Amidst the wild west of user authentication, this study introduces a new sheriff in town: the Self-Sovereign Authentication Scheme (SSASy). Traditional authentication methods, like passwords, are often fraught with usability and security concerns, leading users to find workaround ways that compromise the intended security. Federated Identities (FI) offer a convenient alternative, yet, they infringe on users' sovereignty over their identity and lead to privacy concerns. To address these challenges, this study proposes SSASy, which leverages cryptography and browser technology to provide a sovereign, usable, and secure alternative to the existing user authentication schemes. The proposal, which is a proof-of-concept, is comprised of a core library, which provides the authentication protocol to developers, and a browser extension that simplifies the authentication process for users. SSASy is available as an open-source project on GitHub for practical demonstration on multiple browser stores, bringing our theoretical study into the realm of tangible, real-world application. SSASy is evaluated and compared to existing authentication schemes using the "Usability-Deployability-Security" (UDS) framework. The results demonstrate that, although other authentication schemes may excel in a specific dimension, SSASy delivers a more balanced performance across the three dimensions which makes it a promising alternative.

No description available.

No description available.

Neste trabalho, estudamos o problema de corte bidimensional multiperíodo com sobras aproveitáveis, que consiste em cortar objetos grandes visando a produção de um conjunto de itens menores. Supomos um horizonte de planejamento finito com uma quantidade finita de períodos entre os tempos inicial e final. Primeiramente consideramos uma versão determinística em que conhecemos, à priori, os itens solicitados em uma ordem de trabalho e o custo dos objetos a cada período. Algumas das sobras geradas durante o processo de corte dos itens solicitados em um período podem ser utilizadas como objetos no futuro. As sobras que podem ser usadas no futuro são denominadas sobras aproveitáveis. De forma geral, uma sobra é considerada aproveitável se possui dimensões iguais ou superiores as de algum item de uma lista pré-definida para o período. O objetivo é minimizar o custo total dos objetos utilizados para satisfazer a ordem de trabalho dos itens solicitados de todo o horizonte considerado. Havendo soluções com o mesmo custo, desejamos encontrar aquela que, no fim do horizonte de tempo considerado, maximize o valor das sobras aproveitáveis remanescentes. Apresentamos uma modelagem matemática do problema usando uma formulação em dois níveis, que é transformada em um modelo de programação linear inteira mista, devido às características do problema. Considerando a dificuldade em resolver o modelo desenvolvido, apresentamos uma proposta de uma abordagem heurística baseada em Programação Dinâmica Aproximada (PDA) para lidar com o problema proposto. Outras opções baseadas em estratégias do tipo horizonte rolante e relax-and-fix também são consideradas. Consideramos também o cenário onde não conhecemos de antemão os itens da ordem de trabalho e o custo dos objetos, mas temos informações das distribuições de probabilidade de ambos. Nesse caso, apresentamos uma abordagem baseada em programação dinâmica aproximada para estimar a melhor estratégia a ser seguida em cada período. Comparamos os resultados obtidos pela PDA com os resultados encontrados por um método guloso. Em cenários adequados, os resultados mostram que a PDA consegue soluções superiores ao método guloso. / In this research, we study the multi-period two-dimensional cutting problem with usable leftover, which consists of cutting objects to produce a set of items. We assume a finite planning horizon with a finite amount of periods between the initial and final times. First we consider a deterministic version in which we know, a priori, the set of ordered items and the cost of the objects at each period. Some of the leftovers generated during the cutting process of the ordered items in a period may be used as objects in the future. The leftovers that can be used in the future are called usable leftovers. In general, a leftover is considered usable if it has dimensions equal to or greater than that of some item from a predefined list for the period. The goal is to minimize the total cost of the objects used to cut the set of ordered items of the entire considered horizon. If there are solutions with the same cost, we wish to find one that, at the end of the considered time horizon, maximizes the value of the remaining usable leftovers. We present a mathematical model of the problem using a bilevel formulation, which is transformed into a mixed integer linear programming model, due to the characteristics of the problem. Considering the difficulty in solving the developed model, we propose a heuristic approach based on approximate dynamic programming (ADP) to deal with the proposed problem. Other options based on the rolling horizon and relax-and-fix strategies are also considered. We also consider the scenario where we do not know in advance the set of ordered items and the cost of the objects, but we have information about the probability distributions of both. In this case, we present an approach based on approximate dynamic programming to estimate the best strategy to be followed at each period. We compared the results obtained by the ADP with the results found by a greedy method. In suitable scenarios, the results show that the ADP achieves superior solutions to the greedy method.

