Ky Nguyen

Full name: Nguyễn Ngọc Kỷ

I'm a Temporary Lecturer and Research Fellow (equivalent to Attaché Temporaire d'Enseignement et de Recherche position in the French academic system) at École normale supérieure. In December 2024, I completed my PhD in Cryptography at École normale supérieure, for which I'm profoundly grateful to be under the supervision of David Pointcheval and Duong Hieu Phan. Previously I was normalien at École normale supérieure (Computer Science 2018) and alumnus (no graduation) at Ho Chi Minh City University of Technology (K2015).

Research

PhD Thesis

Multi-User Computation over Encrypted Data
[Thesis (PDF)] [Defense Slides (PDF)]

Preprints

1. Traitor Tracing in Multi-sender Setting. (TMCFE: Traceable Multi-client Functional Encryption) Cryptology ePrint Archive, Report 2025/364 (2025) [Paper]
   With Xuan Thanh Do, Dang Truong Mac, Duong Hieu Phan, Quoc-Huy Vu.
2. Chosen-Ciphertext Security for Functional Encryption with Multiple Users: Definitions and Generic Concrete Constructions. Cryptology ePrint Archive, Report 2025/025 (2025) [Paper]
   (Old title: Chosen-Ciphertext Security for Inner Product FE: Mutli-Client and Multi-Input, Generically.)
3. Dynamic Decentralized Functional Encryption with Strong Security. Cryptology ePrint Archive, Report 2022/1532 (2022) [Paper]
   With David Pointcheval, Robert Schädlich. (Old title: Function-Hiding Dynamic Decentralized Functional Encryption for Inner Products.)

Journal papers

1. Decentralized Multi-Client Functional Encryption with Strong Security. IACR Communications in Cryptology 1(2) (2024) [Paper]
   With David Pointcheval, Robert Schädlich.
2. The Eleventh Power Residue Symbol. Journal of Mathematical Cryptology 15(1), 111 - 122 (2021) [Paper]
   With Marc Joye, Oleksandra Lapiha, David Naccache.

Conference papers

1. Multi-Client Functional Encryption with Public Inputs and Strong Security. In: Public-Key Cryptography - IACR PKC 2025. Springer (2025) [Paper]
   With Duong Hieu Phan, David Pointcheval.
2. Dynamic Decentralized Functional Encryption: Generic Constructions with Strong Security. In: Public-Key Cryptography - IACR PKC 2025. Springer (2025) [Paper]
   With David Pointcheval, Robert Schädlich.
3. Pairing-Free Blind Signatures from Standard Assumptions in the ROM. In: Advances in Cryptology - IACR CRYPTO 2024. Springer (2024) [Paper]
   With Julia Kastner, Michael Reichle.
4. Optimal Security Notion for Decentralized Multi-Client Functional Encryption. In: Proceedings of the 21st International Conference on Applied Cryptography and Network Security (ACNS' 23). Springer (2023). [Paper]
   With Duong Hieu Phan, David Pointcheval.
5. Multi-Client Functional Encryption with Fine-Grained Access Control. In: Advances in Cryptology - IACR ASIACRYPT 2022. Springer (2022) [Paper]
   With Duong Hieu Phan, David Pointcheval.
6. Cumulatively All-Lossy-But-One Trapdoor Functions from Standard Assumptions. In: Proceedings of the 13th Conference on Security in Communication Networks (SCN' 22). Springer (2022) [Paper]
   With Benoît Libert, Alain Passelègue.
7. WI is Almost Enough: Contingent Payment All Over Again. In: Proceedings of the 2020 ACM SIGSAC Conference on Computer and Communications Security (CCS' 20). Association for Computing Machinery, New York, NY, USA (2020) [Paper] [Tool]
   With Miguel Ambrona, Masayuki Abe.

Teaching

• Autumn 2024: Algorithmique at École normale supérieure (Tutorials)
• Autumn 2024: Algorithmique et Applications at CPES - PSL University (Tutorials)
• Spring 2024: Initiation à la Cryptologie at École normale supérieure (Tutorials)
• Autumn 2024, 2023, 2022: Introduction to Zero-Knowledge Proofs at ESILV (Lectures + Tutorials)
• Autumn 2022: Symmetric Cryptography at ESILV (Lectures + Tutorials)
• Spring 2022: Asymmetric Cryptography at ESILV (Lectures + Tutorials)

Professional/Academic Service

• Member in Program Committee of: International Conference on Cryptology and Network Security - CANS (2025)
• External reviewer for: Designs, Codes and Cryptography ; Journal of Cryptology ; Asiacrypt (2024, 2022) ; Crypto (2025, 2023) ; Eurocrypt (2025, 2024, 2023) ; Public-Key Cryptography (2024, 2023) ; Theory of Cryptography Conference (2024)
• Elected member in: the Scientific Council of École normale supérieure (Mandate 2023-2025) ; the Laboratory Council of the Computer Science department at École normale supérieure (Mandate 2024-2025).

Contact