Abstract: Li et al have proposed an efficient threshold multi-signature based on the discrete logarithm，which can resist conspiracy attacks.On the other hand，they have claimed that their scheme could withstand several possible attacks.However，Michels and Horster have succeeded in producing a forgery，which shows that Li et al’s scheme is insecure.This paper tries to improve the security of Li et al’s scheme based on the factorization problem and the discrete logarithm modulo a large composite problem.The improved scheme prevents efficiently conspiracy attack while providing more efficient performance than other schemes in terms of computation complexity.

摘要： Li等人提出了一个基于离散对数的门限签名方案，此方案很有效地防止了合谋攻击。但Michels 和Horster 成功地对Li等人的方案伪造了一个有效的签名，从而证明了此方案的不安全性。在Li 等人方案的基础上，利用大数分解和离散对数问题设计了一个新的强壮的门限签名方案，新方案避免了原方案的缺陷，同时可以有效地防止合谋攻击，且更安全有效。