# CS Measures for Nuclear Power Plant Protection: A Systematic Literature Review
## 3 Related Work  
To the best of the author's knowledge, only one work in the literature has reviewed CS measures for NPPs.  
The authors of [14] discussed the history of the implementation and application of CS in nuclear power plants. A total of 51 studies on the subject were reviewed by the authors. The authors cited regulations, policies, guidelines, CS frameworks, and software security measures as some of the most adopted strategies for CS assurance in NPPs. A list of major issues to be addressed was pointed out by the authors:  
* Development and testing;
* Secure design;
* Biological approaches to security;
* Usable security;
* CS metrics;
* Anomaly and misuse detection systems;
* Policy security;
* Cyber retaliation;
* CS related to legal issues;
* The economics of CS;
* In security cyber defense;
* Spam dealing.  
While the authors raised relevant criticisms of software and CS hazards, their work was limited in providing an understanding of the interdependencies among preventive measures.  
In addition to this work, a number of reviews were identified that focused on CS for other sectors of critical infrastructure. Many of the requirements and measures observed in these works can be applicable to the nuclear domain or could be adapted to serve as cyber defense tools for NPPs' I&C systems.  
For example, the authors of [15] conducted a review of Smart Grid CS. In their work, the authors reviewed and categorized solutions based on the five categories that make up different components of the Smart Grid: Process Control System (PCS) Security, Smart Meter Security, Power System State Estimation Security, Smart Grid Communication Protocol Security, and Smart Grid Simulation for Security Analysis.  
The authors of [16] conducted a systematic review of countermeasures available to combat internal threats in healthcare critical infrastructure. According to their analysis, there was high heterogeneity across raw data, which indicated that the effectiveness of security measures varied significantly and that no single solution was able to totally mitigate an insider threat. For this reason, the authors suggested that a combination of security measures be utilized, which should grant an additional layer of protection according to the defense-in-depth model. The authors concluded by stating that significant work still needs to be undertaken to create more effective IDPS techniques. Further work also needs to be undertaken to create a model of threat mitigation that takes into account an unknown malicious insider, as well as to understand the nature of insider threats so that new technologies can be developed around potential further findings.  
The authors of [17] conducted a survey of the risks, types of systems involved, and additional information used to develop and maintain a robust process control system for SCADA systems in critical infrastructure. The authors stated that an essential element and key factor of developing and implementing an SCADA CS program is the selection and implementation of a risk-based assessment method.  
In Table 3, a summary of the recommendations from the authors of the above works is given, together with the domains of application and challenges/shortcomings noted in their works.  
As can be noted from Table 3, many of the works described above provided limited descriptions of the analyzed solutions; this makes it challenging to compare them to each other, but also allows the development of a well-structured framework. For this reason, in the following sections, we will be describing all of the CS measures proposed in the literature for NPP protection based on their characteristics. This will later allow for comparisons of these solutions and identification of gaps and challenges.