Cryptanalysis of group signature scheme from ID-based signature scheme

In [1], C. Castelluccia presented the relationships between Identity-based (ID-based) signature schemes and group signature schemes. The methods of using Identity-based signature schemes to implement group signature schemes is also described. In [2], adopting such model, S. Popescu put forth an Identity-based group signature scheme. Such ideology is rather novel and creative. However, in this paper, we show that there are some security flaws in Castelluccia's model. We also present a security analysis of Popescu's scheme and demonstrate that the scheme is insecure either.