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An asymmetric key is a feature of asymmetric cryptography, also known as public-key cryptography, which is a method of encrypting and decrypting data using two different keys: a public key and a private key. The public key can be shared with anyone, while the private key must be kept secret by the owner. The public key and the private key are mathematically related, but it is computationally infeasible to derive one from the other. Asymmetric cryptography can be used for various purposes, such as digital signatures, key exchange, and encryption. For example, if Alice wants to send a message to Bob, she can use Bob’s public key to encrypt the message, and only Bob can decrypt it using his private key. Alternatively, if Bob wants to prove that he is the author of a message, he can use his private key to sign the message, and anyone can verify it using his public key. Asymmetric cryptography has some advantages over symmetric cryptography, which uses the same key for both encryption and decryption. For instance, asymmetric cryptography does not require a secure channel to distribute the keys, and it can provide non-repudiation and authentication. However, asymmetric cryptography also has some drawbacks, such as higher computational complexity, larger key sizes, and higher network overhead.

According to the ISA/IEC 62443-3-2 standard, a security zone is a grouping of systems and components based on their functional, logical, and physical relationship that share common security requirements. The primary objective of defining a security zone is to apply a consistent level of protection to the assets within the zone, based on their criticality and risk assessment. A security zone may contain assets from different vendors, different levels in the Purdue model, or different physical locations, as long as they have the same security requirements. A security zone may also be subdivided into subzones, if there are different security requirements within the zone. A conduit is a logical or physical grouping of communication channels connecting two or more zones that share common security requirements.

Ransomware is a type of malicious software (malware) designed to block access to a computer system or data, typically by encrypting files, until a sum of money (ransom) is paid. This form of attack is increasingly targeting industrial automation and control system (IACS) environments due to the critical nature of these systems. Unlike phishing (which tricks users into revealing sensitive information) or DDoS attacks (which disrupt availability), ransomware specifically encrypts data and extorts the victim.

ISO/IEC 15408, also known as the Common Criteria for Information Technology Security Evaluation, is an international standard that provides a framework for evaluating the security of IT products and systems. The purpose of the standard is to define a common set of requirements for the security functions and assurance measures of IT products and systems, and to establish a common methodology for conducting security evaluations. The standard allows users to specify their security needs and expectations in a Security Target (ST), which may be based on one or more Protection Profiles (PPs) that define security requirements for a class of products or systems. Vendors can then implement or claim compliance with the ST or PPs, and have their products or systems evaluated by independent testing laboratories against the security criteria defined in the standard. The standard also defines a scale of Evaluation Assurance Levels (EALs) that indicate the degree of confidence in the security of the evaluated product or system. The standard is intended to facilitate the development, procurement, and use of secure IT products and systems, and to promote the recognition and acceptance of evaluation results across different countries and regions. References:

ISO/IEC 15408-1:2009 - Common Criteria Evaluation for IT Security - Nemko1

Common Criteria - Wikipedia2

ISO/IEC Standard 15408 — ENISA3

In the OSI model, the Data Link layer (Layer 2) is responsible for error detection/correction and for assigning and handling MAC (Media Access Control) addresses, which are unique identifiers for network interfaces. This layer ensures reliable transmission of data frames between devices on the same local network. The Network layer (Layer 3) handles IP addressing and routing, not MAC addresses.

 A recommended default rule for IACS firewalls is to block all traffic by default, and then allow only the necessary and authorized traffic based on the security policy and the zone and conduit model. This is also known as the principle of least privilege, which means granting the minimum access required for a legitimate purpose. Blocking all traffic by default provides a higher level of security and reduces the attack surface of the IACS network. The other choices are not recommended default rules for IACS firewalls, as they may expose the IACS network to unnecessary risks. Allowing all traffic by default would defeat the purpose of a firewall, as it would not filter any malicious or unwanted traffic. Allowing IACS devices to access the Internet would expose them to potential cyber threats, such as malware, phishing, or denial-of-service attacks. Allowing traffic directly from the IACS network to the enterprise network would bypass the demilitarized zone (DMZ), which is a buffer zone that isolates the IACS network from the enterprise network and hosts services that need to communicate between them. References:

ISA/IEC 62443 Standards to Secure Your Industrial Control System training course1

ISA/IEC 62443 Cybersecurity Fundamentals Specialist Study Guide2

Using the ISA/IEC 62443 Standard to Secure Your Control Systems3

A Host-based Intrusion Detection System (IDS) is a device or software application used to monitor and analyze the internals of a computing system (host) for malicious activity or policy violations. Unlike routers, switches, or even firewalls, which focus on network traffic or connectivity, a host-based IDS operates on individual machines to detect unauthorized activity or changes.

 ISA-TR62443-2-3 is the technical report that describes the requirements for asset owners and industrial automation and control system (IACS) product suppliers that have established and are now maintaining an IACS patch management program. Patch management is the process of applying software updates to fix vulnerabilities, bugs, or performance issues in the IACS components. Patch management is an essential part of maintaining the security and reliability of the IACS environment. The technical report provides guidance on how to establish a patch management policy, how to assess the impact and risk of patches, how to test and deploy patches, and how to monitor and audit the patch management process. References: 1, 2, 3

 The risk analysis category of an IACS consists of two elements: business rationale and risk identification and classification1. Business rationale is the process of defining the scope, objectives, and criteria for the risk analysis, as well as the roles and responsibilities of the stakeholders involved. Risk identification and classification is the process of identifying the assets, threats, vulnerabilities, and consequences of a cyberattack on the IACS, and assigning a risk level to each scenario based on the likelihood and impact of the attack1. These elements are essential for establishing a baseline of the current risk posture of the IACS and determining the appropriate risk treatment measures to reduce the risk to an acceptable level. References: 1: ISA/IEC 62443-3-2:2020, Security for industrial automation and control systems - Part 3-2: Security risk assessment for system design, International Society of Automation, Research Triangle Park, NC, USA, 2020.

A security conduit is a logical or physical grouping of communication channels connecting two or more zones that share common security requirements1. A zone is a grouping of systems and components based on their functional, logical, and physical relationship that share common security requirements1. Therefore, a security conduit consists of assets that enable or facilitate communication between zones, such as wiring, routers, switches, and network management devices. Controllers, sensors, transmitters, and final control elements are examples of assets that belong to a zone, not a conduit. Ferrous, thickwall, and threaded conduit including raceways are physical structures that may enclose or protect wiring, but they are not part of the communication channels themselves. Power lines, cabinet enclosures, and protective grounds are also not part of the communication channels, but rather provide power or protection to the assets in a zone or a conduit. References: 1: Key Concepts of ISA/IEC 62443: Zones & Security Levels | Dragos