This paper addresses the challenge of measuring security, understood as a system property, of cyberphysical systems, in the category of similar properties, such as safety and reliability. First, it attempts to define precisely what security, as a system property, really is. Then, an application context is presented, in terms of an attack surface in cyberphysical systems. Contemporary approaches related to the principles of measuring software properties are also discussed, with emphasis on building models. These concepts are illustrated in several case studies, based on previous work of the authors, to conduct experimental security measurements.
Timely and reliable dissemination of traffic-related information to drivers is a key property that intelligent transportation systems (ITS) should support. Numerous impediments stemming due to (a) physical factors, such as mobility and speed of vehicles, density of vehicles, characteristics of the wireless radio channel, and power and bit rate of radio transceivers, and (b) cyber issues, such as MAC layer access point associations and address resolutions (ARP), network layer addressing, routing and handoffs, and transport layer retransmissions lead to unpredictability in the timely and reliable dissemination of information to drivers. This paper presents compelling arguments in favor of new research directions in this area that are based on a cyber-physical systems (CPS) perspective. In particular, this paper makes three contributions. First, it considers a vehicle-centric perspective to survey and study the physics-and cyber-imposed impediments to the timely and reliable dissemination of information. Second, it presents a promising CPS solution to overcome a subset of the impediments discovered. Third, it outlines lessons learned indicating the need for more focused research and realistic testbeds. The evaluations ISSN 1943-3581 2010 www.macrothink.org/npa 117 presented in the paper are based on simulations conducted in the OMNeT++/INETMANET simulator framework for IEEE 802.11 networks. Lack of open ITS testbeds motivated us to choose simulation as an alternative to conduct our study.
Network Protocols and Algorithms
Embedded systems use increasingly complex software and are evolving into cyber-physical systems (CPS) with sophisticated interaction and coupling between physical and computational processes. Many CPS operate in safety-critical environments and have stringent certification, reliability, and correctness requirements. These systems undergo changes throughout their lifetimes, where either the software or physical hardware is updated in subsequent design iterations. One source of failure in safety-critical CPS is when there are unstated assumptions in either the physical or cyber parts of the system, and new components do not match those assumptions. In this work, we present an automated method towards identifying unstated assumptions in CPS. Dynamic specifications in the form of candidate invariants of both the software and physical components are identified using dynamic analysis (executing and/or simulating the system implementation or model thereof). A prototype tool called Hynger (for HYbrid iNvariant GEneratoR) was developed that instruments Simulink/Stateflow (SLSF) model diagrams to generate traces in the input format compatible with the Daikon invariant inference tool, which has been extensively applied to software systems. Hynger, in conjunction with Daikon, is able to detect candidate invariants of several CPS case studies. We use the running example of a DC-to-DC power converter, and demonstrate that Hynger can detect a specification mismatch where a tolerance assumed by the software is violated due to a plant change.
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