Nonlinear Message Expansion for Hash Function

This paper carries out a statistical analysis on the nonlinear diffusion & propagation of the SHA message expansion. The nonlinear expansion of the message is realized through the rolled-out and folded-over of the integer tent maps, and a piece-wise-nonlinear message expansion scheme is further given. Compared with SHA-256 message expansion, the message expansion mode presented in this paper has enhanced the degree of nonlinear diffusion of the message expansion, and thus improved computation efficiency.