Takeshi Nakai

2011/4  –  2015/3

　B.S. Engineering from The University of Electro-Communications 

2015/4  –  2017/3 

　M.S. Engineering from The University of Electro-Communications (Ohta-Iwamoto Laboratory)

2017/4  –  2020/3 

　SCSK Corporation 

2020/4  –  2021/3 

　Ph.D. in Engineering from The University of Electro-Communications (Iwamoto-Watanabe Laboratory)

　    Dissertation: Private Permutations in Card-Based Cryptography

　JSPS Research Fellow DC1 (Iwamoto-Watanabe Laboratory in The University of Electro-Communications) 

2021/4  –  2022/3 

　JSPS Research Fellow PD (Iwamoto-Watanabe Laboratory in The University of Electro-Communications) 

2022/4  –  present 

　Assistant Professor, Department of Computer Science and Engineering, Toyohashi University of Technology [Lab. Homepage] 

Journal Articles (Refereed)

1. Secure Multi-party Computation with Legally-Enforceable Fairness
   T. Nakai and K. Shinagawa, International Journal of Information Security, vol. 23, Springer, 2024.

2. Card-based Protocols for Private Set Intersection and Union

A. Doi, T. Ono, Y. Abe, T. Nakai, K. Shinagawa, Y. Watanabe, K. Nuida, and M. Iwamoto, New Generation Computing, vol. 42, Springer, 2024.

3. Card-based Cryptography with a Standard Deck of Cards, Revisited: Efficient Protocols in the Private Model

T. Nakai, K. Iwanari, T. Ono, Y. Abe, Y. Watanabe, and M. Iwamoto, New Generation Computing, vol. 42, Springer, 2024.

4. Perfectly-Sound Physical Zero-Knowledge Proofs for Instant Insanity

K. Hatsugai, Y. Abe, T. Nakai, K. Shinagawa, Y. Watanabe, and M. Iwamoto, IEICE transactions on fundamentals, vol. J107-A No.3,  IEICE, 2024  (in Japanese). 

5. Constant-Round Linear-Broadcast Secure Computation with Penalties
   T. Nakai and K. Shinagawa, Theoretical Computer Science, vol. 959, Elsevier, 2023. [arXiv ver.]

6. A Computationally Efficient Card-Based Majority Voting Protocol with Fewer Cards in the Private Model
   Y. Abe, T. Nakai, Y. Watanabe, M. Iwamoto, and K. Ohta, IEICE Transactions on Fundamentals, vol. E106.A, IEICE, 2023. 

7. How to Make a Secure Index for Searchable Symmetric Encryption, Revisited
   Y. Watanabe, T. Nakai, K. Ohara, T. Nojima, Y. Liu, M. Iwamoto, and K. Ohta, IEICE Transactions on Fundamentals, vol. E105.A, IEICE, 2022. [eprint ver.]

8. Efficient Card-based Majority Voting Protocols
   Y. Abe, T. Nakai, Y. Kuroki, S. Suzuki, Y. Koga, Y. Watanabe, M. Iwamoto, and K. Ohta, New Generation Computing, vol. 40, Springer, 2022.

9. Secure Computation for Threshold Functions with Physical Cards: Power of Private Permutations
   T. Nakai, S. Shirouchi, Y. Tokushige, M. Iwamoto, and K. Ohta,  New Generation Computing, vol. 40, Springer, 2022.

10. How to Solve Millionaires’ Problem with Two Kinds of Cards
    T. Nakai, Y. Misawa, Y. Tokushige, M. Iwamoto, and K. Ohta, New Generation Computing, vol. 39, Springer, 2021.

International Conference (Refereed)

1. Secure Computation with Penalties, Revisited: How to Handle Coins with Various Colors
   T. Nakai, The Cryptographers' Track at RSA Conference (CT-RSA 2025), LNCS 15598, Springer, 2025.

