Leung Kwai Ki. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 152-161). / Abstracts in English and Chinese. / Abstract --- p.i / 論文摘要 --- p.iii / Acknowledgements --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Contributions of this thesis --- p.3 / Chapter 1.2 --- Thesis structure --- p.3 / Chapter 2 --- Mobile Agent Paradigm --- p.6 / Chapter 3 --- Analysis on Fault-tolerant Mechanisms --- p.9 / Chapter 3.1 --- Design considerations --- p.9 / Chapter 3.1.1 --- Infrastructure failure --- p.10 / Chapter 3.1.2 --- Unfavorable outcomes --- p.10 / Chapter 3.1.3 --- Exactly-once property --- p.11 / Chapter 3.1.4 --- Blocking --- p.13 / Chapter 3.1.5 --- Network partitioning --- p.14 / Chapter 3.1.6 --- Domino effect --- p.15 / Chapter 3.1.7 --- Inter-agent communications and global consistency --- p.16 / Chapter 3.1.8 --- Platform dependent and platform independent approaches . . --- p.17 / Chapter 3.1.9 --- ACID in mobile agent systems --- p.17 / Chapter 3.2 --- Basic Mechanisms --- p.18 / Chapter 3.2.1 --- Replication mechanisms --- p.19 / Chapter 3.2.2 --- Checkpointing and logging --- p.22 / Chapter 3.2.3 --- Comparison between the replication and checkpointing mechanisms --- p.25 / Chapter 3.2.4 --- Rollback --- p.26 / Chapter 3.2.5 --- Diagnosis and planning --- p.26 / Chapter 3.3 --- Analysis of current approaches --- p.27 / Chapter 3.3.1 --- Infrastructure failure handling --- p.27 / Chapter 3.3.2 --- Unfavorable outcomes prevention --- p.38 / Chapter 3.3.3 --- Diagnosis and planning --- p.40 / Chapter 3.3.4 --- Summary --- p.42 / Chapter 3.4 --- Related work of analysing fault-tolerant mechanisms --- p.43 / Chapter 3.5 --- Summary --- p.43 / Chapter 4 --- Flexible Monitor Chain --- p.45 / Chapter 4.1 --- Overview --- p.45 / Chapter 4.2 --- Assumptions --- p.47 / Chapter 4.3 --- Protocol --- p.48 / Chapter 4.4 --- Different scenarios of failure --- p.51 / Chapter 4.5 --- Performance evaluation --- p.53 / Chapter 4.5.1 --- Simulation model --- p.53 / Chapter 4.5.2 --- Results and discussions --- p.55 / Chapter 4.6 --- Discussions --- p.58 / Chapter 4.6.1 --- Preservation of the exactly-once property --- p.58 / Chapter 4.6.2 --- High flexibility in the management of monitors --- p.59 / Chapter 4.6.3 --- High stability --- p.59 / Chapter 4.6.4 --- Feasibility to be applied in an open environment --- p.60 / Chapter 4.6.5 --- Overcoming the problem of network partitioning --- p.60 / Chapter 4.6.6 --- Lightweightedness --- p.60 / Chapter 4.6.7 --- Global consistency and domino effect --- p.61 / Chapter 4.7 --- Summary --- p.61 / Chapter 5 --- Transaction and Rollback Models --- p.62 / Chapter 5.1 --- Simple E-Marketplace --- p.64 / Chapter 5.2 --- Transaction and rollback models --- p.66 / Chapter 5.2.1 --- Distributed transaction without rollback (Ml) --- p.67 / Chapter 5.2.2 --- A chained-transaction (M2) --- p.67 / Chapter 5.2.3 --- A chained-transaction with flexible rollback scheme (M3) . --- p.69 / Chapter 5.3 --- Performance evaluation --- p.71 / Chapter 5.3.1 --- Experimental setup --- p.71 / Chapter 5.3.2 --- Results and discussions --- p.73 / Chapter 5.4 --- Summary --- p.77 / Chapter 6 --- Dependent Partial Rollback --- p.79 / Chapter 6.1 --- Overview --- p.80 / Chapter 6.2 --- Formal representation --- p.83 / Chapter 6.3 --- Assumptions --- p.85 / Chapter 6.4 --- Protocol --- p.86 / Chapter 6.5 --- Discussions --- p.89 / Chapter 6.5.1 --- Assumption: Weak migration and the effect of a stage --- p.90 / Chapter 6.5.2 --- Assumption: Failure free environment --- p.92 / Chapter 6.5.3 --- Assumption: guarantee of rollback --- p.92 / Chapter 6.5.4 --- Assumption: Domino effect --- p.93 / Chapter 6.5.5 --- Platform independence --- p.94 / Chapter 6.5.6 --- High efficiency --- p.94 / Chapter 6.5.7 --- Stage-based design --- p.94 / Chapter 6.5.8 --- Autonomy --- p.95 / Chapter 6.5.9 --- High flexibility --- p.95 / Chapter 6.6 --- Related Works --- p.96 / Chapter 6.7 --- Implementation of SEMP with dependent partial rollback --- p.97 / Chapter 6.8 --- Summary --- p.99 / Chapter 7 --- Analysis on Security Mechanisms --- p.100 / Chapter 7.1 --- Classifications of security issues --- p.100 / Chapter 7.2 --- Analysis of current approaches --- p.103 / Chapter 7.2.1 --- Encrypting functions and data --- p.103 / Chapter 7.2.2 --- Computing with encrypted functions --- p.106 / Chapter 7.2.3 --- Trusted environment --- p.107 / Chapter 7.2.4 --- Limitation of execution time --- p.109 / Chapter 7.2.5 --- Execution tracing --- p.110 / Chapter 7.3 --- Execution tracing --- p.111 / Chapter 7.4 --- Summary --- p.116 / Chapter 8 --- Execution Tracing with Randomly-Selected Hosts --- p.117 / Chapter 8.1 --- Overview --- p.117 / Chapter 8.2 --- Assumptions --- p.119 / Chapter 8.3 --- Protocol --- p.120 / Chapter 8.4 --- Performance evaluation --- p.121 / Chapter 8.4.1 --- Simple sgent system --- p.121 / Chapter 8.4.2 --- Experimental setup --- p.123 / Chapter 8.4.3 --- Results and discussions --- p.123 / Chapter 8.5 --- Discussions --- p.124 / Chapter 8.5.1 --- Detect the modifications of the code and data --- p.124 / Chapter 8.5.2 --- Against masquerade --- p.125 / Chapter 8.5.3 --- Against skip from re-execution --- p.125 / Chapter 8.5.4 --- Against collaboration --- p.125 / Chapter 8.5.5 --- Higher privacy --- p.126 / Chapter 8.5.6 --- Low workload on the trusted host --- p.126 / Chapter 8.5.7 --- Feasible to be used in the open environment --- p.126 / Chapter 8.5.8 --- Secure data collection --- p.126 / Chapter 8.5.9 --- Comparison with the existing approaches --- p.127 / Chapter 8.5.10 --- Weaknesses --- p.128 / Chapter 8.6 --- Optimizations --- p.128 / Chapter 8.6.1 --- Sampling --- p.128 / Chapter 8.6.2 --- Inserting sub-state and request on demand --- p.129 / Chapter 8.7 --- Summary --- p.129 / Chapter 9 --- FTS Framework --- p.131 / Chapter 9.1 --- Assumptions --- p.132 / Chapter 9.2 --- Abstract framework --- p.132 / Chapter 9.2.1 --- Different agents and their duties --- p.132 / Chapter 9.2.2 --- Messaging --- p.135 / Chapter 9.3 --- Implementation in Jade --- p.135 / Chapter 9.3.1 --- Characteristics of Jade --- p.137 / Chapter 9.3.2 --- Core implementation details --- p.138 / Chapter 9.4 --- Performance Evaluation --- p.144 / Chapter 9.4.1 --- Experimental Setup --- p.144 / Chapter 9.4.2 --- Experimental Results --- p.145 / Chapter 9.5 --- Discussions --- p.147 / Chapter 9.5.1 --- High worker survivability --- p.148 / Chapter 9.5.2 --- Low blocking chance --- p.148 / Chapter 9.5.3 --- Trusted Third Party Hosts --- p.149 / Chapter 9.6 --- Summary --- p.149 / Chapter 10 --- Conclusions and Future Works --- p.150 / Bibliography --- p.152 / Publications --- p.161

