关键词: 分组密码, 扩散结构, 分支数, 构造算法, 矩阵

Abstract: The diffusion structure has important impact on the rate of the diffusion and safety intensity for block cipher.Using the linear transform which has branch numbers as large as possible as the diffusion structure is a main method to devise block cipher.The linear transform is usually achieved by constructing the invertible matrix.A kind of diffusion structure with eight blocks is analyzed，and moreover，a new method to construct binary matrix with maximal branch number is proposed and the corresponding algorithm is proposed too.The algorithm runs fast which can satisfy the applying requirement practically.

Key words: block cipher, diffusion structure, branch number, construction algorithm, matrix