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Transport Layer Security (TLS) is the standard protocol for securing web communications, including HTTP over TLS (HTTPS) in web browsers. TLS provides encryption, authentication, and data integrity, and has replaced SSL as the primary means of securing browser-based communications.

 Layer 2 of the OSI model is the data link layer, which is responsible for transferring data frames between nodes on a network segment. The data link layer is divided into two sublayers: logical link control (LLC) and media access control (MAC). The LLC sublayer deals with issues common to both dedicated and broadcast links, such as framing, flow control, and error control. The MAC sublayer deals with issues specific to broadcast links, such as how to access the shared medium and avoid collisions. The LLC and MAC sublayers are not related to the ISA/IEC 62443 cybersecurity standards, which focus on the security of industrial automation and control systems (IACS). References: https://www.baeldung.com/cs/data-link-sub-layers

https://bing.com/search?q=Layer+2+sublayers

 A vulnerability scanner is a tool that scans a network or a system for known vulnerabilities, such as misconfigurations, outdated software, or weak passwords. A vulnerability scanner can provide valuable information for improving the security posture of a system, but it can also cause serious disruption of a control network if used on a live system. This is because a vulnerability scanner may generate a large amount of network traffic, consume system resources, trigger alarms, or even crash devices by exploiting vulnerabilities. Therefore, a vulnerability scanner should not be used on a live system without proper authorization and precautions. A vulnerability scanner should only be used on a test or isolated network, or during a scheduled maintenance window with minimal impact on the system operation. References: ISA/IEC 62443 Standards to Secure Your Industrial Control System, Module 5: Assessing the Current Security Level, Slide 25.

Role-based access control (RBAC) is a method of restricting access to resources based on the roles of individual users within an organization. RBAC assigns permissions and responsibilities to roles, rather than to individual users, and then assigns users to those roles. This way, users can only perform the actions that are relevant and necessary for their role, and not access or modify any other resources that are beyond their scope of authority. RBAC is one of the security countermeasures that can be implemented in a defense-in-depth strategy, which is a layered approach to protect industrial automation and control systems (IACS) from cyber threats. RBAC can help prevent unauthorized access, misuse, or sabotage of IACS resources, as well as reduce the risk of human error or insider attacks.

A control system, in the context of ISA/IEC 62443, refers to the hardware and software components of an Industrial Automation and Control System (IACS). This includes PLCs, SCADA, DCS, HMIs, sensors, actuators, and supporting networks and applications used to monitor and control physical processes.

 Safety management staff are stakeholders of the CSMS, which stands for Cybersecurity Management System. The CSMS is a framework for managing the cybersecurity of industrial automation and control systems (IACS) based on the ISA/IEC 62443-2-1 standard1. The CSMS defines the objectives, policies, metrics, and governance for the overall ICS security program2. The CSMS also includes the processes for risk assessment, security design, implementation, monitoring, and improvement3. Safety management staff are involved in the CSMS development and implementation, as they are responsible for ensuring the safety of the IACS and the people, environment, and assets that depend on it. Safety management staff need to coordinate with the security management staff to align the safety and security requirements, identify and mitigate the safety risks arising from cyber threats, and monitor and respond to safety incidents caused by cyberattacks. References:

1: ISA/IEC 62443-2-1: Establishing an Industrial Automation and Control Systems Security Program, ISA, 2010.

2: A Practical Approach to Adopting the IEC 62443 Standards - ISAGCA

3: ISA ISA-IEC-62443 ISA/IEC 62443 Cybersecurity Fundamentals Specialist Online Training - Exam4Training

[4]: Using the ISA/IEC 62443 Standards to Secure Your Control System, ISA, 2018.

