Research Of Proxy Signature Schemes

With the development of the Internet,the human society's reliance on the network gradually increased.At the same time,the network security becomed more important.Cryptology,as one of the core technologies that guarantee the network and information security,its content is becoming richer.The basic objective of cryptology is achieving information integrity,authentication and nonrepudiation,usability and so on.Among them,privacy and authentication are two important aspects of the information security.Digital signature is the primary method to provide the authentication,it also is one of the important aspect of research of modern cryptology.With the demand of application increasing,the basic digital signature schemes can not meet the needs of some applications,and some digital signature schemes which possess certain characteristics are required,the proxy signature scheme is one of these schemes.Proxy signature solved the problem of delegation of signing right, and in practice,played an important role,so got wide attention of scholars that is at home and abroad.In this paper we mainly study the proxy signature,especially the threshold proxy signature and designated-verifier proxy signature,we summarize the properties, classification and development of the proxy signature,and by studying and analyzing various proxy schemes,improve scheme that have weakness,and propose new proxy signature schemes.First,this paper analyzes Tsai et al's threshold proxy signature scheme with known signatures,and shows that Tsai et al's scheme is vulnerable against the conspiracy of the original signer and SA,and propose an improvement that can overcome the above weakness.Secondly,in this paper,based on the study of proxy signature schemes,threshold proxy signature schemes and designated-verifier proxy signature schemes,we propose a CA-based and safe threshold proxy signature scheme with designated-verifier.In the ordinary threshold proxy signature schemes,any person can verify the validity of the threshold proxy signature.However,in certain circumstances,we does not want anyone can verify the validity of threshold proxy signatures,but that only the designated person can verify the threshold proxy signature.Our study is based on this demand.In our sheme,the original signer delegate the signing right to n proxy signers, when t or more proxy singers coorperatively sign messages on behalf of the original signer,they can designate a verifier and only the designated verifier can check the validity of the proxy signature.When it is needed,the actual proxy signers or the designated verifier can further convert the proxy signatures into pulic verifiable ones.In addition,we analyze the security of the new scheme,and prove that it satisfies strong unforgeability,identifiability,undeniability,prevention of misuse,resist conspiracy attack,etc.Finally,in the research of designated-verifier proxy signature scheme,most papers only consider designating one verifier,but in practical applications,in some cases,it need to designate several verifiers.In this paper,based on the in-depth study and analyze of identity-based signature schemes and designated-verifier proxy signature schemes,we propose a ID-based Designated-Multi-verifier Proxy Signature Scheme.In our scheme,when the proxy signer sign messages on behalf of the original signer,he designates several verifiers,and only when the designated verifiers cooperate,they can check the validity of the proxy signature.In addition,through the use of identity-based cryptography,users can use their public information(such as name,address,etc.)as their public key,this make the scheme more simple and effective.By analyzing the proposed scheme,we prove that our scheme is a strong designated verifier proxy signature scheme,and has many properties i.e.unforeability.