为评估一类广义Feistel密码的安全性能，利用迭代结构对该分组密码抵抗差分密码分析和线性密码分析的能力进行了深入的研究。在轮函数都是双射的假设条件下，证明了4r （r≥1）轮广义 Feistel密码至少有（8/3） r-[（rmod3）/3]＋（rmod3）/3个轮函数的输入差分非零。当r ≥6时，本文的结果比现有结果至少提高20％。从而利用轮函数的最大差分和线性逼近概率，就可以估算出4r（r≥1）轮广义Feistel密码最大差分特征概率和最大线性逼近概率的上界。%To evaluate the security of a class of generalized Feistel ciphers ,the security evaluation against differential and linear cryptanalyses is investigated deeply using iterative structure .If round functions are all bijective ,then the number of active round functions for 4r-round (r≥1 ) ciphers are not less than (8/3 )r-[(rmod3 )/3 ]+ (rmod3 )/3 .The result is at least improved 20% than the existing result when r≥6 .So the upper bounds of maximum differential characteristic and linear approximation proba-bilities for 4r-round (r≥1 ) ciphers can be estimated if maximum differential and linear approximation probabilities for round func-tion are given .
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