A Scalable Encryption Scheme for Multi-Privileged Group Communications

Security issues in multi-privileged group communications containing multiple data streams are rather difficult to solve, as there are multiple access privileges among users. Traditional key management schemes use a key graph to manage all the keys in a group, which makes one key being shared by many users resulting in the "one-affect-many" problem. In a key-policy attribute-based encryption (KP-ABE) system, a ciphertext is labeled with a set of attributes and users\´ keys are associated with access policies, so that a ciphertext can be decrypted by multiple users when the attributes associated with the ciphertext satisfy an access policy in the users\´ keys. However, KP-ABE can not achieve a scalable revocation mechanism when applied to multi-privileged group communications. In this paper, we propose a scalable encryption scheme for multi-privileged group communications (EMGC), which uniquely combines a collusion resistant broadcast encryption system and a KP-ABE system with a non-monotone access control. Using our scheme, a user can not only join/leave a group at will, but also change his access privilege on demand, while requiring a small number of re-keying operations. Therefore, our scheme, which can accommodate a dynamic group of users, is more applicable to multi-privileged group communications.