一类特殊的滤波生成器研究

Research on a Special Kind of Filter Generators

本文针对滤波函数输入端个数m小于移存器级数n的一类滤波生成器,通过构造一个等价系统,分析不同拍位滤波函数输入状态之间的关系,建立等式方程,将密钥的求取转化成一个齐次方程组的求解问题。

In this paper, we consider a special kind of filter generators. For these filter generators, the input bits of the filter functions are less than the degree of LFSRs. According to the particularities of this kind of filter generators and the properties of LFSRs, we construct an equivalent system. By analyzing the relationships between the input states of the filter function and the states of LFSR in the equivalent system, we get a number of linear equations and an example is described to attack this kind of filter generators in section four.