臺灣博碩士論文加值系統

隨著網際網路的進步，每位合法的使用者都可藉由網路來完成各種的交易，因此使用者在網路上所從事的各種活動必須是在安全且保密的環境下完成，在這種開放式的網路環境下，遠端系統與使用者都必須了解到對方的合法性，因此如何在一個分散式的網路環境中確認對方身分，並提供一個安全的網路交易環境，一直都是一個非常重要的議題。
而在傳統的使用者驗證機制中，通常必須儲存通行密碼表於遠端伺服器中，以供驗證時使用，但儲存於遠端伺服器中的通行密碼表卻有容易外洩出去或是遭有心人士入侵，並竄改通行密碼表內容的風險，過去所討論的使用者驗證機制環境中，大多屬於單一遠端伺服器驗證架構，當要登入不同伺服器時，則必須再使用不同的使用者識別碼與密碼來登入，這樣將造成使用者的不便，因其必須記住不同伺服器的登入資料；在2003年，Lin 等人提出了一個多重伺服器的驗證方式，但還是有些缺點存在，而本研究將修正這些缺點並提出五種設計架構來達成多重伺服器的驗證方式，這些架構分別應用在不同環境中。
針對時間戳記(Timestamp)所造成時間不同步的問題，本研究提出一個可調整的時間戳記來適應不同的需求；對於Timestamp的機制，不但能解決時間不同步的問題，而對於Nonce的機制，也不需儲存相對應的資料表。因此，本研究所提機制可以滿足以下特性：多重伺服器驗證環境、不需儲存密碼表於伺服器端、合法使用者可自由選擇自己的登入帳號與密碼、合法使用者與伺服器之間的相互驗證、較少的時間成本、允許合法使用者可以在註冊後採離線方式更改自己的密碼與解決時間不同步的問題。

Computer systems and their interconnections via networks have increased the dependence of both organizations and individuals on stored information. This dependence, in turn, has led to a heightened awareness of the need for information security and the protection of data and resources from electronic eavesdropping, electronic fraud and network-based attacks. Consequently, cryptography and security have matured, leading to the development of improved network security.
In a traditional password scheme, each user has an identity (ID) and a secret password (PW). If a person wants to login to network system, he/she must submit his/her ID and its corresponding PW. Then, through a dictionary of verification tables, a network system authenticates its users. Such a verification table has some risks of modification because passwords are stored in a remote system. Therefore, these remote password schemes still do not work well in the multi-server environment. In 2003, Lin et al. proposed a new remote user authentication scheme for a multi-server environment. There are some drawbacks in the changing password phase. We propose six multi-server authentication schemes and revise these drawbacks.
In this thesis, we propose a new Adaptive Timestamp structure. An Adaptive Timestamp not only has no User Table but also has no serious time synchronization problem.
These schemes achieve merits: the scheme can be used in multi-server environments; the system does not need to maintain any verification table; the users who have registered with various servers do not need to remember different login passwords for each. Besides, our scheme can also withstand replay and modification attacks. Therefore, it allows users to choose their passwords freely, and a user can be removed from the system easily when the subscription expires.

Table of Contents
中文摘要(Abstract in Chinese) vi
Abstract viii
誌謝 x
Table of Contents xi
List of Figures xiii
List of Tables xiv
1. Introduction 1
1.1 The Criteria of Multi- Server Authentication Scheme 3
1.2 Research Approach and Scope 4
1.3 Thesis Organization 6
2. Related Theories and Schemes 7
2.1 One-Way Hash Function 7
2.2 Lagrange Interpolation 8
2.3 ElGamal Digital Signature Scheme 9
2.4 Overview of the Lin et al.’s Scheme 11
2.5 Overview of the Juang’s Scheme 20
3. Multi-Server Environments 26
3.1 The Weakness of Lin et al.’s Scheme 26
3.2 Preliminary 30
3.3 An Adaptive Timestamp 31
3.4 Scheme I：Based on a Circle 33
3.5 Scheme II：Based on Lagrange Interpolation 42
3.6 Scheme III：Based on a Plane 48
3.7 Scheme IV：Based on Hash Function 56
3.8 Scheme V：Based on Three Dimensions 65
4. Analysis 73
4.1 Security Analysis 73
4.2 Efficiency Analysis 76
4.3 Capacity Analysis 78
5. Conclusions and Future Works 80
5.1 Conclusions 80
5.2 Future Research Topics and Directions 81
Bibliography 83
Vita 87
List of Figures
Fig.2.1 The registration phase of Lin et al.’s scheme.15
Fig.2.2 The changing passwords of Lin et al.’s scheme.19
Fig.3.1 The concept of the process of the attack. 29
Fig.3.2 The structure of an adaptive timestamp. 32
Fig.3.3 The registration phase on a circle. 34
Fig.3.4 The login phase on a circle. 36
Fig.3.5 The authentication phase on a circle. 38
Fig.3.6 The changing of the password phase on a circle.41
Fig.3.7 The registration phase on a plane. 50
Fig.3.8 The registration phase based on hash function. 58
Fig.3.9 The changing password based on hash function. 64
Fig.3.10 The registration phase on three dimensions. 67
List of Tables
Table 4.1 Comparisons of computation costs. 77
Table 4.2 Comparisons of storage cost and communication cost.78
Table 5.1 Comparisons among the smart card-based schemes.81

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