Research On Two Kinds Of Group Oriented Digital Signature

With the rapid development of e-commerce and e-government, simply replacingthe handwritten signature with the common digital signature can not fully meet theneeds. Research on digital signature with special nature becomes an important researchdirection in certification theory. In this paper, focusing on the specific application needs,the group oriented digital signature algorithms are studied.Group signature and proxy signature belong to the special group oriented digitalsignature, which has a very broad application prospects in real life. Group signatureallows any members in group sign documents on behalf of the whole group, and itprovides good anonymity for the group members. At the same time, if necessary, thegroup manager can identify the true signer. Proxy signature allows an original signer todelegate his signing capability to a proxy signer, and then the proxy signer creates asignature on behalf of the original signer. The thesis mainly studies these two kinds ofspecial signature. In the research of this field, the main achievements are as follows:(1) Uses the properties of bilinear pairing to analyze the security of twoidentity-based group signature schemes. One is proposed by Khalid and the other byTan et al. We show that both schemes are untraceable. In addition, Khalid’s scheme doesnot satisfy the property of correctness, and we present a method of coalition attack toTan’s scheme by adding a random number.(2) Proposes new schemes to improve the drawbacks of Lu’s two proxy signatureschemes for mobile communication. The new improved schemes can protect the proxysigners to resist the attacks from the original signer.(3) Cryptanalyzes Sun et al.’s proxy multi-signature scheme and Liu et al.’smulti-proxy signature scheme. By giving concrete attacks, we show that Sun et al.’sscheme is vulnerable to insider attack. That is, a dishonest proxy signer can reconstructa new warrant and generate forged proxy signatures on any illegal messages which arenot delegated by the original signers. In addition, we disprove Liu et al.’s securityclaims and show that a successful universal forgery is feasible of the Liu et al.’s scheme.(4) Analyses Jin-Wen’s certificateless multi-proxy signature scheme and shows thatis broken by a type II adversary. To avoid these attacks, the improved scheme is given,and we prove that the improved scheme is secure in the random oracle model.