Biblio

The concepts of information flow security and refinement are known to have had a troubled relationship ever since the seminal work of McLean. In this work we study refinements that support changes in data representation and semantics, including the addition of state variables that may induce new observational power or side channels. We propose a new epistemic approach to ignorance-preserving refinement where an abstract model is used as a specification of a system's permitted information flows, that may include the declassification of secret information. The core idea is to require that refinement steps must not induce observer knowledge that is not already available in the abstract model. Our study is set in the context of a class of shared variable multiagent models similar to interpreted systems in epistemic logic. We demonstrate the expressiveness of our framework through a series of small examples and compare our approach to existing, stricter notions of information-flow secure refinement based on bisimulations and noninterference preservation. Interestingly, noninterference preservation is not supported “out of the box” in our setting, because refinement steps may introduce new secrets that are independent of secrets already present at abstract level. To support verification, we first introduce a “cube-shaped” unwinding condition related to conditions recently studied in the context of value-dependent noninterference, kernel verification, and secure compilation. A fundamental problem with ignorance-preserving refinement, caused by the support for general data and observation refinement, is that sequential composability is lost. We propose a solution based on relational pre-and postconditions and illustrate its use together with unwinding on the oblivious RAM construction of Chung and Pass.

We study the use of Multiform Logical Time, as embodied in Esterel/SyncCharts and Clock Constraint Specification Language (CCSL), for the specification of assume-guarantee constraints providing safe driving rules related to time and space, in the context of Automated Driving Assistance Systems (ADAS). The main novelty lies in the use of logical clocks to represent the epochs of specific area encounters (when particular area trajectories just start overlapping for instance), thereby combining time and space constraints by CCSL to build safe driving rules specification. We propose the safe specification pattern at high-level that provide the required expressiveness for safe driving rules specification. In the pattern, multiform logical time provides the power of parameterization to express safe driving rules, before instantiation in further simulation contexts. We present an efficient way to irregularly update the constraints in the specification due to the context changes, where elements (other cars, road sections, traffic signs) may dynamically enter and exit the scene. In this way, we add constraints for the new elements and remove the constraints related to the disappearing elements rather than rebuild everything. The multi-lane highway scenario is used to illustrate how to irregularly and efficiently update the constraints in the specification while receiving a fresh scene.

Reactive systems respond to requests from an environment with appropriate timing. Because reactive systems are used widely in infrastructure, it is necessary that they are developed without flaws. Automatic synthesis of reactive systems from particular specifications is an ideal technique for ensuring development without flaws. Several tools for synthesis have been proposed, e.g., Lily, AcaciaPlus and Unbeast. Among them, AcaciaPlus can synthesize systems compositionally, and enables synthesis from large-scale specifications that could not previously be treated. However, the modularization of specifications depends largely on the computation time required for synthesis; this is not a trivial problem. In this paper, we discuss the modularization of specifications to enable efficient synthesis of reactive systems.

Industrial control systems have stringent safety and security demands. High safety assurance can be obtained by specifying the system with possible faults and monitoring it to ensure these faults are properly addressed. Addressing security requires considering unpredictable attacker behavior. Anomaly detection, with its data driven approach, can detect simple unusual behavior and system-based attacks like the propagation of malware; on the other hand, anomaly detection is less suitable to detect more complex \textbackslashtextbackslashemph\process-based\ attacks and it provides little actionability in presence of an alert. The alternative to anomaly detection is to use specification-based intrusion detection, which is more suitable to detect process-based attacks, but is typically expensive to set up and less scalable. We propose to combine a lightweight formal system specification with anomaly detection, providing data-driven monitoring. The combination is based on mapping elements of the specification to elements of the network traffic. This allows extracting locations to monitor and relevant context information from the formal specification, thus semantically enriching the raised alerts and making them actionable. On the other hand, it also allows under-specification of data-based properties in the formal model; some predicates can be left uninterpreted and the monitoring can be used to learn a model for them. We demonstrate our methodology on a smart manufacturing use case.