Theory Study For Group Digital Signature

Digital signatures oriented group mainly conclude Threshold Proxy signature , Group signature and Ring signature , it is a more important part of digital signature . Digital signatures oriented group have developed for ten years , the background of its application is very wide . Digital signatures oriented group is widely used in the proxy issue of signature authority , electronic vote , electronic auction and run . They are very important digital signatures , Although they are continuously developing , digital signatures oriented group still have many problems that need being solved , such as the problem of coalition-resistance of threshold proxy signature scheme , the problem of canceling the group members , the problem of not using knowledge signatures in the group signature . So digital signatures oriented group have very important significance in the theoretical study .This paper mainly discusses Threshold Proxy signature and Group signature in digital signatures oriented group . Especially this paper deeply discusses threshold proxy signature scheme with known signers , and ACJT2000 group signature scheme , and analyses their securities , and improves some defective schemes , totally this paper sets up some more secure digital signatures oriented group schemes .First this paper discusses threshold proxy signature scheme with known signers . Kim first proposed the threshold proxy signature scheme , then Sun proposed an nonrepudiable threshold proxy signature scheme with known signers based on this scheme. In Sun's scheme , actual proxy signers cannot deny the signatures they have signed. However , his scheme is vulnerable against the conspiracy attack of t proxy signers. So Chien-Lung Hsu proposed a new proxy signature scheme based on Sun's scheme with the others , this scheme not only is nonrepudiable , but also can be against conspiracy attack of proxy signers.But through studying threshold proxy signature scheme with known signers of Chien-Lung Hsu , this paper discovers that this scheme cannot be against the attack that the original signer frames other proxy signers with some proxy signers , and any t proxy signers together can issue proxy keys instead of original signer . So this paper will set up a new threshold proxy signature scheme with known signers based Chien-Lung Hsu's scheme , and make it be able to resist our attack . It improves proxy signatures building step of Chien-Lung Hsu's scheme that this paper sets up a coalition-resistance threshold proxy signature scheme with known signers . And through analyzing security , our scheme is more security than Chien-Lung Hsu's .ACJT2000 group signature scheme is a important classical scheme , now foundation of many group signature schemes bases on it . ACJT2000 group scheme can make the group manager increase operation efficiency opening members , so improve practices . Meanwhile, the scheme can resist coalition attack under the strong RSA assumption . But, this paper indicates the scheme is insecurity and make an attack, which makes any group members can fabricate a valid group signature and group manager can not open the signature. The intension of this attack is strong , it make anyone be able to attack ACJT2000 group signature scheme through fair and foul , which sufficiently explain ACJT2000 group signature scheme is suspect . In Asiacript 2006 , a paper which contents are an analysis for security of ACJT2000 group signature scheme also points out insecurity . But our attack is better than this paper's , so it is deeply affective that we make security analysis for ACJT2000 group signature scheme . Then this paper sets up a new group signature scheme based ACJT2000 group signature scheme , and proves that this scheme not only have excellence of ACJT2000 group signature scheme , but can resist our attack and attack in Asiacript 2006 .