The reconfigurable aperture (RECAP) is a reconfigurable antenna consisting of a dense array of electronically controlled elements, which can be manipulated to support many antenna functions within a single architecture. RECAPs are explored herein as an enabling technology for future software defined and cognitive radio architectures, as well as compact wireless devices supporting many bands and services. First, the concept of a parasitic RECAP is developed and analyzed for various communication applications. This begins with the analysis of existing RECAP topologies (e.g. planar and parasitic) using a hybrid method combining full wave simulations and network analysis. Next, a performance versus complexity analysis is performed to assess the use of a parasitic RECAP for the most critical communications functions: pattern synthesis, MIMO communications and physical-layer wireless security. To verify simulation results, a prototype parasitic RECAP is also built and deployed in real propagation environments. Given the potential of adaptive and reconfigurable architectures for providing enhanced security, an idealized reconfigurable antenna is analyzed, resulting in the concept of secure array synthesis. The objective is to find optimal array beamforming for secure communication in the presence of a passive eavesdropper in a static line-of-sight (LOS) channel. The method is then extended to the case of multipath propagation environments. The problem is solved by casting it into the form of a semi-definite program, which can be solved with convex optimization. The method is general and can be applied to an arbitrary array topology with or without antenna mutual-coupling. Due to complexity of the problem, initial attention has been restricted to idealized reconfigurable antennas (smart antennas), where excitation amplitude and phase at each element can be controlled independently. Lastly, reconfigurable antennas are investigated as a solution to support the emerging application of over-the-air (OTA) testing in a low-cost and compact way, resulting in the concept of the reconfigurable over-the-air chamber (ROTAC). First, an idealized two-dimensional ROTAC is analyzed, revealing that the fading distribution, spatial correlation, frequency selectivity, and multipath angular spectrum can be controlled by proper specification of the random loads. Later, a prototype of ROTAC is built to study the fading statistics and angular characteristics of the multipath fields inside a practical chamber.

Picture Archiving and Communication Systems (PACS) have been traditionally constrained to the premises of the healthcare provider. This has limited the availability of these systems in many parts of the world and mandated major costs in infrastructure for those who employ them. Public cloud services could be a solution that eases the cost of ownership and provides greater flexibility for PACS implementations. This could make it possible to bring medical imaging services to places where it was previously unavailable and reduce the costs associated with these services for those who utilize them. Moving these systems to public cloud infrastructure requires that an authentication and encryption policy for communications is established within the PACS environment to mitigate the risks incurred by using the Internet for the communication of medical data. This thesis proposes a framework which can be used to create an authenticated and encrypted channel to secure the communications with a cloud-based PACS. This framework uses the Transport Layer Security (TLS) protocol and X.509 certificates to create a secured channel. An enterprise style PKI is used to provide a trust model to authorize endpoints to access the system. The validity of this framework was tested by creating a prototype cloud-based PACS with secured communications. Using this framework will provide a system based on trusted industry standards which will protect the confidentiality and integrity of medical data in transit when using a cloud-based PACS service.

