Au Man Ho Allen. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 60-68). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Preliminaries --- p.5 / Chapter 2.1 --- Complexity Theory --- p.5 / Chapter 2.2 --- Algebra and Number Theory --- p.7 / Chapter 2.2.1 --- Groups --- p.7 / Chapter 2.2.2 --- Additive Group Zn and Multiplicative Group Z*n --- p.8 / Chapter 2.2.3 --- The Integer Factorization Problem --- p.9 / Chapter 2.2.4 --- Quadratic Residuosity Problem --- p.11 / Chapter 2.2.5 --- Computing e-th Roots (The RSA Problem) --- p.13 / Chapter 2.2.6 --- Discrete Logarithm and Related Problems --- p.13 / Chapter 2.3 --- Public key Cryptography --- p.16 / Chapter 2.3.1 --- Encryption --- p.17 / Chapter 2.3.2 --- Digital Signature --- p.20 / Chapter 2.3.3 --- Identification Protocol --- p.22 / Chapter 2.3.4 --- Hash Function --- p.24 / Chapter 3 --- Paillier Cryptosystems --- p.26 / Chapter 3.1 --- Introduction --- p.26 / Chapter 3.2 --- The Paillier Cryptosystem --- p.27 / Chapter 4 --- Identity-based Cryptography --- p.30 / Chapter 4.1 --- Introduction --- p.31 / Chapter 4.2 --- Identity-based Encryption --- p.32 / Chapter 4.2.1 --- Notions of Security --- p.32 / Chapter 4.2.2 --- Related Results --- p.35 / Chapter 4.3 --- Identity-based Identification --- p.36 / Chapter 4.3.1 --- Security notions --- p.37 / Chapter 4.4 --- Identity-based Signature --- p.38 / Chapter 4.4.1 --- Security notions --- p.39 / Chapter 5 --- Identity-Based Cryptography from Paillier System --- p.41 / Chapter 5.1 --- Identity-based Identification schemes in Paillier setting --- p.42 / Chapter 5.1.1 --- Paillier-IBI --- p.42 / Chapter 5.1.2 --- CGGN-IBI --- p.43 / Chapter 5.1.3 --- GMMV-IBI --- p.44 / Chapter 5.1.4 --- KT-IBI --- p.45 / Chapter 5.1.5 --- Choice of g for Paillier-IBI --- p.46 / Chapter 5.2 --- Identity-based signatures from Paillier system . . --- p.47 / Chapter 5.3 --- Cocks ID-based Encryption in Paillier Setting . . --- p.48 / Chapter 6 --- Concluding Remarks --- p.51 / A Proof of Theorems --- p.53 / Chapter A.1 --- "Proof of Theorems 5.1, 5.2" --- p.53 / Chapter A.2 --- Proof Sketch of Remaining Theorems --- p.58 / Bibliography --- p.60

This study examined the potential use of keystroke dynamics to create keyprints (typing fingerprints) to authenticate individuals in online assessment situations. The implications of this study are best understood in terms of the keystroke behavioral biometric. While previous studies considered the degree to which keystroke typing patterns are unique, this study was set up to determine how well keyprints are able to identify individuals when typing under various treatment conditions (copy typing, free typing, and typing with mild or moderate impediments). While authentication can be difficult when attempting to correctly identify individual users, the results of this study indicate that keyprints can be a solid indicator of negative cases (i.e., flagging situations where a typing sample is likely not the correct individual). As anticipated, typing with a temporary impediment does diminish the algorithms' ability to identify students. This is also the case when user samples are typed under conditions different from those in which the keyprint baseline signature was captured (i.e., copy versus free typing). The ability to identify individuals is also challenging when using small comparison samples. However, the ability of the system to identify negative cases functions fairly well in each instance.

Illicit software that seeks to steal user information, deny service, or cause general mayhem on computer networks is often discovered after the damage has been done. The ability to discover network behavior of software before a computer network is utilized would allow administrators to protect and preserve valuable resources. Static reverse engineering is the process of discovering in a offline environment how a software application is built and how it will behave. By automating static reverse engineering, software behavior can be discovered before it is executed on client devices. Fingerprints are then built from the discovered behavior which is matched with known malicious fingerprints to identify potentially dangerous software.

<p>It is important for the military to know as much as possible about how easily detected their vehicles are. One way among many used to detect vehicles is the use of radar sensors. The radar reflecting characteristics of military vehicles are therefor often rigorously tested. With measurements and simulations it is possible to calculate likely detection distances to a vehicle from different angles. This process often produces very large data sets that are hard to analyze.</p><p>This thesis discusses and implements a method for visualizing the detection distance data set and also discusses a lot of related issues with a focus on computer graphics.</p><p>The main concept is called spherical displacement and the idea is to visualize the detection distances as a surface with the imagined vehicle in the center point. Detection is likely inside the surface but not on the outside. This concept is the next step from the colored sphere where the colors represent the detection distance which was previously used.</p><p>The thesis project resulted in a visualization tool that uses the new concept and can handle large data sets. The spherical displacement concept is more intuitive and shows detail better than the colored sphere visualization.</p>

Due to ubiquity of internet, the development of electronic commerce is growing up rapidly. Many payment mechanisms of electronic transactions are proposed, such as electronic cash, credit cards, and electronic wallets. Electronic cash (e-cash) is like the digital version of paper cash, which possesses some key features such as anonymity and untraceability, and it can be used on the Internet for various electronic transactions. In general, electronic cash is classified into two types which are on-line electronic cash and off-line electronic cash. Each of them is suitable for different applications and environments. All of the proposed electronic cash schemes only focus on one of two types. In these schemes, users must decide which type of electronic cash they will use later before withdrawing. However, in this thesis we propose a novel electronic cash scheme which supports a user to withdraw a generic e-cash and then decide to spend it as an on-line e-cash or an off-line e-cash. Our proposed scheme is more convenient for users and more flexible for the bank and shops. It not only satisfies the necessary properties of electronic cash but also provides flexibility.

