Research On Ring Signature Schemes And Their Applications

Digital signature is one of the great tools in information security. In order to adapt to different application environments, many specific signature schemes have been proposed, such as group signature, blind signature, proxy signature, threshold signature, ring signature and the like. As a widely used signature scheme, ring signature achieves the property of unconditional anonymity for signers. And it has become the focus of the cryptography research. With the in-depth study of ring signature, a variety of ring signature schemes and the applications are put forward recently. However, there exist many problems to be solved. For instance, the problem of the signature size depending on the group size, the problem of key exposure and the problem of whether the ring signature can be used to construct other protocols instead of the group signature, etc. This dissertation aims to propose new schemes to solve the problems mentioned above, and to apply the ring signature to some applications.The achievements in the field of ring signature and its applications are surveyed first. The concept, sorts and applications of ring signature are studied. Then, some problems and open problem in this field are concluded. After studying the proposed ring signature schemes, a provably secure short ring signature based on one-way accumulator is proposed, which is also used to construct multi-party concurrent signatures. This is a solution to the problem of the signature size depending on the group size.With the purpose of solving the key exposure problem, the forward-secure theory is adopted. And a forward-secure ring signature scheme based on conic curve over Z_n is presented, which is easier to accomplish for embedding plaintext, computing element order and points in curves, and speeding up the inverse operation. In addition, new forward-secure ring signature scheme based on bilinear pairings is also proposed, which is proved to be secure in standard model. After comparing the ring signature with group signatures, a short linkable ring signature scheme is presented. A new fair e-cash protocol based on the proposed scheme is also given. That provides a solution for member revocation problem of existing e-cash protocol based on group signatures. Moreover, a new multi-bank e-cash system by using blind ring signatures and linkable ring signatures is presented, by which the client anonymity control and bank anonymity control are achieved respectively.An identity-based deniable ring signature scheme based on the short ring signature in the dissertation is given. In the scheme, an identity-based chameleon hash function is adopted. It can be concluded that the scheme is the only scheme which satisfies the requirements of the deniable ring authentication and the constant-size signature.A new model of verifiable certificateless ring signcryption schemes (VCRSS) is proposed. It is an important cryptographic primitive for private and anonymous communication. An efficient VCRSS scheme based on bilinear pairing is also given. In anonymous communications, the scheme allows the message sender to send the message anonymously, while the confidentiality and authenticity of the message are realized at the same time. If necessary, the real sender can prove his/her identity. The scheme does not require the use of any certificate to ensure the authenticity of public keys, and the the problem of key escrow is eliminated.Finally, the work of the dissertation is concluded.