Improving File Hierarchy Attribute-Based Encryption Scheme with Multi-authority in Cloud

With the rapid development of cloud computing technology, users tend to store their data remotely in the cloud to save storage space and enjoy scalable services. However, the cloud servers are not entirely trusted. Ciphertext-policy attribute-based encryption (CP-ABE) is considered as an effective cryptographic approach to prevent the untrusted cloud severs from leaking private data. Since in some areas such as medical and business, the shared data has the feature of multi-level hierarchy, so it makes sense to construct a hierarchy ABE scheme. Recently, Guo et al. proposed a PHR hierarchy multi-authority CP-ABE scheme, which implements global identifier (GID) hiding and hierarchical access control. Unfortunately, we find that the recursive operation (DecryptNode(CT, SK, (x, y))) defined in their scheme during the decryption phase is doubtable. Based on the analysis, we propose an improving file hierarchy MA-ABE scheme. The scheme preserves the security and privacy of the original scheme but reduces the user's decryption overhead. In addition, we solve the shortcoming which exists in Guo's scheme and the other corresponding schemes.