Dynamic Intransitive Noninterference Revisited

The paper studies dynamic information flow security policies in an automaton-based model. Two semantic interpretations of such policies are developed, both of which generalize the notion of TA-security [van der Meyden ESORICS 2007] for static intransitive noninterference policies. One of the interpretations focuses on information flows permitted by policy edges, the other focuses on prohibitions implied by absence of policy edges. In general, the two interpretations differ, but necessary and sufficient conditions are identified for the two interpretations to be equivalent. Sound and complete proof techniques are developed for both interpretations. Two applications of the theory are presented. The first is a general result showing that access control mechanisms are able to enforce a dynamic information flow policy. The second is a simple capability system motivated by the Flume operating system

On Reductions from Multi-Domain Noninterference to the Two-Level Case

The literature on information flow security with respect to transitive policies has been concentrated largely on the case of policies with two security domains, High and Low, because of a presumption that more general policies can be reduced to this two-domain case. The details of the reduction have not been the subject of careful study, however. Many works in the literature use a reduction based on a quantification over "Low-down" partitionings of domains into those below and those not below a given domain in the information flow order. A few use "High-up" partitionings of domains into those above and those not above a given domain. Our paper argues that more general "cut" partitionings are also appropriate, and studies the relationships between the resulting multi-domain notions of security when the basic notion for the two-domain case to which we reduce is either Nondeducibility on Inputs or Generalized Noninterference. The Low-down reduction is shown to be weaker than the others, and while the High-up reduction is sometimes equivalent to the cut reduction, both it and the Low-down reduction may have an undesirable property of non-monotonicity with respect to a natural ordering on policies. These results suggest that the cut-based partitioning yields a more robust general approach for reduction to the two-domain case.Comment: changed title, abstract; reordered introduction; added some clarifying figures; merged two main results into on