| Summary: | 碩士 === 國立臺灣大學 === 電機工程學研究所 === 90 === Due to the fast progress of computers and communication networks, more and more electronic services are provided. Many of them require digital signatures such as voting and document issuing. By distributing power of generating signatures among a group of people, threshold signatures not only secure the group private key but also increase the availability of the signing service. Existing threshold signatures are based on either discrete logarithm or RSA. However, most of them require many exponential operations and some even have very cumbersome mathematical structures. In this thesis, we propose a user and signer efficient threshold signature scheme based on QR to achieve security as well as efficiency. Two modifications are also presented, the first one to enhance availability of signing service and the second one to add anonymity and traceability. These proposed schemes are shown to be correct, secure, robust, as well as computationally efficient. Also adversaries would not be able to forge signatures on a message. The efficiency of proposed schemes would meet the need for more and more sophisticated and advanced electronic and Internet services.
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