A. Tiwari, B. Dutertre, Dejan Jovanovic, Thomas de Candia, P. Lincoln, J. Rushby, Dorsa Sadigh, S. Seshia
We present an approach for detecting sensor spoofing attacks on a cyber-physical system. Our approach consists of two steps. In the first step, we construct a safety envelope of the system. Under nominal conditions (that is, when there are no attacks), the system always stays inside its safety envelope. In the second step, we build an attack detector: a monitor that executes synchronously with the system and raises an alarm whenever the system state falls outside the safety envelope. We synthesize safety envelopes using a modifed machine learning procedure applied on data collected from the system when it is not under attack. We present experimental results that show effectiveness of our approach, and also validate the several novel features that we introduced in our learning procedure.
{"title":"Safety envelope for security","authors":"A. Tiwari, B. Dutertre, Dejan Jovanovic, Thomas de Candia, P. Lincoln, J. Rushby, Dorsa Sadigh, S. Seshia","doi":"10.1145/2566468.2566483","DOIUrl":"https://doi.org/10.1145/2566468.2566483","url":null,"abstract":"We present an approach for detecting sensor spoofing attacks on a cyber-physical system. Our approach consists of two steps. In the first step, we construct a safety envelope of the system. Under nominal conditions (that is, when there are no attacks), the system always stays inside its safety envelope. In the second step, we build an attack detector: a monitor that executes synchronously with the system and raises an alarm whenever the system state falls outside the safety envelope. We synthesize safety envelopes using a modifed machine learning procedure applied on data collected from the system when it is not under attack. We present experimental results that show effectiveness of our approach, and also validate the several novel features that we introduced in our learning procedure.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125294580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We introduce a new problem formulation for understanding the threats and vulnerabilities of process control systems. In particular, we consider an adversary that has compromised sensor or actuator signals of a control system and needs to identify the best time to launch an attack. We have previously shown that attackers might not be able to reach if the timing of their Denial-of-Service (DoS) attacks is not chosen strategically: Therefore, if the timing of a DoS attack is not chosen correctly, the attack can have limited impact; however, if the timing of the attack is chosen carefully, the attack has higher chances of succeeding. We formulate the problem of selecting a good time to launch DoS attacks as an optimal stopping problem that the adversary has to solve in real-time. In particular, we use the theory for the Best-Choice Problem to identify an optimal stopping criteria and then use a low pass filter to identify when the time series of a process variable has reached its peak. We identify some of the complexities associated with solving the problem and outline directions for future work.
{"title":"Is this a good time?: deciding when to launch attacks on process control systems","authors":"M. Krotofil, A. Cárdenas","doi":"10.1145/2566468.2576852","DOIUrl":"https://doi.org/10.1145/2566468.2576852","url":null,"abstract":"We introduce a new problem formulation for understanding the threats and vulnerabilities of process control systems. In particular, we consider an adversary that has compromised sensor or actuator signals of a control system and needs to identify the best time to launch an attack. We have previously shown that attackers might not be able to reach if the timing of their Denial-of-Service (DoS) attacks is not chosen strategically: Therefore, if the timing of a DoS attack is not chosen correctly, the attack can have limited impact; however, if the timing of the attack is chosen carefully, the attack has higher chances of succeeding. We formulate the problem of selecting a good time to launch DoS attacks as an optimal stopping problem that the adversary has to solve in real-time. In particular, we use the theory for the Best-Choice Problem to identify an optimal stopping criteria and then use a low pass filter to identify when the time series of a process variable has reached its peak. We identify some of the complexities associated with solving the problem and outline directions for future work.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"81 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124117305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The increased prevalence of attacks on Cyber-Physical Systems(CPS) as well as the safety-critical nature of these systems, has resulted in increased concerns regarding the security of CPS. In an effort towards the security of CPS, we consider the detection of attacks based on the fundamental notion of a system's energy. We propose a discrete-time Energy-Based Attack Detection mechanism for networked cyber-physical systems that are dissipative or passive in nature. We present analytical results to show that the detection mechanism is effective in detecting a class of attack models in networked control systems (NCS). Finally, using simulations we illustrate the effectiveness of the proposed approach in detecting attacks.
