Ihsan, R. Maharani, P. Nursetia, H. Rosyad, W. P. Taruno. “Brain Electrical Capacitance Volume Tomography Signals Analysis with Moving Maximum Lyapunov Exponents”. Advanced Science, Engineering and Medicine 7.10 (2015)

Journal Articles

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

2. S. Narisada, H. Okada, K. Fukushima, S. 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. H. Okada, A. Takayasu, K. Fukushima, S. Kiyomoto, T. 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. H. Okada, A. Takayasu, K. Fukushima, S. Kiyomoto, T. 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. H. Okada, K. 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．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 

2. 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. 

3. 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.

4. 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.

5. 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. 

6. 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. 

7. 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

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

• 2025-present Associate Editor of IEICE Trans. Fundamentals

• 2025 Secretary, IWSEC 2025

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

• 2020 Program committee,  SCIS 2020

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)