Insecurity of an Dynamic User Revocation and Key Refreshing for Attribute-Based Encryption Scheme

Cloud computing has generated a major impact on the global IT ecosystem, which promises economic advantages, speed, agility, flexibility, virtually infinite elasticity and innovation. However, data security and privacy remain the biggest barriers to widespread adoption of cloud services. To address the problem of fine-grained access control over encrypted data that is faced by cloud services, ciphertext-policy attribute-based encryption (CP-ABE) technology was proposed in recent years and has aroused great concern of researchers. Although CP-ABE schemes provide the ability for data owner-centric protection in cloud services, they are not very practical with the respect to the efficiency and scalability of access right revocation and key refreshing. Recently Xu and Martin proposed a dynamic user revocation and key refreshing model for CP-ABE schemes, and presented a concrete construction based on Bethencourt et al.´s CP-ABE scheme. They claimed that their construction is efficient and provable secure. However, after revisiting the construction, we demonstrate that cloud service provider can not perform data retrieval task in their construction, and their construction cannot achieve one-to-many encryption.