We address the security issue of the data which mobile agents gather as they are traversing the Internet. Our goal is to devise a security protocol that truly secures the data which mobile agents gather. Several cryptographic protocols were presented in the literature asserting the security of gathered data. Formal verification of the protocols reveals unforeseen security flaws, such as truncation or alteration of the collected data, breaching the privacy of the gathered data, sending others data under the private key of a malicious host, and replacing the collected data with data of similar agents. So the existing protocols are not truly secure. We present an accurate security protocol which aims to assert strong integrity, authenticity, and confidentiality of the gathered data. The proposed protocol is derived from the Multi-hops protocol. The protocol suffers from security flaws, e.g. an adversary might truncate/ replace collected data, or sign others data with its own private key without being detected. The proposed protocol refines the Multi-hops protocol by implementing the following security techniques: utilization of co-operating agents, scrambling the gathered offers, requesting a visited host to clear its memory from any data acquired as a result of executing the agent before the host dispatches the agent to the succeeding host in the agent???s itinerary, and carrying out verifications on the identity of the genuine initiator at the early execution of the agent at visited hosts, in addition to the verifications upon the agent???s return to the initiator. The proposed protocol also implements the common security techniques such as public key encryption, digital signature, etc. The implemented security techniques would rectify the security flaws revealed in the existing protocols. We use STA, an infinite-state exploration tool, to verify the security properties of a reasonably small instance of the proposed protocol in key configurations. The analysis using STA reports no attack. Moreover, we carefully reason the correctness of the security protocol for a general model and show that the protocol would be capable of preventing or at least detecting the attacks revealed in the existing protocols.

