Identity-Based Broadcast Proxy Re-Encryption with Dynamic Functionality for Flexible Data Sharing in Cloud Environments

Cloud computing has witnessed widespread adoption across numerous sectors, primarily due to its substantial storage capacity and powerful computational resources. In this context, secure data sharing in cloud environments is critically important. Identity-based broadcast proxy re-encryption (IB-BPRE) has emerged as a promising solution; however, existing IB-BPRE schemes lack dynamic functionality—specifically, the ability to support user revocation and addition without updating re-encryption keys. Consequently, data owners must frequently reset and distribute these keys in response to user membership changes, leading to increased system complexity and communication overhead. In this paper, we propose an identity-based broadcast proxy re-encryption scheme with dynamic functionality (IB-BPRE-DF) to address this challenge. The proposed scheme utilizes a symmetric design of re-encryption keys to enable dynamic user updates while preserving a constant re-encryption key size. Furthermore, IB-BPRE-DF is constructed under the (f,g,F)-GDDHE assumption and achieves semantic security in the random oracle model. Performance evaluations demonstrate that IB-BPRE-DF significantly reduces both the communication overhead (by maintaining a constant size for the re-encryption key and re-encrypted ciphertext) and the computational burden (with near-zero computational cost for generating the re-encryption key) for resource-constrained users. This work provides a practical and scalable cryptographic solution for secure and efficient data sharing in dynamic cloud environments.