Transformation of Encryption with Identity-Based Approach for Versatile Encrypted Data Sharing in Public Cloud

The rapid adoption of public cloud platforms has revolutionized data storage and sharing but has simultaneously introduced significant security and access control challenges. Traditional encryption techniques often fall short in enabling dynamic, fine-grained, and efficient data access for multiple users. To address these limitations, this paper presents a novel Identity-Based Encryption Transformation (IBET) model that integrates Identity-Based Encryption (IBE) with Identity-Based Broadcast Encryption (IBBE). The proposed scheme facilitates secure data sharing by enabling transformation of IBE ciphertexts into IBBE ciphertexts, thereby allowing newly authorized users to access previously encrypted data without re-encryption. This identity-driven approach eliminates the need for complex certificate management while ensuring confidentiality and scalability. A concrete IBET scheme is designed using bilinear pairing cryptography, and its security is formally proven under adaptive adversary models. Extensive simulations were conducted in a controlled environment using Python and the Charm-Crypto library, and performance was evaluated based on encryption time, transformation efficiency, and decryption overhead. Results indicate that the IBET model outperforms conventional IBE and IBBE schemes in terms of flexibility, computational efficiency, and scalability, making it a robust solution for secure and versatile data sharing in public cloud infrastructures.