Privacy-Preserving Decentralized Access Control for Cloud Storage Systems

Along with a large amount of data being outsourced to the cloud, it is imperative to enforce a secure, efficient and privacy-aware access control scheme on the cloud. Decentralized Attribute-based Encryption (ABE) is a variant of multi-authority ABE scheme which is regarded as being more suited to access control in a large-scale cloud. Constructing a decentralized ABE scheme should not need a central Attribute Authority (AA) and any cooperative computing, where most schemes are not efficient enough. Moreover, they introduced a Global Identifier (GID) to resist the collusion attack from users, but corrupt AAs can trace a user by his GID, resulting in the leakage of the user´s identity privacy. In this paper, we design a privacy-preserving decentralized access control framework for cloud storage systems, and propose a decentralized CP-ABE access control scheme with the privacy preserving secret key extraction. Our scheme does not require any central AA and coordination among multi-authorities. We adopt Pedersen commitment scheme and oblivious commitment based envelope protocols as the main cryptographic primitives to address the privacy problem, thus the users receive secret keys only for valid identity attributes while the AAs learn nothing about the attributes. Our theoretical analysis and extensive experiment demonstrate the presented scheme´s security strength and effectiveness in terms of scalability, computation and storage.