新型网络环境中访问控制模型的研究

随着网格、P2P、无线通信网等技术的普及和飞速发展，访问控制技术取得了长足的进步，同时也面临着巨大的挑战。如何构建安全、灵活、可扩展的访问控制模型是这种新型网络环境下访问控制技术迫切需要解决的问题。本文围绕该环境中的访问控制需求，从委托模型、基于位置的访问控制模型、P2P环境下的动态信任评估模型以及访问控制模型的形式分析四个方面，对访问控制模型研究领域出现的若干关键技术展开研究，取得了以下四个方面的主要成果：第一，在分析Bertino等人提出的一个基于周期时间的访问控制模型的基础之上，指出它虽然可以清晰地表达访问权限可适用的时间范围，但模型本身并没有对已经具有权限的用户如何使用和传播权限强加任何限制，难以实施权限委托这一安全策略。针对这一缺陷，我们讨论了用户到用户的委托访问权限的限制，对权限委托的临时性、时序依赖性和受限传播性这些约束特性进行形式化建模，给出了基于周期时间的自主委托模型PDACDM的形式化定义及其一致性证明。第二，在分析前人所做的各种上下文研究工作的基础上，借助数学的形式语言，给出了一种依赖于空间上下文的访问控制模型SC-RBAC。该模型采用层次式的位置模型给空间客体建模，采用逻辑位置表达不同粒度的位置，引入了空间角色和有效会话角色等概念，证明了层次化的空间角色集合在数学上可构建格模型以实施多级安全策略和中国墙策略，提出了3类空间限制，借鉴和改进了RBAC本身的安全属性，提出了一些新的安全不变量，证明了模型的基本安全定理，并给出了一个简单的应用实例。这一研究成果为解决无线移动网络中的访问控制问题奠定了理论基础。第三，指出了设计一个P2P环境下的信任评估模型需要考虑的主要因素，如时间因素、系统稳定性等。着重分析了P2P环境下的信任模型在识别不诚实反馈、防止恶意节点的策略性动态改变行为、计算节点间相似度、激励机制等方面的不足。给出了一个基于时间窗的动态信任评估模型TWTrust，统一考虑了信任、信誉与激励三者的关系。通过仿真试验结果证明，该模型在信任计算误差和事务失败率等性能指标上有较大提高，能较好处理恶意节点策略性动态改变行为、不诚实反馈对系统的攻击和相似度计算中的稀疏性问题。这一信任模型的提出有望简化P2P下访问控制的实施。第四，在深入分析和对比目前可用于规范和验证访问控制模型的形式化方法和证明工具的基础之上，选取了证明能力强的Isabelle证明系统对支持空间上下文的SC-RBAC模型进行了形式分析，总结了用Isabelle语言对SC-RBAC模型属性和规则进行形式规范的方法，并且研究了基于Isabelle系统证明模型规范内部一致性和正确性的实用方法。

基于ARM Linux的门禁系统的设计与实现

门禁系统主要负责对出入通道进行管制，是社区楼宇安全监控系统的一部分。传统的门禁系统通常采用密码识别、卡片识别的方式进行验证，由于密码、卡片容易被盗用、丢失，系统安全性不高。在通信方式上传统门禁系统通常采用RS485或者RS232连接，传输距离、速度和连接终端数均受限制。本文提出的人像识别门禁系统解决方案采用ARM-Linux系统平台，依靠社区宽带综合业务网的传输和存储能力，结合密码、RFID和人像识别三种识别方式，利用网络技术和生物识别技术达到识别率高、响应速度快、扩展能力强的要求，并能够与驻地网的其它业务集成，提供业务级的联动服务。此外，该门禁系统还支持用户使用电话开门，由服务器完成对用户来电的识别和防伪验证。本文工作的主要贡献是：参与了ARM-Linux系统的裁剪、移植和声卡驱动的修改；建立了ARM-Linux交叉编译环境；完成了门禁前端软件系统的整体设计和实现；完成了服务器软件电话呼叫响应子系统的设计。

