Research Of Several Problems Of Proxy Signature

With the rapid development and widely application of the digitalcommunication system and computer network environment, traditional handwrittensignature is gradually expierenced to have much weakness. A new way is expected torealize the signing of long-distance files, and trading nations. Digital signature isformulated in this case. As a special digital signature, proxy signature has the proxyfunction, frequently used in the fields of e-commerce, e-government and mobilecommunication and so on. In 1996, Mambo, Usuda and Okamoto firstly advanced theconcept of proxy signature, showed proxy signature should have properties ofundeniability, verifiability, unforgeability, distinguishability and so on, and proposed threetypes of delegation: full delegation, partial delegation, delegation with warrant. It providesfoundation for proxy signature. Afterwards many proxy signature schemes have beenproposed one after another. The research of proxy signature has gradually become theactive field of cryptography. However, many proxy signature schemes either havepotential security hazard or have low efficiency. With the need of practical application, thelimitation of many schemes are more and more obvious. So it is of greate significance todesign secure and efficent proxy signature schemes with special properties.This paper we mainly research proxy signature with special properties. In view ofthese issues include how to hide the identity of proxy signers, how to limit the proxysignature power, how to perform blind signature by multi proxy signers, how to dispersethe power of signers and verifiers, how to withstand the public key substitution attack,forgery attack and collusion attack, how to solve the problem of using secure channel, werespectively propose different solutions, it widen the research of proxy signature andenrich its practical application.The mairr contributions of this paper are as follows:1. Anonymous proxy signature and limited proxy signature are studied. A newanonymous proxy signamre scheme based on Schnorr cryptosystem is proposed andforward secure anonymous proxy signature scheme is also designed combining forwardsignature. Through the security analysis of W-Z-L scheme, an improved scheme based onsquare root modulo composites is proposed and the security weakness of W-Z-L scheme is overcome. In the new scheme, the data can be transmitted through the public channeland less time is spent in generating and verifying signature.2. Multi-proxy blind signature model is established. Combining multi-proxysignature with blind signature, a multi-proxy blind signature scheme from bilinearpairings is proposed, which is secure and efficient. In the scheme, blind signature can beperformed by multi proxy signers and delegation can be transmitted through publicchannel.3. Multi-proxy multi-signature is analysed and threshold multi-proxy multi-signaturemodel is constructed. Through the cryptanalysis of a multi-proxy multi-signature schemepresented by Li, we conclude that his scheme is insecure, because a malicious receiver ofproxy signature or manager of proxy signers can forge the signature for a message. Toovercome the weakness, the improved scheme is presented, which not only need not havea manager of proxy signers and compute the inverse element, but can control the time andmessages of proxy signature. A threshold multi-proxy multi-signature scheme is proposedcombining threshold signature and multi-proxy multi-signature for the fast time. In thescheme, multi-original signers can delegate their signing capability to a group of proxysigners and every proxy signature key can be shared by other members of the proxysigner group, so delegation can be performed by some original signers and message canbe signed by some proxy Signers. Moreover, the proxy signature time can be controlledand the proxy signature right can be recalled according to original signer's need.4. Threshold proxy signcryption scheme with shared verification is proposed. Theconcepts of shared verification and signcryption are introduced into threshold proxysignature, and a secure and efficient threshold proxy signcryption scheme with sharedverification is presented. In the scheme, any t or more proxy signers can sign a messageon behalf of an original signer, and only t or more verifiers of the specified grouptogether can recover the message and verify the validity of proxy signcryption. Thescheme also has the merits of secrecy, public verifiability and pubic delegation.