A Security Drawback of Group Blind Signature Lys98 and Its Improvements
Liao Meng-jie, HE Da-ke · Journal of the China Railway Society · 2005
At the international financial cryptograph conference in 1998(FC98),Lysyanskaya and Ramzan introduced a new cryptograph scheme called a Group Blind Signature Lys98,which combined,for the forst time,the existing notions of a group digital signature and a blind digital signature.They considerd their scheme possible to satisfy multed security requirements to resisit coalition attacks.We have found that Lys98 is not able to resist coalition attacks.Some collection of group members may collude and combine their secret membership keys in such a manner that they generate a valid,yet untraceable group signature.In the end of the paper two modified schemes are presented to prevent this kind of attack.