题目：The phantom of differential characteristics

报告人：孙兵，空军长春飞行学院第41期飞行学员

报告时间：2017年10月28日21:30-22:30

报告地点：知新楼B1201

摘要：A block cipher is usually designed with a specific key schedule which is very difficult to be exploited in the differential cryptanalysis. In this talk, we study a profound effect of the key schedules on the differential characteristics. Noticing the sensitivity in the probability of the characteristics to specific keys, we label the keys where a characteristic is of nonzero probability by the effective keys. We propose the concept of singular characteristics which are characteristics with no effective keys, and exploit an algorithm by studying the key schedule to sieve them out which is successfully applied to the AES-128 and PRINCE. Interestingly, a valid characteristic in AES-128 is shown be singular in AES-192, and the singular characteristics turn out to be the majority in some differentials of AES-128. Moreover, taking the possible mismatch or conflict of effective keys in a differential or multiple differentials into consideration, we present singular clusters with concrete examples found in the AES and PRINCE. Our results indicates a gap over the perspectives of the designer and the attacker on the fundamental assumptions of the differential characteristics in block ciphers, thus, a closer look at the characteristics is inevitable before any attack is claimed.

报告人简介：孙兵，空军长春飞行学院第41期飞行学员，2009年毕业于国防科技大学，获理学博士学位，比利时鲁汶大学访问学者，现为国防科技大学理学院数学与系统科学系讲师。主要从事对称密码算法的分析与设计研究，在CRYPTO、EUROCRYPT 等密码学国际学术会议和期刊发表学术论文50余篇，出版学术专著1部。