Abstract

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When complex systems are constructed from simpler components it is important to know how properties of the components behave under composition. In this article, we present various compositionality results for security properties. In particular, we introduce a novel security property and show that this property is, in general, composable although it is weaker than forward correctability. Moreover, we demonstrate that certain nontrivial security properties emerge under composition and illustrate how this fact can be exploited. All compositionality results that we present are verified with the help of a single, quite powerful lemma. Basing on this lemma, we also re-prove several already known compositionality results with the objective to unify these results. As a side effect, we obtain a classification of known compositionality results for security properties.

Abstract-The idea of building secure systems by plugging together "secure" components is appealing, but this requires a definition of security which, in addition to taking care of toplevel security goals, is strengthened appropriately in order to be compositional. This approach has been previously studied for information-flow security of shared-variable concurrent programs, but the price for compositionality is very high: a thread must be extremely pessimistic about what an environment might do with shared resources. This pessimism leads to many intuitively secure threads being labelled as insecure.Since in practice it is only meaningful to compose threads which follow an agreed protocol for data access, we take advantage of this to develop a more liberal compositional security condition. The idea is to give the security definition access to the intended pattern of data usage, as expressed by assumption-guarantee style conditions associated with each thread. We illustrate the improved precision by developing the first flow-sensitive security type system that provably enforces a noninterference-like property for concurrent programs.

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