# Feasibility Assessment of a Fine-Grained Access Control Model on Resource Constrained Sensors
## 6 Conclusions  
Smart objects enabling the envisioned pervasive scenarios and advanced use cases are expected to provide services toward achieving improved user experience, higher interoperability and greater manageability. In such environments, where massive deployments are expected, smart things are inexpensive and thus implemented in devices with constrained resources. However, they are also critical components since they handle essential information that needs to be available, keeping the confidentiality and integrity; therefore, security needs to be ensured in an efficient manner. Current approaches addressing the principle of least privilege, based on the expressiveness and updating of the policy to be enforced in the sensors, are challenged by feasibility constraints. The conducted performance evaluation is focused on an innovative access control model based on a hybrid architecture and a policy language for dynamic fine-grained policy enforcement in the sensor. Such policy enforcement is based on local context conditions and corresponding obligations not only during secure session establishment but also afterward, when the security association is in use, to control the behavior of the access. Such a dynamic policy cycle avoiding local storage is enabled by an efficient message exchange protocol named Hidra. The Hidra protocol assures mutual authentication, expressive policy injection, tight policy enforcement in the secure association establishment and derived resource access, as well as the accounting for further tracking and auditing purposes. The proposed feasibility assessment is based on a test-bed implementation of an innovative access control model for very-constrained devices: C0 and C1 CDSs. The experimental performance analysis, focusing on three key performance indicators, i.e., the response time, the power consumption and the memory footprint, provides remarkable results. Based on these measurements, the performance evaluation of this proposal demonstrates the feasibility of this analyzed access control model for resource-constrained sensors. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Version** & **Text** & **Data** & **Bss** \\ \hline HidraR & 63,940 & 1548 & 5682 \\ Only connectivity & 45,396 & 338 & 4442 \\ Difference & 18,544 & 1210 & 1240 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Footprint increment through _size_ command. Supplementary Materials:The following are available online at [[https://www.youtube.com/watch?v=sW4t9](https://www.youtube.com/watch?v=sW4t9) MLiRJ0&t=5s]([https://www.youtube.com/watch?v=sW4t9](https://www.youtube.com/watch?v=sW4t9) MLiRJ0&t=5s), Video S1: Expressive-Policy-based access control for resource-constrained sensors. The work described in this paper was performed at the Training and Research Unit UFI11/16 supported by the UPV/EHU. This work was partially funded by the Department of Economic Development and Competitiveness of the Basque Government through the _SEKUltrasun TEKnologiak SEKUTEK KK-2017/00044_ collaborative research project. All authors conceived of and designed the experiments; [PERSON] and [PERSON] performed the experiments; [PERSON], [PERSON], [PERSON] and [PERSON] analyzed the data; [PERSON] contributed with analysis tools; [PERSON] mainly wrote the paper; and [PERSON], [PERSON] and [PERSON] did internal review. The authors declare no conflict of interest. The following abbreviations are used in this manuscript: