Empowering mobile code using expressive security policies

sekar @ cs.sunysb.edu Existing approaches for mobile code security tend to take a conser-vative view that mobile code is inherently risky, and hence focus on confining it. Such confinement is usually achieved using access control policies that restrict mobile code from taking any action that can potentially be used to harm the host system. While such policies can be helpful in keeping "bad applets " in check, they pre-clude a large number of useful applets. We therefore take an alter-native view of mobile code security, one that is focused on empow-ering mobile code rather than disabling it. We propose an approach wherein highly expressive security policies provide the basis for such empowerment, while greatly mitigating the risks posed to the host system by such code. Our policies are represented asextended finite state automata, (a generalization f the finite-state automata to permit he use of variables) that can enforce these policies effi-ciently. We have built a prototype implementation f our approach for Java. Our implementation is based on rewriting Java byte code so that security-relevant events are intercepted and forwarded to the policy enforcement automata before they are executed. Early ex-perimental results indicate that such expressive, nabling policies can be supported with low overheads