Research On Concurrent Signatures And Ring Signatures

Fair exchange in digital signatures is one of the fundamental problems in cryptography. Fair exchange is a necessary feature in many widespread applications for electronic commerce. Concurrent signatures contribute a novel approach for the traditional problem of fair exchange of signatures. In concurrent signature schemes, two entities can produce two signatures that are not binding, until an extra piece of information (namely the keystone) is released by one of the parties. Upon release of the keystone, both signatures become binding to their true signers concurrently. Concurrent signatures provide a more economical tool to realize practical exchange than the reliance on a TTP. It surpasses the former method by far. However its price is cannot achieve the complete fairness. Generally speaking, compared with former schemes, concurrent signatures are very efficient which do not require a special trusted third party, and do not rely on a computational balance between the parties. So concurrent signatures are economical and have been widely used in electronic commerce. However, the expansion from two-party concurrent signatures to multi-party concurrent signatures is a hotspot and difficulty.Most existing concurrent signatures are constructed from ring signatures, for ring signatures can provide anonymity and thus concurrent signatures constructed from ring signature are ambiguous. Ring signatures can be viewed as simplified group signatures. Ring signatures can provide full anonymity for there is no group manager in a ring signature scheme. So ring signatures become the hotspot and have been widely used in anonymous election selection, e-government, electronic cash system, key distribution in key management and multiparty secure computation.This paper mainly study on ring signatures and multi-party concurrent signatures, combining with identity-based signatures. The main works are as follows:(1) According to the characteristic of concurrent signatures, proposed a new identity-base multi-party concurrent signature scheme by improving the multi-party concurrent signature scheme proposed by Dongvu Tonien and combining the identity-based signatures. The new scheme which binding the identity and public keys reduced the management cost.(2) By means of analysis on the ring signature scheme of Zhang-Kim, proposed a new ring signature scheme on the basis of identity-base multi-party concurrent signature scheme in(1).