CloudTrustChain: A Blockchain-Based Authentication and Privacy Framework for Fine-Grained Cloud Access Control

Cloud computing enables organizations and individuals to store and access large volumes of data through remote infrastructure. However, centralized access-control mechanisms can create security and privacy challenges because authorization decisions, identity information, and access logs may depend on a single administrative authority. This paper proposes an Authentication–Privacy Chain (APC), a blockchain-based cloud access-control framework designed to combine user authentication, privacy protection, fine-grained authorization, integrity verification, and auditable access management. The proposed framework separates authentication from authorization and records critical access-control events on a permissioned blockchain rather than storing sensitive cloud data directly on the ledger. A policy engine evaluates identity, role, attributes, validity period, revocation status, and resource permissions before granting access. Cryptographic hashing is used to verify data integrity, while encryption protects the actual cloud content. Mathematical models are presented for authorization accuracy, false-acceptance rate, false-rejection rate, privacy exposure, latency, throughput, storage overhead, and availability. A conceptual comparison with centralized access control, conventional cloud RBAC, and blockchain-based access control is also presented. The graphs and numerical examples in this paper are illustrative analytical models rather than measured experimental results. The proposed APC architecture provides a structured approach for reducing unauthorized access, improving auditability, and strengthening privacy in cloud environments.