In recent years, the subject of online privacy has been attracting much interest, especially as more Internet users than ever are beginning to care about the privacy of their online activities. Privacy concerns are even prompting legislators in some countries to demand from service providers a more privacy-friendly Internet experience for their citizens. These are welcomed developments and in stark contrast to the practice of Internet censorship and surveillance that legislators in some nations have been known to promote. The development of Internet systems that are able to protect user privacy requires private information retrieval (PIR) schemes that are practical, because no other efficient techniques exist for preserving the confidentiality of the retrieval requests and responses of a user from an Internet system holding unencrypted data. This thesis studies how PIR schemes can be made more relevant and practical for the development of systems that are protective of users' privacy. Private information retrieval schemes are cryptographic constructions for retrieving data from a database, without the database (or database administrator) being able to learn any information about the content of the query. PIR can be applied to preserve the confidentiality of queries to online data sources in many domains, such as online patents, real-time stock quotes, Internet domain names, location-based services, online behavioural profiling and advertising, search engines, and so on. In this thesis, we study private information retrieval and obtain results that seek to make PIR more relevant in practice than all previous treatments of the subject in the literature, which have been mostly theoretical. We also show that PIR is the most computationally efficient known technique for providing access privacy under realistic computation powers and network bandwidths. Our result covers all currently known varieties of PIR schemes. We provide a more detailed summary of our contributions below: Our first result addresses an existing question regarding the computational practicality of private information retrieval schemes. We show that, unlike previously argued, recent lattice-based computational PIR schemes and multi-server information-theoretic PIR schemes are much more computationally efficient than a trivial transfer of the entire PIR database from the server to the client (i.e., trivial download). Our result shows the end-to-end response times of these schemes are one to three orders of magnitude (10--1000 times) smaller than the trivial download of the database for realistic computation powers and network bandwidths. This result extends and clarifies the well-known result of Sion and Carbunar on the computational practicality of PIR. Our second result is a novel approach for preserving the privacy of sensitive constants in an SQL query, which improves substantially upon the earlier work. Specifically, we provide an expressive data access model of SQL atop of the existing rudimentary index- and keyword-based data access models of PIR. The expressive SQL-based model developed results in between 7 and 480 times improvement in query throughput than previous work. We then provide a PIR-based approach for preserving access privacy over large databases. Unlike previously published access privacy approaches, we explore new ideas about privacy-preserving constraint-based query transformations, offline data classification, and privacy-preserving queries to index structures much smaller than the databases. This work addresses an important open problem about how real systems can systematically apply existing PIR schemes for querying large databases. In terms of applications, we apply PIR to solve user privacy problem in the domains of patent database query and location-based services, user and database privacy problems in the domain of the online sales of digital goods, and a scalability problem for the Tor anonymous communication network. We develop practical tools for most of our techniques, which can be useful for adding PIR support to existing and new Internet system designs.

This thesis treats a protocol for anonymous database search (or if one prefer, a protocol for user-private information retrieval), that is based on the use of combinatorial configurations. The protocol is called P2P UPIR. It is proved that the (v,k,1)-balanced incomplete block designs (BIBD) and in particular the finite projective planes are optimal configurations for this protocol. The notion of n-anonymity is applied to the configurations for P2P UPIR protocol and the transversal designs are proved to be n-anonymous configurations for P2P UPIR, with respect to the neighborhood points of the points of the configuration. It is proved that to the configurable tuples one can associate a numerical semigroup. This theorem implies results on existence of combinatorial configurations. The proofs are constructive and can be used as algorithms for finding combinatorial configurations. It is also proved that to the triangle-free configurable tuples one can associate a numerical semigroup. This implies results on existence of triangle-free combinatorial configurations.

