HSecure: A Client-Side Hybrid Cryptographic Framework for Secure Cloud Storage and Sharing

Cloud computing offers scalable and cost-effective storage solutions but poses significant security challenges due to multi-tenancy, third-party infrastructure management, and increased attack surfaces. This paper presents HSecure, a client-side hybrid encryption framework that ensures confidentiality, integrity, and controlled access to cloud-stored data. The proposed architecture operates in three modules: secure file upload, secure file download, and controlled file sharing. Files are encrypted block-wise using a hybrid AES ⊕ Blowfish scheme, while encryption keys are safeguarded with user passwords and RSA-based key encapsulation for sharing scenarios. The design separates encrypted files and keys across distinct storage domains and integrates structured logging for auditability. A security analysis demonstrates resilience against threats including brute-force, replay, and man-in-the-middle attacks, while maintaining practical performance for real-world deployments. The modular approach ensures scalability and adaptability to evolving cloud security needs.