M.Com. (Computer Science) / The area covered in this study is that of logical security models. A logical security model refers to the formal representation of a security policy which allows the subsequent movement of rights between subjects and objects in a system. The best way to illustrate the goal of this study, is with the following abstract from the submitted article, which originated from this study. 'The original protection graph rewriting grammar used to simulate the different operations of the Take/Grant model is reviewed. The productions of the PGR-grammar is then expanded, by adding a new context which is based on the different security classes found in the Bell Grid LaPadula model [14].' The first goal of this study was to take the Take/Grant security -model and expand it. This expansion included the concept of assigning a different security class to each subject and object in the model. This concept was derived from the Bell and LaPadula model as discussed in chapter 2 of this study. The next goal that was defined, was to expand the PGR-grammar of [28], so that it would also be able to simulate .the operations of this expanded Take/Grant model. The .PGR-grammar consisted of different permitting and forbidding node and edge contexts. This PGR-grammar was expanded by adding an additional context to the formal representation. This expansion is explained in detail in chapter 5 of this study. The third goal was to take the expansions, mentioned above, and implement them in a computer system. This computer system had to make use of an expert. system in order to reach certain conclusions. Each of the operations of the Take/Grant model must be evaluated, to determine whether that rule can be applied or not. The use of the expert system is explained in chapters 6 and 7 of this study. This study consists out of eight chapters in the following order. Chapter 2 starts of with an introduction of some of the most important logical security models. This chapter gives the reader background knowledge of the different models available, which is essential for the rest of the study. This chapter, however, does not discuss the Take/Grant model in detail. This is done in chapter 3 of the study. In this chapter the Take Grant model is discussed as a major input to this study. The Send Receive model is also discussed as a variation of the Take/Grant model. In the last section of the chapter a comparison is drawn between these two models. Chapter 4 formalizes the Take/Grant model. The protection graph rewriting grammar (PGR-grammar), which is used to simulate the different operations of the Take/Grant model, is introduced...

M.Com. (Computer Science) / Please refer to full text to view abstract

M.Sc. (Computer Science) / Computer security is a key component in any computer system. Traditionally computers were not connected to one another. This centralized configuration made the implementation of computer security a relatively easy task. The closed nature of the system limited the number of unknown factors that could cause security breaches. The users and their access rights were generally well defined and the system was protected from outside threats through simple, yet effective control measures. The evolution of network environments changed the computer environment and in effect also computer security. It became more difficult to implement protection measures because the nature of the environment changed from closed to open. New defenses had to be developed for security issues like unknown parameters, increased points of attack, unknown paths of information etc. Businesses and the general public today depend on network systems and no person can ignore these and other related security problems. The widespread publicity of attacks, and better customer awareness on security issues, created a need for new solutions for computer security. Security organisations, businesses and universities are addressing these problems through the development of security standards and security solutions.Today computer systems are becoming more "safe" through new products such as encryption and decryption algorithms, single-sign on password facilities, biometrics systems, smart cards, firewalls etc. Another important security consideration is Access Control. Access Control is responsible for controlling the actions of users to resources.

M.Sc. (Computer Science) / Please refer to full text to view abstract

A hybrid and configurable access control model is designed to satisfy the requirements of using different access control models in the same schema. The idea is arised to completely combine and configure the two main access control models, discretionary and mandatory which have been widely used in many systems so far with their advantages and disadvantages. The motivation originates from the fact that / in real life usage, discretionary based systems needs some strict policies and mandatory based systems needs some flexibility. The model is designed to combine these two appoaches in a single and configurable model, with some required real life extensions, in a conflictfree fashion and configurable degree of combination. Implementation of the model has been done and main important cases which shows the power and expressiveness of the model are designed and implemented. The authorization process is in the responsibility of the model which can be combined with secured authentication and auditing schemas. The new approaches as Role-Based, Context-Based and Temporal access control can easily be embedded in the model due to its generic and modular design.

When sharing data across multiple sites, service applications should not be trusted automatically. Services that are suspected of faulty, erroneous, or malicious behaviors, or that run on systems that may be compromised, should not be able to gain access to protected data or entrusted with the same data access rights as others. This thesis proposes a context flow model that controls the information flow in a distributed system. Each service application along with its surrounding context in a distributed system is treated as a controllable principal. This thesis defines a trust-based access control model that controls the information exchange between these principals. An online monitoring framework is used to evaluate the trustworthiness of the service applications and the underlining systems. An external communication interception runtime framework enforces trust-based access control transparently for the entire system.

published_or_final_version / abstract / Computer Science and Information Systems / Master / Master of Philosophy

published_or_final_version / Computer Science / Master / Master of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The need for Shared Situational Awareness (SSA) in accomplishing joint missions by coalition militaries, law enforcement, the intelligence community, and the private sector creates a unique challenge to providing access control. In this thesis we investigate the capabilities and limitations of Role-Based Access Control (RBAC) to control the dissemination of SSA in a coalition environment. Our case study is that of controlling access to SSA in the Maritime Domain Awareness (MDA) environment. MDA exemplifies both rapid change in membership of coalitions and the roles of coalition participants. We explore the access policy and roles played by the participants in the MDA environment, in addition to the characteristics of those roles. We make use of feasible scenarios to provide us with a base for applying models to the situation. The models that are applied to the scenario provide the formal methods that prove that RBAC policies and derivatives such as Distributed Role Based Access Control (DRBAC), Coalition Based Access Control (CBAC) and Temporal Role Based Access Control (TRBAC) can be used in conjunction with the Information Broker (IB) concept to provide adequate access control policies.