Block ciphers are characterized by their high speed, easy standardization and hardware and software implementation, usually as the core system of data encryption, digital signature, authentication and key management in information and network security. It is difficult to separate the security analysis and design of cryptographic algorithms. On the one hand, in the process of ciphers security analysis, experience can be accumulated for the design of more secure ciphers. On the other hand, in the design of cryptographic algorithms, there will be a lot of practical significance of technology and application value of knowledge. SPN block ciphers are an important part of block ciphers, which is of great significance to be studied and analyzed. Square is a block cipher with substitution-permutation network, which operates on 128-bit blocks and 128-bit keys. By studying the structural characteristics and the properties of truncated differential of Square, we construct a 4-round meet-in-the middle distinguisher by using differential enumeration technique and multiple sets, and give a meet-in-the-middle attack on 6-round Square. The new distinguisher is determined by 10 parameters. Based on the new distinguisher, we extend the meet-in-the-middle attack on 6-round Square for the first time with 2109 chosen plantexts, 2109 computations and 284memories.%分组密码具有速度快、易于标准化和便于软硬件实现等特点,通常是信息和网络安全中实现数据加密、数字签名、认证及密钥管理的核心体制.密码算法的安全性分析与设计两者难以分离,一方面,在对密码进行安全性分析的过程中,可以为设计出更加安全的密码积累经验,另一方面,在密码算法的设计中也会涉及很多具有现实意义的技术和应用价值的知识.作为分组密码的一个重要组成部分—SPN型分组密码,对其进行研究和分析具有很大的现实意义.Square是SPN型分组密码其中之一,其密钥长和分组长都为128 bit.通过研究Square算法的结构特征和一类截断差分的性质,利用差分枚举技术和多重集构造了Square算法的4轮中间相遇区分器,给出了对6轮Square密码算法的中间相遇攻击.新的区分器由10个参数决定.基于新的区分器,实现了对6轮Square算法的中间相遇攻击,攻击数据复杂度为2109,时间复杂度为2109,存储复杂度为284.
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