Security of Wang et al.'s group-oriented (t,n) threshold signature schemes with traceable signers

Abstract

A forgery attack on the group-oriented (t,n) threshold signature schemes was described. The scheme consists of three phases namely the initiation, the individual signature generation and verification phase, and the group signature generation and verification phase. In the Tseng-Jan's (T-J) attack, an attacker without any secret keys of group members can use any previous valid group signature to forge a valid group signature. The new attack proved to be more fundamental than the T-J attack as it could not be recognized or blocked at the designated clerk level of the signature schemes.