## 7 Results
### Current State of Research in CLC for C-ITS  
In this section we will detail the current theoretical work of CLC, specifically for C-ITSs. The amount of research in CLC is massive. A quick search on \"_certificateless cryptography_\", \"_CLC_\" and \"_CL-PKC_\" in Scopus, Google Scholar, Springer Link, IEEE Xplore and similar databases gives several thousand hits. It is more difficult to extract the exact number \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Gaps** & **Description** & **Going Forward** \\ \hline Proof-of-Concepts & Various concepts of CLC-based solutions have been proposed, such as for authentication [41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58], aggregated signing [44, 59, 60, 61, 62, 63, 64], key agreement [65, 66], and sign-cryption [67, 68, 69, 70, 71, 72, 73]. However, common for these proposals is that they have either been tested in a controller lab environment [42, 47, 48, 59, 64, 60, 64] or only theoretically [41, 43, 45, 49, 50, 52, 53, 60, 62, 63, 65, 66, 67, 73, 75], typically using a desktop or laptop computer. This has lead to quite similar, theoretical performances as they are based on matching setups (e.g., using MIRACL lib. Omnet++, Veins simulations, etc.); even more so when the same PoC are used between authors [43, 44, 45, 52, 53, 67]. Hence, little is still known about performance in a production-like environment and context. & Beyond employee training, education, and recruitment of relevant competences within organisations, science communication plays a role in affecting the practitioners individual 'awareness-knowledge'. Bridging academia and industry--e.g., by extended networking and increased collaboration between industry and academia–could, similarly, influence standardization projects. & Further harmonization of terms, security models, nomenclature, and grouping of protocols in CLC for C-ITSs is needed to better bridge industry, standardization bodies, and academic work on the topic. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overview of the identified and grouped gaps and what could be done, going forward, to address each gap. of papers addressing C-ITS since several papers only use VANET or V2X as illustrative scenarios, where the essence of the research is the mathematical framework rather than the applicability. Therefore, we applied a filtering process during the synthesis of the collected data, where the inclusion criteria was to have either (or both) a proof-of-concept implementation and a significant detailed part of the paper related to VANET, V2X or other related C-ITS concepts. From the analysis we grouped the remaining articles into Authentication, Aggregated signatures, Key agreement and Signcryption. Although most of the articles refer to authentication solutions, our grouping provides a more detailed distinction of proposed techniques. In the main category Authentication single-signature solutions were in the majority. We summarize the findings in Table 4. We note that there exists no surveys for CLC-based security solutions for C-ITSs specifically. However, some surveys are included in Table 4 if they partially included papers relevant for the intersection of C-ITSs and CLC, and in that case, the proportion of schemes implemented are only counted from the set of CLC-based schemes mentioned in the survey. In the analyzed time frame of 2022-2023 there was no proof-of-concept implementations on-site, i.e., corresponding to level 5 in CLC TRL. The majority of implementations, and, thereby, performance analysis of CLC schemes, were made on laptops and/or PC clients with varying specifications in both Ubuntu and Windows. The most-used programming library for the cryptographic operations was MIRACL, e.g., in [67, 68, 69, 46, 60, 61]. A few projects, e.g., [68, 60, 61], also used network traffic simulations for testing the protocols communication complexity; the most used simulation tool was Omnet++.