A cavitação e a dinâmica de bolhas são tópicos bastante recorrentes na literatura, devido sobretudo a seus efeitos em diversos tipos de fenômenos, como transferência de calor e escoamento em tubos. Considerando fases líquidas, sabe-se que estas estruturas de cavidade estão normalmente associadas ao equilíbrio metaestável, alcançado devido a quedas locais de pressão ou ao superaquecimento de uma substância pura (ou quase). Nestes casos é necessária a inicialização da mudança de fase através de algum mecanismo adequado, o qual gera uma sequência rápida de fenômenos. Apesar de comumente associado a danos, recentemente vários estudos vêm mostrando aplicações práticas deste tema, além de um campo ainda pouco explorado, que é o das macro cavidades. Essas cavidades podem ser geradas através do aquecimento de água a baixa pressão, sob condições específicas, criando sequências explosivas e formando movimentos como pistão para a água no interior de um invólucro convenientemente dimensionado. Este fenômeno mostra-se semelhante em diversos aspectos às micro cavidades, mais especificamente às cavidades próximas a superfícies livres, embora, sem dúvida, em escala muito maior. Os aspectos mencionados foram filmados com câmeras de alta velocidade e as características observadas foram comparadas com aquelas observadas em micro escala. Vários testes foram desenvolvidos de forma a melhor entender a dinâmica da formação e colapso dessas estruturas, sobretudo levando em conta um comportamento mais unidimensional para a evolução da bolha. Através de várias aproximações e análise de diferentes hipóteses para a variação de pressão e para a força de resistência, soluções analíticas e numéricas foram obtidas para a força exercida no fundo do contêiner e para a expansão e colapso das bolhas ao longo do tempo. As soluções propostas, em comparação com os dados experimentais, mostraram boa concordância entre si, sugerindo que os aspectos fundamentais da dinâmica da cavidade foram devidamente considerados e quantificados. / Cavitation and bubble dynamics are fairly recurring topics in literature, mostly due to their effects in various types of phenomena such as heat transfer and flow in pipes. Considering liquid phases, it is known that these cavity structures are normally associated with the metastable equilibrium, reached due to local pressure drop or overheating of a pure substance (or nearly so). In these cases, the phase change require a startup via some appropriate mechanism, which generates a fast sequence of phenomena. Although commonly associated with damage, recently several studies shown practical applications of these topics, and a still little explored field emerged, which is the field of macro cavities. These cavities can be generated by heating water at a low pressure, under specific conditions, creating an explosive sequences and forming piston like movements for the water inside a properly scaled casing. This phenomenon appears to be similar in many aspects to micro cavities, more specifically for cavities near free surfaces, although, without doubt, on a much larger scale. The mentioned aspects were filmed with high-speed cameras and the main features were compared with those observed in micro scale. Several tests have been developed to better understand the dynamics of the formation and collapse of these structures, especially taking into account a more one-dimensional behavior to the evolution of the bubble. Through various approximations, and analysis of different assumptions for the variation of pressure and the resistance force, analytical and numerical solutions were obtained for the force exerted on the bottom of the container and the expansion and collapse of bubbles over time. The proposed solutions in comparison with experimental data showed good agreement between each other suggesting that the fundamental aspects of the dynamics of the cavity were properly considered and quantified.

