In this thesis, we explain linear secret sharing schemes, in particular multiplicative threshold linear secret sharing schemes, over fields and rings in a compact and concise way. We explain two characterisations of linear secret sharing schemes, and in particular, we characterise threshold linear secret sharing schemes. We develop an algorithm to generate all multiplicative $(t+1)$-out-of-$n$ threshold linear secret sharing schemes over a field $mathbb{Z}sb{p}$. For the ring $mathbb{Z}sb{2sp{32}}$, we explain the generation of secret sharing schemes for threshold access structures and prove the non-existence of $(t+1)$-out-of-$n$ threshold linear secret sharing schemes with $n > t+1$.

The SIM cards are going through several new enhancements both in the underlying hardware and its capabilities. They are becoming secure wireless networked devices containing embedded sensors. This thesis assess how this new SIM capabilities together with its pervasiveness and security can support the development and design of trust-based applications. It reviews the new trust possibilities based on the identity factor, connectivity and context-awareness sensors on the SIM. Moreover, we present a specific use-case around a seamless trust builder for social networks, which makes use of sensed inputs towards building hard contextual evidences to trust relations. We conclude with the description of the challenges of building this evidence based trust-builder and the necessary steps to going from the prototype we developed to a real application which may accurately describe trust relations.

Problem description: The objective of this project was to create a simple model of the European power system and to investigate the effect an increasing amount of on- and offshore wind power will have on the North European power market in general and Norway in particular. The scenarios contain increasing amounts of installed wind power capacity, both on- and offshore. Emphasis was to be on the area surrounding the North Sea. The project covers the following issues: - Simulations of simplified power system scenarios set in the years 2005, 2020 and 2030. - Study how an increasing amount of installed wind power will affect energy prices, power production distribution, and power transmission flows. - Investigate how an offshore grid consisting of interconnections between offshore wind farms will affect the system. The task: The simulations in this project were performed using simple power market model. The model included 6 price areas: Denmark West, Denmark East, Norway, Sweden/Finland, Germany and UCTE/Others. The existing market model was modified in the following manner: - Split Norway into three price areas: Norway North, Middle and South - Add the Netherlands - Add the United Kingdom - Add corresponding offshore price areas for areas neighbouring the North Sea. Wind series were generated for each wind generator using reanalysis data. Scenarios were created for the years 2005, 2020 and 2030. In these scenarios, wind power capacities are increasing as time progresses. The 2020 and 2030 scenarios have been simulated with two alternative grid configurations: one where the offshore areas are connected only to their respective onshore areas and one where the offshore areas are also interconnected in an offshore grid. In total 7 different scenarios were simulated. Results: Wind power is able to supplant a large share of energy originally produced by con-ventional thermal generators. The presence of an offshore grid does not have any dramatic effects on energy production for the system, though it is possible to conclude that the presence of an offshore grid may contribute to slightly shift the power system in favour of renewable energy sources. Wind power will cause a significant reduction in energy prices in all areas, resulting in reduced energy costs for the entire system. Analysis of lost wind and hydro power reveals the importance of sufficient transmission capacity when large quantities of wind power are added to the system. Scenario 4 features enormous quantities of lost hydro power in the North and Middle of Norway due to transmission limitations. Analyses of power transmissions reveal that the offshore grid is over-dimensioned. Rationalizing the grid by reducing transmission capacities to more realistic levels will give a more cost-effective solution. This was demonstrated by performing a quick simulation and analysis of a scenario featuring such a rationalized grid. Wind power will cause more frequent variations in hydro power generation, due to balancing needs. Parts of the increased variability in the hydro generators can be explained by the increasing amount of wind power in the system, while other parts are most likely caused by limitations in the simulation model itself. Conclusion: Given the number of assumptions made in the grid, in cost calculations and in the model at large, it is more important to focus on general trends than on concrete numerical values. However, it is clear that increasing the amount of on- and offshore wind power in the European power system will have a beneficial impact to society's energy costs. It is also clear that wind power has the potential to dramatically reduce CO2-emissions caused by power generation. The offshore grid seems to be more beneficial to the power producers than to consumers since it causes slightly higher energy prices and providing a measure of flexibility as to where offshore wind power production is sent. Wind power will present challenges, especially regarding transmission grid development. A sufficiently dimensioned grid will be essential to the successful implementation of such amounts of wind power, both with respect to profitability and in order to avoid waste of potential wind or hydro energy.

