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As blockchain technology gains traction for enhancing data security and operational efficiency, traditional centralized authentication systems remain a significant bottleneck. This paper addresses the challenge of integrating decentralized authentication and access control within distributed networks. We propose a novel solution named ChainGuard, a fully decentralized authentication and access control mechanism based on smart contracts. ChainGuard eliminates the need for a central server by leveraging blockchain technology to manage user roles and permissions dynamically. Our scheme supports user interactions across multiple organizations simultaneously, enhancing security, efficiency, and transparency. By addressing key challenges such as scalability, security, and transparency, ChainGuard not only bridges the gap between traditional centralized systems and blockchain's decentralized ethos but also enhances data protection and operational efficiency., Comment: accepted at the 2025 IEEE Consumer Communications & Networking Conference (CCNC 2025)

Conflicting transactions within blockchain networks not only pose performance challenges but also introduce security vulnerabilities, potentially facilitating malicious attacks. In this paper, we explore the impact of conflicting transactions on blockchain attack vectors. Through modeling and simulation, we delve into the dynamics of four pivotal attacks - block withholding, double spending, balance, and distributed denial of service (DDoS), all orchestrated using conflicting transactions. Our analysis not only focuses on the mechanisms through which these attacks exploit transaction conflicts but also underscores their potential impact on the integrity and reliability of blockchain networks. Additionally, we propose a set of countermeasures for mitigating these attacks. Through implementation and evaluation, we show their effectiveness in lowering attack rates and enhancing overall network performance seamlessly, without introducing additional overhead. Our findings emphasize the critical importance of actively managing conflicting transactions to reinforce blockchain security and performance., Comment: This work has been accepted at the 2024 IEEE Global Communications Conference (Globecom 2024)

Although wide-scale integration of cloud services with myriad applications increases quality of services (QoS) for enterprise users, verifying the existence and manipulation of stored cloud information remains an open research problem. Decentralized blockchain-based solutions are becoming more appealing for cloud auditing environments because of the immutable nature of blockchain. However, the decentralized structure of blockchain results in considerable synchronization and communication overhead, which increases maintenance costs for cloud service providers (CSP). This paper proposes a Merkle Hash Tree based architecture named Entangled Merkle Forest to support version control and dynamic auditing of information in centralized cloud environments. We utilized a semi-trusted third-party auditor to conduct the auditing tasks with minimal privacy-preserving file metadata. To the best of our knowledge, we are the first to design a node sharing Merkle Forest to offer a cost-effective auditing framework for centralized cloud infrastructures while achieving the immutable feature of blockchain, mitigating the synchronization and performance challenges of the decentralized architectures. Our proposed scheme outperforms it's equivalent Blockchain-based schemes by ensuring time and storage efficiency with minimum overhead as evidenced by performance analysis.