The File Transfer Protocol (FTP) is an application layer protocol that moves files between local and remote file systems. It runs on top of TCP, like HTTP. To transfer a file, 2 TCP connections are used by FTP in parallel: control connection and data connection. The control connection is used to send commands and responses between the client and the server, while the data connection is used to transfer the actual file. FTP is one of the standard communication protocols defined by the TCP/IP model and it does not fit neatly into the OSI model. However, since the OSI model is a reference model that describes the general functions of each layer, FTP can be considered as an application layer protocol in the OSI model, as it provides user services and interfaces to the network. The application layer is the highest layer in the OSI model and it is responsible for providing various network services to the users, such as email, web browsing, file transfer, remote login, etc. The application layer interacts with the presentation layer, which is responsible for data formatting, encryption, compression, etc. The presentation layer interacts with the session layer, which is responsible for establishing, maintaining, and terminating sessions between applications. The session layer interacts with the transport layer, which is responsible for reliable end-to-end data transfer and flow control. The transport layer interacts with the network layer, which is responsible for routing and addressing packets across different networks. The network layer interacts with the data link layer, which is responsible for framing, error detection, and medium access control. The data link layer interacts with the physical layer, which is responsible for transmitting and receiving bits over the physical medium. References:

File Transfer Protocol (FTP) in Application Layer1

FTP Protocol2

What OSI layer is FTP?3

Defense in depth is a concept of cybersecurity that involves applying multiple layers of protection to a system or network, so that if one layer fails, another layer can prevent or mitigate an attack. Defense in depth is based on the principle that no single security measure is perfect or sufficient, and that multiple countermeasures can provide redundancy and diversity of defense. Defense in depth can also increase the cost and complexity for an attacker, as they have to overcome more obstacles and exploit more vulnerabilities to achieve their goals. Defense in depth is one of the key concepts of the ISA/IEC 62443 series of standards, which provide guidance and best practices for securing industrial automation and control systems (IACS). The standards recommend applying defense in depth strategies at different levels of an IACS, such as the network, the system, the component, and the policy and procedure level. The standards also define different zones and conduits within an IACS, which are logical or physical groupings of assets that share common security requirements and risk levels. By applying defense in depth strategies to each zone and conduit, the security of the entire IACS can be improved. References:

ISA/IEC 62443-1-1:2009, Security for industrial automation and control systems - Part 1-1: Terminology, concepts and models1

ISA/IEC 62443-3-3:2013, Security for industrial automation and control systems - Part 3-3: System security requirements and security levels2

ISA/IEC 62443-4-1:2018, Security for industrial automation and control systems - Part 4-1: Product security development life-cycle requirements3

ISA/IEC 62443-4-2:2019, Security for industrial automation and control systems - Part 4-2: Technical security requirements for IACS components4

ISA/IEC 62443 recommends using a firewall to segment and protect the plant floor (Operational Technology or OT network) from the rest of the company’s Information Technology (IT) networks. Firewalls enforce security policies by controlling and monitoring traffic, helping to prevent unauthorized access and potential threats from traversing between business and control networks. Hubs and switches do not provide security; routers may offer some basic filtering, but firewalls are explicitly designed for this purpose.

According to the ISA/IEC 62443-3-2 standard, implementing countermeasures is one of the steps in the security risk assessment for system design. The standard defines a comprehensive set of engineering measures to guide organizations through the process of assessing the risk of a particular industrial automation and control system (IACS) and identifying and applying security countermeasures to reduce that risk to tolerable levels. The standard recommends the following steps for implementing countermeasures:

Establish the risk tolerance: This step involves determining the acceptable level of risk for the organization and the system under consideration, based on the business objectives, legal and regulatory requirements, and stakeholder expectations. The risk tolerance can be expressed as a target security level (SL-T) for each zone or conduit in the system.

Select common countermeasures: This step involves selecting the appropriate security countermeasures for each zone or conduit, based on the SL-T and the existing security level (SL-A) of the system. The standard provides a list of common countermeasures for each security level, covering the domains of physical security, network security, system security, and application security. The selected countermeasures should be documented and justified in the security risk assessment report. References: ISA/IEC 62443 Cybersecurity Series Designated as IEC Horizontal Standards, Cybersecurity Risk Assessment According to ISA/IEC 62443-3-2