A delegateable signature scheme(DSS)which was first introduced by Barak is mainly based on the non-interactive zero-knowledge proof(NIZK)for preventing the signing verifier from telling which witness(i.e.,restricted subset)is being used. However,the scheme is not significantly efficient due to the difficulty of constructing NIZK.We first show that a non-interactive witness indistinguishable(NIWI)proof sys- tem and a non-interactive witness hiding(NIWH)proof system are easier and more efficient proof models than NIZK in some cases.Furthermore,the witnesses em- ployed in these two protocols(NIWI and NIWT)cannot also be distinguished by the verifiers.Combined with theΣ-protocol,we then construct NIWI and NIWH proofs for any NP statement under the existence of one-way functions and show that each proof is different from those under the existence of trapdoor permutations.Finally,based on our NIWI and NIWH proofs,we construct delegateable signature schemes under the existence of one-way functions,which are more efficient than Barak's scheme under the existence of trapdoor permutations.
In this paper, we present an improved identity-based society oriented signature scheme with anonymous signers, which satisfies: ① when members leave or join an organiza- tion, the public verification key and the signature verification procedure are unchanged; ② a user participates in several organizations at the same time, her secret key is only related with her identity. However, no previous schemes have these two properties.
