EOABS: expressive outsourced attribute-based signature

Emerging attribute based signature (ABS) can be used in the system to protect the individual privacy from being divulged. However, heavy computational cost is required during the signing phase because it grows linearly with the size of attributes. Besides, traditional ABS only supports threshold access structure, which impedes system managers to define more flexible access policy. Aiming at tackling the problems above, we utilize the outsourcing technique with which users can deliver majority of the computation operation to an untrusted cloud server without revealing the private signing key, then propose an expressive outsourced attribute based signature scheme. The proposed scheme is proven unforgeable under selective-attribute chosen message attack in the standard model. Comparing with existing work, our scheme not only reduces users' computation overhead, but also supports more flexible access structure. Finally, experiments are performed to illustrate the efficiency and practicality of our scheme.