Proof-Carrying Apps: Contract-Based Deployment-Time Verification

For extensible software platforms in safety-critical domains, it is important that deployed plug-ins work as specified. This is especially true with the prospect of allowing third parties to add plug-ins. We propose a contract-based approach for deployment-time verification. Every plug-in guarantees its functional behavior under a specific set of assumptions towards its environment. With proof-carrying apps, we generalize proof-carrying code from proofs to artifacts that facilitate deployment-time verification, where the expected behavior is specified by the means of design-by-contract. With proof artifacts, the conformance of apps to environment assumptions is checked during deployment, even on resource-constrained devices. This procedure prevents unsafe operation by unintended programming mistakes as well as intended malicious behavior. We discuss which criteria a formal verification technique has to fulfill to be applicable to proof-carrying apps and evaluate the verification tools KeY and Soot for proof-carrying apps.