臺灣博碩士論文加值系統

數位簽章是電子時代對數位文件的一種保護機制，然而，基於現實環境的應用，簽章者會希望在某些情況將簽署文件的權限指派給代理簽章者。這樣的方式可以解決原始簽章者出國等等的問題。但是為了降低風險，簽章者可能指派權限給組織中多個代理人，當代理人到達一定人數同意文件內容時，才能簽署數位文件，因此發展出門檻代理簽章。在(t, n)門檻代理簽章中，原始簽章者將簽章的權限指派給有n個代理簽章者的群組，其中最少要有t個代理簽章者同意才能代表原始簽章者共同簽署文件，但是數量少於t個人則不能簽署。然而在應用時，不同時期數位文件安全需求時常有所變動，當數位文件安全性較高時，所需的代理簽章者人數門檻也較高，在另一個時期對文件的安全性需求降低時，所需的門檻值可以隨著降低以提昇效率。但是在過去的論文中，代理簽章者的數量t必須一開始就決定，無法隨著安全性需求作有彈性的變動。在這篇論文中，我們提出一個新的方法，能有效的解決此問題，藉由公告相對的參數值來改變門檻值t，當結合此門檻值的代理人及公告的參數值即能產生合法的代理簽章，這樣的結果能夠因應安全需求提高或降低時彈性的改變門檻值。另外，此方法可讓代理群組內的每一個代理人能自行計算出自己的代理簽章金鑰，因此不需要使用安全通道傳送每個代理人的代理簽章金鑰。因此，這個新方法能提供現實環境中較實際的應用。

Digital signature is a mechanism to protect digital documents in electronic generation nowadays. However, according to the application of the actual circumstances, the original signer may wish to delegate the power of signing message to a designated proxy signer in some conditions. This solves the problem if the original signer is traveling. In order to reduce risk, the original signer may delegate the power of signing messages to several designate proxy signers. When the proxy signers achieve a certain number to approve the contents of the digital document, they will be able to sign the digital document. For this reason, the threshold proxy signature has been developed. In (t, n) threshold proxy signature, the original signer delegates the power of signing messages to a proxy group with n designated proxy signers. Any t or more proxy signers of the group can cooperatively issue a proxy signature on behalf of the original signer, but (t-1) or less proxy signers cannot. However, security requirements of individual digital documents vary often in actual applications. When higher document security is required, the number of proxy signers in the proxy group should be increased. On the other hand, a lower number of proxy signers are required in order to achieve higher efficiency. In the past, the threshold value t of the proxy signers must decide at the beginning. No flexibility is provided. In this paper, we proposed a new scheme to solve this problem. We can announce the parameters to change the threshold value t. Once the combined proxy signers of threshold value t and announcing parameters that can generate a legal proxy signature, this result can enable the security to increase or reduce the threshold value flexibility. Additionally, this method can let each proxy signer create their own proxy signing key. Original signer does not need to use a secure channel to submit the partial proxy signing key. Therefore, the new scheme provides an easy and convenient way to delegate the power of digitally signed documents.

誌謝 i
摘要 ii
Abstract iii
目錄 v
圖目錄 vii
表目錄 viii
第一章 緒論 1
1.1 研究背景 1
1.2 門檻代理簽章需滿足的特性 3
1.2.1 祕密性(Secrecy) 3
1.2.2 不可偽造性(Unforgeability) 3
1.2.3 不可否認性(Nonrepudiation) 3
1.2.4 代理保護(Proxy Protected) 3
1.2.5 時間限制(Time Constraint) 4
1.2.6 識別簽章者(Known Signers) 4
1.3 研究動機與貢獻 4
1.4 論文架構 5
第二章 文獻研究與回顧 6
2.1 門檻代理簽章 6
2.1.1 H. M. Sun 的門檻代理簽章 6
2.1.2 C. L. Hsu 等人改善Sun的門檻代理簽章 9
2.1.3 C. Y. Yang 等人提昇Hsu效率的門檻代理簽章 12
2.2 Diffie-Hellman金鑰交換法 14
2.3 Lagrange內插多項式(Lagrange Interpolating Polynomial) 16
第三章 可動態調整門檻值的代理保護簽章法 18
3.1 代理分享產生(Proxy Share Generation) 19
3.2 代理簽章產生(Proxy Signature Generation) 20
3.3 代理簽章驗證(Proxy Signature Verification) 20
3.4 動態的安全需求變更 22
3.4.1 安全需求降低 22
3.4.2 安全需求提高 22
第四章 討論與安全性分析 24
4.1 討論 24
4.2 安全性分析 24
4.2.1 祕密性(Secrecy) 24
4.2.2 不可偽造性(Unforgeability) 25
4.2.3 不可否認性(Nonrepudiation) 25
4.2.4 代理保護(Proxy Protected) 25
4.2.5 時間限制(Time Constraint) 25
4.2.6 識別簽章者(Known Signers) 26
4.3 效能評估 26
第五章 結論與未來研究方向 29
參考文獻 30

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