| Summary: | 碩士 === 東海大學 === 資訊工程與科學系 === 93 === As the team-work becomes more and more important, to prevent the group secret from stolen also becomes more serious. Group-Oriented Cryptosystem helps these groups to withstand their secret messages in a secure environment. However, the net makes the attacker to cheat these groups becoming easier. It is because that to commit a crime by the net is quick, long distance, and hard to be conscious. So Group-Oriented Cryptosystem must prevent every kind of attacks such as forging message, replaying message, impersonating legal users, and so on. Furthermore, the performance of a group-oriented cryptosystem is also important, because that people say: “Time is money.”
In this paper, we have two group-oriented cryptosystems. First, we propose a secret sharing scheme to solve the problem of using a group key in access structures. It improves the efficiency problem in previous schemes. Then we proposed a multisignature scheme based on Elliptic Curve Cryptography to deal with the group signature. It not only revises the weakness in Zhang-Xiao’s scheme, but also improves its efficiency.
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