中文摘要：

本文讨论S-盒保熵性，提出组合函数和S-盒的条件熵、保熵性定义，并利用条件熵给出一种判定组合函数、S-盒满足k阶相关免疫的充要条件和理想保熵的条件，给出了具有理想保熵性组合函数和S-盒的一般代数表达式及其安全缺陷．最后，利用熵与Walsh谱的内在联系，提出组合函数和S-盒满足实际保熵的安全条件，以指导实际应用中组合函数及S-盒的应用设计．

英文摘要：

In this paper the entropy preservability of S-Box is discussed and the definitions of condition entropy and entropy preservability of nonlinear S-Box and combining function are presented. Then the sufficient and necessary conditions for judging combining function or S-Box between condition entropy and correlation immunity and the ideal entropy preservability condition of combining function and S-Box are given. Finally, the applied entropy preservability conditions of combining function and S-Box are obtained through analyzing the inherent relation between entropy and Walsh spectrum.