Research Of Proxy Digital Signature Schemes

With the rapid development of computer communication networks, it is deeply hoped that people can finish their trading activities quickly in the distance by the means of electronic apparatus. As a result, digital signature came into being which is widely used in E-commerce. Digital signature has been playing a very important role in the fields of information security, identity authentication, proxy digital signature can settle some proxy problems which other normal digital signature scheme cann't solve. Because of this particularity, proxy digital signature can be widely applied to many fields, such as e-election, mobile communication, mobile agent, e-commerce activities and so on. Since the year of 1996 when Mambo, Usuda and Okamoto firstly advanced the concept of proxy signature, many proxy signature schemes have been proposed, such as proxy multi-signature scheme, threshold proxy signature scheme and proxy blind digital signature scheme. And plentiful achievem ents have been made in the studies of proxy digital signature. However, the security of many proxy signature schemes proposed are based on their anti-cryptanalysis abilities, other than the security of their private key. As we all known, anyone can construct a new and security proxy signature scheme through choosing a famous proxy signature and bigger security parameters, but, once the signature private key was stolen, the disaster result will come. The common method which prevents private key being revealed is to share the private key by many severs, such as threshold signature scheme. However, the cost of such kind of schemes is expensive through many severs sharing the private key, and even if by many severs to share the key, the thief can get all share key by the same method for the security hole of the sever operate system. So the security of the distribution is not the same secure as people think. The technique of forward security is a kind of techniques to keep the private key secure in a short period, whose main idea is that the key revealing of the present period doesn't effect the security of the keys in previous periods, that means the signatures before the present key is revealed are all secure and effective. So it is of great significance to research secure efficient feasible proxy signature schemes in combining forward security technique. This paper made some meaningful attempts in the fields mentioned above.Chapter1, introduction of the backgrounds in which proxy digital signature e -merged, meaning in reality and development. Chapter2, introduction of some relative mathematics and cryptology. Chapter3, introduction of three classical signature systems, and three basical proxy signature protocols. The following three chapters, the main part of this paper, in this part, the author analyzed several already-proposed signature schemes and raised some new proxy signature schemes. The last part is the conclusions to the paper.The main contribution of this paper are as follows:1. Through the analysis of the exsisted attacks in threshold proxy signature schemes, we propose a new threshold proxy signature based on parings. The new scheme not only can resist conspiracy attack, but also can revoke the proxy signer's proxy signing capability conveniently, and can change the part proxy signer's proxy signing key effectively when needs.2. Through the analysis of a forward security digital signature scheme of ECC cryptography scheme, we proved that it has no forward security at all. we proposed a new digital signature scheme based on ECC, which not only has forward security, but also has backward security.3. Through combining forward security characteristic and proxy signature scheme, we proposed another new proxy digital signature scheme with forward security which promotes the security in application of the proxy digital signature.