报告题目：Information-Theoretic Security

主讲人：Yu Long Chen （Postdoctoral Researcher at KU Leuven's COSIC group）

报告时间：2026年03月30日（星期一）16:00-17:00

报告地点：厦门大学西部片区信息学院3号楼103会议室

报告摘要：In this talk, we study the problem of attacking multiple users under indistinguishability security notions. Conventional multi-user security does not adequately capture the cost of compromising several targets. To address this gap, we extend the power-bound framework of Beyne and Chen(CRYPTO 2024) by introducing multi-target power bounds.We first show that for independent users, like in standard-model constructions,single-user power bounds can be lifted to multi-target bounds.Applying this approach to the PRP-PRF switching lemma, we recover the expected linear behavior: attacking u independent users requires u times as many queries as to attack one user.Our main contribution addresses the dependent user setting, which naturally arises for ideal-model constructions where users have independent keys but share a common public primitive. We show how to lift single-user power bounds to multi-target bounds in the presence of such cross-user dependencies.Instantiating our method for the Even-Mansour reveals a sharp dichotomy: when the number of primitive queries dominates, the cost of attacking u users grows linearly with u;otherwise, the complexity increases only by a factor of \sqrt{u}. This matches known precomputation attacks.

报告人简介：Yu Long Chen is a cryptography researcher specializing in information-theoretic security. He received his Ph.D. in cryptography from KU Leuven under the supervision of Bart Preneel and is currently a postdoctoral researcher at KU Leuven's COSIC group. He previously worked for three years at the Computer Security Division of the U.S. National Institute of Standards and Technology (NIST), where he contributed to the development of federal cybersecurity standards, including the SP 800-series and FIPS 140-3. At NIST, he served as the technical expert for the NIST accordion mode project, co-authored NIST Interagency Report 8552 (Requirements for Cryptographic Accordions), and played a central role in the technical evaluation that led to the selection of the HCTR2 technique as the accordion construction.

His research develops new security models for cryptographic modes of operation motivated by emerging deployment settings and constraints found in modern computing systems. His work has appeared in leading venues such as CRYPTO, EUROCRYPT, and ASIACRYPT, and he is a co-designer of Elephant, a finalist in the NIST Lightweight Cryptography standardization project.

邀请人：计算机科学与技术系 沈耀斌副教授