Planning the deployment of fault-tolerant wireless sensor networks

Since Wireless Sensor Networks (WSNs) are subject to failures, fault-tolerance becomes an important requirement for many WSN applications. Fault-tolerance can be enabled in different areas of WSN design and operation, including the Medium Access Control (MAC) layer and the initial topology design. To be robust to failures, a MAC protocol must be able to adapt to traffic fluctuations and topology dynamics. We design ER-MAC that can switch from energy-efficient operation in normal monitoring to reliable and fast delivery for emergency monitoring, and vice versa. It also can prioritise high priority packets and guarantee fair packet deliveries from all sensor nodes. Topology design supports fault-tolerance by ensuring that there are alternative acceptable routes to data sinks when failures occur. We provide solutions for four topology planning problems: Additional Relay Placement (ARP), Additional Backup Placement (ABP), Multiple Sink Placement (MSP), and Multiple Sink and Relay Placement (MSRP). Our solutions use a local search technique based on Greedy Randomized Adaptive Search Procedures (GRASP). GRASP-ARP deploys relays for (k,l)-sink-connectivity, where each sensor node must have k vertex-disjoint paths of length ≤ l. To count how many disjoint paths a node has, we propose Counting-Paths. GRASP-ABP deploys fewer relays than GRASP-ARP by focusing only on the most important nodes – those whose failure has the worst effect. To identify such nodes, we define Length-constrained Connectivity and Rerouting Centrality (l-CRC). Greedy-MSP and GRASP-MSP place minimal cost sinks to ensure that each sensor node in the network is double-covered, i.e. has two length-bounded paths to two sinks. Greedy-MSRP and GRASP-MSRP deploy sinks and relays with minimal cost to make the network double-covered and non-critical, i.e. all sensor nodes must have length-bounded alternative paths to sinks when an arbitrary sensor node fails. We then evaluate the fault-tolerance of each topology in data gathering simulations using ER-MAC.

WLAN Security Processor

A novel wireless local area network (WLAN) security processor is described in this paper. It is designed to offload security encapsulation processing from the host microprocessor in an IEEE 802.11i compliant medium access control layer to a programmable hardware accelerator. The unique design, which comprises dedicated cryptographic instructions and hardware coprocessors, is capable of performing wired equivalent privacy, temporal key integrity protocol, counter mode with cipher block chaining message authentication code protocol, and wireless robust authentication protocol. Existing solutions to wireless security have been implemented on hardware devices and target specific WLAN protocols whereas the programmable security processor proposed in this paper provides support for all WLAN protocols and thus, can offer backwards compatibility as well as future upgrade ability as standards evolve. It provides this additional functionality while still achieving equivalent throughput rates to existing architectures. © 2006 IEEE.

Fault reconstruction in linear dynamic systems using multivariate statistics

Treasure et al. (2004) recently proposed a new sub space-monitoring technique, based on the N4SID algorithm, within the multivariate statistical process control framework. This dynamic-monitoring method requires considerably fewer variables to be analysed when compared with dynamic principal component analysis (PCA). The contribution charts and variable reconstruction, traditionally employed for static PCA, are analysed in a dynamic context. The contribution charts and variable reconstruction may be affected by the ratio of the number of retained components to the total number of analysed variables. Particular problems arise if this ratio is large and a new reconstruction chart is introduced to overcome these. The utility of such a dynamic contribution chart and variable reconstruction is shown in a simulation and by application to industrial data from a distillation unit.

Performance analysis of a metro WDM ring networks with variable-length packets under symmetric and asymmetric traffic

In this paper, we discuss and evaluate two proposed metro wavelength division multiplexing (WDM) ring network architectures for variable-length packet traffic in storage area networks (SANs) settings. The paper begins with a brief review of the relevant architectures and protocols in the literature. Subsequently, the network architectures along with their medium access control (MAC) protocols are described. Performance of the two network architectures is studied by means of computer simulation in terms of their queuing delay, node throughput and proportion of packets dropped. The network performance is evaluated under symmetric and asymmetric traffic scenarios with Poisson and self-similar traffic. (C) 2011 Elsevier Inc. All rights reserved.

Detecting Anomalies in Graphs with Numeric Labels

This paper presents Yagada, an algorithm to search labelled graphs for anomalies using both structural data and numeric attributes. Yagada is explained using several security-related examples and validated with experiments on a physical Access Control database. Quantitative analysis shows that in the upper range of anomaly thresholds, Yagada detects twice as many anomalies as the best-performing numeric discretization algorithm. Qualitative evaluation shows that the detected anomalies are meaningful, representing a com- bination of structural irregularities and numerical outliers.

The Impact of EU Privacy Legislation on Biometric System Deployment: Protecting citizens but constraining applications

Biometric systems provide a valuable service in helping to identify individuals from their stored personal details. Unfortunately, with the rapidly increasing use of such systems, there is a growing concern about the possible misuse of that information. To counteract the threat, the European Union (EU) has introduced comprehensive legislation that seeks to regulate data collection and help strengthen an individual’s right to privacy. This article looks at the implications of the legislation for biometric system deployment. After an initial consideration of current privacy concerns, it examines what is meant by ‘personal data’ and its protection, in legislation terms. Also covered are issues around the storage of biometric data, including its accuracy, its security, and justification for what is collected. Finally, the privacy issues are illustrated through three biometric use cases: border security, online bank access control and customer profiling in stores.

