Decentralized Multi-Client Attribute Based Functional Encryption

Functional encryption (FE) allows users to learn only functional values from the encrypted data. However, in existing FE schemes, all legitimate users get the same decryption results. Functional encryption that allows users to get different decryption results based on user attributes/policies has many useful practical applications. For example, a company may only authorize department heads of other sections to query the average sale figures of the sales department from the encrypted sales database. In this paper, we combine techniques from Attribute Based Encryption(ABE) and Multi Client Function Encryption (MCFE) to propose a primitive that we call "Multi-Client Attribute Based Functional Encryption scheme (MCABFE)" which allows only authorized users to obtain functional values based on the users' attributes/policies, and give the first MCABFE scheme for inner product functionality from simple and wellstudied assumptions. Then we extend our new primitive and propose a "Decentralized Multi-Client Attribute Based Functional Encryption scheme (DMCABFE)" in which no trusted party is required in the setup phase and the generation of functional decryption keys, and also give an instantiation for inner product functionality.