{"title":"Energy-based attack detection in networked control systems","authors":"E. Eyisi, X. Koutsoukos","doi":"10.1145/2566468.2566472","DOIUrl":"https://doi.org/10.1145/2566468.2566472","url":null,"abstract":"The increased prevalence of attacks on Cyber-Physical Systems(CPS) as well as the safety-critical nature of these systems, has resulted in increased concerns regarding the security of CPS. In an effort towards the security of CPS, we consider the detection of attacks based on the fundamental notion of a system's energy. We propose a discrete-time Energy-Based Attack Detection mechanism for networked cyber-physical systems that are dissipative or passive in nature. We present analytical results to show that the detection mechanism is effective in detecting a class of attack models in networked control systems (NCS). Finally, using simulations we illustrate the effectiveness of the proposed approach in detecting attacks.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117175606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This work considers the problem of performing resilient sensor fusion using past sensor measurements. In particular, we consider a system with n sensors measuring the same physical variable where some sensors might be attacked or faulty. We consider a setup in which each sensor provides the controller with a set of possible values for the true value. Here, more precise sensors provide smaller sets. Since a lot of modern sensors provide multidimensional measurements (e.g. position in three dimensions), the sets considered in this work are multidimensional polyhedra. Given the assumption that some sensors can be attacked or faulty, the paper provides a sensor fusion algorithm that obtains a fusion polyhedron which is guaranteed to contain the true value and is minimal in size. A bound on the volume of the fusion polyhedron is also proved based on the number of faulty or attacked sensors. In addition, we incorporate system dynamics in order to utilize past measurements and further reduce the size of the fusion polyhedron. We describe several ways of mapping previous measurements to current time and compare them, under different assumptions, using the volume of the fusion polyhedron. Finally, we illustrate the implementation of the best of these methods and show its effectiveness using a case study with sensor values from a real robot.
{"title":"Resilient multidimensional sensor fusion using measurement history","authors":"Radoslav Ivanov, M. Pajic, Insup Lee","doi":"10.1145/2566468.2566475","DOIUrl":"https://doi.org/10.1145/2566468.2566475","url":null,"abstract":"This work considers the problem of performing resilient sensor fusion using past sensor measurements. In particular, we consider a system with n sensors measuring the same physical variable where some sensors might be attacked or faulty. We consider a setup in which each sensor provides the controller with a set of possible values for the true value. Here, more precise sensors provide smaller sets. Since a lot of modern sensors provide multidimensional measurements (e.g. position in three dimensions), the sets considered in this work are multidimensional polyhedra. Given the assumption that some sensors can be attacked or faulty, the paper provides a sensor fusion algorithm that obtains a fusion polyhedron which is guaranteed to contain the true value and is minimal in size. A bound on the volume of the fusion polyhedron is also proved based on the number of faulty or attacked sensors. In addition, we incorporate system dynamics in order to utilize past measurements and further reduce the size of the fusion polyhedron. We describe several ways of mapping previous measurements to current time and compare them, under different assumptions, using the volume of the fusion polyhedron. Finally, we illustrate the implementation of the best of these methods and show its effectiveness using a case study with sensor values from a real robot.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130976525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Network security monitoring using machine learning algorithms is a topic that has been well researched and found to be difficult to use. We propose to use a specific approach in restricted IP network environments and leverage the network state information and information from individual connections for increased level of sensitivity. The approach is meant for use in restricted IP networks which exhibit a level of determinism that enables the use of machine learning approach. In this work we use algorithm called Self-Organizing Maps. We introduce an implementation of self-organizing maps engine built on top of the Bro network security monitor. An implemented selection of initial features for the Self-Organizing Maps is provided and a sample sub-set is used when training a SOM lattice for network data from an industrial control system environment. The anomaly detection prototype described in this paper is meant as a complementary mechanism, not a standalone solution for network security monitoring.
