Controllable Ring Signatures

This paper introduces a new concept called controllable ring signature which is ring signature with additional properties as follow. (1) Anonymous identification: by an anonymous identification protocol, the real signer can anonymously prove his authorship of the ring signature to the verifier. And this proof is non-transferable. (2) Linkable signature: the real signer can generate an anonymous signature such that every one can verify whether both this anonymous signature and the ring signature are generated by the same anonymous signer. (3) Convertibility: the real signer can convert a ring signature into an ordinary signature by revealing the secret information about the ring signature. These additional properties can fully ensure the interests of the real signer. Especially, compared with a standard ring signature, a controllable ring signature is more suitable for the classic application of leaking secrets. We construct a controllable ring signature scheme which is provably secure according to the formal definition.