###### Abstract  
The increasing interconnectivity of devices on the Internet of Things (IoT) introduces significant security challenges, particularly around authentication and data management. Traditional centralized approaches are not sufficient to address these risks, requiring more robust and decentralized solutions. This paper presents a decentralized authentication protocol leveraging blockchain technology and the IPFS data management framework to provide secure and real-time communication between IoT devices. Using the Ethereum blockchain, smart contracts, elliptic curve cryptography, and ASCON encryption, the proposed protocol ensures the confidentiality, integrity, and availability of sensitive IoT data. The mutual authentication process involves the use of asymmetric key pairs, public key registration on the blockchain, and the Diffie-Hellman key exchange algorithm to establish a shared secret that, combined with a unique identifier, enables secure device verification. Additionally, IPFS is used for secure data storage, with the content identifier (CID) encrypted using ASCON and integrated into the blockchain for traceability and authentication. This integrated approach addresses current IoT security challenges and provides a solid foundation for future applications in decentralized IoT environments. I +
Footnote †: footnote  
Blockchain technology has emerged as a powerful solution for addressing IoT security concerns. Its decentralized architecture eliminates single points of failure, while its inherent properties of transparency, immutability, and distributed consensus provide enhanced security and resilience [7, 8]. Despite its potential, IoT devices are often constrained by limited computational power, energy, and bandwidth, making the direct application of blockchain-based solutions complex. Furthermore, secure key management, efficient data storage, and real-time data sharing remain significant hurdles in realizing scalable and effective blockchain-based IoT systems [9, 10, 11]. In this paper, we propose a decentralized authentication protocol tailored to the unique requirements of IoT environments. Our approach integrates key technologies, including the Ethereum blockchain, the interplanetary file system (IPFS), elliptic curve cryptography (ECC), and the ASCON lightweight encryption algorithm. This protocol achieves mutual authentication between IoT devices, ensures that sensitive data are accessible only to authorized entities, and provides traceability for all communications. It is designed to address the resource limitations of IoT devices while maintaining high security standards. The key contributions of this approach are as follows:  
* Decentralized Authentication Framework: The proposed protocol employs asymmetric cryptography and the Diffie-Hellman key exchange to establish a shared secret, enabling secure and verifiable mutual authentication between devices. * Advanced Data Security: By leveraging ASCON encryption, the protocol ensures the confidentiality and integrity of IoT data during transmission and storage. * Decentralized Data Management: The integration of IPFS allows for secure, decentralized data storage, reducing dependency on centralized servers and improving data availability. * Traceability through Blockchain: Encrypted content identifiers (CIDs) are stored on the Ethereum blockchain, providing a transparent and immutable audit trail for data exchanges. * Scalability and Efficiency: The protocol is optimized for resource-constrained IoT environments, ensuring minimal computational and communication overhead while supporting large-scale deployments. The rest of this paper is structured as follows: Section 2 reviews related works. Section 3 presents the background necessary to understand the proposed approach, including foundational concepts and technologies. Section 4 provides a detailed description of the proposed protocol's architecture and design. Section 5 evaluates the protocol's performance and security, highlighting its effectiveness and addressing potential challenges.