{"title":"A module for anomaly detection in ICS networks","authors":"Matti Mantere, Mirko Sailio, S. Noponen","doi":"10.1145/2566468.2566478","DOIUrl":"https://doi.org/10.1145/2566468.2566478","url":null,"abstract":"Network security monitoring using machine learning algorithms is a topic that has been well researched and found to be difficult to use. We propose to use a specific approach in restricted IP network environments and leverage the network state information and information from individual connections for increased level of sensitivity. The approach is meant for use in restricted IP networks which exhibit a level of determinism that enables the use of machine learning approach. In this work we use algorithm called Self-Organizing Maps. We introduce an implementation of self-organizing maps engine built on top of the Bro network security monitor. An implemented selection of initial features for the Self-Organizing Maps is provided and a sample sub-set is used when training a SOM lattice for network data from an industrial control system environment. The anomaly detection prototype described in this paper is meant as a complementary mechanism, not a standalone solution for network security monitoring.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"262 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114074921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this talk I will discuss the need to establish clear differences between reliability and security for protecting cyber-physical systems (CPS). This is particularly important given the recent interest from researchers in exploring the vulnerability of a CPS when an attacker has partial control of the sensor or actuator signals, which has led to the proposal of several anomaly detection schemes for CPS by using data collected from physical sensors (as opposed to traditional network sensors). In the general setting, data obtained from normal behavior of the system is used to create a model and then any outlier is considered an anomaly and a potential failure or attack; however, this line of research is very similar to the fault-detection, and safety mechanisms that have been deployed in control systems for decades. In particular, the protection of control systems has traditionally been enforced by several safety mechanisms, which include bad data detection, protective relays, safety shutdowns, interlock systems, robust control, and fault-tolerant control; however, so far there has not been a systematic study that tries to identify how much these protection mechanisms can help against attacks (as opposed to failures or accidents), and how can they be broken by an attacker and potentially fixed by a system designer that incorporates attack models in the design of their system. In this talk I describe how current protection mechanisms are analogous to how error correcting codes are used in communications: they protect against a vast majority of random faults and accidents; however they are not secure against attacks - the way cryptographic hash functions are. As a community we need to revisit protection mechanisms available from control theory and then analyze them from a security perspective, giving new guidelines on security metrics and new ways to design attack-resilient CPS. In addition, we also need to avoid falling into the trap of proposing security mechanisms that are evaluated using similar tools from reliability.
{"title":"From CRCs to resilient control systems: differentiating between reliability and security for the protection of cyber-physical systems","authors":"A. Cárdenas","doi":"10.1145/2566468.2566469","DOIUrl":"https://doi.org/10.1145/2566468.2566469","url":null,"abstract":"In this talk I will discuss the need to establish clear differences between reliability and security for protecting cyber-physical systems (CPS). This is particularly important given the recent interest from researchers in exploring the vulnerability of a CPS when an attacker has partial control of the sensor or actuator signals, which has led to the proposal of several anomaly detection schemes for CPS by using data collected from physical sensors (as opposed to traditional network sensors). In the general setting, data obtained from normal behavior of the system is used to create a model and then any outlier is considered an anomaly and a potential failure or attack; however, this line of research is very similar to the fault-detection, and safety mechanisms that have been deployed in control systems for decades. In particular, the protection of control systems has traditionally been enforced by several safety mechanisms, which include bad data detection, protective relays, safety shutdowns, interlock systems, robust control, and fault-tolerant control; however, so far there has not been a systematic study that tries to identify how much these protection mechanisms can help against attacks (as opposed to failures or accidents), and how can they be broken by an attacker and potentially fixed by a system designer that incorporates attack models in the design of their system. In this talk I describe how current protection mechanisms are analogous to how error correcting codes are used in communications: they protect against a vast majority of random faults and accidents; however they are not secure against attacks - the way cryptographic hash functions are. As a community we need to revisit protection mechanisms available from control theory and then analyze them from a security perspective, giving new guidelines on security metrics and new ways to design attack-resilient CPS. In addition, we also need to avoid falling into the trap of proposing security mechanisms that are evaluated using similar tools from reliability.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"15 5-6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120892039","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Individuals sharing information can improve the cost or performance of a distributed control system. But, sharing may also violate privacy. We develop a general framework for studying the cost of differential privacy in systems where a collection of agents, with coupled dynamics, communicate for sensing their shared environment while pursuing individual preferences. First, we propose a communication strategy that relies on adding carefully chosen random noise to agent states and show that it preserves differential privacy. Of course, the higher the standard deviation of the noise, the higher the cost of privacy. For linear distributed control systems with quadratic cost functions, the standard deviation becomes independent of the number agents and it decays with the maximum eigenvalue of the dynamics matrix. Furthermore, for stable dynamics, the noise to be added is independent of the number of agents as well as the time horizon up to which privacy is desired. Finally, we show that the cost of ε-differential privacy up to time T, for a linear stable system with N agents, is upper bounded by O(T3⁄ Nε2).
