# Mutual Authentication Protocol for D2D Communications in a Cloud-Based E-Health System
## 8 Conclusions  
The application of e-health/m-health to the monitoring, diagnosis, and treatment of patients speeds up the provision of medical services. In many cases, the patient does not need to leave his/her home for a doctor's appointment, which facilitates access to medical advice for patients with limited mobility, the elderly or patients located in hard access areas.  
The protocols analyzed showed interest in the development of efficient and safe e-health/m-health/TMIS systems for protecting patients' data and their respective identities. Our protocol showed itself to be suitable to e-health/m-health/TMIS and outperformed those of [PERSON] et al. [7] and [PERSON] et al. [6]. The protocol designed by [PERSON] et al. [7] does not control the access to patients' mobile devices for avoiding their system's exposure to intruders, if the device is lost or stolen, which is a problem with a simple solution. The protocol designed by [PERSON] et al. [6] fails to avoid the denial of service (DoS) attack. In addition, both protocols do not support D2D communication.  
Furthermore, reductions in computational and communication costs are reinforced by using symmetric cryptography. Asymmetric cryptography demands more resource consumption than symmetric cryptography due to the execution of more complex operations such as elliptic curves [25]. Moreover, there are some common misconceptions such as to consider asymmetric cryptography safer than symmetric cryptography. In terms of cryptoanalysis, the length of the key and the computational work involved in breaking a cipher are essential for security evaluation. Symmetric cryptography is suitable to be used in situations in which costs must be reduced, such as for the resource-constrained devices used for m-health.  
The performance and security analyses conducted confirmed that resource consumption could be reduced in our proposed solution when compared with other solutions that use asymmetric cryptography with no impact on the system's security through the use of symmetric cryptography.  
Future studies include storage cost analysis and comparison with related works and development of other mutual authentication protocols based on asymmetric cryptography for cloud-based e-health systems that accomplish more security objectives, as the objectives presented by [PERSON] et al. [26], with reduced resource consumption.  
The development of authentication and authorization protocols, considering CPS (cyber physical systems) ([27; 28; 29]) as well as security evaluation based on integrated systems of ambient-assisted living (AAL) and e-health (as in [PERSON] et al. [30]) has also been considered. Finally, the influence of the mobility on the authentication of D2D communications ([31; 32; 33]) will be explored.  
Data curation, A.P.G.L.; Formal analysis, A.P.G.L.; Investigation, A.P.G.L. and P.R.L.G.; Methodology, P.R.L.G.; Project administration, P.R.L.G.; Supervision, P.R.L.G.; Validation, A.P.G.L.; Writing-original draft, A.P.G.L.; Writing-review & editing, P.R.L.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES), which granted a scholarship to [PERSON] while pursuing her master degree course.  
The authors declare no conflict of interest.