Study On Proxy Signature Based On Discrete Logarithm Problem

Nowadays, the demand for internet information security becomes more and more important. In the domain of electronic commerce, electronic voting, electronic government, internet bank, and so on, digital signature is the most important technology for the internet information security. Because of the need on digital signature, various signature schemes were proposed according to various domain. The emphasis is on designing a digital signature scheme that could be proved to be secure according to the security of formal definition of the digital signature. The two aspects of cipher encoding and cryptanalysis were steady subjects in the domain of information security. Generally speaking, a new scheme with some kinds of security could be proved to be not safe enough within one year. Then another scheme which is safer than the last one will be proposed in a quite short time. The interaction between cipher encoding and cryptanalysis had accelerated the growth of the security of information.In this paper, we at first introduced some relevant mathematical knowledge and cryptography concepts which were used in the improved schemes, including the group, the ring, the field, the finite field and the discrete logarithm. And we introduced some cryptography concepts, including proxy signature scheme, nominative signature scheme, proxy blind signature scheme and multi-level signature scheme, etc.Based on some kinds of proxy digital signature schemes, we proposed several schemes having better security property. In these schemes, the main research results are as follows.First of all, we analyzed a nominative proxy signature scheme, proposed several forge attacks on the proxy signature part of the scheme. We pointed out that this signature is not secure enough, and then proposed a method of solution. In the nominative signature part, we developed the property of nomination by changing the nominative signature equation and verification equation. Then we proposed a strong nominative proxy signature scheme based on the combination of the two properties.Secondly, we proposed a thought to extend a proxy signature to multi-level proxy signature scheme based on the existing proxy signature scheme suggested by Cai Mian. We gave a concrete multi-level proxy signature scheme, proposed a blind signature based on the security analysis of two existing blind signature schemes. And we proposed a multi-level proxy blind signature scheme by combining the new scheme with the blind signature, and gave a security analysis of the new scheme.