Yi-Fu Lai

Profile

Nice to meet you! I am Yi-Fu Lai hailing from Taiwan. Since October 2023, I've been working as a post-doc researcher in Eike Kiltz's lab within CASA at Ruhr-Universität Bochum. Before that, I was a mathematics PhD student at the University of Auckland, where I was fortunate to have Steven Galbraith as my advisor, starting from 2020.

(PhD Thesis: Advanced Isogeny-based Cryptosystems.)

My primary research interest is in constructing cryptosystems that are provably secure from post-quantum assumptions. I am particularly interested in advancing the boundaries of the existing cryptographic paradigms and exploring the limits of cryptographic tools. In pursuit of this goal, I also enjoy doing cryptographic analysis and reductions to understand the essences of cryptosystems.

Keywords: Post-quantum cryptography, isogeny cryptography, lattice cryptography, code cryptography, public-key cryptosystems; oblivious transfers, ring signatures, group signatures, blind signatures, generic proof systems, zkSNARKs, identification schemes, verifiable random functions.

If you have any questions or are interested in my research, feel free to reach out to me.

Contact

Yi-Fu.Lai [at] ruhr-uni-bochum de ; 27182818284fu.lai [at] gmail com

Publications & Preprints

Asiacrypt2025. Tanuki: New Frameworks for (Concurrently Secure) Blind Signatures from Post-Quantum Groups Actions. Lucjan Hanzlik, Yi-Fu Lai, Marzio Mula, Eugenio Paracucchi, Daniel Slamanig, Gang Tang. (ia.cr/2025/1100)
Hidden Number Problems in Fiat-Shamir based Post-Quantum Signatures. Yi-Fu Lai, Jonas Meers, Julian Nowakowski (ia.cr/2025/913)
(Note) A Note on Isogeny Group Action-Based Pseudorandom Functions. Yi-Fu Lai. (ia.cr/2024/2042)
CiC-2024. Erebor and Durian:Full Anonymous Ring Signatures from Quaternions and Isogenies. Giacomo Borin, Yi-Fu Lai, Antonin Leroux. (ia.cr/2024/1185)
PKC2024. A Simpler and More Efficient Reduction of DLOG to CDH for Abelian Group Actions. Steven Galbraith, Yi-Fu Lai, Hart Montgomery. (ia.cr/2024/191)
PKC2024. Breaking Parallel ROS: Implication for Isogeny and Lattice-based Blind Signatures. Shuichi Katsumata, Yi-Fu Lai, Michael Reichle. (ia.cr/2023/1603)
Indocrypt2023. Malleable Commitments from Group Actions and Zero-Knowledge Proofs for Circuits based on Isogenies. Mingjie Chen, Yi-Fu Lai, Abel Laval, Laurane Marco, Christophe Petit. (ia.cr/2023/1710)
Crypto2023. CSI-Otter: Isogeny-based (Partially) Blind Signatures from the Class Group Action with a Twist. Shuichi Katsumata, Yi-Fu Lai, Jason T. LeGrow, Ling Qin. (ia.cr/2023/1239) Video
CiC-2024. CAPYBARA and TSUBAKI: Verifiable Random Functions from Group Actions and Isogenies. Yi-Fu Lai (ia.cr/2023/182)
ACNS2023. Efficient Isogeny Proofs Using Generic Techniques. Kelong Cong, Yi-Fu Lai, Shai Levin. (ia.cr/2023/037)
PQCrypto2022. Attack on SHealS and HealS: the Second Wave of GPST. Steven Galbraith and Yi-Fu Lai. (ia.cr/2022/443) Video
Eurocrypt2022. Group Signatures and More from Isogenies and Lattices: Generic, Simple, and Efficient. Ward Beullens, Samuel Dobson, Shuichi Katsumata, Yi-Fu Lai, Federico Pintore, (ia.cr/2021/1366) Video
Collusion Resistant Revocable Ring Signatures and Group Signatures from Hard Homogeneous Spaces. Yi-Fu Lai, Samuel Dobson. (ia.cr/2021/1365) (Stop updating due to impracticability.)
Eurocrypt2021. Compact, Efficient and UC-Secure Isogeny-Based Oblivious Transfer. Yi-Fu Lai, Steven Galbraith, Cyprien Delpech de Saint Guilhem,(ia.cr/2020/1012) Video

Journal Articles

CiC-2024. Erebor and Durian:Full Anonymous Ring Signatures from Quaternions and Isogenies. Giacomo Borin, Yi-Fu Lai, Antonin Leroux. Communications in Cryptology 2024. Open Access Link
CiC-2024. CAPYBARA and TSUBAKI: Verifiable Random Functions from Group Actions and Isogenies. Yi-Fu Lai. Communications in Cryptology 2024. Open Access Link
DCC-2024. CSI-Otter: Isogeny-based (Partially) Blind Signatures from the Class Group Action with a Twist. Shuichi Katsumata, Yi-Fu Lai, Jason T. LeGrow, Ling Qin. Designs, Codes and Cryptography, 2024. Springer. Full version of [C:KLLQ23] Open Access Link
DCC-2023. Group Signatures and More from Isogenies and Lattices: Generic, Simple, and Efficient. Ward Beullens, Samuel Dobson, Shuichi Katsumata, Yi-Fu Lai, Federico Pintore. Designs, Codes and Cryptography, 2023. Springer. Full version of [EC:BDKLP22] Open Access Link

