Research On Threshold Cryptography Related Technology

The development of computer and network has been changing lifestyle, people can finish many activities, such as mailing, shopping in a flash, and computer and network are becoming basic tools in our life. Although new technologies are critical to enhance work efficiency, it brings along with many issues such as e-asset are stolen in e-commerce, private data are leaked, and e-banks are attacked. How to solve the security of data storage and transportation is turn into the key factor of development of network based applications, all above problems are the tasks of information security. As the basic of information security, cryptography are the emphasis of many researchers, threshold cryptography is one of the branches of cryptography technology. Some means are taken to distribute some privilege, for example, sign, encryption and authentication, into a group which is consisted with many members in threshold cryptography technology, these privilege can be taken into effect only if more than threshold number members cooperate effectively, then the security risks of key lost or privilege abuse will be lowered or avoided and the security and fault tolerant ability are bettered, so it has been applied to many fields such as digital signature, secure multiparty computation.Since the concept of threshold emerges, it attracts a lot of attentions from researchers, and a lot of research results have been proposed. Although these results are valuable for further study on threshold cryptography and they give lights on design new threshold cryptography scheme, there are some defects remain, such as some of them can not resist cheating, without scalability, shares are unreuseable etc.This dissertation mainly discusses threshold cryptography related technology, for example, threshold secret sharing, threshold encryption, threshold signature; the results of this paper are listed as below.1. Threshold secret sharing schemes were investigated. In many previous secret sharing schemes, the dealer and participants are supposed to be honest, however, this assumption are unreasonable. In addition, most previous secret sharing scheme is one-time secret sharing scheme, that is to say, it can only used to share one master secret one time, the shares of all members need to be redistributed once if a new secret to be shared, this will produce great computation cost inevitably, and it can hardly be put into practice. To eliminate these shortcomings, a verifiable threshold secret sharing scheme and two multi-secret sharing schemes are proposed in the paper, the former scheme not only can detect cheating from the dealer and participants of the scheme, and it can identify the identification of the cheater as well. The newly verifiable secret sharing scheme is more robust than previous code based secret sharing scheme, so that it can resist coalition attack. The shares of the modified schemes are reuseable, and they are scalable.2. Group signature schemes are investigated. Signature is the basis of threshold signature. According to the problem that requires complex authenticating in previous VES schemes, a new efficient id-based verifiably encrypted signature scheme is proposed based on Shim signature scheme, and the new scheme does not use any zero-knowledge proofs to provide verifiability, thus eliminates computation burden from complicated interaction. This scheme is provably secure in the random oracle model. Security is critical to group signature, taking account of lack of bilateral security in previous schemes, a novel bilateral secure group signature scheme is presented. Next, a designated verifier ring signature scheme that follows the idea of previous pairing based ring scheme was presented. To realize confidentiality and anonymity in group signature, and to meet the requirement of proxy signature in group signature, a designated verifier ring signature and a designated verifier ring proxy signature are presented in this paper.3. Threshold signature schemes are investigated. Based on Shamir threshold scheme and Schnorr signature, a novel threshold signature scheme was proposed. The proposed scheme not only has the property of threshold signature generation, but also has the property of threshold signature verification. In other words, at the group signature generation stage, the combiner of group signature can construct a valid signature of the signing group, and no less than k member in the verifying group can cooperate to verify the validity of the signature Furthermore, the scheme in this paper are group oriented signature scheme with distinguished signing authorities, in which the signers do not have to sign the whole documents but only a part of the document. By this, the efficiency of the system is enhanced and the security of system is ensured.4. Threshold encryption schems are investigated. Authenticated encryption schemes are applied into applications whose communication requirement is low, such as key agreement for that it can combine plaintext and signature into one body. However, authenticated signature scheme are unfit to modern distribute system. A novel threshold authenticated encryption scheme is proposed, it meets security requirements such as confidentiality, non-repudiation and non-forgeability.