In recent years, the subject of online privacy has been attracting much interest, especially as more Internet users than ever are beginning to care about the privacy of their online activities. Privacy concerns are even prompting legislators in some countries to demand from service providers a more privacy-friendly Internet experience for their citizens. These are welcomed developments and in stark contrast to the practice of Internet censorship and surveillance that legislators in some nations have been known to promote. The development of Internet systems that are able to protect user privacy requires private information retrieval (PIR) schemes that are practical, because no other efficient techniques exist for preserving the confidentiality of the retrieval requests and responses of a user from an Internet system holding unencrypted data. This thesis studies how PIR schemes can be made more relevant and practical for the development of systems that are protective of users' privacy. Private information retrieval schemes are cryptographic constructions for retrieving data from a database, without the database (or database administrator) being able to learn any information about the content of the query. PIR can be applied to preserve the confidentiality of queries to online data sources in many domains, such as online patents, real-time stock quotes, Internet domain names, location-based services, online behavioural profiling and advertising, search engines, and so on. In this thesis, we study private information retrieval and obtain results that seek to make PIR more relevant in practice than all previous treatments of the subject in the literature, which have been mostly theoretical. We also show that PIR is the most computationally efficient known technique for providing access privacy under realistic computation powers and network bandwidths. Our result covers all currently known varieties of PIR schemes. We provide a more detailed summary of our contributions below: Our first result addresses an existing question regarding the computational practicality of private information retrieval schemes. We show that, unlike previously argued, recent lattice-based computational PIR schemes and multi-server information-theoretic PIR schemes are much more computationally efficient than a trivial transfer of the entire PIR database from the server to the client (i.e., trivial download). Our result shows the end-to-end response times of these schemes are one to three orders of magnitude (10--1000 times) smaller than the trivial download of the database for realistic computation powers and network bandwidths. This result extends and clarifies the well-known result of Sion and Carbunar on the computational practicality of PIR. Our second result is a novel approach for preserving the privacy of sensitive constants in an SQL query, which improves substantially upon the earlier work. Specifically, we provide an expressive data access model of SQL atop of the existing rudimentary index- and keyword-based data access models of PIR. The expressive SQL-based model developed results in between 7 and 480 times improvement in query throughput than previous work. We then provide a PIR-based approach for preserving access privacy over large databases. Unlike previously published access privacy approaches, we explore new ideas about privacy-preserving constraint-based query transformations, offline data classification, and privacy-preserving queries to index structures much smaller than the databases. This work addresses an important open problem about how real systems can systematically apply existing PIR schemes for querying large databases. In terms of applications, we apply PIR to solve user privacy problem in the domains of patent database query and location-based services, user and database privacy problems in the domain of the online sales of digital goods, and a scalability problem for the Tor anonymous communication network. We develop practical tools for most of our techniques, which can be useful for adding PIR support to existing and new Internet system designs.

The three chapters of this thesis revolve around the trade in English stocks in the Amsterdam market during the 18th century. In the first chapter I use the primitive communication technology of that time to identify the impact of news on stock price volatility. I find that the arrival of news through sailing boats can explain between 30 and 50% of the price movements of the English stocks in Amsterdam. In the second chapter I provide evidence for the use and revelation of private information in the Amsterdam market. I show that price movements in Amsterdam and London are correlated, even when no information could be transmitted between the two markets. In the final chapter (joint with Hans-Joachim Voth) we study the impact of distressed trade in Amsterdam on stock prices. We show that prices responded immediately to news about the distress, but that actual distressed transactions were delayed. / Esta tesis estudia el negocio en acciones ingleses en el mercado de valores de Amsterdam durante el siglo XVIII. En capítulo uno aplico la comunicación primitiva de esa época para identificar el impacto de noticias sobre la volatilidad de cotizaciones de acciones. Observo que la llegada de noticias mediante barco a vela explica entre 30 y 50% de los movimientos en las cotizaciones de acciones ingleses en el mercado de Amsterdam. En capítulo dos enseño que en Amsterdam se utilizó información privada sobre las acciones ingleses. Muestro una correlación entre los movimientos en las cotizaciones de Amsterdam y Londres, incluso cuando no hay intercambio de información entre los dos mercados. En el último capítulo (junto con Hans-Joachim Voth) estudiamos el impacto de transacciones forzados en Amsterdam sobre las cotizaciones. Mostramos que las cotizaciones responden notablemente a noticias sobre la necesidad de negociar, pero que las transacciones forzados fueron aplazadas.

