All-in-one group-oriented cryptosystem based on bilinear pairing

This paper presents a novel all-in-one group-oriented cryptosystem (AGOC) in which the ciphertext can have one of four levels of confidentiality. These levels depend on whether decryption is allowed by (1) only one specified recipient, (2) every member of the group, (3) members of a specified subset acting cooperatively, and (4) members of any predetermined authorized subset, or any t out of n members, acting cooperatively. The newly proposed AGOC has the following merits: (1) every member of the receiving group needs to keep only one private key, (2) both ciphertexts and system parameters are of constant size, and (3) the scheme is secure against a chosen ciphertext attack in the random oracle model.