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Energy saving policies applied to modem buildings and air recirculation systems promote the build up of high levels of VOCs in indoor air. The growing concern related to the air quality in indoor environments requires the replacement of ineffective traditional purification methods, with an efficient and cost effective technology. Photocatalytic oxidation that utilise TiO2, represents a promising candidate for this purpose. However, the formulation of photocatalysts that can efficiently utilise a sustainable energy source (i.e. solar light), still represents an ambitious target in this field. In this study, different TiO2-based photocatalysts were synthesised by modified sol-gel and/or hydrothermal routes. The materials were characterised by XRD, SEM, N2 sorption (BET and BJH methods), UV-vis Spectroscopy and XPS. The photocatalytic activity of TiO2-based materials was systematically investigated at different light intensities, in a gas-phase flatplate photoreactor, using trichloroethylene (TCE) as model pollutant, and compared with that of the commercial product TiO2 Degussa P-25. This research provides insights into the influence of preparation parameters on different synthetical pathways for the preparation of highly active TiO2- based photocatalysts. The general approach to this investigation is based on the study of the influence of several processing parameters on morphological, textural and crystallographic properties of the photocatalysts, in order to correlate the material's features with their photocatalytic properties. The preparation of a wide range of pristine TiO2 allowed assessing a clear correlation between phase composition and crystal size and the photocatalytic performance. A series of highly active anatase photocatalysts was prepared. The best photocatalyst has an optimum crystal size of 28 nm and exhibits a photocatalytic activity that exceeds that of P-25 by a factor of over 2 times. A new TiO2/WO3 nanocomposites with peculiar crystallographic properties of the W component was developed by a novel one-step hydrothermal synthesis. The synthesis conditions were optimised with respect to the photocatalytic activity. Overall, the optimisation of the properties that enable an efficient interfacial charge transfer rate at the catalyst surface was found to be of fundamental importance for the design of improved TiO2-based photocatalysts.

Our lives today rely on the secure operation of computers in a diverse set of sectors, from energy to medicine. However, today's computers execute software bloated with complexity. Their large codebases provide a rich and versatile system, but most functionalities are often not needed in their target applications. This increases the trusted computing base (TCB) – the software and hardware that needs to be trusted for the system to work correctly. A large TCB is undesirable, as it gives attackers a higher likelihood to find and exploit vulnerabilities. Most of this complexity comes from the system software, that is, the operating system (OS) and the hypervisor. Despite this, the system software's codebase cannot generally be removed from the TCB, as it executes with the highest privileges. Thanks to additional hardware primitives, Trusted Execution Environments (TEEs) break this paradigm, allowing even system software to be removed from the TCB. Most CPU manufacturers and architectures support some form of TEE: they can be found on Intel and AMD CPUs, as well as on ARM and RISC-V architectures. Their advent is promising, as they aim to let applications operate securely both when the (more privileged) system software is malicious and when a physical attacker can tamper with the system. Arguably, however, the guarantees that can be provided against such a strong and privileged attacker are not fully understood and often lead to TEE designs that make compromises invalidating the protections that they aim to provide. For example, previous work shows that the OS can abuse the CPU memory management interface to get notified when the TEE accesses attacker-specified memory regions, breaking data confidentiality. Understanding the capabilities of privileged attackers thus leads to more accurate designs and a more secure computing environment for everyone. In this thesis, we contribute to the efforts of understanding the capabilities of privileged attackers in the context of TEEs in four main directions. First, we develop the Frontal attack, which shows that leveraging the OS to issue interrupts frequently leads to the CPU exposing detailed instruction execution timings, which can be used as a side channel. This side channel is detailed enough to leak encryption keys from a TEE and thus break data confidentiality. Second, we show that current commercial TEEs struggle to provide code confidentiality against a privileged attacker. Notably, we observe that using interpreters or JIT compilers inside TEEs – a popular choice due to their convenience and flexibility – leaks significantly more confidential instructions compared to a baseline where native instructions are used instead. The third and fourth contributions relate to attestation protocols, which are used to verify that a TEE is protecting a given application. We emphasize the impact of previously neglected aspects in attestation protocols in both these contributions. In the third contribution, we highlight that relay attacks, while once thought to be tolerable given the TEE protections, enhance the capabilities of a privileged attacker. Finally, in the fourth contribution, we show that current attestation protocols implicitly assume trust in the TEE manufacturer at runtime – despite the manufacturers often claiming otherwise. While this implicit trust in the TEE manufacturer is often overlooked, our analysis shows that it is a concrete threat in practice and should thus be accounted for in future attestation protocols.

Abstract: This dissertation used Institutional Ethnography (IE) to explore the experiences of street involved youth in Edmonton and to uncover how institutional, organizational, and social mechanisms shape their experiences. Drawing from Community-Based Participatory Research methods, I collaborated with Edmonton youth living in homelessness to explore their experiences of living on the streets during extensive downtown revitalization. This research used observations, interviews, focus groups and Photovoice methodologies to understand how youth enter into homelessness and their experiences once homeless. Youth participants identified many social issues they encounter daily. One prominent issue that youth encountered when navigating the streets of Edmonton was that they were often banned from local shelters for various reasons. Because of these bans, youth were often placed in unsafe situations such as sleeping in garbage bins, sleeping alone on the streets or turning to survival sex to get shelter. Through this dissertation, I sought to understand how service bans happen and the conditions that lead to youth banning. In exploring this phenomenon, I found that banning practices became the lens through which to understand and connect systemic issues that cause and perpetuate homelessness to the experiences of this specific group of youth. This Institutional Ethnography shows how the experiences of youth, including banning, are connected and organized by the socio-political ideologies of neoliberalism and colonialism that exist in Edmonton and beyond. By focusing on one specific issue in one organization, this IE illustrates how to connect larger systems organization to youth’s lived experiences.

In this thesis we explore the idea of making (proof-of-work) blockchains mutable, by proposing and implementing μchain, a mutable blockchain that enables modifications of blockchains' history. Blockchains are, by common definition, distributed and immutable data structures that store a history of events, such as transactions in a digital currency system. While the very idea of mutable event history may seem controversial at a first glance, we show that μchain does not undermine security guarantees provided by immutable blockchains. In particular, all mutations in our system are controlled by fiat, enforced by consensus and are verifiable in the same way as regular transactions. At the same time, μchain provides a solution to a number of challenging problems, such as the patching of vulnerable smart contracts and removal of abusive content from blockchain history. It also gives rise to new blockchain applications that were not possible with immutable blockchains. For instance, governments and companies could now maintain registers of citizens and customers, while preserving their legislated rights to be forgotten. Banks could consider consolidation of cryptocurrency with traditional payments, which is hard to achieve without the ability to revert transactions. To further illustrate the power of μchain on more concrete examples, we present two new applications, the collaborative recommendation system with the ability to censor inappropriate content, and a time-lock encryption mechanism that provides a method to decrypt messages after a certain deadline has passed.