Description
This paper presents an extension to a Multi-Level Secure (MLS) data model that requires the classification of data and users into multiple security levels. In MLS systems, cover stories allow information provided to users at lower security levels to differ from information provided to users at higher security levels. Previous versions of the MLS model did not permit cover stories for key attributes, because the key is used to relate the various cover stories for a particular entity. We have extended the MLS model to include non-key related cover stories so that key attributes can also have different values at different security levels. In this paper we describe the necessary model changes and modifications to the relational algebra, which are required to implement non-key related cover stories. We demonstrate the improvements made by these changes and discuss the implementation and performance of a system based on the described concepts.