Community

Research Visits

We submit so we review. I am happy to contribute to the following peer-review process:

Program Committee:

Eurocrypt2026, CT-RSA2025, ISC2025

Reviewing for the following conferences:

Asiacrypt2021/ PQCrypto2021/ Eurocrypt2022/ Mathcrypt2022/ AsiaCCS2023/ Eurocrypt2023/ Crypto2023/ Asiacrypt2023/ Mathcrypt2023/ Eurocrypt2024/ Asiacrypt2024/ Eurocrypt2025/ PKC2025/ Crypto2025/ Asiacrypt2025

I have been fortunate enough to visit the following institutes and departments for academic communications:

CISPA, Germany: 31 Mar 2025 - 5 April 2025
Wuhan University, China: 03 Jan 2025 - 13 Jan 2025
AIST, Japan: 22 May 2023 - 20 Jul 2023
IBM Research Zurich, Switzerland: 4 Jul 2022 - 22 Jul 2022
COSIC KU Leuven, Belgium: 21 Jun 2022 - 1 Jul 2022
University of Birmingham: 13 Jun 2022 - 20 Jun 2022
CWI Amsterdam, Netherlands: 3 Jun 2022 - 10 Jun 2022

Available Slides

"Leakage Resilience of Post Quantum Signature -- with a Focus on LESS" @ Link
"A Simpler and More Efficient Reduction of DLOG to CDH for Abelian Group Actions" @ (PKC2024 Link).
"Breaking Parallel ROS: Implication for Isogeny and Lattice-based Blind Signatures." @ (PKC2024 Link).
"CSI-Otter: Isogeny-based (Partially) Blind Signatures from the Class Group Action with a Twist and a New ROS Attack." (Leuven Isogeny Day 4 Link)
"CSI-Otter: Isogeny-based (Partially) Blind Signatures from the Class Group Action with a Twist" (Google Drive Link)
"Attack on SHealS and HealS: the Second Wave of GPST" (PQCrypto2022 Link) in PQCrypto2022 Video
"Group Signatures and More from Isogenies and Lattices: Generic, Simple, and Efficient" (Eurocrypt2022 Link) in Eurocrypt2022 Video
" Compact, Efficient and UC-Secure Isogeny-Based Oblivious Transfer" (Eurocrypt2021 Link) in Eurocrypt2021 Video

Selected Talks/Seminars

Seminar: "Leakage Resilience of Post Quantum Signature -- with a Focus on LESS" @ CISPA, Germany.
Talk: "Leakage Resilience of Post Quantum Signature -- with a Focus on LESS" @PQC Workshop 2024, University of Auckland, New Zealand.
Talk: "A Simpler and More Efficient Reduction of DLOG to CDH for Abelian Group Actions" @ PKC2024, Australia.
Talk: "Breaking Parallel ROS: Implication for Isogeny and Lattice-based Blind Signatures." @ PKC2024, Australia.
Seminar: "A Simpler and More Efficient Reduction of DLog to CDH for Abelian Group Actions" 0328.2023 @ Ruhr-University Bochum, Germany.
Seminar: "A Simpler and More Efficient Reduction of DLog to CDH for Abelian Group Actions" 0229.2023 @ Université libre de Bruxelles, Belgium.
Seminar: "CSI-Otter: Isogeny-based (Partially) Blind Signatures from the Class Group Action with a Twist and a New ROS Attack." 1020.2023 @ CWI seminar, Neatherland.
Talk: "CSI-Otter: Isogeny-based (Partially) Blind Signatures from the Class Group Action with a Twist and a New ROS Attack." 1013.2023 @ KU Leuven, Belgium. (Leuven Isogeny Day 4)
Seminar: "CSI-Otter: Isogeny-based (Partially) Blind Signatures from the Class Group Action with a Twist" 0623.2023 @ University of Birmingham seminar, UK.
Seminar: "Isogeny-based Cryptosystems (with a Focus on Blind Signature)." 0616.2023 @ AIST, Japan.
Talk: "Attack on SHealS and HealS: the Second Wave of GPST." @ PQCrypto2022, Online.
Talk: "Group Signatures and More from Isogenies and Lattices: Generic, Simple, and Efficient." 0707.2022 @ IBM Zurich, Switzerland.(An Ordinary Day in Supersingularland)
Talk: "Attack on SHealS and HealS: the Second Wave of GPST." 0630.2022 @ COSIC-KU Leuven, Belgium.
Talk: "Group Signatures and More from Isogenies and Lattices: Generic, Simple, and Efficient." 0613.2022 @ University of Birmingham, UK.
Talk: "Group Signatures and More from Isogenies and Lattices: Generic, Simple, and Efficient." @ Eurocrypt2022, Norway.
Seminar: "Group Signatures and More from Isogenies and Lattices: Generic, Simple, and Efficient." 0610.2022 @ CWI Amsterdam, Netherlands.
Talk: "Compact, Efficient and UC-Secure Isogeny-Based Oblivious Transfer." @ Eurocrypt2021, Croatia.
Talk: "Compact, Efficient and UC-Secure Isogeny-Based Oblivious Transfer." May 2021 @ University of Auckland.

Seminar: in a team. / Talk: more open or larger.

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