In order to construct new perfect nonlinear functions, investigating the preimage distributionsof perfect nonlinear functions is very important.
为构造新的完全非线性函数，研究完全非线性函数的原像分布特征具有十分重要的作用。
2
Secondly, the construction of the initial structure and the skipping steps is proposed and the technology and method of preimage attack of MD5 is analyzed in detail.
其次通过介绍初始结构和过渡结构的构建，详细解析了对MD5进行原像攻击的技术和方法；
3
The preimage entropies in the dynamical systems are investigated. The correct proof of the result about preimage branch entropy:"graph mapping has zero preimage branch entropy"is given.