Proxy Signature Scheme

This paper is mainly focused on the project in aspect of proxy signature. Proxy signature is a special class of digital signatures which allows an original signer to delegate his/her signature capability or signature right to a designated person who is called a proxy signer to sign on specified documents on behalf of the original signer. The primary difference between proxy signature and digital signature is that there is an intermediate component, which is called proxy signer between original signer and signature receiver, is added in proxy signature.In real world, proxy signature is an ordinary familiar practical activity. Its expression form is various and application range wide. For example, a company employer delegates his/her employee to sign on a contract on behalf of him/her or the company;an administrative leader delegates his or her secretary to examine and approve a document;a bank depositor delegates an agent to deal with the bank transaction operations for him or her;a customer delegates a commodity broker to purchase goods;and so on, which is the application of proxy signature in daily life. In proxy signature process, an important fact is that the original signer should delegate the signature right to proxy signer. The relationship between original signer and proxy signer is "delegate and delegated" , and the proxy signer signs on the given documents according to the authorization of original signer, and he can't deny what he has done or counterfeited the right of signature to gain his ends because the proxy signer is therepresentative of the original signer. Likewise, original signer can' t deny what he has done or abuse the right of signature and let the proxy signer to undertake corresponding signature responsibility. So both of them should not deny what they have done.In traditional proxy signature study, the most important question to be discussed is the impartiality of the positions of original signer and proxy signer, many non-repudiable proxy signature schemes have been proposed to solve this problem for recent years. Obviously, the most important problem is the relationship between original signer and proxy signer, however, other than the above, there are interactions among the original signer, proxy signer and signature receiver. They are parts of the signature activity and can' t be separated, which make up of the whole process of proxy signature. The receiver validates the accepted proxy signatures to confirm them. The signature receiver may deny the accepted proxy signature, or refuse to accept the proxy signature, or do what is not propitious to the signer. So it is important and practical to study the relationship among the original signer, proxy signer and signature receiver.This paper suggests that the relationship between original signer and proxy signer should be considered, and regards the signature receiver, which is discussed and analyzed in the signature activity, as a factor of proxy signature scheme. The origin of this paper is that among the original signer, proxy signer and signature receiver, each of them may deny their deeds or aggress designedly. It' s an important way for the security of signature to check the identities of the threefactors. The research purpose of this paper is to propose a new idea which is a constraint for the signature receiver, and to improve the traditional method that analyzes the original signer and proxy signer merely, and to regard the three factors (original signer, proxy signer and signature receiver of which the proxy signature activity consists) as a whole to analyze and study. The research method of this paper is based on following ideas: In proxy signature activity, the security is primary. The important step for security is to check the identities of three factors participating in proxy signature activity. When original signer delegates the right of signature, he must know the identity of the signature receiver and there is a constraint for the signature receiver because the signature goal and object of the original signer is open and known. The signature receiver should check the identity of the signer lest the identity is denied or negated when he accept the proxy signature. The production of this paper is to propose a proxy signature idea based on the identities validation of the original signer, proxy signer and signature receiver, which ensures the validity of the three factors, prevents the three factors from denying the signature and meets the request of the trueness. The idea is comprehensive, compulsory and reliable.