Research And Applications Of Structured Multi-signature

With the rapid development of information technology, we have already stepped into the information society and the computer network has become the foundation we live by. Because of the more and more severe security problems of computer network, how to keep information secret and to avoid forgery is becoming a subject that people pay much attention to. Among the computer security technologies, digital signature, which has been applied to many fields such as electronic business and electronic government affairs, is a key method to solve the information security problems.Digital signature, first proposed by Diffie and Hellman in 1976, is the analog of traditional handwritten signature. Multi-signature is a special signature oriented to groups, which involves more than one person in the signing process. The signing order can be divided into two kinds: sequential and broadcasting. Most proposed multi-signature schemes follow one of the above signing orders and lack the mixture of both two, which cannot satisfy the complicated signing order in practical applications.Recently the structured multi-signature has been proposed to combine both sequential and broadcasting orders together effectively. The signing order becomes structured so that signers can sign in a more flexible and complicated order. However, there are few structured multi-signature schemes having been raised up and the existing ones all have some deficiency, especially security and efficiency in practical applications. So how to design a secure and efficient structured multi-signature scheme is of great value in research.Beginning with the basic theory and implementing technology of digital signature, the thesis analyzes the three public-key cryptosystems on which digital signature mainly bases and discusses some typical signature schemes. The status quo of researches on multi-signature and structured multi-signature is introduced subsequently. Several structured multi-signature schemes proposed recently are analyzed in the thesis and the discussion is focused on the ElGamal based schemes. The thesis points out the insecure cases in the original scheme such as conspiracyof inner members to cheat or deny and presents an improved scheme to solve these problems by adding a reliable signature-center and a time-stamp. Besides, the two-level signing structure in the original scheme is extended to multi-level structure so that the improved scheme can apply to all kinds of complicated signing structures and become more generalized.Considering the practicality, the thesis also discusses and implements the central algorithms involved in the improved scheme including choosing parameters, generating big random numbers, determining prime numbers, calculating primitive element and the module operations of big integers. In addition, the executing efficiency of the above algorithms is analyzed in the thesis.