Traditional group signatures have the demerit that the group manager has the absolute power in revoking the signer's identity.The unconditional anonymity of ring signature provides chances for the criminals.We give a new group signature scheme based on the idea of ring signature.Compared with the old ones

this scheme has the following advantages:(1)The right of the group manager is restricted

he can only revoke the identity of the signer with the receiver's co-operation.(2)The signer can choose the public keys he wants to realize his anonymous scope.(3)Easy for users to join and leave

it only needs the group manager to add or delete the public key of the corresponding user.