Exclusion-Intersection Encryption and Its Application to Searchable Encryption⋆

Identity (or identifier) based encryption has shown to be a useful cryptographic schema enabling secure yet flexible role-based access control. In this paper, we propose a new notion named as exclusionintersection encryption: the sender can specify the targeted groups that are legitimated and interested in reading the documents in the encryption algorithm; there exists a trusted key generation centre generating the intersection private decryption keys on request. This special private key can only be used to decrypt the ciphertext which is of all the specified groups’ interests, its holders are excluded from reading the documents targeted to any subset of the groups (e.g. the ciphertext of only a single group’s interest). One of the applications of this new notion is to support an ad-hoc joint project of two groups which needs extra helpers that are not from either group. Another interesting application of the proposed scheme is an encrypted audit log that supports conjunctive field keyword searching, which is the first in the literature.