A simplified approach to user controllable threshold signatures

A threshold signature scheme typically assumes that the shared signing function can only be activated by a quorum number of servers. Therefore, it is inappropriate for settings where an organization employs some servers for a threshold protection of its private signing function. That is, if anyone has the power to activate the signing function of servers, they can easily compute valid signatures for a specific organization without knowing the secret private key. In this paper, we present a model of the threshold signature scheme in which the user possesses the controllability to activate his private signing functions and the secret private key is shared among several servers. Moreover, our scheme is applicable to both discrete-log based threshold signatures and RSA based threshold signatures.