Multi-authority attribute-based encryption scheme with constant-size ciphertexts and user revocation

Ciphertext-policy attribute-based encryption (CP-ABE) is regarded as one of the most suitable technologies for data access control in cloud storage system. It gives data owners direct and flexible control on access policies. However, there still exists practicality concerns in CP-ABE applications, for example, the key escrow problem, user revocability, and large ciphertext size. Considering these problems, we propose a multi-authority attribute-based encryption scheme with constant-size ciphertexts and user revocation for threshold access policy in this paper. The security proof shows that the proposed scheme is selectively secure under the augmented multi-sequence of exponents decisional Diffie-Hellman assumption, and it also achieves forward security, backward security, and collusion-resistance.