High-pass filtering that is one of the most efficient methods in removing long-period noise of accelerograms is investigated for its effect on nonlinear oscillator deformation response. Within this context, uncertainty in filter cut-off periods that would significantly modify the low-frequency content of accelerograms come into prominence for obtaining reliable long-period displacement response. Analog and digital ground-motion records from recently compiled Turkish strong-motion database are used and these records are high-pass filtered with a consistent methodology by randomly generated filter cut-offs that represent different filter cut-off decisions of the analysts. The uncertainty in inelastic spectral and residual displacements (SDIE and SDR, respectively) due to variations in filter cut-offs is examined to derive the usable period ranges where the effect of high-pass filtering is tolerable. Non-degrading, stiffness degrading and stiffness and strength degrading oscillator behavior are considered in these analyses. The level of nonlinear behavior in single degree of freedom (SDOF) response is described by varying the yield strength (R, normalized yield strength) and displacement ductility (&micro / ) levels. The usable period ranges that depend on magnitude, recording quality, level of inelasticity and level of degradation are determined for SDIE through robust probabilistic methodologies.

<p>Användbarhet är en term som används för att bedöma kvaliteten hos ett gränssnitt. God användbarhet är viktig då den ger en ökad produktivitet och andra affärsfördelar i form av färre misstag och bättre kvalitet på slutprodukten. Användbarhet är en viktig designprincip men är en svår egenskap att uppfylla hos applikationer. </p><p>Studien behandlar användbarhet ur olika perspektiv, dels det teoretiska genom litteraturgenomgång, dels det praktiska genom intervjuer och observationer. Syftet var att förklara vad användbarhet är, hur det bedöms och vad man kan göra för att bygga in egenskapen i applikationer man utvecklar. För att exemplifiera och finna verklig förankring har jag valt att observera hur användare interagerar med ett existerande gränssnitt för bibliotek, Horizon. </p><p>Slutsatser kring studien är att Horizon inte används till allt den var tänkt att användas till, vilket i princip är ett dåligt betyg för en applikation. Samtidigt är detta inget större problem då den negativa verkan på verksamheten kan i det här fallet vara en definitionsfråga: är studenternas produktivitet när det gäller att söka och beställa litteratur kritisk? </p><p>När det gäller användbarhet i utvecklingsskedet kan man konstatera att även om intentionerna varit goda så har användbarhetsarbetet kring Horizon inte infriat förväntningarna. Vad som gått fel är varken sensationellt eller ovanligt; det har handlat om avsaknaden av slutanvändarens perspektiv, organisatoriska problem och möjligen också bristande kunskap om användbarhet i en eller annan form. En betydelsefull insikt som inte nämns i litteraturen men som togs upp är att beakta leverantörens marknadsställning när man ska köpa ett system. Trots bristerna, som ofta relaterar till brott mot designkonventioner, upplevs Horizon som ett bra och ändamålsenligt verktyg av sina användare. </p> / <p>Usability denotes the quality of a user interface. Even though usability is an important design principle, efforts to incorporate this quality in applications often fail. In this paper I study usability from a theoretical and a practical perspective. The goal is to explain usability and how to incorporate usability in applications. In order to exemplify, I study usability within the context of the library application Horizon. </p><p>This study shows that Horizon is only partially utilized by its users which in principle is a bad grade for an application. Partial use is however in this case, not a serious problem since the negative effects partial use imply could very well be a matter of definition: is the productivity of students, when it comes to searching and ordering library material, critical for the organization? </p><p>When it comes to usability in the development phases of a project, once again one can conclude that good intentions exist but efforts fail all the same and Horizon is no exception. This time we can attribute failure to the lack of the end users’ perspective, organizational problems and perhaps also unsufficient knowledge of usability in one form or another. An important conclusion, which has not been mentioned in the literature, is the importance of considering the market position of a presumptive vendor when buying a generic system. Despite the flaws (often related to violations of well established design principles) presented in this paper, Horizon is considered a good, effective and efficient application by its users.</p>

