关键词: 密码学, 序列密码, 布尔函数, 弹性函数, 非线性度

Abstract: In recent years, research of almost optimal resilient Boolean functions develops rapidly, and it is important to improve the nonlinearity degree of almost optimal functions. Analysis and improvement of an almost optimal function with good performance was given, and an almost optimal function with even variables was constructed using concatenating construction method. A nonlinear optimal function with higher nonlinearity was got while maintaining its resilience and algebraic degree, which improved the performance of the function. And the construction method was also given to construct an elastic Boolean function with high nonlinearity. Analysis shows that the proposed construction method is simple and easy to implement, the nonlinearity is improved with m resilience and unchanged algebraic degree.

Key words: cryptography, steamcipher, Boolean function, resilient function, nonlinearity