# Defense and Security Mechanisms in the Internet of Things: A Review
## 7 Conclusions  
This manuscript comprehensively surveys security and defense mechanisms proposed for IoT environments. We focused on key agreement and authentication protocols (security mechanisms) and anomaly and cyber-attack detection methods (defense mechanisms). Our examination of the theoretical dimensions of IoT ecosystems, security and defense strategies, and potential cyber-attacks that may affect the security of these environments provides valuable insights and enhances the understanding of IoT security. This review is distinctive by approaching the security mechanisms of IoT from a two-legged stance--the security protocols and security systems. It systematically compares authentication and key agreement protocols, highlighting their crucial role in securing communication in IoT, unlike similar works. Furthermore, the paper demonstrates the complementary nature of intrusion detection and prevention systems while stressing the need to integrate newer AI techniques for better anomaly detection. This review is not like other reviews because apart from compiling previous works, it has also found some gaps in research that needed further investigation, such as energy-efficient designs and adaptable algorithms for combating persistent threats. Such leads are the pillars of possible future work, such as lightweight cryptographic protocols or scalable methods powered by AI against specific, localised attack scenarios. Regarding the security mechanisms represented by security protocols, we highlighted the crucial role of authentication and key agreement processes during the communication between smart devices. The first process ensures the parties' identities, and the second process improves the messages' encryption. In reviewing anomaly and cyber-attack detection methods, we highlighted that we can use various AI techniques. The systems, like IDSs and IPSs, play complementary roles in security. They focus on monitoring network traffic and identifying suspicious events. Furthermore, we emphasised the obstacles that security and defense systems must confront. Future security problems for IoT environments encompass enhancing scalability, optimising energy efficiency, augmenting privacy, and assuring resistance against cyber-attacks. We may address these concerns by optimising cloud infrastructure, blockchain consensus mechanisms, lightweight data processing algorithms, and sophisticated cryptographic protocols. Detecting anomalies in large systems like IoT requires scalable algorithms for real-time data processing. As devices and data grow, systems must maintain high performance and low latency. Detection algorithms must be flexible to recognise new attacks and adapt to changing threats. Balancing false alarms with high-threat detection is crucial, as false positives can reduce operational efficiency and incident management costs. Energy-efficient and resource-optimised detection methods are essential in resource-constrained systems. Detecting internal threats is also challenging due to specific characteristics and data processing techniques. Based on remarks from this review, our future research will focus on creating new security methods, such as lightweight, energy-efficient, and scalable security protocols. We will remember that IoT devices have limited resources, which makes implementing cryptographic algorithms too demanding. These limitations are connected to limited computing power, memory, or battery. Also, we will focus on testing AI methods in the case of less-known or niche attacks, which can have hazardous consequences for users and their data or devices. **Author Contributions:** Conceptualization, S.S.; methodology, S.S. and J.P.; validation, S.S., J.P. and M.K. ; investigation, S.S., J.P. and M.K. ; data curation, S.S., J.P. and M.K. ; writing--original draft preparation, S.S., J.P. and M.K. ; writing--review and editing, S.S., J.P. and M.K. ; visualization, S.S.; supervision, S.S.; project administration, S.S. All authors have read and agreed to the published version of the manuscript.