Stéphane Lafortune

Lilian Kawakami Carvalho, Yi-Chin Wu, Raymond Kwong et al.

The deployment of control systems with network-connected components has made feedback control systems vulnerable to attacks over the network. This paper considers the problem of intrusion detection and mitigation in supervisory control systems, where the attacker has the ability to enable or disable vulnerable actuator commands and erase or insert vulnerable sensor readings. We present a mathematical model for the system under certain classes of actuator enablement attacks, sensor erasure attacks, or sensor insertion attacks. We then propose a defense strategy that aims to detect such attacks online and disables all controllable events after an attack is detected. We develop an algorithmic procedure for verifying whether the system can prevent damage from the attacks considered with the proposed defense strategy, where damage is modeled as the reachability of a pre-defined set of unsafe system states.The technical condition of interest that is necessary and sufficient in this context, termed "GF-safe controllability", is characterized. We show that the verification of GF-safe controllability can be performed using diagnoser or verifier automata. Finally, we illustrate the methodology with a traffic control system example.

Shoma Matsui, Stéphane Lafortune

There is an increasing need to study the vulnerability of communication protocols in distributed systems to malicious attacks that attempt to violate properties such as safety or nonblockingness. In this paper, we propose a common methodology for formal synthesis of successful attacks against two well-known protocols, the Alternating Bit Protocol (ABP) and the Transmission Control Protocol (TCP), where the attacker can always eventually win, called For-all attacks. This generalizes previous work on the synthesis of There-exists attacks for TCP, where the attacker can sometimes win. We model the ABP and TCP protocols and system architecture by finite-state automata and employ the supervisory control theory of discrete event systems to pose and solve the synthesis of For-all attacks, where the attacker has partial observability and controllability of the system events. We consider several scenarios of person-in-themiddle attacks against ABP and TCP and present the results of attack synthesis using our methodology for each case.

Sahar Mohajerani, Yiding Ji, Stephane Lafortune

This paper develops a novel compositional and abstraction-based approach to synthesize edit functions for opacity enforcement in modular discrete event systems. Edit functions alter the output of the system by erasing or inserting events in order to obfuscate the outside intruder, whose goal is to infer the secrets of the system from its observation. We synthesize edit functions to solve the opacity enforcement problem in a modular setting, which significantly reduces the computational complexity compared with the monolithic approach. Two abstraction methods called opaque observation equivalence and opaque bisimulation are first employed to abstract the individual components of the modular system and their observers. Subsequently, we propose a method to transform the synthesis of edit functions to the calculation of modular supremal nonblocking supervisors. We show that the edit functions synthesized in this manner correctly solve the opacity enforcement problem.

Eunsuk Kang, Stephane Lafortune, Stavros Tripakis

System development often involves decisions about how a high-level design is to be implemented using primitives from a low-level platform. Certain decisions, however, may introduce undesirable behavior into the resulting implementation, possibly leading to a violation of a desired property that has already been established at the design level. In this paper, we introduce the problem of synthesizing a property-preserving platform mapping: A set of implementation decisions ensuring that a desired property is preserved from a high-level design into a low-level platform implementation. We provide a formalization of the synthesis problem and propose a technique for synthesizing a mapping based on symbolic constraint search. We describe our prototype implementation, and a real-world case study demonstrating the application of our technique to synthesizing secure mappings for the popular web authorization protocols OAuth 1.0 and 2.0.