An ID-Based Anonymous-Message Anonymous Signature Scheme

Anonymity is an important cryptographical tool to protect user´s privacy and identity. In a general ring signature scheme, a member of the ring anonymously produces a signature ¿ on a message, where the actual identity of the signer is unknown and the signed message is known for a verifier. However, in some cases, to protect the signer´s benefit, we do not hope that a verifier know which message is signed. If necessary, the identity of the signer and the signed message can be revealed. To address it, in this work, we extend ring signature notion to present a novel notion: anonymous-message anonymous signature scheme. In this kind of signature, it allows that a member of the ring produces a signature on one of several messages on behalf of the ring. Not only is the identity of the signer kept anonymous, but also the signed message is kept anonymous. After a concrete scheme is given, we show that the security of the scheme is closely related to the RSA problem, which does not rely on (the rather new and untested) assumptions related to bilinear maps.