臺灣博碩士論文加值系統

　　代理簽章機制可應用於各種商務行為上，例如：當有一份重要文件需要原始簽章者簽署才能成效，但若該原始簽章者臨時無法簽署等意外狀況發生，即可以使用代理簽章方式解決問題。為確保代理簽章的可靠性，因此它必須能滿足以下安全需求：身分辨識性、不可否認性、可驗證性和不可偽造性等。此外，在某些情況下，代理簽章必須具備防止外人攻擊的能力，以保護簽章者的身份或隱私。
　
　　近期有許多代理簽章方法的研究陸續被提出，當中Yu等人（2009）提出一套匿名代理簽章方法來保護代理簽章者的隱私，該研究表示透過他們的方法可有效完成代理簽章者的匿名。然而，我們發現，在他們的方法中代理簽章者的身份仍是可被取得的。因此，本研究提出一個新的匿名代理簽章方法，以確保代理簽章者匿名。根據分析比較，我們的方法比 Yu等人的方法更具有安全性與效率。

　　Proxy signature schemes can be used in many business applications such as when the original signer is not present to sign important documents. Any proxy signature scheme has to meet the identifiability, undeniability, verifiability and unforgeability security requirements. In some conditions, it may be necessary to protect the proxy signer’s privacy from outsiders or third parties. Recently, several studies about proxy signature schemes have been conducted but only Yu et al.’s anonymous proxy signature scheme proposed in 2009 attempting to protect the proxy signer’s privacy from outsiders. They claimed their scheme can make the proxy signer anonymous. However, based on our research, we determined that this was not the case and the proxy signer’s privacy was not anonymous. Hence, in this paper, we propose a new anonymous proxy signature scheme that truly makes the proxy signer anonymous while making it more secure and efficient when compared with Yu et al.’s scheme in 2009. Our proxy signature scheme consists of two constructions. First, we mainly use random numbers and bilinear pairings to attain the anonymous property in our proxy. Secondly, we increase the security and efficiency of our proxy through modifications.

1. Introduction 1
　
2. Background 4
　
3. Review of Yu et al.’s scheme 5
3.1 Yu et al.’s APS scheme 5
3.2 Weakness of Yu et al.’s scheme 9
　
4. Proposed scheme 13
4.1 The new proposed APSs scheme 13
4.2 Correctness 16
4.3 Security analyses 17
　
5. Comparisons 22
　
6. Conclusions 24
　
Reference 25

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