Submitted by Alison Vanceto (alison-vanceto@hotmail.com) on 2017-01-16T11:11:48Z No. of bitstreams: 1 DissJHC.pdf: 5301084 bytes, checksum: 69f3b369ca40bc9639ba8d1f296e4d6e (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2017-01-17T12:10:12Z (GMT) No. of bitstreams: 1 DissJHC.pdf: 5301084 bytes, checksum: 69f3b369ca40bc9639ba8d1f296e4d6e (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2017-01-17T12:10:25Z (GMT) No. of bitstreams: 1 DissJHC.pdf: 5301084 bytes, checksum: 69f3b369ca40bc9639ba8d1f296e4d6e (MD5) / Made available in DSpace on 2017-01-17T12:10:32Z (GMT). No. of bitstreams: 1 DissJHC.pdf: 5301084 bytes, checksum: 69f3b369ca40bc9639ba8d1f296e4d6e (MD5) Previous issue date: 2016-06-20 / Não recebi financiamento / This thesis explored aspects that can help balance the level of user control and system autonomy for intelligent privacy agents in the context of the Internet of Things. This proposed balance could be reached considering aspects related to wanting to be interrupted to have control and being able to be interrupted to exert this control. Through literature review of interruption and privacy literature, variables related to these two perspectives were identified. This led to the variable set "Intelligent Privacy Interruptions”. To verify and validate this set, two research actions were performed. The first one was an online survey that allowed us to perform a sanity check that these variables were acceptable in this work’s context. The second was an experience sampling user study with 21 participants that allowed us to better understand how user behavior is informed by these variables. Based on these two interventions it was possible to note that the selected variables seem to show relevance and that they can be used to inform the development and design of privacy agents. The limitations of the partial results notwithstanding, through a quantitative analysis of data collected form the user study and the qualitative analysis of the exit interviews, it was possible to note a common mental process between the participants of the user study when deciding whether to withhold or delegate decision control to the agent. Future studies should be performed to verify the possibility of expansion and creation of a behavior and preference model that can be integrated to the decisionmaking system of intelligent privacy agents. / Este trabalho investigou aspectos que podem ajudar a balancear o nível de controle de usuários e de autonomia de agentes inteligentes de privacidade no contexto da Internet das Coisas. Entende-se que esse balanceamento proposto poderia ser alcançado considerando aspectos relacionados a “querer” ser interrompido para ter controle e “poder” ser interrompido para exercer o controle. Por meio de revisão da literatura de interrupções e privacidade, variáveis relacionadas a esses dois aspectos foram identificadas, embasando a proposta de um conjunto de variáveis para “Interrupções de Privacidade Inteligentes”. Para verificar e validar esse conjunto de variáveis, duas ações de pesquisa foram feitas. A primeira foi um questionário online que serviu como uma verificação inicial de que as variáveis são adequadas ao novo contexto proposto por esse trabalho. A segunda foi um estudo de amostragem de experiência com 21 usuários para se entender melhor como essas variáveis podem vir a informar o comportamento de usuários. Os resultados obtidos sugerem que as variáveis selecionadas apresentam relevância e que podem ser usadas para informar o desenvolvimento e design de agentes de privacidade. Embora os resultados ainda sejam limitados, principalmente pela duração do estudo e grupo e número de usuários, através da análise quantitativa dos dados coletadas no estudo com usuários e da análise qualitativa das entrevistas realizadas pós-estudo notou-se um processo mental comum entre os usuários participantes do estudo para as tomadas de decisão de reter o controle ou delegá-lo ao agente. Estudos futuros devem ser realizados, procurando verificar a possibilidade de expandir o relacionamento das variáveis para a criação de um modelo de comportamento e preferência dos usuários que seja integrável ao sistema de decisão de agentes inteligentes de privacidade.

