P.: Software verification using k-induction

Abstract. We present combined-case k-induction, a novel technique for veri-fying software programs. This technique draws on the strengths of the classical inductive-invariant method and a recent application of k-induction to program verification. In previous work, correctness of programs was established by sepa-rately proving a base case and inductive step. We present a new k-induction rule that takes an unstructured, reducible control flow graph (CFG), a natural loop oc-curring in the CFG, and a positive integer k, and constructs a single CFG in which the given loop is eliminated via an unwinding proportional to k. Recursively ap-plying the proof rule eventually yields a loop-free CFG, which can be checked using SAT-/SMT-based techniques. We state soundness of the rule, and investi-gate its theoretical properties. We then present two implementations of our tech-nique: K-INDUCTOR, a verifier for C programs built on top of the CBMC model checker, and K-BOOGIE, an extension of the Boogie tool. Our experiments, using a large set of benchmarks, demonstrate that our k-induction technique frequently allows program verification to succeed using significantly weaker loop invariants than are required with the standard inductive invariant approach.