Cloud-Based e-Health Systems: A Comprehensive Review and Future Directions with Security and Privacy-Preserving Challenges

Abstract Cloud computing has revolutionized e-health by enabling scalable storage and access to electronic health records (EHRs),By providing scalable storage and access to electronic health records (EHRs), cloud computing has transformed e-health. However, it also poses serious security and privacy threats that compromise patient confidence and legal compliance. In order to improve resilience against changing threats, this study carefully explores these issues, assesses current cryptographic and non-cryptographic solutions, and suggests a hybrid blockchain-integrated framework. We support proactive, patient-centric approaches to protect sensitive health data in multi-tenant cloud systems, arguing that present mechanisms are inadequate in tackling insider threats and data sovereignty challenges based on previous scholarly evaluations. The rapid adoption of cloud-based e-health systems promises enhanced interoperability, cost-efficiency, and data-driven diagnostics, but introduces formidable security and privacy-preserving challenges that threaten patient trust and regulatory adherence. This paper provides a comprehensive literature review of key threats—including data breaches, insider attacks, re-identification risks, and compliance conflicts under frameworks like GDPR and HIPAA—drawing from seminal works spanning 2017 to 2025. We critically evaluate cryptographic solutions (e.g., homomorphic encryption, attribute-based encryption), non-cryptographic approaches (e.g., differential privacy, role-based access controls), and emerging hybrids like blockchain-integrated architectures, highlighting their trade-offs in performance, scalability, and resilience. Keywords: Cloud-based e-health, Privacy-preserving techniques, Security challenges, Electronic health records (EHRs), Data confidentiality