Abstract

Although the risk assessment discipline has been studied from long ago as a means to support security investment decision-making, no holistic approach exists to continuously and quantitatively analyze cyber risks in scenarios where attacks and defenses may target different parts of Internet of Things (IoT)-based smart grid systems. In this paper, we propose a comprehensive methodology that enables informed decisions on security protection for smart grid systems by the continuous assessment of cyber risks. The solution is based on the use of attack defense trees modelled on the system and computation of the proposed risk attributes that enables an assessment of the system risks by propagating the risk attributes in the tree nodes. The method allows system risk sensitivity analyses to be performed with respect to different attack and defense scenarios, and optimizes security strategies with respect to risk minimization. The methodology proposes the use of standard security and privacy defense taxonomies from internationally recognized security control families, such as the NIST SP 800-53, which facilitates security certifications. Finally, the paper describes the validation of the methodology carried out in a real smart building energy efficiency application that combines multiple components deployed in cloud and IoT resources. The scenario demonstrates the feasibility of the method to not only perform initial quantitative estimations of system risks but also to continuously keep the risk assessment up to date according to the system conditions during operation.

Highlights

  • Protecting Information Technologies (IT) and Operational Technologies (OT) systems from all potential risk situations and assessing their security level are two of the major challenges in industrial cybersecurity research

  • We propose decoration of the defenses in the system attack-defense trees (ADTs) with three risk attributes similar to those proposed for threats: (i) The probability of the defense to successfully counteract the attack event, which ranges in the interval [0,1]; (ii) the impact the defense can protect as a percentage of the impact of the attack that can be avoided when adopting the defense, whose interval is [0,10]; and (iii) the normalized cost of the application of the countermeasure mechanism for the defender, which ranges within the [0,10] interval as well

  • We introduced a holistic continuous risk assessment methodology for smart grid systems based on the use of ADTs to capture the relationships between threats and defenses in distributed system parts

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Summary

Introduction

Protecting Information Technologies (IT) and Operational Technologies (OT) systems from all potential risk situations and assessing their security level are two of the major challenges in industrial cybersecurity research. Internet of Things (IoT) scenarios, such as modern smart grid systems, where the attack surface spans to multiple intelligent complementary services based on IoT and private cloud resources. These systems require holistic security approaches that support experts in managing risks in all system components, including third-party services, which often lack details of the security and privacy measures they adopt.

Related Works
Quantitative Risk Assessment Methodology
Step 1
Attack Risk Attributes Decoration
Defense Risk Mitigation Attributes Decoration
Estimation of Risk Attributes on Leaf-Nodes
Risk Assessment in Countered Nodes
Risk Propagation Algorithm
Risk Severity Metrics Proposed
Step 3
Step 4
Example a 3-D relationshipmatrix matrix T
Step 5
Validation in a Smart Building Energy Efficiency System
Simplified
1: System
Step 2
4: Risk-Driven
Discussion
Conclusions

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