Today people from all lifestyles, government officials, researchers and executives use internet. The people start to depend on internet for their daily life. However, the increased dependence comes with a great risk. The popularity and potential of internet attracts users with illegal intentions as well. The attackers generally establish a connection chain by logging in to a number of intermediary hosts before launching an attack at the victim host. These intermediary hosts are called as stepping-stones. On the victim side, it becomes hard to detect that the peer communicating with the victim is whether a real originator of the connection or it is merely acting as an intermediary host in the connection chain. This master dissertation proposed an approach based on Interarrival packet time to distinguish an incoming connection from a connection coming via some intermediary hosts. The proposed approach uses information available at the receiving end and applicable to encrypted traffic too. The approach was successfully tested for SSH, Telnet, FTP, HTTP and SMTP protocols and implemented in to an intrusion detection system for corresponding protocols. The main applications for the proposed approach are Manual intrusion detection, Tor usage detection and Spam messages detection. The approach is also applicable for the digital forensics investigations. Keywords : Network security, Stepping stone detection, Manual intrusion detection, Tor usage detection, Spam detection and Digital forensics investigation.

In the first part of the thesis, we have focused on providing a brief overview of Petname Systems starting from the introductory concept of Entity, Identity and Identity Management with a brief description on different IdM architectures. We have found that the Petname Model is well suited to be integrated in the Personal SP Identity model. We also provided a brief description on Identity Theft and the Phishing attack with different attack techniques and defense mechanisms. Then we summarized the history and evolution of the Petname Model in one place. Previously it was scattered among several web articles. We have formally defined the properties of Petname Systems and explained how this set of properties can satisfy the essential security usability principles. It is our belief that if these properties are followed in developing applications based on the Petname Model, it will improve the user experience and improve overall security by removing security vulnerabilities related to poor usability. The thesis has also analyzed two available Petname-based applications for server identification management and shown that they represent an improvement in usability, but unfortunately do not satisfy all the specified Security Usability principles. In the second part, we have developed the UniPet, a Petname Model based application with similar functionalities of the Petname Tool and the TrustBar, that utilizes the concept of aiding user in identifying SP identities securely on their side. We have deployed several technologies to meet the complex level of interaction the UniPet asks for. We have provided a brief discussion on each of the technologies to better understand the UniPet architecture. We have also shown that the UniPet has been a major improvement on GUI and on the security usability issues over those two applications. The UniPet satisfies all the properties of a Petname System and thus is fully compliant with the Security Usability principles. We believe that the UniPet will provide the users with an improved and secure browsing experience.

Session Initiation Protocol (SIP) has been used for signaling in many Voice over IP (VoIP) applications. Being more cost-effective than conventional circuit-switched systems, IP-based telecommunication systems are extensively employed by many service providers. As these systems gain more popularity, the need for dimensioning of such systems grows correspondingly. Moreover, accurate information about system capacity is necessary for future improvements of the system, as well as service provision and implementation planning. For these reasons, a solution supporting system performance evaluation is useful and beneficial in several ways. The goal of this research was to develop a performance evaluation framework for a SIP-based telecommunication system. The developed framework facilitates measurements of the maximum number of requests which can be processed by a system, and the amount of time required for call session establishment. With a user-friendly interface, the framework enables system testers to perform experiments using simulated SIP traffics, as well as to deal with results interpretation easily. In order to achieve the objective, studies of related technologies and available tools for SIP traffic generation have been carried out. Afterwards, the performance evaluation framework is designed and implemented. Lastly, the developed framework is used for evaluating the performance of EasyVPaBX, a SIP-based call handling system, in various system configurations. Keywords: SIP, Performance, Evaluation, Dimensioning, Measurement

With the continuous development of the Internet technologies new routing requirements have surfaced. In response, several adaptive, stochastic routing algorithms have been purposed. The Cross Entropy Ant System (CEAS) is an adaptive, robust and distributed routing and management system based on the swarm intelligence. Several prototype implementations and enhancements have been made on this system, however the level of TCP friendliness the CEAS may provide is yet an important issue. In order to investigate the level of TCP friendliness, the behavior of the CEAS system during different network dynamics needs to be understood. For this reason, the behavior of the CEAS system under different network event and its corresponding effects on TCP performance is examined first using a simple network. Later the level of TCP performance is measured on complex networks. Also the load sharing capabilities of the CEAS system is investigated the efficiency of the system to manage and update according to the network load. Additionally the results are compared against the results obtained from the standard Link State Routing protocol and the Distance Vector Routing protocol under similar conditions. In this work, we find that the update process in response to the change in network dynamics is slower on CEAS compared to the other systems. However, the update process speeds up with the increase in the ant rates. During such period the use of multiple path reduces the TCP performance. We also find that large amount of packets loop around some links during link failures. Such looping reduces the TCP performance significantly. However, implementing previous hop memory technique removes such loops and also help TCP resume transmission immediately after the link failure. Compare to the LSRP and the DVR, we find that CEAS manages network resources more efficiently to produce higher TCP performance. We find that the CEAS diverts the data traffic on the basis of the quality of the path rather than the length of the path. We also find that the CEAS system handles multiple TCP stream independently with equal priority. But the smaller transition delay on the ants compared to the data packet reduces the TCP performance to some extent. However, forcing the ants to experience longer queuing delay according to the traffic load improves the TCP performance as well as helps CEAS update more accurately.

