Sistemas online como Facebook, Twitter, Digg, e comunidades BitTorrent (entre vários outros) oferecem um processo leve para a obtenção de identidades (por exemplo, confirmar um endereço de e-mail válido; os requisitos podem variar dependendo do sistema), de modo que os usuários possam cadastrar-se facilmente nos mesmos. Tal conveniência vem com um preço, no entanto: com um pequeno esforço, um atacante pode obter uma grande quantidade de contas falsas (ataque Sybil), e utilizá-las para executar atividades maliciosas (que possam prejudicar os usuários legítimos) ou obter vantagens indevidas. É extremamente desafiador (senão impossível) desenvolver uma única solução de gerenciamento de identidades que seja ao mesmo tempo capaz de oferecer suporte a uma variedade de usuários usando dispositivos heterogêneos e adequada para uma diversidade de ambientes (por exemplo, sistemas distribuídos de larga escala, Internet das Coisas, e Internet do Futuro). Como consequência, a comunidade de pesquisa tem focado no projeto de soluções de gerenciamento de identidades customizadas, em cenários com um conjunto bem definido de propósitos, requisitos e limitações. Nesta tese, abordamos o problema de contas falsas em sistemas distribuídos de larga escala. Mais especificamente, nos concentramos em sistemas baseados no paradigma para- par e que podem acomodar esquemas de gerenciamento de identidades leves e de longo prazo (ex., sistemas de compartilhamento de arquivos e de live streaming, sistemas de detecção de intrusão colaborativos, entre outros); leves porque os usuários devem obter identidades sem precisar fornecer “provas de identidade” (ex., passaporte) e/ou pagar taxas; e longo prazo porque os usuários devem ser capazes de manter suas identidades (ex., através de renovação) por um período indefinido. Nosso principal objetivo é propor um arcabouço para precificar adaptativamente as solicitações de identidades como uma abordagem para conter ataques Sybil. A ideia chave é estimar um grau de confiança para as solicitações de identidades, calculada como função do número de identidades já concedidas em um dado período, considerando a origem dessas solicitações. Nossa abordagem baseia-se em prova de trabalho e usa desafios criptográficos como um recurso para conter atacantes. Nesta tese, nós também concentramos esforços na reformulação dos desafios tradicionais, de modo a torná-los “verdes” e “´uteis”. Os resultados obtidos via simulação e experimentação mostraram a viabilidade técnica de usar desafios verdes e ´uteis para o gerenciamento de identidades. Mais importante, eles mostraram que caracterizar as solicitações de identidades com base na origem das mesmas constitui uma abordagem promissora para lidar com a redução substancial da disseminação de contas falsas. / Online systems such as Facebook, Twitter, Digg, and BitTorrent communities (among various others) offer a lightweight process for obtaining identities (e.g., confirming a valid e-mail address; the actual requirements may vary depending on the system), so that users can easily join them. Such convenience comes with a price, however: with minimum effort, an attacker can obtain a horde of fake accounts (Sybil attack), and use them to either perform malicious activities (that might harm legitimate users) or obtain unfair benefits. It is extremely challenging (if not impossible) to devise a single identity management solution at the same time able to support a variety of end-users using heterogeneous devices, and suitable for a multitude of environments (e.g., large-scale distributed systems, Internet-of-Things, and Future Internet). As a consequence, the research community has focused on the design of system-specific identity management solutions, in scenarios having a well-defined set of purposes, requirements, and constraints. In this thesis, we approach the issue of fake accounts in large-scale, distributed systems. More specifically, we target systems based on the peer-to-peer paradigm and that can accommodate lightweight, long-term identity management schemes (e.g., file sharing and live streaming networks, collaborative intrusion detection systems, among others); lightweight because users should obtain identities without being required to provide “proof of identity” (e.g., passport) and/or pay taxes; and long-term because users should be able to maintain their identities (e.g., through renewal) for an indefinite period. Our main objective is to propose a framework for adaptively pricing identity requests as an approach to limit Sybil attacks. The key idea is to estimate a trust score for identity requests, calculated as a as function of the number of identities already granted in a given period, and considering their source of origin. Our approach relies on proof of work, and uses cryptographic puzzles as a resource to restrain attackers. In this thesis, we also concentrate on reshaping traditional puzzles, in order to make them “green” and “useful”. The results obtained through simulation and experimentation have shown the feasibility of using green and useful puzzles for identity management. More importantly, they have shown that profiling identity requests based on their source of origin constitutes a promising approach to tackle the dissemination of fake accounts.

