On practical specification and enforcement of obligations

Obligations are an important and indispensable part of many access control policies, such as those in DRM (Digital Rights Management) and healthcare information systems. To be able use obligations in a real-world access control system, there must exist a language for specifying obligations. However, such a language is currently lacking. XACML (eXtensible Access Control Markup Language), the current de facto standard for specifying access control policies, seems to integrate obligations as a part of it, but it treats obligations largely as black boxes, without specifying what an obligation should include and how to handle them. In this paper we examine the challenges in designing a practical approach for specifying and handling obligations, and then propose a language for specifying obligations, and an architecture for handling access control policies with these obligations, extending XACML\u27s specification and architecture. In our design, obligations are modeled as state machines which communicate with the access control system and the outside world via events. We further implement our design into a prototype system named ExtXACML, based on SUN\u27s XACML implementation. ExtXACML is extensible in that new obligation modules can be added into the system to handle various obligations for different applications, which shows the strong power of our design