The Research Of Dynamic Threshold Signature Without A Trusted Party

With the improvement of social information degree,the computer network anddata communication develop rapidly.People pay more and more attention oninformation security.Digital signature is an important way to ensure informationsecurity,assure data integrity and achieve authentication.The thresholdsignature,which is based on secret sharing,diffuses responsibilities and improvessecurity,reliability and robustness of the system.It has a wide application inmilitary,electronic commerce,science and culture.In this thesis,we expatiate on some knowledge that refers to cryptology andintroduce the emergence and principle of secret sharing and digital signature.Weanalyze and discuss some typical schemes on secrete sharing and thresholdsignature.To resolve the problems and deficiencies of these schemes, we provide adynamic threshold signature scheme without a trusted party which has thefollowing features：1.Based on secret sharing without a trusted party,each member randomlyselects a secret polynomial to generate its own secret share.The group’s private keyis hidden by the secret shares of all members.At least t legal members cooperate tosign the message without exposing the group’s private key,which prevent theauthority cheat.So the scheme improves system’s security and robustness.2.Renewing the secret shares of all members periodically,so that anyinformation learned by the adversary becomes obsolete.Hence the scheme enhancessystem’s security and usability.3.Adding and deleting the group members dynamically withoutchanging the group’s public key,which increases the system’s practicality.We use VC++6.0to design a prototype system based on this scheme inWindows XP.We also introduce some key algorithms in the scheme: thecalculation of big number,big prime choice algorithm,Lagrange interpolationalgorithm and so on.The result shows that the scheme which has goodsecurity,robustness and practicality,is right and feasible.