In an attribute-based signature (ABS), users sign messages with any predicate of their attributes issued from an attribute authority. Under this notion, a signature attests not to the identity of the individual who signed a message, but a claim regarding the attributes the underlying signer possesses. In ABS, users cannot forge signatures with attributes they do not possess even through colluding. On the other hand, a legitimate signer remains anonymous without the fear of revocation and is indistinguishable amongst all the users whose attributes satisfying the predicate specified in the signature. ABS are useful in many important applications such as anonymous authentication and attribute-based messaging systems. In this paper, we propose two efficient ABS constructions supporting flexible threshold predicate by exploring a new technique to generate signatures. Compared with the existed schemes, the new constructions provide better efficiency in terms of the computational cost and ...