LiCi分组密码算法的不可能差分分析

LiCi是由Patil等人(2017)提出的轻量级分组密码算法。由于采用新型的设计理念，该算法具有结构紧凑、能耗低、占用芯片面积小等优点，特别适用于资源受限的环境。目前该算法的安全性备受关注，Patil等人声称：16轮简化算法足以抵抗经典的差分攻击及线性攻击。该文基于S盒的差分特征，结合中间相遇思想，构造了一个10轮的不可能差分区分器。基于此区分器，向前后各扩展3轮，并利用密钥编排方案，给出了LiCi的一个16轮的不可能差分分析方法。该攻击需要时间复杂度约为2^83.08次16轮加密，数据复杂度约为2^59.76选择明文，存储复杂度约为2^76.76数据块，这说明16轮简化的LiCi算法无法抵抗不可能差分攻击。

Impossible Differential Cryptanalysis of LiCi Block Cipher

LiCi algorithm is a newly lightweight block cipher. Due to its new design idea adopted by Patil et al, it has the advantages of compact design, low energy consumption and less chip area, thus is is especially suitable for resource-constrained environments. Currently, its security receives extensively attention, and Patil et al. claimed that the 16-round reduced LiCi can sufficiently resist both differential attack and linear attack. In this paper, a new 10-round impossible differential distinguisher is constructed based on the differential characteristics of the S-box and the meet-in-the-middle technique. Moreover, on the basis of this distinguisher, a 16-round impossible differential attack on LiCi is proposed by respectively extending 3-round forward and backward via the key scheduling scheme. This attack requires a time complexity of about 283.08 16-round encryptions, a data complexity of about 259.76 chosen plaintexts, and a memory complexity of 276.76 data blocks, which illustrates that the 16-round LiCi cipher can not resist impossible differential attack.