二次指数发生器截位序列的密码分析

二次指数发生器是一种广泛使用的伪随机数发生器。该文指出在已知移位b和模数p的条件下，若已知连续的wn满足| un wn|是一个很小的数时，在多数情况下可以恢复出二次指数发生器的乘子a。说明了若已知连续的wn满足| un  wn|是一个很小的数时，在多数情况下可以恢复出二次指数发生器的乘子a和移位b。结论显示了将二次指数发生器直接应用于密码学必须十分慎重。

Truncated Sequences Cryptanalysis of Quadratic Generator

Quadratic generator is a kind of widely used pseudorandom number generator.This paper studies the cryptanalysis of the quadratic generator.It shows given the shift b,modular p and sufficiently many of the most significant bits of several sets of the form u_n,u_(n 1),u_(n 2),how to disclose the multiplier a and the initial value u_0,if u_n does not lie in a small set,where u_n,u_(n 1),u_(n 2)are outputs of the quadratic generator.Then it shows that given the modular p and sufficiently many of the most significant bits of several sets of the form u_n,u_(n 1),u_(n 2),u_(n 3),one may disclose the a,b and the initial value u_0 if u_n does not lie in another small set.The results of this paper show that it should be careful when quadratic generator is used in a cryptosystem