A Safety-security Integrated Analysis Approach For CBTC Critical Subsystems

The train control system ensures the efficient and safe operation of trains,which plays the core role as the "brain" and "central nervous system" of urban rail transit.Due to the fundamental safety-critical attribute of urban rail transit,safety analysis and assessment methods for train control systems oriented to system random failures have tended to be mature and been widely applied.However,with the wide applications of computer,communication and control technologies,negligible security risks have been introduced,which require urgent attention.As malicious and subjective security risks were not considered in traditional safety analysis methods,a safety-security integrated analysis approach based on extended fault tree for urban rail transit train control systems was proposed in the thesis.The main work is as follows:Firstly,based on the definitions,the risk evolution paths,the analysis standards and methods,and the relationships between safety and security were analyzed.According to the coupling features of safety and security from the risk propagation principles,the safety-security analysis approach based on extended fault tree was proposed.Secondly,the safety-security analysis model was established.The general fault tree and the extended attack tree with the description of system vulnerabilities were combined,where the attack tree was adjusted to suitable for the standard structure of the fault tree.The key analysis indicators from the perspective of overall risk and basic events were provided.For the probability evaluation of security risks,the cost of attacks,the difficulty of attacks and the probability of attacks being detected were determined.Thirdly,the proposed analysis approach was applied to the critical scenario of CBTC critical subsystem.Based on the function process and security threats,the corresponding CBTC extended fault tree model was established.According to minimum cut sets and structural importance,the risk occurrence probability and consequence severity were calculated and analyzed.Considering the system architecture and safety protection mechanisms of the CBTC system,the effects caused by security on safety were determined.Finally,the results showed that the propagation of information security risk was restricted by the existing safety mechanisms of the train control systems,and it was difficult to affect the system safety in the current urban rail transit train control system.However,the fail-safe principle makes it easy that security attacks trigger safety protection such as braking and degraded operation of the train control system,which leads to the decrease of system operation efficiency.