Cryptanalysis on Generalization of Threshold Signature and Authenticated Encryption for Group Communications

Wang et al proposed generalization of threshold signature and authenticated encryption for group communications (denoted as W-C-L scheme). It is shown here that their schemes are insecure. One is W-C-L scheme can't withstand equation attack that they claimed. The other is W-C-L scheme is not the real threshold shared verification. Recently, an improved scheme (denoted as T-J-C scheme) on W-C-L scheme is proposed by Tseng et al