Information security (InfoSec) policies are widely used by institutions as a form of InfoSec control measure to protect their information assets. InfoSec policies are commonly documented in natural language, which is prone to ambiguity and misinterpretation, thereby making it hard, if not impossible, for users to comply with. These misinterpretations may lead the students or staff members to wrongfully execute the required actions, thereby making institutions vulnerable to InfoSec attacks. According to the literature review conducted in this work, InfoSec policy documents are often not followed or complied with; and the key issues facing InfoSec policy compliance include the lack of management support for InfoSec, organisational cultures of non-compliance, intentional and unintentional policy violation by employees (the insider threat), lack of policy awareness and training as well as the policy being unclear or ambiguous. This study is set in the higher education context and explores the extent to which the non-compliance problem is embedded within the policy documents themselves being affected by ambiguity. A qualitative method with a case study research strategy was followed in the research, in the form of an inductive approach with a cross-sectional time horizon, whereby a selection case of relevant institutional InfoSec policies were analysed. The data was collected in the form of academic literature and InfoSec policies of higher education institutions to derive themes for data analysis. A qualitative content analysis was performed on the policies, which identified ambiguity problems in the data. The findings indicated the presence of ambiguity within the policy documents, making it possible to misinterpret some of the policy statements. Formal methods were explored as a possible solution to the policy ambiguity. A framework was then proposed to address ambiguity and improve on the clarity of the semantics of policy statements. The framework can be used by policy writers in paying attention to the presence of ambiguity in their policies and address these when drafting or revising their policy documents. / School of Computing

A cavitação e a dinâmica de bolhas são tópicos bastante recorrentes na literatura, devido sobretudo a seus efeitos em diversos tipos de fenômenos, como transferência de calor e escoamento em tubos. Considerando fases líquidas, sabe-se que estas estruturas de cavidade estão normalmente associadas ao equilíbrio metaestável, alcançado devido a quedas locais de pressão ou ao superaquecimento de uma substância pura (ou quase). Nestes casos é necessária a inicialização da mudança de fase através de algum mecanismo adequado, o qual gera uma sequência rápida de fenômenos. Apesar de comumente associado a danos, recentemente vários estudos vêm mostrando aplicações práticas deste tema, além de um campo ainda pouco explorado, que é o das macro cavidades. Essas cavidades podem ser geradas através do aquecimento de água a baixa pressão, sob condições específicas, criando sequências explosivas e formando movimentos como pistão para a água no interior de um invólucro convenientemente dimensionado. Este fenômeno mostra-se semelhante em diversos aspectos às micro cavidades, mais especificamente às cavidades próximas a superfícies livres, embora, sem dúvida, em escala muito maior. Os aspectos mencionados foram filmados com câmeras de alta velocidade e as características observadas foram comparadas com aquelas observadas em micro escala. Vários testes foram desenvolvidos de forma a melhor entender a dinâmica da formação e colapso dessas estruturas, sobretudo levando em conta um comportamento mais unidimensional para a evolução da bolha. Através de várias aproximações e análise de diferentes hipóteses para a variação de pressão e para a força de resistência, soluções analíticas e numéricas foram obtidas para a força exercida no fundo do contêiner e para a expansão e colapso das bolhas ao longo do tempo. As soluções propostas, em comparação com os dados experimentais, mostraram boa concordância entre si, sugerindo que os aspectos fundamentais da dinâmica da cavidade foram devidamente considerados e quantificados. / Cavitation and bubble dynamics are fairly recurring topics in literature, mostly due to their effects in various types of phenomena such as heat transfer and flow in pipes. Considering liquid phases, it is known that these cavity structures are normally associated with the metastable equilibrium, reached due to local pressure drop or overheating of a pure substance (or nearly so). In these cases, the phase change require a startup via some appropriate mechanism, which generates a fast sequence of phenomena. Although commonly associated with damage, recently several studies shown practical applications of these topics, and a still little explored field emerged, which is the field of macro cavities. These cavities can be generated by heating water at a low pressure, under specific conditions, creating an explosive sequences and forming piston like movements for the water inside a properly scaled casing. This phenomenon appears to be similar in many aspects to micro cavities, more specifically for cavities near free surfaces, although, without doubt, on a much larger scale. The mentioned aspects were filmed with high-speed cameras and the main features were compared with those observed in micro scale. Several tests have been developed to better understand the dynamics of the formation and collapse of these structures, especially taking into account a more one-dimensional behavior to the evolution of the bubble. Through various approximations, and analysis of different assumptions for the variation of pressure and the resistance force, analytical and numerical solutions were obtained for the force exerted on the bottom of the container and the expansion and collapse of bubbles over time. The proposed solutions in comparison with experimental data showed good agreement between each other suggesting that the fundamental aspects of the dynamics of the cavity were properly considered and quantified.