Submitted by Daniella Santos (daniella.santos@fgv.br) on 2009-11-30T17:28:59Z No. of bitstreams: 1 Tese_Rafael_Coutinho_Costa_Lima.pdf: 555268 bytes, checksum: a06061bb98e0ddefd846ff6034a22317 (MD5) / Approved for entry into archive by Antoanne Pontes(antoanne.pontes@fgv.br) on 2009-12-01T11:42:43Z (GMT) No. of bitstreams: 1 Tese_Rafael_Coutinho_Costa_Lima.pdf: 555268 bytes, checksum: a06061bb98e0ddefd846ff6034a22317 (MD5) / Made available in DSpace on 2009-12-01T11:42:43Z (GMT). No. of bitstreams: 1 Tese_Rafael_Coutinho_Costa_Lima.pdf: 555268 bytes, checksum: a06061bb98e0ddefd846ff6034a22317 (MD5) / This thesis consists of three chapters that have as unifying subject the frame-work of common agency with informed principals. The first two chapters analyze the economic effects of privately informed lobbying applied to tariff protection (Chapter 1) and to customs unions agreements (Chapter 2). The third chapter investigates the choice of retailing strutures when principals (the producers) are privately informed about their production costs. Chapter 1 analyzes how lobbying affects economic policy when the interest groups have private information. I assume that the competitiveness of producers are lobbies private information in a Grossman and Helpman (1994) lobby game. This allows us to analyze the e¤ects of information transmission within their model. I show that the information transmission generates two informational asymmetry problems in the political game. One refers to the cost of signaling the lobby's competitiveness to the policy maker and the other to the cost of screening the rival lobby's competitiveness from the policy maker. As an important consequence information transmission may improve welfare through the reduction of harmful lobbying activity. Chapter 2 uses the framework of chapter 1 to study a customs union agreement when governments are subject to the pressure of special interest groups that have better information about the competitiveness of the industries they represent. I focus on the agreement's effect on the structure of political influence. When join a customs union, the structure of political pressure changes and with privately informed lobbies, a new effect emerges: the governments can use the information they learn from the lobby of one country to extract rents from the lobbies of the other country. I call this the 'information transmission effect'. This effect enhances the governments'bargaining power in a customs union and makes lobbies demand less protection. Thus, I find that information transmission increases the welfare of the agreement and decreases tari¤s towards non-members. I also investigate the incentives for the creation of a customs union and find that information transmission makes such agreement more likely to be politically sustainable. Chapter 3 investigates the choice of retailing structure when the manufacturers are privately informed about their production costs. Two retailing structures are analyzed, one where each manufacturer chooses her own retailer (exclusive dealing) and another where the manufacturers choose the same retailer (common agency). It is shown that common agency mitigates downstream competition but gives the retailer bargaining power to extract informational rents from the manufacturers, while in exclusive dealing there is no downstream coordination but also there are no incentives problem in the contract between manufacture and retailer. A pre- liminary characterization of the choice of the retailing structure for the case of substitute goods shows that when the uncertainty about the cost increases relatively to the size of the market, exclusive dealing tends to be the chosen retailing structure. On the other hand, when the market is big relatively to the