Composability of Security Property

A secure system consists of many sub——systems, even though every one of those sub systems satisfies a certain security property, the composed system may not be secure, i.e. the composition maybe not satisfy the security property. It does mean that the security property should be composable. In order to solve such problems, a new multilevel security property based on a new concept of noninterference is introduced and the seurity property is proven to be composable in this paper.