Threshold untraceable signature for group communications

Lee et al. (2000) have proposed an untraceable (t,n) threshold signature scheme which can be extended to give the original signers the ability to prove they are the true signers. The present authors add the requirement of (k,l) threshold-shared verification to the scheme of Lee et al. In the proposed scheme, any t participants can represent a group to sign messages with/without anonymity, and k verifiers can represent another group to authenticate the signature.