The media industry has during the last decade migrated services from dedicated medianetworks to more shared resources and lately also the public internet and public data centers. Inorder to cater for such transition, several protocols have been designed to meet the demand forhigh-quality media transport over lossy infrastructure, protocols such as SRT and RIST. Thepurpose of Reliable Internet Stream Transport (RIST) and Secure Reliable Transport (SRT) is tohave all vendors of broadcasting equipment support an interoperable way of communication. Thelack of interoperability locks consumers into one particular vendor’s family of products - most oftenthis equipment only supports a proprietary technology. Interoperability creates a more competitivemarket space which benefits consumers and gives vendors an incentive to be more innovative intheir solutions. The purpose of this thesis is to assess the performance of these protocols by comparing theirperformance to a proprietary solution (named ÖÖÖ in this thesis and seen as an establishedsolution in the industry). The challenge is to test these protocols in a lab environment, but have theresults represent real-world use. For this, a large subset of samples is needed along with samplesmeasured over a long period. This sampling was made possible by writing a script which automatesthe sampling process. The results indicate that the versions of RIST and SRT tested in this thesis to some extentcompare well to the selected established protocol (ÖÖÖ). In many scenarios, SRT even did muchbetter, mainly when a line with a single feed was tested. For instance, when the network suffered a2% drop rate and utilized retransmission SRT performed the best and was the only protocol whichhad some samples where no packets were dropped during one hour of measurements. Whenrunning all three protocols at the same time, SRT also did the best in a network with up to 12% droprate. The results in this thesis should give a broadcaster an idea of which of these protocols willfulfill their requirements in a broadcast application. / I mediabranschen finns det en efterfrågan på utrustning som har inslag av interoperabilitet.Anledningen till detta är att någon som köper produkter från en viss återförsäljare inte vill låsas in idenna återförsäljares ”ekosystem” i flera år framöver. Då en studio sällan uppgraderar hela sinproduktionskedja på samma gång ger interoperabilitet möjligheten att köpa utrustning från andraåterförsäljare när man ska uppgradera något i produktionslinan. Detta leder till en merkonkurrenskraftig marknad samt ger incentiv till nya innovativa lösningar. Detta examensarbete går ut på att utvärdera lösningar som tagits fram för att främjainteroperabilitet och jämföra dem med en existerande proprietärlösning. Reliable Internet StreamTransport (RIST) och Secure Reliable Transport (SRT) är två protokoll som tagits fram för just dettasyfte. Utmaningen med att utvärdera dessa protokoll är att i en labbmiljö få resultat som reflekteraranvändandet av protokollen i verkligheten. Detta har gjorts med hjälp av ett program som tagitsfram i detta examensarbete. Med detta program har testandet kunnat automatiseras. Resultaten i detta examensarbete visar potential hos båda RIST och SRT. SRT är i vissascenarion till och med bättre än den proprietära lösningen. Protokollen visar något buggigtbeteende i vissa instanser, såsom att i vissa fal sluta fungera och inte kunna återgå till normalfunktion utan manuell interaktion. Allt som allt är dock protokollen i de flesta fallen testade i dettaexamensarbete ett godtyckligt alternativ till den jämförda proprietära lösningen.

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Emergency response is highly time-critical and information dependent: every moment counts and organizations need to access various information that supports their decision making and informs them about the scale and location of the emergency, the damages, and the availability of human and physical resources. This kind information can originate from many different places and the situation can be stressful as there is a need to communicate quickly, reliably and accurately within their own organization, but also inter-organizationally. ICTs make it possible to access and spread information with speed and efficiency, but other factors, such as different professional cultures, can still hinder information sharing. There is a growing need in emergency organizations to develop understanding for how communications between emergency responders can be secured. It seems important to consider how emergency responders respond to security objectives, since the assumptions for secure communications may not only be developed on the premise of ICT, but also how the emergency actors appreciate the emergency environments in terms of secure communications.The aim of this research is to develop understanding of information security and secure communications in a context where it has not been well researched. The research looks at secure emergency communications from a socio-technical viewpoint and concentrates on the communication inside and between the emergency organizations of police, the paramedics, and the rescue department in the municipality of Kemi, and more specifically on the communications of operative emergency actors while they are working in the preparedness and response phases of emergency management. Two persons from each organization were interviewed using semi-structured interviews, and the empirical data was used for writing the appended papers that are the basis of this thesis work.The research started by doing an extensive literature review and analysis on the field of secure emergency communications. The results show that while technical developments on the field aim at effective and secure technologies, organizational aspects of emergency communications seem to involve not only emergency actors, but also how these actors more and more utilize information technology. The landscape for emergency management is becoming very diverse, which challenges the way that secure emergency communications can be understood. The developers of future emergency communications structures not only need to ensure the technical aspects of confidentiality, availability and integrity of information, but they also need to take into account the social rules, norms and structures that guide the emergency communication. Next, this research sought out to re-conceptualize the role of information security in emergency response. A conceptual basis encompassing technical, cognitive and organizational information security layers as a relationship between association and connectivity was developed by synthesizing Actor Network Theory and Theory of Organizational Routines. The approach of combining two theoretical accounts details the enactment of information security in emergency response so as to understand how cognition ties technical security features with organizational security issues. Without the cognitive layer, the technical and organizational aspects of information security remain static or disconnected to the actions performed during emergency response. Theoretically the approach contributes constructively to describe an alternative approach to information security research to address the gap between formal and informal criteria of information security.Lastly, the research sought out to explore the current situation of the case organizations in detail concerning their level of information security, communication challenges faced, and training offered. It was learned that different aspects of information security are valued depending on whether emergency responders work in preparation periods or if they are responding to an emergency: 1) When working in their own respective organizations the most important aspect was information confidentiality 2) When responding to emergency the most important aspects were information availability and integrity. Most communication challenges present in emergency communications can be seen to arise when responding to emergencies. This is not something currently being taken into account in the case organizations. The basic training of emergency actors and the training and guidelines of each organization largely concentrate on confidentiality issues, and tools and communications training that would be needed to ensure information availability and integrity when responding to an emergency is not prioritized. To overcome the communication challenges present in emergency communications and to ensure confidentiality, availability and integrity of emergency information, those responsible for information security in emergency organizations must therefore provide up to date information security training and awareness building, but also tools and communications training that supports inter-organizational communication.

