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

by Tsang Hin Chung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 118-124). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Authentication and Transaction Protocol --- p.2 / Chapter 1.2 --- E-Commerce Enabler --- p.3 / Chapter 2 --- Literature Review --- p.4 / Chapter 2.1 --- Cryptographic Preliminaries --- p.4 / Chapter 2.1.1 --- One-Way Hash Function --- p.4 / Chapter 2.1.2 --- Triple DES --- p.5 / Chapter 2.1.3 --- RSA --- p.7 / Chapter 2.1.4 --- Elliptic Curve --- p.8 / Chapter 2.2 --- Smart Cards --- p.8 / Chapter 2.2.1 --- Smart Card Operating Systems --- p.11 / Chapter 2.2.2 --- Java Card --- p.12 / Chapter 2.3 --- Authentication Protocol --- p.14 / Chapter 2.3.1 --- Properties --- p.15 / Chapter 2.3.2 --- Survey --- p.16 / Chapter 2.4 --- Transaction Protocol --- p.19 / Chapter 2.5 --- BAN Logic --- p.20 / Chapter 2.5.1 --- Notation --- p.20 / Chapter 2.5.2 --- Logical Postulates --- p.22 / Chapter 2.5.3 --- Protocol Analysis --- p.25 / Chapter 3 --- Authentication Protocol --- p.26 / Chapter 3.1 --- Formulation of Problem --- p.26 / Chapter 3.2 --- The New Idea --- p.27 / Chapter 3.3 --- Assumptions --- p.29 / Chapter 3.4 --- Trust Model --- p.29 / Chapter 3.5 --- Protocol --- p.30 / Chapter 3.5.1 --- Registration --- p.30 / Chapter 3.5.2 --- Local Authentication --- p.31 / Chapter 3.5.3 --- Remote Authentication --- p.33 / Chapter 3.5.4 --- Silent Key Distribution Scheme --- p.35 / Chapter 3.5.5 --- Advantages --- p.37 / Chapter 3.6 --- BAN Logic Analysis --- p.38 / Chapter 3.7 --- Experimental Evaluation --- p.43 / Chapter 3.7.1 --- Configuration --- p.44 / Chapter 3.7.2 --- Performance Analysis --- p.45 / Chapter 4 --- Transaction Protocol --- p.51 / Chapter 4.1 --- Assumptions --- p.52 / Chapter 4.2 --- Protocol --- p.55 / Chapter 4.3 --- Conflict Resolution Policy --- p.58 / Chapter 4.4 --- Justifications --- p.58 / Chapter 4.5 --- Experimental Evaluation --- p.59 / Chapter 4.5.1 --- Configuration --- p.59 / Chapter 4.5.2 --- Performance Analysis --- p.60 / Chapter 5 --- E-Commerce Builder --- p.65 / Chapter 5.1 --- Overview --- p.66 / Chapter 5.2 --- Design of Smart RAD --- p.68 / Chapter 5.2.1 --- Mechanism --- p.68 / Chapter 5.2.2 --- Java Card Layer --- p.69 / Chapter 5.2.3 --- Host Layer --- p.71 / Chapter 5.2.4 --- Server Layer --- p.72 / Chapter 5.3 --- Implementation --- p.73 / Chapter 5.3.1 --- Implementation Reflection --- p.73 / Chapter 5.3.2 --- Implementation Issues --- p.76 / Chapter 5.4 --- Evaluation --- p.77 / Chapter 5.5 --- An Application Example: Multi-MAX --- p.79 / Chapter 5.5.1 --- System Model --- p.79 / Chapter 5.5.2 --- Design Issues --- p.80 / Chapter 5.5.3 --- Implementation Issues --- p.80 / Chapter 5.5.4 --- Evaluation --- p.84 / Chapter 5.6 --- Future Work --- p.89 / Chapter 6 --- Conclusion --- p.91 / Chapter A --- Detail Experimental Result --- p.93 / Chapter A.1 --- Authentication Time Measurement --- p.94 / Chapter A.2 --- On-Card and Off-Card Computation Time in Authentication --- p.95 / Chapter A.3 --- Authentication Time with Different Servers --- p.96 / Chapter A.4 --- Transaction Time Measurement --- p.97 / Chapter A.5 --- On-card and Off-card Computation Time in Transaction --- p.97 / Chapter B --- UML Diagram --- p.99 / Chapter B.1 --- Package cuhk.cse.demo.applet --- p.99 / Chapter B.2 --- Package cuhk.cse.demo.client --- p.105 / Chapter B.3 --- Package server --- p.110 / Chapter C --- Glossary and Abbreviation --- p.115 / Bibliography --- p.118

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Secured long-distance communication has always been an important topic for people handling sensitive information. Now with the arrival of ``intelligent`` mobile phones eavesdropping and information gathering is as easy as never. Luckily smartphones present not only problems in terms of security but also an opportunity to protect ones privacy. This thesis attempts to construct a generic software architecture of a communicator which could be capable of transferring voice, video and other various forms of binary data in a secure way. It will analyse and use different communication channels to reach a maximum level of data authenticity, integrity and confidentiality in an environment where a central security element needs to be avoided. The resulting architecture will be tested on a Voice-over-IP (VoIP) application prototype for the mobile Google Android platform to show whether the approach is practically usable on currently available phones.

