<![CDATA[This study addresses security challenges in distributed networks, particularly in IoT and healthcare systems, where data breaches, latency, and scalability issues remain critical concerns. General Background: Distributed environments increasingly face cyber threats and limitations of centralized security models. Specific Background: Blockchain technology offers decentralized validation, immutability, and transparency but suffers from performance and scalability constraints. Knowledge Gap: Existing solutions lack integrated frameworks combining efficient consensus, encryption, real-time analytics, and empirical validation in large-scale and real-world environments. Aims: This study proposes a blockchain-based security framework integrating Proof-of-Authority consensus, AES-256 encryption, smart contracts, and AI-driven threat detection. Results: Experimental evaluation through simulations and a hospital deployment with 250 IoT devices shows data integrity up to 98%, latency reduced to 23 ms, and attack detection time of 35 ms, outperforming centralized systems despite moderate energy increase. Novelty: The framework uniquely combines PoA, AI analytics, and smart contract automation within a scalable architecture validated in real-world scenarios. Implications: The findings support deployment in critical sectors such as healthcare and smart energy, providing a reliable and transparent approach to secure data transmission in distributed networks. Keywords: Blockchain Security, Distributed Networks, IoT Data Protection, Proof-of-Authority, Threat Detection Key Findings Highlights High integrity maintained during cyberattack scenarios across large-scale networks Rapid detection and mitigation achieved in real-time operational settings Practical deployment validated through hospital-based IoT environment]]>
