Efficient Collaborative Access Control Encryption Scheme for Cloud Storage

To address the limitations of traditional access control schemes in cloud storage environments—such as high computational and storage overhead, difficulty in supporting collaborative user access, and vulnerability to malicious collusion attacks—this article proposes a Chinese remainder theorem (CRT)-based anti-collusion collaborative access control encryption scheme for cloud storage. Our solution introduces a dynamic authorization mechanism for collaborative nodes, enabling data owners (DOs) to designate collaborative nodes in access policies and generate collaborative secret values. By integrating threshold secret sharing technology, these collaborative secret values are embedded into group user keys. Leveraging the modulus orthogonality of CRT, our scheme imposes two conditions for collaborative access: 1) the attribute sets of group users must satisfy the collaborative access policy and 2) the collaborative secret value shares held by group members must meet a predefined threshold. This design not only supports legitimate collaborative decryption but also automatically identifies cross-group collaboration as a collusion attack without requiring trusted third-party authorities. Security analysis demonstrates that our scheme ensures data confidentiality. Experimental evaluations show significant advantages in computation and storage efficiency compared to typical schemes such as ciphertext-policy ABE (CP-ABE) and CP-WABE-certification authority (CA).