中文摘要：

LBlock算法是2011年提出的轻量级分组密码，适用于资源受限的环境．目前，关于LBlock最好的分析结果为基于14轮不可能差分路径和15轮的相关密钥不可能差分路径，攻击的最高轮数为22轮．为研究LBlock算法抵抗不可能差分性质，结合密钥扩展算法的特点和轮函数本身的结构，构造了新的4条15轮相关密钥不可能差分路径．将15轮差分路径向前扩展4轮、向后扩展3轮，分析了22轮LBlock算法．在已有的相关密钥不可能差分攻击的基础上，深入研究了轮函数中S盒的特点，使用2类相关密钥不可能差分路径．基于部分密钥分别猜测技术降低计算量，分析22轮LBlock所需数据量为2^61个明文，计算量为2^59.58次22轮加密．

英文摘要：

Abstract LBlock is a lightweight block cipher aiming at constrained resources, which was proposed in ACNS 201]. It is known that 14 round differential rules and 15 round related-key differential rules have been proposed not long ago, based on which the best results using impossible differential attack on LBloek reach to the maximum round of 22. To analyze the impossible differential property of LBlock cipher, combining with the characteristic of the key schedule and structure of round function, four 15-round related-key differential rules are constructed. Then, using the differential rule to extend the 4-round forward, and 3-round afterward, 22-round LBloek is proposed. On the basis of the existing related-key impossible differential attack, the S-boxes in the round function are discussed, and two kinds of related-key differential rules are applied. Based on the technology of partial key-byte guessing to reduce the time complexity, it is show that the attack on 22-round requires the data complexity of 2^61 chosen plaintexts and time complexity of 2^59.58 22-round encryptions.