Security Measures for Grids Against Rank-1 Undetectable Time-Synchronization Attacks

Marguerite Marie Nathalie Delcourt, Jean-Yves Le Boudec
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2022
Journal paper

Abstract

Time-synchronization attacks on phasor measurement units (PMUs) pose a real threat to smart grids; it was shown that they are feasible in practice and that they can have a nonnegligible negative impact on state estimation, without triggering the bad data detection mechanisms. Previous works identified vulnerability conditions when targeted PMUs measure a single phasor. Yet, PMUs are capable of measuring several quantities. We present novel vulnerability conditions in the general case, where PMUs measure any number of phasors and can share the same time reference. One is a sufficient condition that does not depend on the measurement values. We propose a security requirement that prevents it and provide a greedy offline algorithm that enforces it. If this security requirement is satisfied, there is still a possibility that the grid can be attacked, although we conjecture that it is very unlikely. We identify two sufficient and necessary vulnerability conditions, which depend on the measurement values. For each, we provide a metric that shows the distance between the observed and vulnerability conditions. We recommend their monitoring for security. Numerical results on the IEEE-39 bus benchmark with real load profiles show that the measurements of a grid satisfying our security requirement are far from vulnerable.

Official source

https://infoscience.epfl.ch/record/294626?ln=en

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This work focuses on the security of critical infrastructures against time-synchronization attacks (TSA). A TSA can impact any network that relies on the dynamic analysis of data, by altering the time synchronization between its nodes. Such attacked networks can start failing. Some TSAs are thwarted by cyber-security tools such as authentication and confidentiality algorithms. However, such tools cannot counter TSAs that are implemented physically. Such TSAs are undetectable but they may be detected if they lead to non-plausible observations. The identification of TSAs requires in-depth knowledge of the system's operation.We focus on TSAs in two settings. First, we consider smart grids. Their control and operation require the timely knowledge of the system state, which is inferred from an estimate computed from measurements. We consider phasor measurements taken from phasor measurement units (PMUs). However, they require a precise time synchronization, which is a weakness as existing synchronization methods are vulnerable to attacks. We aim to assess the vulnerability of the synchrophasor-based state estimation of a system, by exploring the feasibility and detectability of TSAs on PMUs. A widespread technique to make the state estimation more robust is to couple it with a bad-data detection (BDD) scheme. However, it is known that false data injection attacks and TSAs can impact the state estimation without being detected by the BDD algorithms. We present practical attack strategies for undetectable TSAs and novel vulnerability conditions. One of them is a static condition that does not depend on the measurement values. We propose a security requirement that prevents it and a greedy offline algorithm that enforces it. If this requirement is satisfied, the grid may still be attacked, although we reason that it is unlikely. We identify two sufficient and necessary vulnerability conditions which depend on the measurement values. For each, we provide a metric that shows the distance between the observed and vulnerability conditions. Enforcing our requirement requires increasing the amount of measurement points of the grid. We investigate the benefits of utilizing the three-phase model instead of the direct-sequence model for security. We show that if the power system is unbalanced, then the use of the three-phase model enables to detect attacks that are undetectable if the direct-sequence model is used. Numerical results from simulations with real load profiles from the Lausanne grid, confirm our findings. Second, we consider sensor networks for passive-source localization. We focus on the localization of a passive source from time difference of arrival (TDOA) measurements. Such measurements are highly sensitive to time-synchronization offsets. We first illustrate that TSAs can affect the localization and we show that residual analysis does not enable the detection and identification of TSAs. Second, we propose a two-step TDOA-localization technique that is robust against TSAs. It uses a known source to define a weight for each pair of sensors, reflecting the confidence in their synchronization. We then use the weighted least-squares estimator with the new weights and the TDOA measurements received from the unknown source. Our method either identifies the network as being too corrupt, or gives a corrected estimate of the unknown position along with a confidence metric. Numerical results illustrate the performance of our technique.

EPFL2021

Security Vulnerabilities of the Cisco IOS Implementation of the MPLS Transport Profile

Sergio Barreto Andrade, Udaya Upul Kumara Jayasinghe, Jean-Yves Le Boudec, Miroslav Popovic, Teklemariam Tsegay Tesfay

We are interested in the security of the MPLS Transport Profile (MPLS-TP), in the context of smart-grid communication networks. The security guidelines of the MPLS-TP standards are written in a complex and indirect way, which led us to pose as hypothesis that vendor solutions might not implement them satisfactorily. To test this hypothesis, we investigated the Cisco implementation of two MPLS-TP OAM (Operations, Administration, and Maintenance) protocols: bidirectional forwarding detection (BFD), used to detect failures in label-switched paths (LSPs) and protection state coordination (PSC), used to coordinate protection switching. Critical smart grid applications, such as protection and control, rely on the protection switching feature controlled by BFD and PSC. We did find security issues with this implementation. We implemented a testbed with eight nodes that run the MPLS-TP enabled Cisco IOS; we demonstrated that an attacker who has access to only one cable (for two attacks) or two cables (for one attack) is able to harm the network at several points (e.g., disabling both working and protection LSPs). This occurred in spite of us implementing the security guidelines that are available from Cisco for IOS and MPLS-TP. The attacks use forged BFD or PSC messages, which induce a label-edge router (LER) into believing false information about an LSP. In one attack, the LER disables the operational LSP; in another attack, the LER continues to believe that a physically destroyed LSP is up and running; in yet another attack, both operational and backup LSPs are brought down. Our findings suggest that the MPLS-TP standard should be more explicit when it comes to security. For example, to thwart the attacks revealed here, it should mandate either hop by hop authentication (such as MACSec) at every node, or an ad-hoc authentication mechanism for BFD and PSC.

2014

Cybersecurity Solutions for Active Power Distribution Networks

Teklemariam Tsegay Tesfay

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EPFL2017