Invariants of knots coming from twisted signatures have played a central role in the study of knot concordance. Unfortunately, except in the simplest of cases, these signature invariants have proven exceedingly difficult to compute. As a consequence, many knots which presumably can be detected by these invariants are not a well understood as they should be. We study a family of signature invariants of knots and show that they provide concordance information. Significantly, we provide a tractable means for computing these signatures. Once armed with these tools we use them first to study the knot concordance group generated by the twist knots which are of order 2 in the algebraic concordance group. With our computational tools we can show that with only finitely many exceptions, they form a linearly independent set in the concordance group. We go on to study a procedure given by Cochran-Harvey-Leidy which produces infinite rank subgroups of the knot concordance group which, in some sense are extremely subtle and difficult to detect. The construction they give has an inherent ambiguity due to the difficulty of computing some signature invariants. This ambiguity prevents their construction from yielding an actual linearly independent set. Using the tools we develop we make progress to removing this ambiguity from their procedure.

In last few years we have observed a significant increase in the usage of computing devices and their capabilities to communicate with each other. With the increase in usage and communicating capabilities the higher level of network security is also required. Today the main devices used for the network security are the firewalls and IDS/IPS that provide perimeter defense. Both devices provide many overlapping security features but they have different aims, different protection potential and need to be used together. A firewall is an active device that implements ACLs and restricts unauthorized access to protected resources. An IDS only provides information for further necessary actions, not necessarily perimeter related, but some of these needed actions can be automated, such as automatic blocking in the firewall of attacking sites, which creates an IPS. This thesis report analyzed some common firewall and IDS products, and described their security features, functionalities, and limitations in detail. It also contains the comparison of the security features of the both devices. The firewall and IDS perform different functions for the network security, so they should be used in layered defense architecture. The passwords, firewalls, IDSs/IPSs and physical security all together provide a layered defense and complement each other. The firewall and IDS alone cannot offer sufficient network protection against the network attacks, and they should be used together to enhance the defense-in-depth or layered approach.

It is important for the military to know as much as possible about how easily detected their vehicles are. One way among many used to detect vehicles is the use of radar sensors. The radar reflecting characteristics of military vehicles are therefor often rigorously tested. With measurements and simulations it is possible to calculate likely detection distances to a vehicle from different angles. This process often produces very large data sets that are hard to analyze. This thesis discusses and implements a method for visualizing the detection distance data set and also discusses a lot of related issues with a focus on computer graphics. The main concept is called spherical displacement and the idea is to visualize the detection distances as a surface with the imagined vehicle in the center point. Detection is likely inside the surface but not on the outside. This concept is the next step from the colored sphere where the colors represent the detection distance which was previously used. The thesis project resulted in a visualization tool that uses the new concept and can handle large data sets. The spherical displacement concept is more intuitive and shows detail better than the colored sphere visualization.

Due to resource-saving and efficiency consideration, electronic voting (e-voting) gradually replaces traditional paper-based voting in some developed countries. An anonymous e-voting system that can be used in elections with large electorates must meet various security requirements, such as anonymity, uncoercibility, tally correctness, unrecastability, verifiability, and so on. Especially, the uncoercibility property is an essential property which can greatly reduce the possibility of coercion and bribe. Since each voter can obtain one and only one voting receipt in an electronic voting system, coercers or bribers can enforce legal voters to show their voting receipts to identify whether the enforced voters follow their will or not. It turns out that the coercion and bribe will succeed more easily in digital environments than that in traditional paper-based voting. In this dissertation, we analyze four possible scenarios leading to coercion and discover that the randomization property is necessary to blind-signature-based e-voting systems against coercion. Based on this result, we extend our research and come up with two provably secure randomized blind signature schemes from different cryptographic primitives, which can be adopted as key techniques for an electronic voting system against coercion and bribery.

Due to the growing interest in electronic commerce, more and more transactions now happen online. Thus, fair transactions between customers and merchants are getting important. To gain the fairness of the exchange of digital items, fair exchange protocols have been proposed and well studied. Most of the traditional fair exchange protocols are concerned about the exchange of digital items, such as digital signatures, contracts, and documents. Recently, researchers pay attention to the exchange of digital goods along with electronic cash, and have proposed some fair transaction protocols based on electronic cash. To buy digital contents via electronic cash through network, the anonymity property as traditional cash possesses must be guaranteed. It means that the payment information of the customer cannot be revealed to anyone else including the trusted third party (TTP) who helps the customer and the merchant with resolving possible disputes in the protocol. Since the customer and the merchant may not trust each other in an electronic transaction. In a fair exchange protocol, a TTP is employed to achieve true fairness. An on-line TTP has to take part in all transactions while they are proceeding. Despite it can gain true fairness, it is inefficient due to on-line interaction with the TTP. On the other hand, an off-line TTP does not need to join in the transaction protocol in normal cases. Instead, it participates in the protocol only when disputes happen. It is efficient and fair, and more feasible in practical situations. In this thesis, we propose a fair transaction protocol based on electronic cash. With the extended research on electronic cash, we have designed a fair transaction protocol that is suitable for any electronic cash system. By using an off-line TTP, the protocol is more efficient and practical. Furthermore, payment information of the customer cannot be known to anyone else including the TTP, and thus, the anonymity of the customer is protected completely in our protocol.