My research investigates three questions: How do we customize protocols and implementations to account for the unique requirement of each setting and its target community, what are necessary steps that we can take to transition secure computation tools into practice, and how can we promote their adoption for users at large? In this dissertation I present several of my works that address these three questions with a particular focus on one of them. First my work on "Hecate: Abuse Reporting in Secure Messengers with Sealed Sender" designs a customized protocol to protect people from abuse and surveillance in online end to end encrypted messaging. Our key insight is to add pre-processing to asymmetric message franking, where the moderating entity can generate batches of tokens per user during off-peak hours that can later be deposited when reporting abuse. This thesis then demonstrates that by carefully tailoring our cryptographic protocols for real world use cases, we can achieve orders of magnitude improvements over prior works with minimal assumptions over the resources available to people. Second, my work on "Batched Differentially Private Information Retrieval" contributes a novel Private Information Retrieval (PIR) protocol called DP-PIR that is designed to provide high throughput at high query rates. It does so by pushing all public key operations into an offline stage, batching queries from multiple clients via techniques similar to mixnets, and maintain differential privacy guarantees over the access patterns of the database. Finally, I provide three case studies showing that we cannot hope to further the adoption of cryptographic tools in practice without collaborating with the very people we are trying to protect. I discuss a pilot deployment of secure multi-party computation (MPC) that I have done with the Department of Education, deployments of MPC I have done for the Boston Women’s Workforce Council and the Greater Boston Chamber of Commerce, and ongoing work in developing tool chain support for MPC via an automated resource estimation tool called Carousels.

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The Internet has been growing rapidly during the past threedecades, evolving into a new paradigm called the Internet ofThings where all electronic devices are to be connected tothe global network. One of the most crucial needs forcommunication in this future global network is assuring its security.Datagram Transport Layer Security is a de facto standard protocolto secure end-to-end communication in the IoT. However, there isalso an increasing need for secure and efficient groupcommunication due to the frequently resource-constrained IoTenvironment. A DTLS adaptation for multicast communication hasbeen already proposed but protection of responses to multicastrequests has not been fully addressed yet. Furthermore, there is nopublicly available implementation of this adaptation. This thesis work is conducted in collaboration with SICS SwedishICT which is a research organization with a focus on appliedComputer Science. We have implemented the existing DTLS-basedapproach for multicast communication for the Contiki OS. We havealso implemented an approach for efficient response protectionthat was initially proposed at SICS and that we analyse andenhance in this thesis. Finally, we have experimentally evaluatedour and other approaches on a constrained hardware platform interms of memory requirements, communication performance andenergy consumption. We demonstrate advantages of our approachbased upon obtained results. / Internet har vuxit snabbt under de tre senaste decennierna, ochutvecklas till ett nytt paradigm kallat Internet of Things där allaelektroniska enheter kopplas till det globala nätverket. Ett av deviktigaste behoven för kommunikation i detta framtida globalanätverk är att garantera säkerhet. Datagram Transport LayerSecurity protokollet är en de facto-standard för säker end-to-endkommunikation i IoT. Det finns emellertid också ett ökande behovav säker och effektiv gruppkommunikation på grund av att IoTmiljöni regel är resursbegränsad. En anpassning av DTLS förmulticast-kommunikation har föreslagits men skydd av svar påmulticast-förfrågningar har ännu inte till fullo behandlats.Dessutom finns ingen offentligt tillgänglig implementation av dennaanpassning. Detta examensarbete utförs i samarbete med SICS Swedish ICTsom är en forskningsorganisation med fokus på tillämpaddatavetenskap. Vi har implementerat den existerande DTLSbaseradelösningen för multicast-kommunikation föroperativsystemet Contiki. Vi har också implementerat en lösningför effektivt skydd av svar på förfrågningar som ursprungligenföreslogs hos SICS och som vi analyserar och förbättrar i dettaexamensarbete. Slutligen har vi experimentellt utvärderat vår ochandra metoder på en begränsad hårdvaruplattform när det gällerminnesbehov, kommunikationsprestanda och energiförbrukning. Vivisar fördelar med vår metod baserat på de erhållna resultaten.