Hierarchical Fuzzy Identity-Based Encryption

In a Fuzzy Identity-Based Encryption (FIBE) scheme, a user with the private key for an identity ID is able to decrypt a ciphertext encrypted with another identity ID if and only if ID and ID' are within a certain distance of each other as judged by some metric. The existing literature on FIBE assumes that all attributes are equally important. However, this assumption may not be appropriate in some situations. In this paper, we consider the problem of FIBE with attributes of different importance level. In this setting, the set of possible attributes admits a hierarchical structure such that, during decryption process, attributes in lower levels can be replaced by those in higher levels. To solve this case, a new scheme called Hierarchical Fuzzy Identity-Based Encryption (HFIBE) was introduced then it was provided with a formal definition of security and an implementation method. The security of our proposed scheme is in the Selective-ID security model under the Decisional Modified Bilinear Diffe-Hellman assumption.