Biblio

Side-channels have been increasingly demonstrated as a practical threat to the confidentiality of private user information. Being able to statically detect these kinds of vulnerabilites is a key challenge in current computer security research. We introduce a new technique, path-cost analysis (PCA), for the detection of side-channels. Given a cost model for a type of side-channel, path-cost analysis assigns a symbolic cost expression to every node and every back edge of a method's control flow graph that gives an over-approximation for all possible observable values at that node or after traversing that cycle. Queries to a satisfiability solver on the maximum distance between specific pairs of nodes allow us to detect the presence of imbalanced paths through the control flow graph. When combined with taint analysis, we are able to answer the following question: does there exist a pair of paths in the method's control flow graph, differing only on branch conditions influenced by the secret, that differs in observable value by more than some given threshold? In fact, we are able to answer the specifically state what sets of secret-sensitive conditional statements introduce a side-channel detectable given some noise parameter. We extend this approach to an interprocedural analysis, resulting in a over-approximation of the number of true side-channels in the program according to the given cost model. Greater precision can be obtained by combining our method with predicate abstraction or symbolic execution to eliminate a subset of the infeasible paths through the control flow graph. We propose evaluating our method on a set of sizeable Java server-client applications.