臺灣博碩士論文加值系統

繼Mambo等人提出代理簽章法後, 有許多不同的代理簽章法被提出。在這些代理簽章法中，驗證者必須用代理簽章的公開金鑰來驗證代理簽章，以維護代理人的權益。所以在這些代理簽章法中，代理人的身份必須是公開的。但是在現實生活中，有很多情況下，代理人並不希望別人知道他真實的身份，以避免無謂的干擾。因應此種實際上的需求，我們提出了匿名的代理簽章法。
除了滿足代理簽章法的基本要求之外，我們的匿名的代理簽章法有許多優點，首先我們的方法滿足了由Mambo等人所提出的七種性質。再者，在我們的方法中，代理人的身份是匿名的，除了原始簽章者之外，沒有任何人知道代理人真實的身份。雖然代理人的身份是匿名的，但是原始簽章者與公正的第三者，在代理簽章有爭議發生時，他們仍可以正確的指出代理人的身份。這種匿名的性質，除了使代理人避免受干擾之外，對驗證者而言，也較為方便，因為當他要驗證代理簽章時，只需要利用原始簽章者的公開金鑰去驗證代理簽章即可。除此之外，在我們的方法中，代理人只需使用代理人自己的秘密金鑰，即可簽署一份代理簽章，所以不需要額外的負擔去記憶代理的秘密金鑰。即使同時為多個不同原始簽章者做代理人的服務時，此代理人也只要使用代理人自己的秘密金鑰即可簽署代理簽章。同時，我們的方法提供了對原始簽章者以及代理簽章者公平的保護。原始簽章者給予代理簽章者的授權憑證，代理簽章者必須將其使用在代理簽章中，因而保護了原始簽章者。而代理簽章者在簽署代理簽章時，必須使用到唯有代理簽章者才擁有的秘密金鑰，因而保護了代理簽章者。因此，此匿名的代理簽章法同時保護了原始簽章者以及代理簽章者。
因應群體導向的需求，我們也提出了匿名的多人授權代理簽章法以及匿名的門檻式授權代理簽章法。此外，對於Chang等人的多人簽章法與內部攻擊法，也提出一個有效的修正方法。

Since Mambo et al. proposed the concept of proxy signature schemes, there are many kinds of proxy signature schemes are proposed. In these schemes, in order to protect proxy signers, the public keys of proxy signers should be used to verify proxy signatures. So the identity of the proxy signer is public in these proxy signature schemes. Actually, in many situations, the proxy signer doesn’t want that anyone knows his identity in order to avoid disturbance. Therefore the anonymous proxy signature scheme with undeniable agents is proposed here. Except satisfying the basic requirements of proxy signature schemes, our schemes have many advantages. First of all, our scheme satisfies the seven properties proposed by Mambo et al. Additionally, the proxy signer in our scheme is anonymous. If any dispute happens, the original signers and the trust third party can prove the identity of the proxy signer. It is convenient for the verifier validating the proxy signature only by the public key of the original singers without knowing who the proxy signer is. Moreover, there is no additional load to remember the proxy secret key, so the load of the proxy signers is reduced. Our scheme provides the fair protection for the original signers and proxy signer. Due to the group-oriented application, the anonymous proxy multi-signature schemes with undeniable agents and the anonymous proxy (t, n) threshold signature schemes with a mutually trusted party are also proposed. Moreover, an efficient repair on Chang et al.’s multi-signature scheme is proposed to remove the insider attack.

Chapter 1 Introduction ………………………………………………. P. 9
Chapter 2 Review of the Past Research Results……….……………. P. 13
2.1 Review of Chaum and van Antwerpen’s Disavowal Protocol…. P. 13
2.2 Review of Girault’s Self-certified Public Key
System Based on RSA……………………………………. P. 15
2.3 Review of Chang et al.’s ElGamal-like Schemes ……………… P. 16
2.3.1 Review of Chang et al.’s Digital Signature Schemes P. 16
2.3.2 Review of Chang et al.’s Multi-signature Schemes… P. 17
Chapter 3 Our Anonymous Proxy Signature Schemes
with Undeniable Agents ..………………………………... P. 19
3.1 The System Description ……………..…………….…………….. P. 19
3.2 Security Analysis and Discussions ………………………………. P. 23
3.3 A Comparison with Shum and Wei’s Strong Proxy
Signature Scheme …………………………. …………..…. P. 28
Chapter 4 Our Anonymous Proxy Multi-signature Scheme
with Undeniable Agents………………………………….. P. 31
4.1 The System Description …………………………………………. P. 31
4.2 Security Analysis and Discussions……………………………….. P. 35
Chapter 5 Our Anonymous Proxy (t, n) Threshold Signature
Scheme with A Mutually Trusted Party .………………… P. 37
5.1 The System Description…………………………………………… P. 37
5.2 Security Analysis and Discussions ………………………………. P. 41
Chapter 6 A Repaire on Chang et al.’s ElGamal-like
Multi-signature Scheme ………………………………….. P. 42
6.1 An Attack on Chang et al.’s ElGamal-like
Multi-signature Schemes…………………………………. P. 42
6.2 Our Improvement..………………………………………………… P. 44
6.3 The Security and Performance Analysis ………………………… P. 47
6.3.1 Security Analysis… ……………………………………….... P. 47
6.3.2 Performance Analysis ……………………….. ………….… P. 52
Chapter 7 Conclusions .…………………………………………………. P. 55
References .……………………………………………………………..… P. 57

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