Cross-layer Energy-Efficiency Optimization of Packet Based Wireless MIMO Communication Systems

Energy in today's short-range wireless communication is mostly spent on the analog- and digital hardware rather than on radiated power. Hence,purely information-theoretic considerations fail to achieve the lowest energy per information bit and the optimization process must carefully consider the overall transceiver. In this paper, we propose to perform cross-layer optimization, based on an energy-aware rate adaptation scheme combined with a physical layer that is able to properly adjust its processing effort to the data rate and the channel conditions to minimize the energy consumption per information bit. This energy proportional behavior is enabled by extending the classical system modes with additional configuration parameters at the various layers. Fine grained models of the power consumption of the hardware are developed to provide awareness of the physical layer capabilities to the medium access control layer. The joint application of the proposed energy-aware rate adaptation and modifications to the physical layer of an IEEE802.11n system, improves energy-efficiency (averaged over many noise and channel realizations) in all considered scenarios by up to 44%.

Energy Saving - Another Perspective for Parameter Optimization of P and PI Controllers

Modern control methods like optimal control and model predictive control (MPC) provide a framework for simultaneous regulation of the tracking performance and limiting the control energy, thus have been widely deployed in industrial applications. Yet, due to its simplicity and robustness, the conventional P (Proportional) and PI (Proportional–Integral) control are still the most common methods used in many engineering systems, such as electric power systems, automotive, and Heating, Ventilation and Air Conditioning (HVAC) for buildings, where energy efficiency and energy saving are the critical issues to be addressed. Yet, little has been done so far to explore the effect of its parameter tuning on both the system performance and control energy consumption, and how these two objectives are correlated within the P and PI control framework. In this paper, the P and PI controllers are designed with a simultaneous consideration of these two aspects. Two case studies are investigated in detail, including the control of Voltage Source Converters (VSCs) for transmitting offshore wind power to onshore AC grid through High Voltage DC links, and the control of HVAC systems. Results reveal that there exists a better trade-off between the tracking performance and the control energy through a proper choice of the P and PI controller parameters.

Establishment of stackable community networks

Uma das áreas de investigação em Telecomunicações de interesse crescente prende-se com os futuros sistemas de comunicações móveis de 4a geração e além destes. Nos últimos anos tem sido desenvolvido o conceito de redes comunitárias, no qual os utilizadores se agregam de acordo com interesses comuns. Estes conceitos têm sido explorados de uma forma horizontal em diferentes camadas da comunicação, desde as redes comunitárias de comunicação (Seattle Wireless ou Personal Telco, p.ex.) até às redes de interesses peer-to-peer. No entanto, estas redes são usualmente vistas como redes de overlay, ou simplesmente redes de associação livre. Na prática, a noção de uma rede auto-organizada, completamente orientada ao serviço/comunidade, integralmente suportada em termos de arquitetura, não existe. Assim este trabalho apresenta uma realização original nesta área de criação de redes comunitárias, com uma arquitetura subjacente orientada a serviço, e que suporta integralmente múltiplas redes comunitárias no mesmo dispositivo, com todas as características de segurança, confiança e disponibilização de serviço necessárias neste tipo de cenários (um nó pode pertencer simultaneamente a mais do que uma rede comunitária). Devido à sua importância para os sistemas de redes comunitárias, foi dado particular atenção a aspetos de gestão de recursos e controlo de acessos. Ambos realizados de uma forma descentralizada e considerando mecanismos dotados de grande escalabilidade. Para isso, é apresentada uma linguagem de políticas que suporta a criação de comunidades virtuais. Esta linguagem não é apenas utilizada para o mapeamento da estrutura social dos membros da comunidade, como para, gerir dispositivos, recursos e serviços detidos pelos membros, de uma forma controlada e distribuída.

Electronic health records for mobile citizens: a secure and collaborative architecture

Durante as ultimas décadas, os registos de saúde eletrónicos (EHR) têm evoluído para se adaptar a novos requisitos. O cidadão tem-se envolvido cada vez mais na prestação dos cuidados médicos, sendo mais pró ativo e desejando potenciar a utilização do seu registo. A mobilidade do cidadão trouxe mais desafios, a existência de dados dispersos, heterogeneidade de sistemas e formatos e grande dificuldade de partilha e comunicação entre os prestadores de serviços. Para responder a estes requisitos, diversas soluções apareceram, maioritariamente baseadas em acordos entre instituições, regiões e países. Estas abordagens são usualmente assentes em cenários federativos muito complexos e fora do controlo do paciente. Abordagens mais recentes, como os registos pessoais de saúde (PHR), permitem o controlo do paciente, mas levantam duvidas da integridade clinica da informação aos profissionais clínicos. Neste cenário os dados saem de redes e sistemas controlados, aumentando o risco de segurança da informação. Assim sendo, são necessárias novas soluções que permitam uma colaboração confiável entre os diversos atores e sistemas. Esta tese apresenta uma solução que permite a colaboração aberta e segura entre todos os atores envolvidos nos cuidados de saúde. Baseia-se numa arquitetura orientada ao serviço, que lida com a informação clínica usando o conceito de envelope fechado. Foi modelada recorrendo aos princípios de funcionalidade e privilégios mínimos, com o propósito de fornecer proteção dos dados durante a transmissão, processamento e armazenamento. O controlo de acesso _e estabelecido por políticas definidas pelo paciente. Cartões de identificação eletrónicos, ou certificados similares são utilizados para a autenticação, permitindo uma inscrição automática. Todos os componentes requerem autenticação mútua e fazem uso de algoritmos de cifragem para garantir a privacidade dos dados. Apresenta-se também um modelo de ameaça para a arquitetura, por forma a analisar se as ameaças possíveis foram mitigadas ou se são necessários mais refinamentos. A solução proposta resolve o problema da mobilidade do paciente e a dispersão de dados, capacitando o cidadão a gerir e a colaborar na criação e manutenção da sua informação de saúde. A arquitetura permite uma colaboração aberta e segura, possibilitando que o paciente tenha registos mais ricos, atualizados e permitindo o surgimento de novas formas de criar e usar informação clínica ou complementar.