2. Card-based Secure Sorting Protocols based on the Sorting Networks
   K. Kato, T. Nakai, and K. Suzuki, 11th International Conference on Advanced Informatics: Concepts, Theory and Applications (ICAICTA 2024), IEEE, 2024.

3. Search Result Verifiability in Multi-User Dynamic Searchable Symmetric Encryption
   M. Son, T. Nakai, and K. Suzuki, 11th International Conference on Advanced Informatics: Concepts, Theory and Applications (ICAICTA 2024), IEEE, 2024.

4. Constant-Deposit Multiparty Lotteries on Bitcoin for Arbitrary Number of Players and Winners
   S. Uchizono, T. Nakai, Y. Watanabe, and M. Iwamoto, 26th Annual International Conference on Information Security and Cryptography (ICISC 2023), LNCS 14562, Springer, 2024.

5. Single-Shuffle Card-Based Protocols with Six Cards per Gate
   T. Ono, K. Shinagawa, T. Nakai, Y. Watanabe, and M. Iwamoto, 26th Annual International Conference on Information Security and Cryptography (ICISC 2023), LNCS 14562, Springer, 2024.

6. The Two Sheriffs Problem: Cryptographic Formalization and Generalization
   K. Sugimoto, T. Nakai, Y. Watanabe, and M. Iwamoto, 16th Annual International Conference on Combinatorial Optimization and Applications (COCOA 2023), LNCS 14461, Springer, 2023.

7. Secure Multi-Party Computation with Legally-Enforceable Fairness

T. Nakai and K. Shinagawa, 25th International Conference on Information and Communications Security (ICICS 2023), LNCS 14252, Springer, 2023. 

8. An Improvement of Multi-Party Private Set Intersection Based on Oblivious Programmable PRFs
   S. Shimizu, T. Nakai, Y. Watanabe, and M. Iwamoto, 2022 International Symposium on Information Theory and its Applications (ISITA 2022), IEEE, 2022. 

9. Card-based Cryptographic Protocols for Private Set Intersection
   A. Doi, T. Ono, T. Nakai, K. Shinagawa, Y. Watanabe, K. Nuida, and M. Iwamoto, 2022 International Symposium on Information Theory and its Applications (ISITA 2022), IEEE, 2022. 

10. Secure Computation with Non-equivalent Penalties in Constant Rounds
    T. Nakai and K. Shinagawa, 3rd International Conference on Blockchain Economics, Security and Protocols (Tokenomics 2021), Open Access Series in Informatics (OASIcs), vol. 97, Schloss Dagstuhl, 2022. 

11. Four Cards Are Enough for Card-Based Three-Input Voting Protocol Utilizing Private Permutations
    T. Nakai, S. Shirouchi, Y. Tokushige, M. Iwamoto, and K. Ohta, 10th International Conference on Information Theoretic Security (ICITS 2017), LNCS 10681, Springer, 2017.

12. Efficient Card-Based Cryptographic Protocols for Millionaires’ Problem Utilizing Private Permutations
    T. Nakai, Y. Misawa, Y. Tokushige, M. Iwamoto, and K. Ohta, 15th International Conference on Cryptology and Network Security (CANS 2016), LNCS 10052, Springer, 2016.

1. 2025/5: ISEC Activity Commendation

2. 2024/10: The BWS Innovation Research Award

3. 2022/1: SCIS Paper Award

4. 2017/3: The University of Electro-Communications Student Award

5. 2015/3: The University of Electro-Communications Meguro-Kai Award

• Information Processing Society of Japan (IPSJ)

• The Institute of Electronics, Information and Communication Engineers (IEICE)

• The International Association for Cryptologic Research (IACR)

• CSS2025 (Program Committee)

• ICAICTA2024 (Technical Program Committee)

• CSS2024 (Assistant of Program Chair)

• CSS2023 (Program Committee)

• IWSEC2023 (Local Organizing Committee)

• ICAICTA2022 (Local Arrangement Chairs)

• IWSEC2022 (Local Organizing Committee)