costs, common agency emerges as the retailing structure. This thesis has greatly benefited from the contribution of Professors Humberto Moreira and Thierry Verdier. It also benefited from the stimulating environment of the Toulouse School of Economics, where part of this work was developed during the year of 2007. / Esta tese consiste de três artigos que tem como elemento unificador o modelo de agência comum com principais informados. Os dois primeiros capítulos investigam os efeitos econômicos da influência de grupos de pressão (lobbies) sobre a escolha da tarifas de importação (Capítulo 1) e sobre acordos de comércio internacionais (Capítulo 2). O capítulo 3 investiga a escolha da estrutura de revenda quando os produtores possuem informação privada sobre os seus custos. O capítulo 1 analisa como a atividade de lobby afeta a política econômica quando grupos de interesses possuem mais informação que o governo. Modifica- se o modelo de Grossman e Helpman (1994), assumindo que a competitividade dos produtores é informação privada dos lobbies. Isto permite investigar quais os efeitos de transmissão de informação neste modelo. Esta assimetria de informação gera dois efeitos no jogo político, um associado ao problema de sinalização da competitividade do lobby para o governo e outro associado ao custo de um lobby fazer um screening da competitividade do lobby rival junto ao governo. O principal resultado deste modelo é que a transmissão de informação reduz a capacidade de influência dos lobbies, o que aumenta o bem-estar da sociedade. O capítulo 2 aplica o modelo do Capítulo 1 para entender os efeitos de transmissão de informação que surgem em uniões aduaneiras quando os lobbies possuem mais informação que o governo. O foco é dado nos efeitos políticos que surgem nestes acordos. Quando os países formam uma união aduaneira o equilíbrio de forças político e um novo efeito surge: os governos usam as informações privadas do lobby de um país para extrair renda dos lobbies dos outros países. Este efeito aumenta o poder de barganha dos governos dentro de uma união aduaneira e reduzam a capacidade de influência dos lobbies. Desta forma, a transmissão de informação aumenta os benefícios de uma união aduaneira e reduz a tarifas de importação para os países fora do acordo. Além disso, é investigado o papel da transmissão de informação a criação das uniões aduaneiras e o resultado encontrado é que esta aumenta as chances destes acordos serem implementados. O capítulo 3 investiga a escolha da estrutura de revenda quando os produtores possuem informação privada sobre seus custos de produção. Duas estruturas de revenda são analisadas, uma onde cada produtor escolhe um revendedor exclusivo (exclusive dealing) e outra onde ambos os produtores escolhemo mesmo revendedor (agência comum). Agência comum reduz a competição no mercado final, mas dá ao revendedor a capacidade de extrair lucro dos produtores utilizando a informação de um contra o outro. Enquanto que exclusive dealing aumenta a competição entre produtores, mas não cria problemas informacionais entre produtor e revendedor. Uma caracterização preliminar da escolha da estrutura de revenda para o caso de bens substitutos mostra que quando a incerteza quanto sobre o custo aumenta relativamente ao tamanho do mercado, exclusive dealing tende a ser a estrutura de revenda escolhida, enquanto que quando o tamanho do mercado é grande em relação aos custos, agência comum tende a ser a estrutura escolhida. Esta tese se beneficiou enormemente da contribuição dos professores Hum- berto Moreira e Thierry Verdier. Também se beneficiou o estimulante ambiente acadêmico da Toulouse School of Economis, onde parte dela foi desenvolvida du- rante o ano de 2007.

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.

