INFORMATION SECURITY IN OPEN SYSTEMS

An architecture for building secure open systems communicating via untrusted networks is presented. The work is based on the ISO OSI reference model and its security architecture addendum but the results are directly applicable to virtually any layered communications architecture such as the DoD Internet architecture (TCP/IP). A semiformal model for the security of communications between peer entities within an OSI layer and between entire application instances is presented. This model, along with some new concepts introduced, is successfully used to analyze the security functions of open systems. The degree of freedom offered by the OSI Security Architecture in placing the security services and mechanisms defined in the OSI reference model into its layers is restricted in such a way as to not affect the security of the over-all communication service. Well founded placements for various services and mechanisms are proposed. These ideas were tested in practice with a working implementation of secure ISO FTAM service.