There are many variants of leader election algorithm in distributed networks. In this research, an agent based approach to leader election in distributed networks is investigated. Agents have shown to be useful in several ways. In the theoretical perspective, agents sometime help in reducing the message complexity of the system and sometimes help in lowering time complexity. In a more practical sense, agents perform operations independent of the processors, thereby lending a more flexible algorithm supporting different types of networks.

No description available.

Network decontamination is a well known mobile agent problem with many applications. We assume that all nodes of a network are contaminated (e.g., by a virus) and a set of agents is deployed to decontaminate them. An agent passing by a node decontaminates it, however a decontaminated node can be recontaminated if any of its neighbours is contaminated. In the vast literature a variety of models are considered and different assumptions are made on the power of the agents. In this thesis we study variation of the decontamination problem in mesh and tori topologies, under the assumption that when a node is decontaminated, it is immune to recontamination for a predefined amount of time t (called immunity time). After the immunity time is elapsed, recontamination can occur. We focus on three different models: mobile agents (MA), cellular automata (CA), and mobile cellular automata (MCA). The first two models are commonly studied and employed in several other contexts, the third model is introduced in this thesis for the first time. In each model we study the temporal decontamination problem (adapted to the particular setting) under a variety of assumptions on the capabilities of the decontaminating elements (agents for MA and MCA, decontaminating cells for CA). Some of the parameters we consider in this study are: visibility of the active elements, their ability to make copies of themselves, their ability to communicate, and the possibility to remember their past actions (memory). We describe several solutions in the various scenarios and we analyze their complexity. Efficiency is evaluated slightly differently in each model, but essentially the effort is in the minimization of the number of simultaneous decontaminating elements active in the system while performing the decontamination with a given immunity time.

As the important of global data sharing is widely utilized in many corporations, it is well know as multidatabase. However, the system occurs and interesting issue. It is global constraint checking. It is mandatory to set up a potential checking application inside; therefore, global constraint checking needs these following essential characteristics such as 1) mobility 2) heterogeneity and 3) robustness. The effective way to implement the checking is using Aglets which is well recognized as one of the good mobile agent. Aglets is very appropriate because it contains the ability of mobility, and it is 100% Java compatible and open source. In this thesis, we construct the application of global constraint checking following these steps. To begin with starting step, user enters the insert statement. The system then receives the input, and then connection with Global Metadatabase begins. It will optimize the proper route for checking. Its optimized data will be sent out with the mobile agents to the remote sites. Eventually, results will be collected and show to user.

Network decontamination is a well known mobile agent problem with many applications. We assume that all nodes of a network are contaminated (e.g., by a virus) and a set of agents is deployed to decontaminate them. An agent passing by a node decontaminates it, however a decontaminated node can be recontaminated if any of its neighbours is contaminated. In the vast literature a variety of models are considered and different assumptions are made on the power of the agents. In this thesis we study variation of the decontamination problem in mesh and tori topologies, under the assumption that when a node is decontaminated, it is immune to recontamination for a predefined amount of time t (called immunity time). After the immunity time is elapsed, recontamination can occur. We focus on three different models: mobile agents (MA), cellular automata (CA), and mobile cellular automata (MCA). The first two models are commonly studied and employed in several other contexts, the third model is introduced in this thesis for the first time. In each model we study the temporal decontamination problem (adapted to the particular setting) under a variety of assumptions on the capabilities of the decontaminating elements (agents for MA and MCA, decontaminating cells for CA). Some of the parameters we consider in this study are: visibility of the active elements, their ability to make copies of themselves, their ability to communicate, and the possibility to remember their past actions (memory). We describe several solutions in the various scenarios and we analyze their complexity. Efficiency is evaluated slightly differently in each model, but essentially the effort is in the minimization of the number of simultaneous decontaminating elements active in the system while performing the decontamination with a given immunity time.

No description available.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains vii, 61 p. : ill. Includes abstract. Includes bibliographical references (p. 50-52).

There are many variants of leader election algorithm in distributed networks. In this research, an agent based approach to leader election in distributed networks is investigated. Agents have shown to be useful in several ways. In the theoretical perspective, agents sometime help in reducing the message complexity of the system and sometimes help in lowering time complexity. In a more practical sense, agents perform operations independent of the processors, thereby lending a more flexible algorithm supporting different types of networks.