Cryptanalysis And Improvement Of Verifiable Ring Signature Schemes

Digital signature is a method to check the integrity of digital information by use of cryptographic algorithms, and it can effectively replace the conventional handwritten signature. It has important applications in many fields, such as electronic commerce, network and information security. Ring signature is a special kind of digital signature, and got its name due to the signature forms a ring according to certain rules. In the ring signature scheme, any member can sign a ring signature represent all the members of the ring, and the signature verifier cannot reveal the identity of the real signer. However, in some real applications, the verifier has necessary to confirm the identity of the real signer, and then the concept of verifiable ring signature was appeared.This thesis studies the verifiable ring signature schemes. The security flaws of two recently proposed verifiable ring signature schemes(i.e., the L-ICVRS, LI Improved Certificateless Verifiable Ring Signature Scheme and the L-IVPRS, LI Improved Verifiable Proxy Ring Signature Scheme) were pointed out, and they are both found cannot resist forgery attack. In these two schemes, any member in the ring can impersonate as another member to generate a valid signature, but the real identity verification algorithm show that the identity of real signer is the latter. In order to resolve the security flaws, two improved verifiable ring signature schemes are proposed based on the two original schemes. Theoretical analysis shows that the proposed scheme can effectively protect the anonymity of the signer, and can avoid forgery attack at the same time. Besides, in this thesis, a simulation platform based on Java and Java Pairing-based Cryptography(jPBC) software is builded. The security flaws of the original schemes and the correctness and unforgeability of the improved schemes are verified by the experiments.