Arbitrary-State Attribute-Based Encryption with Dynamic Membership

Attribute-based encryption (ABE) is an advanced encryption technology where the privacy of receivers is protected by a set of attributes. An encryptor can ensure that only the receivers who match the restrictions on predefined attribute values associated with the ciphertext can decrypt the ciphertext. However, maintaining the correctness of all users' attributes will take huge cost because it is necessary to renew the users' private keys whenever a user joins, leaves the group, or updates the value of any of her/his attributes. Since user joining, leaving, and attribute updating may occur frequently in real situations, membership management will become a quite important issue in an ABE system. In this paper, we will present an ABE scheme which is the first ABE scheme that aims at dynamic membership management with arbitrary states, not binary states only, for every attribute. Our work also keeps high flexibility of the constraints on attributes and makes users be able to dynamically join, leave, and update their attributes. It is unnecessary for those users who do not change their attribute statuses to renew their private keys when some user updates the values of her/his attributes. Finally, we also formally prove the security of the proposed scheme without using random oracles.