A Secure Dynamic Threshold Signature Scheme

In most available threshold signature schemes, only one group secret key is shared among a group of signers and the threshold value is fixed. However, in many occasions, the number of signers often depends entirely on the significance of the document. The solution usually is to construct a threshold signature scheme for different threshold value. It is obvious that there is a great deal of repeated computation and the efficiency is very low in this method. Motivated by this concern, based on the intractability of the discrete logarithm problem, a new dynamic threshold signature scheme that solves the above problem is proposed in the paper. In the proposed scheme, multiple group secret keys are shared among a group of signers, and each group secret key has its specific threshold value. Different group secret keys can be chosen flexibly to sign documents depending on their significance. Each signer needs to keep only one secret shadow and a secret value, and no public shadow is needed. Analyses show that, compared with the existing schemes, the proposed scheme can resist to various attacks from internal or external attackers, and protect the signature from allied cheating, which indicates that the proposed scheme is capable of providing more security and practicability.