Attribute-based signcryption with hybrid access policy

Attribute-based signcryption (ABSC) can fulfill the functionality of attribute-based signature (ABS) and attribute-based encryption (ABE) in a logical step. Depending on whether the access policy is embedded in the keys or ciphertexts, ABS and ABE are generally divided into two types: key policy and ciphertext policy. In this paper, we propose an ABSC scheme supporting key policy signature and ciphertext policy encryption, called KCP-ABSC, which is the first ABSC scheme with hybrid access policy to our known. The proposed KCP-ABSC scheme is proven to be ciphertext indistinguishability under chosen ciphertext attacks and achieves existential unforgeability under chosen message attack in the standard model. Furthermore, the size of the ciphertext in the new KCP-ABSC scheme is constant, i.e., independent of the number of attributes used in the system.