Seamless integration of heterogeneous networks in multicast environments

Nowadays, communication environments are already characterized by a myriad of competing and complementary technologies that aim to provide an ubiquitous connectivity service. Next Generation Networks need to hide this heterogeneity by providing a new abstraction level, while simultaneously be aware of the underlying technologies to deliver richer service experiences to the end-user. Moreover, the increasing interest for group-based multimedia services followed by their ever growing resource demands and network dynamics, has been boosting the research towards more scalable and exible network control approaches. The work developed in this Thesis enables such abstraction and exploits the prevailing heterogeneity in favor of a context-aware network management and adaptation. In this scope, we introduce a novel hierarchical control framework with self-management capabilities that enables the concept of Abstract Multiparty Trees (AMTs) to ease the control of multiparty content distribution throughout heterogeneous networks. A thorough evaluation of the proposed multiparty transport control framework was performed in the scope of this Thesis, assessing its bene ts in terms of network selection, delivery tree recon guration and resource savings. Moreover, we developed an analytical study to highlight the scalability of the AMT concept as well as its exibility in large scale networks and group sizes. To prove the feasibility and easy deployment characteristic of the proposed control framework, we implemented a proof-of-concept demonstrator that comprehends the main control procedures conceptually introduced. Its outcomes highlight a good performance of the multiparty content distribution tree control, including its local and global recon guration. In order to endow the AMT concept with the ability to guarantee the best service experience by the end-user, we integrate in the control framework two additional QoE enhancement approaches. The rst employs the concept of Network Coding to improve the robustness of the multiparty content delivery, aiming at mitigating the impact of possible packet losses in the end-user service perception. The second approach relies on a machine learning scheme to autonomously determine at each node the expected QoE towards a certain destination. This knowledge is then used by di erent QoE-aware network management schemes that, jointly, maximize the overall users' QoE. The performance and scalability of the control procedures developed, aided by the context and QoE-aware mechanisms, show the advantages of the AMT concept and the proposed hierarchical control strategy for the multiparty content distribution with enhanced service experience. Moreover we also prove the feasibility of the solution in a practical environment, and provide future research directions that bene t the evolved control framework and make it commercially feasible.

Supporting real-time distributed computer-controlled systems with multi-hop P-NET networks

Fieldbus communication networks aim to interconnect sensors, actuators and controllers within process control applications. Therefore, they constitute the foundation upon which real-time distributed computer-controlled systems can be implemented. P-NET is a fieldbus communication standard, which uses a virtual token-passing medium-access-control mechanism. In this paper pre-run-time schedulability conditions for supporting real-time traffic with P-NET networks are established. Essentially, formulae to evaluate the upper bound of the end-to-end communication delay in P-NET messages are provided. Using this upper bound, a feasibility test is then provided to check the timing requirements for accessing remote process variables. This paper also shows how P-NET network segmentation can significantly reduce the end-to-end communication delays for messages with stringent timing requirements.

Adding local priority-based dispatching mechanisms to P-NET networks: a fixed priority approach

In this paper we address the real-time capabilities of P-NET, which is a multi-master fieldbus standard based on a virtual token passing scheme. We show how P-NET’s medium access control (MAC) protocol is able to guarantee a bounded access time to message requests. We then propose a model for implementing fixed prioritybased dispatching mechanisms at each master’s application level. In this way, we diminish the impact of the first-come-first-served (FCFS) policy that P-NET uses at the data link layer. The proposed model rises several issues well known within the real-time systems community: message release jitter; pre-run-time schedulability analysis in non pre-emptive contexts; non-independence of tasks at the application level. We identify these issues in the proposed model and show how results available for priority-based task dispatching can be adapted to encompass priority-based message dispatching in P-NET networks.