A separable threshold ring signature scheme

We present a threshold ring signature scheme (spontaneous anonymous threshold signature scheme) that allows the use of both RSA-based and DL-based public keys at the same time. More generally, the scheme supports the mixture of public keys for any trapdoor-one-way type as well as three-move type signature schemes. This kind of 'separability' has useful applications in practice as a threshold ring signature is no longer limited to support only one particular type of public keys, as required by all the previous schemes. In the paper, we also show that the signature maintains the anonymity of participating signers unconditionally and is existential unforgeable against chosen message attacks in the random oracle model.