To evaluate the performance of a hardware design, it is necessary to select the met- rics of interest. Several metrics can be chosen, but in general three of them are considered basic: area, latency, and power. From these, other metrics of practical interest such as throughput and energy consumption can be obtained. These metrics relate to one another by creating trade-offs that designers need to know to execute the best design decisions. Some works address optimized hardware design for improving one of these metrics. In other works, optimizations are made for two of them. Others analyze the trade-off between two of these metrics. However, the literature lacks of works that analyze the behavior of three metrics together. In this work, we intend to contribute to bridge this gap, proposing a method that allow analyzing trade-offs among area, power, and throughput. To verify the proposed method, the permutation function of crypto- graphic sponge BlaMka was chosen as a case study. No hardware implementation has been found for this algorithm yet. Therefore, an additional contribution is to provide its first hardware design. Combinational and sequential circuits were designed and synthesized for ASIC and FPGA. With the synthesis results, a detailed performance analysis was performed for each platform, starting from a one-dimensional analysis, going through a two-dimensional analysis, and culminating in a three-dimensional analysis. Two techniques were presented for such analysis, namely projections approach and planes approach. Although there is room for improvement, the proposed method is a initial step showing that, in fact, a trade-off between three metrics can be analyzed, and that it is also possible to find balanced performance points. From the two approaches presented, it was possible to derive a criterion to select optimizations when we have restrictions, such as a desired throughput range or a maximum physical size, and when we do not have restrictions, in which case we can choose the optimization with the most balanced performance. / Para avaliar o desempenho de um projeto de hardware, é necessário selecionar as métricas de interesse. Várias métricas podem ser escolhidas, mas em geral três delas são consideradas básicas: área, latência e potência. A partir delas, podem ser obtidas outras métricas de interesse prático, tais como vazão e consumo de energia. Essas métricas relacionam-se entre si, criando trade-offs que os projetistas precisam conhecer para executar as melhores decisões de projeto. Alguns trabalhos abordam o projeto de hardware otimizado para melhorar uma dessas métricas. Em outros trabalhos, as otimizações são feitas para duas delas, mas sem analisar como uma terceira métrica se relaciona com as demais. Outros analisam o trade-off entre duas dessas métricas. Entretanto, a literatura carece de trabalhos que analisem o comportamento de três métricas em conjunto. Neste trabalho, pretendemos contribuir para preencher essa lacuna, propondo um método que permita a análise de trade-offs entre área, potência e vazão. Para verificar o método proposto, foi escolhida a função de permutação da esponja criptográfica BlaMka como estudo de caso. Até o momento, nenhuma implementação em hardware foi encontrada para esse algoritmo. Dessa forma, uma contribuição adicional é apresentar seu primeiro projeto de hardware. Circuitos combinacionais e sequenciais foram projetados e sintetizados para ASIC e FPGA. Com os resultados de síntese, foi realizada uma análise de desempenho detalhada para cada plataforma, a partir de uma análise unidimensional, passando por uma análise bidimensional e culminando em uma análise tridimensional. Duas técnicas foram apresentadas para tal análise tridimensional, chamadas abordagem das projeções e abordagem dos planos. Embora passível de melhorias, o método apresentado é um passo inicial mostrando que, de fato, um trade-off entre três métricas pode ser analisado, e que também é possível encontrar pontos de desempenho balanceado. A partir das duas abordagens, foi possível derivar um critério para selecionar otimizações quando há restrições, como um faixa de vazão desejada ou um tamanho físico máximo, e quando não há restrições, caso em que é possível escolher a otimização com o desempenho mais balanceado.

