An official website of the United States government
Cyber-physical systems (CPS) are required to satisfy safety constraints in various application domains such as robotics, industrial manufacturing systems, and power systems. Faults and cyber attacks have been shown to cause safety violations, which can damage the system and endanger human lives. Resilient architectures have been proposed to ensure safety of CPS under such faults and attacks via methodologies including redundancy and restarting from safe operating conditions. The existing resilient architectures for CPS utilize different mechanisms to guarantee safety, and currently, there is no common framework to compare them. Moreover, the analysis and design undertaken for CPS employing one architecture is not readily extendable to another. In this article, we propose a timing-based framework for CPS employing various resilient architectures and develop a common methodology for safety analysis and computation of control policies and design parameters. Using the insight that the cyber subsystem operates in one out of a finite number of statuses, we first develop a hybrid system model that captures CPS adopting any of these architectures. Based on the hybrid system, we formulate the problem of joint computation of control policies and associated timing parameters for CPS to satisfy a given safety constraint and derive sufficient conditions for the solution. Utilizing the derived conditions, we provide an algorithm to compute control policies and timing parameters relevant to the employed architecture. We also note that our solution can be applied to a wide class of CPS with polynomial dynamics and also allows incorporation of new architectures. We verify our proposed framework by performing a case study on adaptive cruise control of vehicles.
more »
« less
Plan B - Design Methodology for Cyber-Physical Systems Robust to Timing Failures
Many Cyber-Physical Systems (CPS) have timing constraints that must be met by the cyber components (software and the network) to ensure safety. It is a tedious job to check if a CPS meets its timing requirement especially when they are distributed and the software and/or the underlying computing platforms are complex. Furthermore, the system design is brittle since a timing failure can still happen e.g., network failure, soft error bit flip, etc. In this paper, we propose a new design methodology called Plan B where timing constraints of the CPS are monitored at the runtime, and a proper backup routine is executed when a timing failure happens to ensure safety. We provide a model on how to express the desired timing behavior using a set of timing constructs in a C/C++ code and how to efficiently monitor them at the runtime. We showcase the effectiveness of our approach by conducting experiments on three case studies: 1) the full software stack for autonomous driving (Apollo), 2) a multi-agent system with 1/10th scale model robots, and 3) a quadrotor for search and rescue application. We show that the system remains safe and stable even when intentional faults are injected to cause a timing failure. We also demonstrate that the system can achieve graceful degradation when a less extreme timing failure happens.
more »
« less
- Award ID(s):
- 1645578
- PAR ID:
- 10321993
- Date Published:
- Journal Name:
- ACM Transactions on Cyber-Physical Systems
- ISSN:
- 2378-962X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Since many Cyber–Physical Systems (CPS) interact with the real world, they are safety- or mission- critical. Temporal specification languages like STL (Signal Temporal Logic) have been developed to capture the properties that built CPS must meet. However, the existing temporal logics/languages do not provide a natural way to express the tolerance with which the timing properties must be met. As a consequence of this, the specified properties may be vague, the ensuing CPS design may end up being over- or under-provisioned, and the validation of whether the built CPS meets the specified CPS properties may turn out to be erroneous. To address these issues, a run-time verification methodology is proposed, that allows users to explicitly specify the tolerance with which timing properties must be met. To ensure the correctness of measurement-based validation of a built CPS, this article: (i) proposes a test to determine if a given measurement system can validate the properties specified in TTL, and (ii) proposes a measurement-based testing methodology to provide one-sided guarantee that the built CPS meets the specified CPS properties. The guarantees are one-sided in the sense that when the measurement-based testing concludes that the properties are met, then they are guaranteed to be met (so not false positive). However, when the measurement-based testing concludes that the properties were not met, then they may have met (there can be false negative). In order to validate our claims, we built a model of flying paster (part of the printing press that swaps in a new roll of paper when the current roll is about to finish) using Arduino Mega 2560 and two Hansen brushed DC motors and specified the timing constraints among the various events in this system, along with the tolerances with which they should be met in TTL. We generated the testing logic and validated that we get no false positive, even though we encounter 4.04% false negative. The rate of false negatives can be reduced to be less than any arbitrary value by using more accurate measurement equipment.more » « less
-
The adoption of digital technology in industrial control systems (ICS) enables improved control over operation, ease of system diagnostics and reduction in cost of maintenance of cyber physical systems (CPS). However, digital systems expose CPS to cyber-attacks. The problem is grave since these cyber-attacks can lead to cascading failures affecting safety in CPS. Unfortunately, the relationship between safety events and cyber-attacks in ICS is ill-understood and how cyber-attacks can lead to cascading failures affecting safety. Consequently, CPS operators are ill-prepared to handle cyber-attacks on their systems. In this work, we envision adopting Explainable AI to assist CPS oper-ators in analyzing how a cyber-attack can trigger safety events in CPS and then interactively determining potential approaches to mitigate those threats. We outline the design of a formal framework, which is based on the notion of transition systems, and the associated toolsets for this purpose. The transition system is represented as an AI Planning problem and adopts the causal formalism of human reasoning to asssit CPS operators in their analyses. We discuss some of the research challenges that need to be addressed to bring this vision to fruition.more » « less
-
Existing design techniques for providing security guarantees against network-based attacks in cyber-physical systems (CPS) are based on continuous use of standard cryptographic tools to ensure data integrity. This creates an apparent conflict with common resource limitations in these systems, given that, for instance, lengthy message authentication codes (MAC) introduce significant overheads. We present a framework to ensure both timing guarantees for real-time network messages and Quality-of-Control (QoC) in the presence of network-based attacks. We exploit physical properties of controlled systems to relax constant integrity enforcement requirements, and show how the problem of feasibility testing of intermittently authenticated real-time messages can be cast as a mixed integer linear programming problem. Besides scheduling a set of real-time messages with predefined authentication rates obtained from QoC requirements, we show how to optimally increase the overall system QoC while ensuring that all real-time messages are schedulable. Finally, we introduce an efficient runtime bandwidth allocation method, based on opportunistic scheduling, in order to improve QoC. We evaluate our framework on a standard benchmark designed for CAN bus, and show how an infeasible message set with strong security guarantees can be scheduled if dynamics of controlled systems are taken into account along with real-time requirements.more » « less
-
Research in the area of Cyber-Physical Systems (CPS) is hampered by the lack of available project environments in which to explore open challenges and to propose and rigorously evaluate solutions. In this “New Ideas and Emerging Results” paper we introduce a CPS research incubator – based upon a system, and its associated project environment, for managing and coordinating the flight of small Unmanned Aerial Systems (sUAS). The research incubator provides a new community resource, making available diverse, high-quality project artifacts produced across multiple releases of a safety-critical CPS. It enables researchers to experiment with their own novel solutions within a fully-executable runtime environ- ment that supports both high-fidelity sUAS simulations as well as physical sUAS. Early collaborators from the software engineering community have shown broad and enthusiastic support for the project and its role as a research incubator, and have indicated their intention to leverage the environment to address their own research areas of goal modeling, runtime adaptation, safety-assurance, and software evolution.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1145/3516449
