# A Survey on Recent Advanced Research of CPS Security
## 4 Discussion
### Non-Tech Analysis  
In this subsection, we provide a broad view of the global CPS security research situation from the non-tech aspect. We perform statistics on publication time, organization/country of authors, and funding supporters of the papers. Finally, we also show the cooperation among different universities and situations worldwide. In security conferences and journals labeled A/B, the number of papers related to CPS security has increased dramatically over the past five years. In the first three years (2015-2017), the number doubled from 10 to 23. From 2018 to 2019, the number increased more rapidly: 2018 (32), 2019 (62). Figure 2 shows this trend. Figure 3 shows the contributions of different countries, and their proportions are shown in Figure 4. The United States made the most prominent contribution (60 papers), followed by China (20 papers). Germany, Canada, Singapore, and the United Kingdom can be ranked as the third echelon, with 15, 6, 5, and 5 papers, respectively. The UK and Singapore played a major role by publishing five papers, while the other countries published no more than three papers. Figure 4: Proportion of papers from different countries. Figure 3: Number of papers from different countries. Figure 2: Time trend of the number of CPS security-related papers. We also analyze the sponsors and find that the top sponsors are the NSF, U.S. military, NSFC, DFG, etc. The NSF (Nation Science Foundation) is a federal agency in the United States that funds basic scientific research programs. The U.S. military, mainly including U.S. Army Research Office, the U.S. Office of Naval Research, Air Force Research Lab, DARPA, and Department of Defense, has also participated in many scientific research projects. The NSFC (National Natural Science Foundation of China) and the DFG (German Research Foundation) also sponsor many scientific research projects, whose proportions are 10% and 5%, respectively. Figure 5 shows the distributed situation with a pie chart, and Table 4 shows an explanation of the abbreviations. The prevalence and vulnerabilities of CPS have drawn the attention of researchers. Many universities and institutes have created labs to perform CPS security-related studies in recent years. Figure 6 shows the leading university laboratories and institutes and their relations in the research field of CPS security. The USA's universities and research labs are leading the studies. Carnegie Mellon University developed the SmartAuth framework [38] in cooperation with the University of Chicago and Indiana University at Bloomington. The University of California cooperates with the Air Force Research Lab and utilizes high-level numeric feature vectors to find bugs in firmware images [141]. Cornell Tech, Columbia University, and Tel Aviv University from Israel proposed a situational access control framework for the IoT system [43]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Abbr** & **Expansion** & **Country** \\ \hline NSF & National Science Foundation & U.S. \\ USA Military & Army, Navy, Air Force, DARPA, DoD & U.S. \\ NSFC & National Natural Science & China \\ DFG & German Research Foundation & Germany \\ NRF & National Research Foundation & Singapore \\ RFKUL & Research Fund KU Leuven & Germany \\ NSERC & Natural Sciences and Engineering & Canada \\  & Research Council of Canada & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Explanation of the abbreviations. Figure 5: Main sponsors and their attributes. China has also made significant contributions to CPS security research. Zhejiang University in cooperation with the Georgia Institute of Technology proposed a fake message scheduling to protect source location privacy [99]. Xi'an Jiaotong University, Purdue University and Virginia Tech improved the Intel(r) SGX with a \"heartbeat\" protocol to assist key revocation [16]. Donghua University, Shandong University, and Shanghai JiaoTong University performed a ciphertext-only fault analysis on the LED lightweight cryptosystem [102].