Cryptanalysis of Xia-You group signature scheme

Group signature is a variant of digital signatures, which allows members of a group to sign messages anonymously on behalf of the group. The application of group signatures includes e-voting, e-bidding and e-cash. Recently, Xia and You proposed an identity-based group signature scheme with strong separability. In this paper, however, we find that there are several problems in the Xia-You group signature scheme. This scheme is vulnerable to forgery attacks. Any adversary could easily forge a valid group signature for any message without the knowledge of the secret values of the legal members of the group. Furthermore, the Xia-You group signature scheme does not satisfy nearly all other security requirements of group signatures. The signatures are too long to be computed, stored and transmitted.