[Reference: This aligns with the historical evolution of OT security. Initially, security was based on physical isolation rather than network security controls. This is a common topic in CASP+ discussions on OT security challenges., B. communicating over distributed environments: While OT systems can be distributed, the core design assumption, especially for older systems, wasn't centered around interconnectivity in the way modern IT systems are., C. untrustworthy users and systems being present: This is a more modern security principle (Zero Trust). Older OT systems often operated under a model of implicit trust within their isolated environment., D. an available EtherneVIP network stack for flexibility: Ethernet/IP is a relatively newer industrial protocol. Older OT systems often used proprietary or less flexible communication protocols. Also, there is no such thing as EtherneVIP., E. anticipated eavesdropping from malicious actors: While security was a concern, the primary threat model for older, isolated OT systems didn't heavily emphasize external malicious actors due to the assumed isolation., Why A is the Correct Answer:, Air Gap: The concept of an air gap (physical isolation) was the cornerstone of security for many legacy OT systems. These systems were not connected to the internet or corporate networks, making them less susceptible to remote attacks., Legacy Protocols: Older OT systems often used proprietary or serial communication protocols, not designed for internet connectivity., Implicit Trust: Within the isolated environment, there was often an assumption of trust among the connected components., CASP+ Relevance: The challenges of securing legacy OT systems, especially in the face of increasing connectivity, are a key area of focus in CASP+. Understanding the historical context and the shift in security paradigms is crucial., Modern OT Security Considerations (Elaboration):, Convergence: Today, the lines between IT and OT are blurring. OT systems are increasingly connected to corporate networks and the internet, necessitating a shift from isolation-based security to a more comprehensive approach., Threat Landscape: Modern OT systems face a wider range of threats, including targeted attacks from sophisticated actors., Security Controls: Modern OT security involves implementing network segmentation, intrusion detection, access controls, and other measures to protect against these evolving threats., In conclusion, the primary design assumption for many older OT systems was that they would operate in isolated or disconnected environments. This historical context is important for understanding the security challenges faced by organizations today as they integrate these legacy systems into modern, connected environments. This is a core concept discussed in CASP+ in the context of OT security and risk management., =================, , , ]