# Legacy ICS Cybersecurity Assessment Using Hybrid Threat Modeling--An Oil and Gas Sector Case Study
## 4 Case Study & Performance Evaluation
### Stage I: Defining Security Objectives  
**Goals of this stage:** The first stage's goal is to define the objectives for analyzing and managing the various types of cybersecurity risks affecting the ICS. **Output 1--Description of the Application Functionality and Business Objectives:**  
The ICS System consists of a minimum of the following components, as shown in the abstract architecture in Figure 1.  
* **Field Control Station (FCS):** It consists of input/output modules, a CPU, and a communication bus. * **The operator station** is essentially a human interface machine equipped with a monitor, allowing the operator to view the plant's processes, check for any alarms, change settings, and print reports, among other tasks. * **The engineering station** configures all input and output, creates drawings, and monitors anything necessary for the operator station. The most noticeable benefit of systems architecture is its contribution to the design of an integrated plant-wide information and control system through the distribution of various functions throughout the plant. This allows operators and unit supervisors to identify conditions beyond their purview, such as upstream or downstream bottlenecks or plant utility constraints, and initiate corrective measures before these factors negatively impact their operations. Distributed architecture can provide functionally dedicated stations to various disciplines, e.g., maintenance and engineering, so that system and process information can disperse throughout the plant without interfering with operations. For example, without leaving the maintenance shop, the operator can check pressure drops across heat exchangers to determine the degree of fouling. Basically, a distributed control system (DCS) Figure 2 receives input signals from other devices; the DCS-CPU processes and analyzes these signals and then acts based on the results. Numerous sensors and transducers inside the plant transform physical quantities such as pressure and temperature into electrical signals, known as transmitters, which are then transmitted to the DCS system. **Output 2--Definition of the Application Security and Compliance Requirement**  
NIST Special Publication 800-82r2 (Guide to Industrial Control Systems (ICS) Security) [13] states that an ICS implementation should include the following major security objectives:  
* Restricting logical access to the ICS network and network activity. * Restricting physical access to the ICS network and devices. * Protecting individual ICS components from exploitation. * Restricting unauthorized modification of data. * Detecting security events and incidents. \begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Threat** & **Security Property** & **Threat Definitions** & **Explanation/Example** \\ \hline Information disclosure & Confidentiality & system configuration and credential information can be used & The information is exposed to parties that do not/should not have access to it. Information leaks and data breaches are common examples of information disclosure. \\ \hline Denial of service & Availability & DoS/Distrusted DoS & System/information is not available to a legitimate user. \\ \hline Elevation of privilege & Authorization & Elevate to actor privileges on app level/Elevate to actor privileges on system level/Change data in the database. & Malicious or rightful users get more privileges on the content than they are entitled to. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._Maintaining functionality during adverse conditions. * Restoring the system after an incident.