The study aimed to explore and describe the factors influencing disclosure of Human Immunodeficiency Virus (HIV) status to sexual partners by people infected with HIV in Botswana, by undertaking an exploratory and descriptive qualitative study. Data was collected through in-depth interviews with people infected with HIV who had disclosed their HIV status to their partners. The major findings of the study confirmed disclosure as a multi-stage process. People infected with HIV experienced mainly positive and some negative outcomes following disclosure. Disclosure was associated with the discloser’s motivations, personal and cultural beliefs, risk-benefit assessment, individual circumstances (context), previous experiences, and perceived degree of control over private information. The communication privacy management (CPM) theory helped explain the findings. The key factor influencing disclosure was protecting others. Non-disclosers had also seriously considered disclosing to partners. / Health Studies / M.P.H

Le lien entre le choix d’allocation des fonds mutuels et l’information privée que possède leurs gérants sur des facteurs globaux de risque n’a pas été largement analysé. La littérature manque également d'études concernant l'impact de l’information privée globale sur la performance des fonds mutuels investis en actions. Notre travail vise à apporter de nouveaux éclairages sur ce sujet en montrant que l’information privée sur des facteurs globaux de risque est cruciale pour le choix d’investissements et pour la performance des fonds mutuels lorsqu’ils investissent à l’étranger.Dans le premier papier, nous étudions comment l’information privée sur les facteurs globaux, détenue par les gérants des fonds, impacte leurs performances. Après avoir utilisé plusieurs modèles de performances et plusieurs caractéristiques managériales, nous constatons un impact positif et significatif de l'information globale privée sur la performance des fonds mutuels globaux américains. Nous montrons que l’information globale qui permet de générer de la performance est celle qui concerne les secteurs industriels. Ceci est cohérent avec les résultats d'Albuquerque et al. (2009) et de Hiraki et al. (2015). Nous montrons également que l'utilisation du degré de concentration sectorielle (DSC) est un indicateur bruité de l’avantage informationnel possédé par les gérants. Le degré de concentration sectorielle affecte positivement la performance des fonds durant les périodes de stabilité financière. Cependant, cet impact positif n'est significatif que pour les fonds ayant un fort avantage informationnel sur les facteurs globaux.Dans le deuxième article de cette thèse, nous cherchons à éclaircir les choix d'allocation des fonds globaux et l’évaluation de leurs performances au cours de la récente crise des subprimes. Spécifiquement, nous examinons si c’est l’avantage informationnel de leurs gérants sur des facteurs globaux de risque ou leur familiarité avec certains marchés financiers étrangers qui a guidé leur choix d’investissement et leur a permis d’accroître leur performance durant cette crise. Nous contrôlons nos résultats pour le rôle du degré de transparence des marchés financiers ainsi que le degré de protection des investisseurs. Nous constatons que l’avantage informationnel sur les facteurs globaux (industriels) de risque contribue positivement à la création de la performance des fonds sur toute la période d’étude. La «fuite vers la familiarité» au cours de la période de la récente crise financière est nuisible pour la performance des fonds et peut être considérée comme étant un biais. Les gestionnaires de fonds qui recherchent à investir dans des titres familiers pendant la période de crise financière ne créent pas de valeur pour leurs clients.Dans notre troisième papier, nous examinons les déterminants de la stratégie de rotation des portefeuilles dans différentes industries et l’impact de cette stratégie sur la performance des fonds globaux américains. Nous constatons que les fonds mutuels qui s'engagent dans des stratégies de rotation sectorielle améliorent leur performance. Ce résultat est conforme aux résultats de la littérature qui suggèrent que les fonds gérés activement sont plus performants. De plus, nous constatons que la stratégie de rotation industrielle des fonds est influencée positivement et significativement par l’avantage informationnel des gérants sur les facteurs globaux de risque. Cette étude est en accord avec plusieurs articles de la littérature qui soulignent l'importance croissante de l’information sectorielle pour la gestion d’actifs (Hiraki et al., 2015; Schumacher, 2017). Ce papier confirme également différents arguments selon lesquels la rotation sectorielle pourrait être considérée comme une stratégie optimale pour le choix de portefeuille dans le contexte d’internationalisation des marchés financiers (Weiss, 1998, Cavaglia et al., 2004). / This dissertation responds to a lack within the literature about the impact of private global information on mutual funds portfolio holdings and performance. We conduct three essays that aim to explain different controversial topics about the global funds’ performance and investments choices.In the first paper we examine how the private information on global factors is affecting US global funds’ trading profits. After controlling for different performance benchmark models and for several managerial fund characteristics, we find a positive and significant impact of the private global information on mutual funds’ performance. The fund’s informational advantage on global factors is industry-specific rather than country-specific, consistent with the results