Solving the invalid signer-verified signature problem and comments on Xia-You group signature
In general, a signature that has been verified by the signers should be valid when the verifiers verify it later. However, a signer-verified signature would become invalid in Wang et al.'s generalized threshold signature and authenticated encryption scheme and Hsu et al.'s revisions. This problem has not been reported before, and it is called the invalid signer-verified signature problem. This paper discusses the problem and proposes the solution. By the way, we also point out the forgery attack on Xia-You recently published group signature scheme.