Formal Validation of Software for Secure Systems

This paper presents the work currently conducted in the \DS 3 " project 1 which is concerned with the integration and formal validation of oo-the-shelf components in secure systems. It explores two alternate approaches: a top-down approach of encapsulating application components into interoperating controlled modules and checks their assembly; and a bottom-up approach which checks the absence of information ows by examining individual modules. Each of these approaches are eeective at the source or intermediate code level. A pragmatic methodology is given together with an illustrative case study which implements le transfers through a network between machines working at diierent security levels.