Research On Ring Signature And Ring Signcryption

With the rapid development of the internet technology, people can do more and more jobs on the internet. But internet is an open network, For internet is an open network, there exist many security threat in it. To protect the security of the user's data, several technologies were brought forth. As one major part of these protecting technologies, digital signature has been widely used in identity identification, data integrity, undeniable and so on. Ring signature is a kind of digital signature that has special attribute. Ring signature allows one people to sign on some datum on behalf of the whole ring and it doesn't leak the real identity of the real signer. Due to the special attribute of the ring signature, it can be used in key distribution, multi-computing, electronic voting, electronic cash system, and so on.Ring signature was first proposed as a technology called secret leaking. The secret leaker just wants to leak the secret to the given people and doesn't want others to get anything of the secret. So, it is very necessary for ring signature protect the confidentiality of the data. How to achieve the confidentiality and anonymous at the same time? the traditional way is to encrypt the message and the ring signature of the message. However, the cost of this technology is the sum of the cost of the ring signature and the cost of the encryption of the message. For decreasing the cost of the traditional way mentioned above, the ring sigcryption was proposed. The major ideal of ring sigcryption is to integrate the encryption with the signature; it is a lower cost way to fulfill the confidentiality, anonymous and authentication in one logical step. So, Ring signcryption has a very broad application prospects.Since the concept of the ring signature/sigcryption was introduced, lots of ring signature/sigcryption schemes were proposed and some of them were very efficient and secure. However, the major problem of the existing ring signature/sigcryption schemes is that the size of the ring signature/sigcryption is linear to the number of the ring, which means that the size of the signature/signcryption will be tremendous when someone signs a message on behalf of a very big group. So the previous ring signature/sigcryption schemes aren't suited for the big group.In this thesis, we studied the inadequacies of the existing ring signature/sigcryption schemes detailedly, and we proposed three ring signature/signcryption schemes. The research results of this thesis are illustrated as follows:Firstly, we proposed a proven-secure Id-based const-size ring signature scheme based on accumulator. Our scheme has an advantage over the previous schemes either on the size and the computational cost of the signature when someone signs a message on behalf of a large group. The proposed scheme is very efficient, and it is more suited for the big group. Secondly, we proposed an Id-based constant-size ring signcryption scheme. Although there are few constant-size ring signcryption schemes that proven secure without random oracle, but they all have the problem that the size of the key which need to be reserved by user is too long, it makes them unsuited for the case of limited storage space. The proposed constant-size ring sigcryption scheme overcame the flaw mentioned above, and it was proved secure in the random oracle model; it is very efficient in the scenario that just has limited storage space.Finally, we proposed a ring signcryption scheme based on PKI system. Through our research, we found that almost all the ring signcrytion schemes were based on the identity cryptosystem, and few ring signcryptions scheme based on PKI system didn't afford the security proof. In this thesis, we proposed one ring signcryption scheme based on PKI system and we prove its unforgeability in the random model.