Security policies for distributed systems

Abstract

A security policy specifies a security property as the maximal information flow. A distributed system composed of interacting processes implicitly defines an intransitive security policy by repudiating direct information flow between processes that do not exchange messages directly. We show that implicitly defined security policies in distributed systems are enforced, provided that processes run in separation, and possible process communication on a technical platform is restricted to specified message paths of the system. Furthermore, we propose to further restrict the allowable information flow by adding filter functions for controlling which messages may be transmitted between processes, and we prove that locally checking filter functions is sufficient for ensuring global security policies. Altogether, global intransitive security policies are established by means of local verification conditions for the (trusted) processes of the distributed system. Moreover, security policies may be implemented securely on distributed integration platforms which ensure partitioning. We illustrate our results with a smart grid case study, where we use CTL model checking for discharging local verification conditions for each process under consideration. * This work was carried out as part of the DMILS project www.d-mils.org which is funded by the European Commission under the contract Nr. FP7-ICT-3187727 of the 7 th Framework Programme for Information and Communications Technology. The smart grid case study has been supported by the Smart Energy Systems action line of the EIT ICT Labs and the Bavarian Ministry of Economics.