Cryptanalysis and improvement of two threshold signature schemes
Qi You Xie · Journal of China Institute of Communications · 2005
New threshold signature schemes withstanding the conspiracy attack were proposed by Jan and Gan, respectively. However, it would show that their schemes are insecure by presenting a conspiracy attack. Any set of the group could impersonate another set of members to sign any message without holding the responsibility. In case of disputes later, the designated clerk could open the forgery threshold signature, and all the members who were impersonated have no way to deny the signature. To overcome the weakness, a modification to the proposed schemes could satisfy the security requirement. Further, a variant with traceable signers based on the modified scheme is proposed.