Proxy Signature Technology Analysis

The information security has become more and more crucial with the development of computer and network technologies. The digital signature is one of key techniques in information security, especially in the authentication, data integrity, and non-repudiation. It has been widely used in military, communication, e-commerce and e-government, etc., and will become more and more popular after the e-signature law is put in practice. Concentrating on theory, method and application of proxy signature, three principal achievements have been obtained in this thesis.1. Give a forgery attack to a proxy blind multi-signature. Proxy signature and blind signature are two active cryptographic research areas, and have been applied in many occasions respectively. At the same time, to cope with some particular settings, proxy blind signature, two signatures combination, also becomes a current research hotspot. At 2005, Lu had proposed a proxy blind multi-signature scheme. But the scheme is insecure. One forgery attack is presented on it. Using the forgery attack, anyone of the original signers can produce a valid proxy blind multi-signature. And we improve it by adding a dependable secure center.2. Point out the insecure on three proxy signature which deal with multiple signers from bilinear pairings. At 2004, Ji proposed three new types of proxy signature schemes that deal with multiple signers from bilinear pairings. The first type is called a proxy multi-signature scheme. The second type is called a multi-proxy signature scheme, and the third type is called multi-proxy multi-signature scheme. But the three proxy signatures are all insecure. Forgery attacks are presented on the proxy signatures. Using the forgery attacks, anyone of original signers or proxy signers can produce a valid proxy signature, and we give some methods for improving them.3. Present a new forward secure proxy signature scheme from bilinear pairings. Ordinary digital signatures have a fundamental limitation: if the secret key of a signer is compromised, all the signatures of that signer become worthless. To mitigate the damage caused by exposure of secret keys stored on such devices, cryptographic schemes are basically required to meet the notion of forward security. This assumes that key exposure will inevitably occur and seeks instead to minimize the damage. The lifetime of the protocol is divided into several periods and secret keys are updated at the end of each time period via a key update algorithm, while the public key remains for the lifetime of the scheme. So exposure of the secret key corresponding to a given time period does not enable an adversary to break the scheme for any prior time period.