Pseudorandom Sequences Generator Under Feedforward Model

Feedforward model is one of the most classical models in stream ciphers.The theory of linear feedback shift register supports the derivation and development of feedforward model in the history of stream cipher.Most of the feedforward model which based on linear feedback shift register is negative since the idea of algebraic attacks have been proposed.Nowadays the model which is recognized to have a high security is nonlinear feedback shift register based.The main work of this paper include three parts: the first one is the summary and analysis of pseudorandom sequence generator under feedforward model with analyzing the advantages and disadvantages from the security of sequence.The second is to summarize the ideal of algebraic attacks and applied the theory to analyze two types of typical feedforward model nowadays.One is based on nonlinear feedback shift register and the other contains the block structure.The third is the design of a kind of Boolean functions which have excellent cryptographic properties.In the light of the algebraic attack we designed a kind of balanced function with optimal algebraic immunity,and it is proved to have a high nonlinearity and high algebraic degree.