XML-Based Access Control Languages

One of the most challenging problems in managing large, distributed, and heterogeneous networked systems is specifying and enforcing security policies regulating interactions between parties and access to services and resources. Recent proposals for specifying and exchanging access control policies adopt XML-based languages. XML appears in fact a natural choice as the basis for the common security-policy language, due to the ease with which its syntax and semantics can be extended and the widespread support that it enjoys from all the main platform and tool vendors. In this chapter, we first investigate the basic concepts behind access control design and enforcement, and point out different security requirements that may need to be taken into consideration in designing an access control language for Internet information systems. We then focus on XML-based access control languages and, in particular, on the eXtensible Access Control Markup Language (XACML), a recent OASIS standardization effort. XACML is designed to express authorization policies in XML against objects that are themselves identified in XML. The language can represent the functionalities of most policy representation mechanisms.