Combining Graph-Based and Deduction-Based Information-Flow Analysis

Information flow control (IFC) is a category of techniques for
ensuring system security by enforcing information flow properties such as
non-interference. Established IFC techniques range from fully automatic
approaches with much over-approximation to approaches with high pre-
cision but potentially laborious user interaction. A noteworthy approach
mitigating the weaknesses of both automatic and interactive IFC tech-
niques is the hybrid approach, developed by Küsters et al., which – how-
ever – is based on program modifications and still requires a significant
amount of user interaction.
In this paper, we present a combined approach that works without any
program modifications. It minimizes potential user interactions by apply-
ing a dependency-graph-based information-flow analysis first. Based on
over-approximations, this step potentially generates false positives. Pre-
cise non-interference proofs are achieved by applying a deductive theorem
prover with a specialized information-flow calculus for checking that no
path from a secret input to a public output exists. Both tools are fully
integrated into a combined approach, which is evaluated on a case study,
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demonstrating the feasibility of automatic and precise non-interference
proofs for complex programs.