臺灣博碩士論文加值系統

當產生一數位簽章時，簽章者只需使用自己的秘密金匙來簽署電子文件。之後，驗證者利用簽章者的公開金匙驗證簽章者的身份及真實性。但是，假使簽章者遺失了他的秘密金匙，則他可以否認他所簽署過的簽章。由於有"否認"性的問題存在，必需要在簽章中加入一些額外的資訊以增強其不可否認性。在論文中，我們將提出一個包含時戳的新數位簽章方法，它具有公平與不可改變的特性。根據加入的時戳，驗證者可以比較簽名的時間與秘密金匙遺失的時間以確認簽章的簽署者。則我們能得知秘密金匙的擁有者，簽章者，是否簽署了此份簽章。假使時戳是由簽章者自己加入，則無法讓人信服。因此，需要有一"時戳中心"代替簽章者加入時戳且不可偽造簽署者之簽章。驗證者除了驗證簽章的真實性之外，亦能知道簽章是何時所簽署。數位簽章及時戳是一起產生的，沒有時戳中心的協助，簽章者是無法產生具有有效時戳之數位簽章。相反地，沒有簽章者的協助，時戳中心是無法偽造數位簽章上有效時戳。根據此份時戳數位簽章，我們可以驗證簽章者身份的真實及知道這份簽章是何時所簽署。在本論文中，我們亦提出應用時戳的觀念，建構一個新的代理簽章方法。

While a digital signature was generated, the signer merely used his own secret key to sign a document. Later, the verifier used the signer's public key to authenticate the truthfulness and the identity of the signature's owner. But the signer could deny the signature by declaring that he lost his secret key. Owing to the problem of repudiation, some extra information must be appended into the signature to strength the undeniability. A new digital signature scheme attached a time-stamp which is fair and unchangeable is proposed in this thesis. According to the added time-stamp, the verifier could confirm the signer of the signature by comparing the signed date and the secret key's lost time. It would be known whether the secret key's owner, the signer, signed the signature or not. If a time-stamp was appended by the signer, it is not convinced by others. Therefore a TSS can't forge a signature of the signer is needed to substitute for the signer to add a time-stamp. In addition to verifying the signature's reality, the verifier also knows when the signature was signed. In a time-stamped digital signature scheme, the signer and the TSS cooperatively generate a valid time-stamped signature together. Without the help of the TSS, the signer cannot generate a valid digital signature with valid time-stamp. On the contrary, without the help of the signer the TSS cannot generate a valid digital signature of the signer. Depending upon the time-stamped digital signature, we are able to know when the signature was signed and the truthfulness of the signature. The concept of time-stamp is also applied in the proxy signature scheme proposed in our thesis.

Chapter 1 Introduction
1.1 Research Background
1.2 Research Motivation
1.3 Research Purpose
1.4 Research Scope
1.5 Research Procedure
1.6 Thesis Framework
Chapter 2 Literature Review
2.1 ElGamal Signature Scheme
2.2 Linking Schemes
2.2.1 Linking Schemes with Relative Temporal Authentication
2.2.2 The Disadvantages of Linking Schemes
2.3 Blind Signatures
2.4 The Proxy Signatures
Chapter 3 Definition and Classification of Time-Stamped Digital Signature Schemes
3.1 Security Requirements
3.2 Four Classes of Time-Stamped Signature Schemes
Chapter 4 Time-Stamped Digital Signatures
4.1 Nothing Hidden Time-Stamped Signature Scheme
4.1.1 Basic Scheme
4.1.2 Security Considerations
4.1.3 Application
4.2 Message Hidden Time-Stamped Signature Scheme
4.2.1 Basic Scheme
4.2.2 Security Considerations
4.2.3 Meta Schemes
4.2.4 Application
4.3 Parameter Hidden Time-Stamped Signature Scheme
4.3.1 Basic Scheme
4.3.2 Security Considerations
4.3.3 Meta Schemes
4.3.4 The Second Parameter Hidden Time-Stamped Signature Scheme
4.3.5 Application
4.4 Strong Time-Stamped Signature Scheme
4.4.1 Basic Scheme
4.4.2 Security Considerations
4.4.3 Application
4.5 Further Security Analysis on the Proposed Schemes
Chapter 5 Time-Stamped Signature Schemes with Hybrid Temporal Authentication
5.1 Basic Scheme
5.2 Security Considerations
Chapter 6 Time-Stamped Proxy Signatures with Traceable Receivers
6.1 Proxy Signature Key Generation
6.2 Proxy Signature Generation
6.3 Proxy Signature Verification
6.4 Security Considerations
Chapter 7 Discussions and Conclusions

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