非平衡Feistel结构密码算法的不可分辨性

Indifferentiability of unbalanced Feistel structural cryptographic algorithm

为研究不可分辨性对分组密码算法实际保密强度的影响,以国密SMS4分组密码算法使用的非平衡Feistel结构为对象,构建了以区分器为核心的结构模拟器;通过对非平衡Feistel结构迭代特性的考虑,结合形式化证明方法,对非平衡Feistel结构的最小安全边界及其与不可分辨性之间的关联进行了研究和分析。结果表明:以SMS4为代表的非平衡Feistel结构在确保安全强度的前提下,最小能够约简至18轮迭代结构,且该约简结构与随机结构置换具备不可分辨性。

To investigate the effect of indifferentiability on the actual secrecy strength of block cipher algorithm,based on the non-balanced Feistel structure used by SMS4 block cipher algorithm,a structural simulator with a discriminator as the core was constructed.By considering the iterative characteristics of non-balanced Feistel structures and combining with formal proof method,the minimum security boundary of non-balanced Feistel structures and its relation to indifferentiability were studied and analyzed in depth.The results show that the non-balanced Feistel structure represented by SMS4 can be reduced to the minimum 18-round iteration structure on the premise of ensuring the safety strength,and compared with random permutation,the reduced structure has indifferentiability.