Abstract: In a group signature system, the group members can leave at any time. Therefore how to delete a member efficiently is an important research topic. Wang et al. presented an efficient member deletion scheme (Wang deletion scheme) whose computation complexity is irrelative to the numbers of group member deleted, but we prove that it can not delete group members really. Based on the mathematical principle by which to choose parameters in the Wang deletion scheme, the improved one turns the renewing operator of the characteristic key which is used in registration and deletion from publicity to secrecy, and shifts the renewing work from the group member to the group administrator. By the improved scheme, the group members can be deleted effectively without increasing the computation complexity.

Key words: group signature, member deletion, e-hypo-root, renewal operator