Group signature schemes are extended from ordinary digital
signatures motivated by many applications. Zhang et al. proposed an e±-
cient group signature scheme which was claimed more e±cient than the well
known ACJT scheme, due to the reason that expensive signature of knowl-
edge, a component in a majority of group signature schemes, was avoid in
generating the group signature. In this paper, we point out that Zhang et
al.’s scheme actually adopts signature of knowledge, and it is insecure com-
pletely because of inappropriate design.