La cryptographie sur les réseaux est l’une des approches les plus compétitives pour protéger la confidentialité, dans les applications actuelles et l’ère post-quantique. Le problème central qui sert de fondement de complexité de la cryptographie sur réseaux est Learning with Errors (LWE). Il consiste à résoudre un système d’équations bruité, linéaire et surdéterminé. Ce problème est au moins aussi difficile que les problèmes standards portant sur les réseaux, tels que le décodage à distance bornée (BDD pour Bounded Distance Decoding) et le problème du vecteur le plus court unique (uSVP pour unique Shortest Vector Problem). Tous ces problèmes sont conjecturés difficiles à résoudre, même avec un ordinateur quantique de grande échelle. En particulier, le meilleur algorithme connu pour résoudre ces problèmes, BKZ, est très coûteux. Dans cette thèse, nous étudions les relations de difficulté entre BDD et uSVP, la difficulté quantique de LWE et les performances pratiques de l’algorithme BKZ. Tout d’abord, nous donnons une relation de difficulté plus étroite entre BDD et uSVP. Plus précisément, nous améliorons la réduction de BDD à uSVP d’un facteur √2, comparément à celle de Lyubashevsky et Micciancio. Ensuite, Nous apportons un nouvel élément à la conjecture que LWE est quantiquement difficile. Concrètement, nous considérons une version relâchée de la version quantique du problème du coset dièdral et montrons une équivalence computationnelle entre LWE et ce problème. Enfin, nous proposons un nouveau simulateur pour BKZ. Dans ce dernier travail, nous proposons le premier simulateur probabiliste pour BKZ, qui permet de prévoir le comportement pratique de BKZ très précisément. / Lattice-based cryptography is one of the most competitive candidates for protecting privacy, both in current applications and post quantum period. The central problem that serves as the hardness foundation of lattice-based cryptography is called the Learning with Errors (LWE). It asks to solve a noisy equation system, which is linear and over-determined modulo q. Normally, we call LWE problem as an average-case problem as all the coefficients in the equation system are randomly chosen modulo q. The LWE problem is conjectured to be hard even wtih a large scale quantum computer. It is at least as hard as standard problems defined in the lattices, such as Bounded Distance Decoding (BDD) and unique Shortest Vector Problem (uSVP). Finally, the best known algorithm for solving these problems is BKZ, which is very expensive. In this thesis, we study the quantum hardness of LWE, the hardness relations between the underlying problems BDD and uSVP, and the practical performance of the BKZ algorithm. First, we give a strong evidence of quantum hardness of LWE. Concretely, we consider a relaxed version of the quantum version of dihedral coset problem and show an computational equivalence between LWE and this problem. Second, we tighten the hardness relation between BDD and uSVP. More precisely, We improve the reduction from BDD to uSVP by a factor √2, compared to the one by Lyubashevsky and Micciancio. Third, we propose a more precise simulator for BKZ. In the last work, we propose the first probabilistic simulotor for BKZ, which can pridict the practical behavior of BKZ very precisely.

Wireless clients are vulnerable to exploitation by evil twins due to flaws in the authentication process of 802.11 Wi-Fi networks. Current certificate-based wireless authentication protocols present a potential solution, but are limited in their ability to provide a secure and usable platform for certificate validation. Our work seeks to mitigate these limitations by exploring a client-side strategy for utilizing alternative trust models in wireless network authentication. We compile a taxonomy of various trust models for conducting certificate-based authentication of wireless networks and methodically evaluate each model according to desirable properties of security, usability, and deployability. We then build a platform for leveraging alternative certificate-based trust models in wireless networks, present a proof-of-concept using one of the most promising alternative validation models identified--a whitelisting and pinning hybrid--and examine its effectiveness at defending against evil twin attacks in 802.11 networks.

A Trusted Platform Module (TPM) is a security device included in most modern desktop and laptop computers. It helps keep the computing environment secure by isolating cryptographic functions and data from the CPU. A TPM is usually implemented with a small microcontroller which is near the main processor. In addition to a microcontroller, it may employ hardware acceleration to assist in cryptographic computations. When vulnerabilities are found, or new algorithms developed, TPMs become obsolete because the hardware accelerators cannot be upgraded. This thesis presents a proof of concept implementation of a TPM on an FPGA. By using an FPGA, the TPM gains the ability to be upgraded or have new cryptographic modules added. This new design easily fits on the Zynq FPGA used in this work, with room left over for additional functionality. We explore the feasibility of this approach, including the added cost of the FPGA, and the added benefits of reconfigurable hardware.

Collaborative environments allow users to share and access data across networks spanning multiple administrative domains and beyond organisational boundaries. This poses several security concerns such as data confidentiality, data privacy and threats to improper data usage. Traditional access control mechanisms focus on centralised systems and implicitly assume that all resources reside in the one domain. This serves as a critical limitation for inter-organisational collaborative environments, which are characteristically decentralised, distributed and heterogeneous. A consequence of the lack of suitable access control mechanisms for inter-organisational collaborative environments is that data owners relinquish all control over data they release. In these environments, we can reasonably consider more complex cases where documents may have multiple contributors, all with differing access control requirements. Facilitating such cases, as well as maintaining control over the document’s content, its structure and its flow path as it circulates through multiple administrative domains, is a non-trival issue. This thesis proposes an architecture model for specifying and enforcing access control restrictions on sensitive data that follows a pre-defined inter-organisational workflow. Our approach is to embed access control enforcement within the workflow object (e.g. the circulating document containing sensitive data) as opposed to relying on each administrative domain to enforce the access control policies. The architecture model achieves this using cryptographic access control – a concept that relies on cryptography to enforce access control policies.

This research has investigated how anonymity has been achieved in text-based online conversations. It has found that anonymity could be attained without any special provision from a conversation system. The absence of face-to-face contact and use of typed remarks are sufficient to create anonymity.Nevertheless, the lack of special provisions can make it difficult for some to use the anonymity they have attained. Preserving such naturally attained anonymity can be equally difficult for users. System administrators will also have trouble controlling anonymity without special provisions. Will deliberate provisions for anonymity remove these problems?The goal of this research is to determine how anonymity in online conversations could and should be supported. An existing conversation system lacking in special support for anonymity has been selected. Every possible change for the benefit of anonymity has been made to this system. The changes that have been made and why they were made are described in this thesis. The impact of those changes is also discussed. The final outcome of this research is a set of guidelines and standards for supporting anonymity in text-based online conversations.