Threshold signature schemes with traceable signers in group communications

We propose a new group-oriented (t,n) threshold signature scheme that can withstand conspiracy attacks without attaching a secret number. The group's public key is determined by all members, each member signs a message independently and transmits the individual signature to a designated clerk who checks and integrates them into a group signature. A verifier can authenticate the group signature and trace back to find the signers. Further, we develop another threshold signature scheme without a trusted center. The proposed schemes possess all of the characteristics listed in Ham's scheme and are more difficult to break. (C) 1998 Elsevier Science B.V.