List signature is an extension of group signature which has the additional functions of public detection and public identification.Based on the application in large-scale electronic voting systems advanced by the list signature scheme,anyone is able to check the dishonest voting behaviors.If a dishonest voter casts more than one ballot,anyone is able to check the identity of the dishonest voter through signatures from ballots.Meanwhile,this scheme guarantees uniqueness,privacy,verifiability and fairness.Compared to the previous voting schemes,this scheme has a higher communication efficiency and security.

A non-authenticated group key agreement protocol cannot provide participant and message authentication,thus it must depend on an authenticated network channel or use another scheme to provide authentication.This paper indicates that Burmester et al.'s group key agreement protocol which based on the authenticated broadcast channel is unable to withstand the disruption attack of malicious participants in group.This attack leads that other honest participants will not be able to correctly agree on a group key consistently.In this paper,an improved protocol is proposed.The proposed protocol which joins the message authentication method in original protocol can detect the malicious participant.Under the random oracle model,paper proves the improved protocol can withstand the interrupted attack from malicious participant.

Analyzing the resistibility of the MD5 algorithm, this paper tries to give some advice and prediction on how to improve Hash functions.As a widely used Hash function, an iteration of the MD5 algorithm includes 4 rounds, 64 steps and one addition.Through the analyses from steps to rounds, and from rounds to iterations, the authors give the break points of recent research and how to overcome them. Based on the recent research in the Hash world, the authors ameliorate the conclusions of reference 1,make the probability analysis of reference 1confirmable with the ameliorated conclusions,give the biggest k of the k-preimage attack of Wang-like collisions,and give four directions and advice on how to improve Hash functions at the end of this paper.

Signcryption can be used to design efficient subliminal channels.This paper points out that the CLL signcryption scheme has two limitations:it can be forged and cannot be verified when disputes arise,and then modify CLL scheme,so that the ciphertext can be verified publicly and the hidden message only can be recovered by the designated verifier.Based on the proposed signcryption scheme,this paper proposes a threshold subliminal channel which can convey a subliminal message to a group of users.Reconstructing the subliminal message relies on the cooperation of t or more users in the group and the validity of the subliminal message can be verified by them.The massage sender needs not to generate nor get the users' private key.Experiments security and performance analysis show the proposed scheme is secure and efficient.

Zhang et al. proposed a sequential multisignature scheme based on RSA. The scheme has advantages of low computation and communication costs, and so on. However, we find a problem in their scheme that the verifier can not distinguish whether the multisignature is signed by all the signers of the group or only by the last signer. Thus, any single signature created by the last signer can be used as a multisignature created by the whole group members. This paper proposes an improved scheme that can overcome the defect. In the new scheme, the identity messages of all the signers are added in the multisignature and used in verification phase, so that the verifier can know the signature is generated by which signers. Performance analysis shows that the proposed scheme costs less computation than the original scheme in both signature and verification phases. Furthermore, each partial signature is based on the signer's identity certificate, which makes the scheme more secure.

Signcryption provides confidentiality and authenticity efficiently;it can be used to design compact communication protocol.Arbitration mechanism is used for settling disputes in signcryption,but the information that the judge gets also brings some security problems.This paper points out two problems:in some scheme,the arbitrator can decrypt all the signcryptions of a receiver while be gets some kinds of arbitration message;in another schemes,the arbitration mechanism cannot protect the integrity of plain- text.Analyze the two kinds of problems and concludes their reasons separately,we proposed a resolvent that can solve the two prob- lem by changing a secure arbitration message.Based on the attack and analysis,this paper proposes a secure arbitral signcryption (SASC)scheme and proves its IND-CCA2 security and UF-CMA security in random oracle model.Furthermore,SASC is a secure- ly arbitral signcryption scheme,it can protect the integrity of plaintexts by an arbitration message associated with plaintext;and the scheme can resist decryption attacks of arbitrator,even he gets the arbitration message.SASC does not increase computation nor communication overloads;it has no limitation to the length of plaintext,which makes SASC more convenient.Proofs and analysis show that SASC is an efficient and secure scheme.

Publicly verifiable multisignature makes the leakage of information,which is harmful to information security.Designated verifier multisignatures are privacy-oriented signatures that provide message authenticity only to specific receiver,which is suitable for some specific conditions.The paper proposes two designated verifier multisignature schemes based on ElGamal algorithm and designated verifier signature.One is a verifiably sequential multisignature,the other is a broadcasting multisignature.These multisignature schemes have the attribute of specified receiver,can avoid the leakage of information of both receiver and signatures,and resist forgery and coalition.The size of signature does not increase with signer number.These two schemes ensure the security of receiver and signatures.

Using attribute certificates can manage users of RBAC models in distributed system efficiently;the signature in certificate guarantees the validity of the certificate.While the entire work of validating and publishing certificates done by system manager,the task is heavy,so bring out bottleneck in large distributed application.Designing a certificate structure and its proxy publishing based on traceable proxy signature,not merely scattered the task of manager,publisher and proxy signatures can't abuse their power,attackers can not forge certificate and imitate user.In this way,solve the problem of manager's efficiency,and improve the efficiency and security of RBAC system as well.

On the basis of RSA cryptosystem,a user authentication scheme for digital mobile communication networks is proposed,whose security is based on large integer factorization to resist several kinds of attacks including inside-attacks.Pre-calculation was used in user ends to reduce the realtime calculation and make the scheme satisfy real-time requirement of mobile communication system.Compared with the scheme based on DLP,the scheme reduces the computation and storage both in the user ends and the net center,which makes sequential requests more efficient.Analytical results show that the scheme can meet the requirements of mobile communication because of its high security,lower calculative complexity and less storage demands.

Network cryptographic hard disk can solve the problems such as the lack of local storage, local storage with low security and so on. It can provide users secure storage space and secure documents backup. We analyzed the way to realize the network crypto- graphic hard disk, and analyzed the transmission protocol based on AES in, pointed out the shortcomings of authentication protocol and the bottleneck that authentication protocol brought in this system, then designed a new protocol using random numbers for communica- tion, improved the security and efficiency of authentication. With theoretical analysis and test, the method improved the efficiency of signature on server and the efficiency of transmission greatly, and solved the bottleneck of communication on server as well.