In a group signature scheme

any legal member of this group can sign on behalf of this group

and no one can find out which member is the actual signer except the group manager.The focus of this paper is to design a new ID-based group signature without trusted PKG (group manager) or random oracles

and the security of the scheme

such as forward security.According to the analysis result

legal group members can sign on behalf of the group; an arbiter (OM) can open a legal signature to find out the actual signer

and he can also point out that whether the group manager is legal or not.So this is a scheme without trusted PKG without random oracles.Besides

this paper takes advantage of the information of time section to implement the forward security of this scheme in case of key exposure or revocation of group members.