Hibge: Monitorable and traceable anonymous encryption in cloud computing

Privacy problem is an emerging concern when we protect information security in cloud computing. In some application scenarios, the users may require to receive the computing results anonymously from the cloud server. However, complete anonymity brings regulatory issues to practical use. We usually need the encrypted results monitorable by superiors in case of illegal information, and once there are some disputes occurring, a trusted third-party arbitration institution is also required to trace the recipients without any need of decryption. Aiming at this problem, we propose a new cryptographic primitive named Hierarchical Identity-Based Group Encryption (HIBGE). In an HIBGE system, the recipients are organized in a tree-like structure. Recipients with the same function or belonging to the same department make up a group and they are managed by a group manager. When encrypting, the cloud can use the recipient’s identity as the public key, and others only know which group the message is sent to, but cannot know the exact recipient’s identity. Besides, the higher level can monitor the lower’s message, and group manager can trace the recipients’ identity. We then construct a concrete HIBGE scheme, and prove this scheme is semantic secure, anonymous and traceable, with a perfectly zero-knowledge proof. HIBGE scheme can be widely applied in cloud computing.