# Security-Oriented Cyber-Physical Risk Assessment for Cyberattacks on Distribution System
###### Abstract  
With the increasing deployment of advanced sensing and measurement devices, the modern distribution system is evolved into a cyber-physical power distribution system (CPPDS). Due to the extensive application of information and communication technology, CPPDS is prevalently exposed to a wide range of cybersecurity threats. In this paper, a novel security-oriented cyber-physical risk assessment method for CPPDS is proposed. Based on the information model composed of logical nodes, an attack graph of privilege promotion by exploiting the cyber vulnerabilities is constructed. The physical consequence caused by cyberattack is analyzed in detail. By using the Markov decision process (MDP) theory, the cyber-physical risk index (CPRI) is calculated. Furthermore, considering the allocation of the finite defense resource, the modified MDP approach with an attack-defense game is presented. The effectiveness of the proposed method is demonstrated with case studies on a four-feeder IEEE-RTBS test system. c 2023 13 11569 11.11.11.11.11.11.1.11.1.  
infrastructures were proposed. In [24], considering malicious attacks on protection system settings and parameters, a risk evaluation method was presented. In [25], a cyber insurance design considering power system reliability and cyber vulnerability was proposed. For probabilistic cyberattacks against breakers, the impact of a successful attack was analyzed, and a novel adequacy assessment was proposed in [26]. The above studies mainly focus on the risk assessment for a transmission network. With the development of large-scale sensing measurement systems and a more complicated communication network, the modern distribution system has evolved into CPPDS. Due to the openness of the information technologies and terminal equipment, the cybersecurity issue also needs to be brought to attention in CPPDS. However, current studies rarely simultaneously describe the attack process clearly and quantize the physical impacts in detail. In [27], man-in-the-middle and denial-of-service attacks are considered. The impact of different cyber events on a physical power grid is analyzed using an integrated cyber-power modeling and simulation testbed. In [28], a stochastic epidemic network model is developed to evaluate the cyber risk by propagating cyberattacks among graphical vulnerabilities. However, the method lacks a general risk index for cybersecurity assessment. In [29], based on a Bayesian attack graph model, the probability of a remote terminal unit (RTU) potentially being attacked was obtained. The long-term power loss was taken as the physical impact. In [30], the attack path is modeled by a Petri net, and the attack payoff is calculated based on the physical influence coefficients. In [31], a CPDS security assessment method based on the expected failure method and considering combined information attacks is proposed. In [32], an attack probability computation method is proposed. In different possible attack scenarios, the detailed attack model is given. However, these works ignore the cyber reward of the attack process, and the analysis of physical impacts is also not sufficient. The impact of combined information-physical-failure on CPDS is analyzed in [33], but the corresponding attack model is simple and the different attack paths are ignored. In addition, research on risk assessment considering an attack-defense game for CPPDS is rarer, which is also the research focus in this paper. In [34], considering attacker and defender strategies and attack damage, a CPDS risk assessment framework is established. Additionally, a risk assessment and defense resource allocation method based on the game model is proposed. Compared with this literature, our work provides a more comprehensive and detailed attack model and its underlying logic. Furthermore, we have integrated the evaluation of cyber rewards during the attack process into the computation of the assessment index.