## 6 Networked ATM-CPS Security Assurance Architecture
### The Method of ATM-CPS Information Security Assurance Based on Blockchain Trusted Model  
The equipment and system resources in the networked ATM system are characterized by decentralization (all types of communication, navigation, and surveillance equipment are distributed in different places in a wide area in the form of sensors), and information is directly transmitted and served among CNS equipment (sensor nodes). When the networked ATM system is faced with malicious attack and network deception, it shows a certain vulnerability and must establish a trust model to ensure its security. Blockchain technology can support secure data sharing and privacy protection [26; 27; 28; 29; 30]. [PERSON] et al. [26] put forward the block share system, which can effectively verify any part of the shared data record by introducing a new authentication data structure scheme. At the same time, based on zero-knowledge verification, it supports the privacy protection of users. In addition, blockchain technology increases the timeliness while ensuring the authenticity of stored data, and transaction data need to be verified by most nodes before entering the chain, which provides a unified data source for the trust model. As blockchain technology continues to improve, security, such as session keys and message integrity, continues to improve, and communication and computing costs continue to decrease. [PERSON] [27] proposed a framework based on software defined network and blockchain for privacy protection of smart grid cyber-physical system. Aimed at the complex interaction, communication protection, and mutual identification among different subsystems, software-defined network, smart contract, and elliptic curve encryption are combined with blockchain, respectively, to ensure the privacy protection and power safety of smart grid cyber-physical system. [PERSON] et al. [28] used blockchain technology and smart contracts to build a reliable and efficient lightweight certificateless signature scheme, providing protection for the security and privacy transmission of Industrial Internet of Things data. Their solutions not only provide more reliable security for Industrial Internet of Things data but also greatly reduce computing and communication costs. Therefore, this research uses the blockchain technology to build the trust model of the networked ATM system, establish a trusted mechanism among the resources of the networked ATM system, and then realize the information security assurance architecture of the networked ATM system. It regards the blockchain network as a server that provides trust, runs a finite state machine model for the corresponding processing process on it, and records the historical behavior reliably. Digital signature technology and edge computing network are used to design a trust access verification mechanism, which can monitor the networked ATM system in real time and promote resource sharing and collaboration among entities in the system. The trusted model of information security assurance of networked ATM based on blockchain is shown in Figure 9. The design idea of this model is to jointly participate in and maintain the distributed ledger by Civil Aviation Administration of China (CAAC), CAAC ATM Bureau, ATM departments, airports, and airlines. The trust relationship between nodes is established through peer-to-peer network, password, and distributed consensus mechanism. In Figure 9, the blockchain network layer records mainly the data information related to the ATM system.