In this paper, we propose a provably secure group-oriented blind (t, n) threshold signature scheme, which is the first scheme whose security is proved to be equivalent to the discrete logarithm problem in the random oracle model. Based on the scheme, any t out of n signers in a group can represent the group in signing blind threshold signatures, which can be used in anonymous digital e-cash systems or secure voting systems. By means of our proposed scheme, the issue of e-coins is controlled by several authorities. In our scheme, the size of a blind threshold signature is the same as that of an individual blind signature, and the signature verification process is equivalent to that for an individual signature.