Reducing grid harmonics and increasing grid stability are both major issues for the operation of rail vehicles. For stability investigation of complex power systems, simplified system models are in need in order to reduce the model complexity and the simulation time. In this thesis work the effect of modelling a voltage source converter (VSC) for traction power system with and without the detailed pulse width modulated (PWM)-switch model is modeled. Effect of different operating conditions for the switching model on the harmonic content of the system is also analyzed. The same disturbance is imposed for the two models and the low frequency oscillation of the DC- link voltage response is compared and analyzed. The effect of semiconductor switching on the stability limit of the system is also investigated. Furthermore, the performance of a PWM time delay compensation technique during transient is analyzed. The result shows that in the model including the switching the DC- link voltage oscillation is damped and has a better stability margin compared to the average model. In the detailed switching model a converter loss is included while in the average model a no loss ideal case scenario is considered. As far as the switching harmonic is considered, the switching model with an operational condition of a high switching frequency and a switching frequency with an integer multiple of the fundamental frequency has a low harmonic content on the system compared to the operating condition of a low switching frequency which is not integer multiple of the fundamental frequency. A unipolar voltage switching technique has also a tremendous advantage over the bipolar voltage switching technique as far as this harmonic content in the system is concerned. Using a unipolar voltage switching technique reduces the harmonic content in the overall railway system. For triangular carrier modulators, an average time delay from the reference voltage to the actuated PWM terminal voltage of half the switching frequency is assumed .The delay in DC- link voltage control loop caused by the switching dead-time effect was improved by compensation of dead-time in the inverse-park transformation block of the control loop. The comparison of the compensated and non-compensated model proves that the compensated model is better in terms of the overshoot of amplitude of transient.

In order to comply with governmentally announced greenhouse gas emission reductions goals and to consolidate an independent and stable electric power and energy supply, Norway must increase its installed renewable energy based power generation capacity. Profitability estimations, today’s available technical solutions and regulations concerning preservation of natural resources leave construction of new small hydro power plants behind as the most plausible alternative together with construction of wind farms. Global trends such as technologic development and progress and the public opinion indicate that future wind farms in Norway will be located offshore. The assumption is supported by the recent handing out of a concession to an offshore wind farm project for the first time in Norwegian history. The projects name is Havsul 1 and the licence involves construction of 350 MW offshore wind power. Havsul 1 will be located in Mid-Norway, which is the region in Norway where the Norwegian Transmission System Operator (TSO) Statnett is most concerned about their ability to execute their task of assuring safety of power supply in the future. The concern owes to lack of generation capacity and transmission constraints. Experience show that commissioning of large offshore wind farms will impose power balance associated challenges on the TSO. By applying a slightly modified model developed by Sintef of the Nordel synchronous system in the power simulation tool DIgSILENT PowerFactory, grid connection of 350 MW and 1000 MW offshore wind farms to a bus bar representing Mid-Norway were investigated, targeting reduction of frequency excursions. To execute the reduction task, a so-called centralised Load Frequency Control (LFC) scheme was implemented and four hydro power plants were designated to provide regulating power pursuant to a priority key that used their response times as input. To simulate power fluctuations in the time span of hours, real time wind data acquired from the Danish offshore wind farm Horns Rev 1 was used as input in the offshore wind farm model. These data were kindly provided by the Swedish power company Vattenfall. The power fluctuations simulations showed that LFC is a well-fitted tool for bridling frequency excursions in the Nordel synchronous system caused by fluctuating power generation in an offshore wind farm. During the power fluctuations, which were of a particularly challenging kind, the system frequency complied with Statnett’s normal operation requirements of 50 ±0.1 Hz. The results weren’t too surprising since LFC has been used successfully in Europe for many years. They did however show that the amounts of the so-called frequency controlled normal operation reserves in Nordel may need to be expanded in case of a massive expansion in wind power in Norway. Fault Ride Through (FRT) investigations were also conducted by introducing 3-phase short circuit faults at selected bus bars. The simulations showed that the FRT requirements in Norway were not violated even in the worst case simulations. Some choices regarding the setup of the model may have exalted the simulation results.

The work consists in developing a power conversion unit for solar panel connected to the grid. This unit will be a single phase inverter in the low power range (24/48 V - 100/200 W), with digital control and without a DC-DC stage. The final system should be suitable for laboratory work. This master project will be complete, starting with a detailed specification of the project and finishing with an experimental validation.