  An encryption technique is widely used to keep data confidential. Most of the
block symmetric algorithms use substitution functions. Often this functions use
so called S-BOX matrix. In this paper author presents one software tool for
testing and measuring square s-boxes. Based of information theory functions for
testing static and dynamic criteria are presented. These criteria are
mathematically defined for square s-boxes. Two new criteria "private criteria"
a proposed and pseudo codes for they creation and testing are presented.
