The Research Of Anonymous Proxy Signature

With the development of networks and the wide application of information system, there are increasing demands on processing various digital documents in systems of E-Government and E-Commerce. Being a legal replacement for handwritten signatures, digital signature is sure to be more extensively used in the coming years. In 1996, Mambo, Usudu and Okamoto firstly proposed and systematically expounded the concept of proxy signature. If the original signer and the proxy signer have the protocal with the law efficacity, the proxy signer may substitute the original signer to sign the file. As a special digital signature, proxy signature has many important applications in E-commerce, E-elections and mobile agents etc. But there exist some anonymous problems, such as the protection of proxy signer's privacy and the confidentiality of content and so on, which arouse extensive research.After analyzing the flaws and loopholes in the existing proxy signature schemes, we propose three improved schemes, which have higher security and overcome the existing shortcomings in the original schemes. In addition, we propose a anonymous proxy signature based on the elliptic curve crypotosystem, which has the characters of high security and less length of key. Compared with the schemes based on the discrete logarithm problem, the scheme has higher security.The anonymous proxy signature scheme with a credible third party and the anonymous proxy signature scheme without a credible third party are both the anonymous proxy signature schemes based on the protection of proxy signer's privacy and both have certain shortcomings and loopholes, such as original signer's forgery attacks and original signer's public key substitution attacks and so on. Against the defects of the anonymous proxy signature scheme without a credible third party, we present an improved scheme with higher security, which eliminates the above attacks and satisfies the safety requirements of the anonymous proxy signature based on the protection of proxy signer's privacy. The anonymous proxy signature scheme based on the confidentiality of content possesses the defects of designated recipient's forgery attacks and abuse of authority by the proxy signer. The two improved anonymous proxy schemes can overcome the above flaws and satisfy the safety requirements of the anonymous proxy signature based on the confidentiality of content.