Abstract: Based on security analysis of Wang's threshold signature scheme, it is pointed out that only the partial private key is valid in the scheme. A simplified scheme is proposed, of which the security is equal to the one of the rectified Wang's scheme. Both schemes are vulnerable to universal forgery by an insider attacker because their underlying signature schemes are unfit for threshold signature. Then a solution is given for this problem.

Key words: threshold multisignature , Lagrange interpolation, discrete logarithm problem, threshold signature