Revocable Decentralized Multi-Authority Functional Encryption

Attribute-Based Encryption (ABE) is regarded as one of the most desirable cryptosystems realizing data security in the cloud storage systems. Functional Encryption (FE) which includes ABE and the ABE system with multiple authorities are studied actively today. However, ABE has the attribute revocation problem. In this paper, we propose a new revocation scheme using update information, i.e., revocation patch (not update key), in which an encryptor does not need to care about the revocation list. We propose an FE scheme with multiple authorities and no central authority supporting revocation by using revocation patch. Our proposal realizes the revocation on the attribute level. More precisely, we introduce the new concept, i.e., the revocation on the category level that is a generalization of attribute level. We prove that our construction is adaptively secure against chosen plaintext attacks and static corruption of authorities based on the decisional linear (DLIN) assumption.