of Albuquerque et al. (2009) and Hiraki et al. (2015). We also argue that the use of the degree of sector concentration (DSC) as a proxy for the manager’s informational advantage (as employed in some recent papers) is noisy. The performance of funds is mainly driven by the proxy of private information on industrial factors and not by its degree of sector concentration. DSC affects positively the trading profits of funds in periods of good financial stability. However, this positive impact is only significant for funds with a high informational advantage on global factors.In the second paper, we investigate whether this is the private global information or the familiarity with foreign markets which has driven the performance of global funds during the recent subprime crisis. In fact, it has been shown within the literature that fund managers tend to hold familiar stocks during periods of heightened markets. We find that the private information on global factors of risk is the main driver of funds’ performance for the 2005-2016 period including the subprime crisis period. This result holds when considering different familiarity, market transparency and investor’s protection proxies and when employing different performance benchmark models. On the opposite, the familiarity proxies reverse their effect during the financial crisis period. We show that the “flight to familiarity” within this period is detrimental for funds’ performance and rather can be assessed as a bias. Managers that seek familiarity during periods of financial crisis to be “on the safe side” do not create value for their investors. Our results also suggest that during periods of heightened market uncertainties, fund managers can benefit from processing information on industrial factors, consistent with the findings of Albuquerque et al. (2009) and Hiraki et al. (2015).In our third and last paper, we investigate the determinants of fund’s portfolio rebalancing decisions of foreign holdings that belong to different industries and their relative implication on US global funds’ performance. We find that mutual funds that engage in industrial sector rotation strategies enhance their performance. This result is consistent with the literature view that actively managed funds perform better. Moreover, we find that the fund’s industrial rebalancing activity is positively and significantly affected by its informational advantage on global factors. This study is in line with several papers that highlighted the increasing importance of global industry factors for asset allocation (Hiraki et al., 2015; Schumacher, 2017) and consistent with different arguments stating that industry sector rotation can be optimal for future global investing especially with the increasing integration of capital markets (Weiss, 1998; Cavaglia et al., 2004).

This thesis contains four chapters, each of which examines different aspects of the uncertainty facing monetary policymakers.''Monetary policy and market interest rates'' investigates how interest rates set on financial markets respond to policy actions taken by the monetary authorities. The reaction of market rates is shown to depend crucially on market participants' interpretation of the factors underlying the policy move. These theoretical predictions find support in an empirical analysis of the U.S. financial markets.''Predicting monetary policy using federal funds futures prices'' examines how prices of federal funds futures contracts can be used to predict policy moves by the Federal Reserve. Although the futures prices exhibit systematic variation across trading days and calendar months, they are shown to be fairly successful in predicting the federal funds rate target that will prevailafter the next meeting of the Federal Open Market Committee from 1994 to 1998.''Monetary policy with uncertain parameters'' examines the effects  of parameter uncertainty on the optimal monetary policy strategy. Under certain parameter configurations, increasing uncertainty is shown to lead to more aggressive policy, in contrast to the accepted wisdom.''Should central banks be more aggressive?'' examines why a certain class of monetary policy models leads to more aggressive policy prescriptions than what is observed in reality. These counterfactual results are shown to be due to model restrictions rather than central banks being too cautious in their policy behavior. An unrestricted model, taking the dynamics of the economy and multiplicative parameter uncertainty into account, leads to optimal policy prescriptions which are very close to observed Federal Reserve behavior. / <p>Diss. Stockholm : Handelshögskolan, 1999</p>

The study aimed to explore and describe the factors influencing disclosure of Human Immunodeficiency Virus (HIV) status to sexual partners by people infected with HIV in Botswana, by undertaking an exploratory and descriptive qualitative study. Data was collected through in-depth interviews with people infected with HIV who had disclosed their HIV status to their partners. The major findings of the study confirmed disclosure as a multi-stage process. People infected with HIV experienced mainly positive and some negative outcomes following disclosure. Disclosure was associated with the discloser’s motivations, personal and cultural beliefs, risk-benefit assessment, individual circumstances (context), previous experiences, and perceived degree of control over private information. The communication privacy management (CPM) theory helped explain the findings. The key factor influencing disclosure was protecting others. Non-disclosers had also seriously considered disclosing to partners. / Health Studies / M.P.H