A robust and secure multi-authority access control system for cloud storage

Ciphertext-Policy Attribute-based Encryption (CP-ABE) is regarded as an ideal technique for data access control in cloud storage platform. The traditional CP-ABE requires only one trusted authority to manage the whole attribute set and issue associated keys. However, it makes the only-one-authority become a high-risk entity of the system: When the authority is compromised or crashed, the system will break down. In this paper, we propose a robust multi-authority based CP-ABE scheme for cloud storage, in which multiple authorities jointly manage the whole attribute set. In our proposed scheme, attribute associated keys can be distributed if and only if the active authorities involved in the procedure exceed a specified threshold (t). We further prove that our proposed scheme is secure and robust, which can tolerate less than t authorities being compromised or no more than n − t authorities being crashed, where n denotes the total number of authorities.