{"title":"On the cost of differential privacy in distributed control systems","authors":"Zhenqi Huang, Yu Wang, S. Mitra, G. Dullerud","doi":"10.1145/2566468.2566474","DOIUrl":"https://doi.org/10.1145/2566468.2566474","url":null,"abstract":"Individuals sharing information can improve the cost or performance of a distributed control system. But, sharing may also violate privacy. We develop a general framework for studying the cost of differential privacy in systems where a collection of agents, with coupled dynamics, communicate for sensing their shared environment while pursuing individual preferences. First, we propose a communication strategy that relies on adding carefully chosen random noise to agent states and show that it preserves differential privacy. Of course, the higher the standard deviation of the noise, the higher the cost of privacy. For linear distributed control systems with quadratic cost functions, the standard deviation becomes independent of the number agents and it decays with the maximum eigenvalue of the dynamics matrix. Furthermore, for stable dynamics, the noise to be added is independent of the number of agents as well as the time horizon up to which privacy is desired. Finally, we show that the cost of ε-differential privacy up to time T, for a linear stable system with N agents, is upper bounded by O(T3⁄ Nε2).","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"29 9","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120903488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper details the work in progress to formalize methods and algorithms for autonomous decision making, focusing on the implementation of autonomous vehicles. Many different scenarios are to be considered while focusing on a heterogeneous environment of human driven, semi-autonomous, and fully autonomous vehicles. As this work is in its early stages of development, this paper summarizes the work that has been done in the areas of vehicle to vehicle communication with control applications and high-level decision making for autonomous vehicles. The proposed method to be implemented is also presented, which aims to guarantee feasibility, safety, and stability of autonomous systems.
{"title":"Decisions for autonomous vehicles: integrating sensors, communication, and control","authors":"K. Driggs-Campbell, Victor Shia, R. Bajcsy","doi":"10.1145/2566468.2576850","DOIUrl":"https://doi.org/10.1145/2566468.2576850","url":null,"abstract":"This paper details the work in progress to formalize methods and algorithms for autonomous decision making, focusing on the implementation of autonomous vehicles. Many different scenarios are to be considered while focusing on a heterogeneous environment of human driven, semi-autonomous, and fully autonomous vehicles. As this work is in its early stages of development, this paper summarizes the work that has been done in the areas of vehicle to vehicle communication with control applications and high-level decision making for autonomous vehicles. The proposed method to be implemented is also presented, which aims to guarantee feasibility, safety, and stability of autonomous systems.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123106599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Leader-follower formation control is a widely used distributed control strategy that often needs systems to exchange information over a wireless radio communication network to coordinate their formations. These wireless networks are subject to deep fades, where a severe drop in the quality of the communication link occurs. Such deep fades may significantly impact the formation's performance and stability, and cause unexpected safety problems. In many applications, however, the variation in channel state is a function of the system's kinematic states. This suggests that channel state information can be used as a feedback signal to recover the performance loss caused by a deep fade. Assuming an exponentially bursty channel model, this paper proposes a distributed switching scheme under which a string of leader-follower nonholonomic system is almost surely practical stable in the presence of deep fades. Sufficient conditions are derived for each vehicle in the leader follower chain to decide which controller is placed in the feedback loop to assure almost sure practical stability. Simulation results are used to illustrate the main findings in the paper.
{"title":"Distributed switching control to achieve resilience to deep fades in leader-follower nonholonomic systems","authors":"B. Hu, M. Lemmon","doi":"10.1145/2566468.2566473","DOIUrl":"https://doi.org/10.1145/2566468.2566473","url":null,"abstract":"Leader-follower formation control is a widely used distributed control strategy that often needs systems to exchange information over a wireless radio communication network to coordinate their formations. These wireless networks are subject to deep fades, where a severe drop in the quality of the communication link occurs. Such deep fades may significantly impact the formation's performance and stability, and cause unexpected safety problems. In many applications, however, the variation in channel state is a function of the system's kinematic states. This suggests that channel state information can be used as a feedback signal to recover the performance loss caused by a deep fade. Assuming an exponentially bursty channel model, this paper proposes a distributed switching scheme under which a string of leader-follower nonholonomic system is almost surely practical stable in the presence of deep fades. Sufficient conditions are derived for each vehicle in the leader follower chain to decide which controller is placed in the feedback loop to assure almost sure practical stability. Simulation results are used to illustrate the main findings in the paper.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132866609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Utility companies have many motivations for modifying energy consumption patterns of consumers such as revenue decoupling and demand response programs. We model the utility company-consumer interaction as a principal-agent problem and present an iterative algorithm for designing incentives while estimating the consumer's utility function.
{"title":"Energy efficiency via incentive design and utility learning","authors":"L. Ratliff, Roy Dong, Henrik Ohlsson, S. Sastry","doi":"10.1145/2566468.2576849","DOIUrl":"https://doi.org/10.1145/2566468.2576849","url":null,"abstract":"Utility companies have many motivations for modifying energy consumption patterns of consumers such as revenue decoupling and demand response programs. We model the utility company-consumer interaction as a principal-agent problem and present an iterative algorithm for designing incentives while estimating the consumer's utility function.","PeriodicalId":339979,"journal":{"name":"Proceedings of the 3rd international conference on High confidence networked systems","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126932249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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