Magister Legum - LLM / Black Economic Empowerment (BEE) has been a topic of discussion since the dawn of democracy in April 1994. Due to the entrenched inequalities of the past, economic empowerment is very important for the economic growth of the majority of South Africa’s citizens. However, significant economic enrichment of black people has not been made, despite, economic success, legislation, state policies and programme interventions. This economic growth is to be realised through the use of preferential procurement as a policy tool for BEE. Whilst sufficient legislation has been enacted to regulate preferential procurement, to favour black people, much still seems to be lacking in the enforcement of the laws in public procurement. Central to the challenges of preferential procurement is the disharmony between the Framework legislation governing preferential procurement and BEE. This discord has seen two visions being followed for preferential procurement; the Procurement Act refers to the beneficiaries of BEE as historically disadvantaged individuals (HDI; s) and the goals for BEE are measured through specific goals which promotes narrow empowerment; the BBBEE Act on the other hand defines black people as the recipients of BEE and through the BEE Codes broad-based empowerment is promoted through seven core elements. This congruency has not served the promotion of preferential procurement, it has created a hindrance that frustrates economic growth for those it is intended. The other quandary that undermines the success of preferential procurement is willful practices engaged by both tenderers and public officials; skills deficiency in the adjudication of tenders and self-interest. The success of BEE through preferential procurement is dependent on a coherently legislated procurement environment fortified by perceptive public officials. The objective of this thesis is to analyse the impact of these challenges on the success of preferential procurement. The study will highlight the main practices that defeat the use of preferential procurement. This will include an analysis of the various legislation and the amendments thereto. In addition the enquiry will examine the proficiency of public officials in the adjudication of public tendering. Recommendations for a successful preferential public procurement environment will be made. The proposed thesis will utilise, inter alia, relevant legislation, case law, theses, journals, books and policy documents. / South Africa

Cette recherche qualitative examine le processus d’enquête publique de la Commission d’enquête sur l’octroi et la gestion des contrats publics dans l’industrie de la construction1 au Québec. Le principal objectif est de comprendre comment la CEIC construit, pendant ce processus d’enquête, le rôle des agents économiques dans le scandale de corruption et de collusion dans la Ville de Montréal. Notre cadre théorique s’inscrit dans le constructivisme modéré et part de l’idée que les individus appréhendent la réalité sociale et la construisent à partir des représentations et significations qu’ils apprennent et développent lors de la socialisation et des expériences quotidiennes. Leurs activités sont déterminées par ce rapport qu’ils entretiennent avec le monde et par les rapports de pouvoirs entre les individus et groupes sociaux. Les divers documents utilisés ou produits pour et par la commission ont été soumis à une analyse critique du discours. Nous cherchions à comprendre comment par l’utilisation du langage, et à partir de ce qui est dit ou non dans les documents produits par la CEIC, le rôle des entreprises est construit en défendant les intérêts de certains acteurs au détriment des autres. Notre analyse a mis en évidence que les conclusions de la CEIC correspondent à la réponse que le gouvernement lui suggère, de manière assez discrète, dans le mandat. Le rôle des compagnies a été construit à l’aide de trois stratégies adoptées tout au long des travaux. La CEIC réoriente son mandat en définissant les termes après avoir complété l’enquête, en changeant l’ordre des volets et l’objet de son enquête. Ainsi, son enquête porte sur l’obtention des contrats publics et non sur leur octroi : les compagnies sont les principaux acteurs du scandale. Elle décriminalise2 certains comportements et utilise le bouc émissaire fourni dans le mandat, à savoir le crime organisé, pour blanchir les cols blancs et surtout les fonctionnaires et hommes politiques le plus haut placés. Pour y parvenir, elle doit cependant contredire ses propres définitions des termes du mandat. La peur collective envers la violence et la perception de la mafia par les citoyens ont facilité cette décriminalisation sélective des comportements. Finalement, les compagnies sont présentées comme ayant été contaminées par l’infiltration du crime organisé dans l’industrie et cette contamination, ces compagnies l’ont transmise à quelques fonctionnaires. Nous sommes arrivés à la conclusion que le rôle des entreprises n’a pas été construit en partant de l’interprétation du mandat, comme le suggère notre question de recherche, mais de manière à calquer les conclusions qui y étaient suggérées : les crimes en col blanc s’expliquent par l’infiltration de la mafia dans l’industrie. En procédant ainsi, la CEIC a contribué à la sauvegarde et au renforcement du statu quo.

京都大学 / 新制・課程博士 / 博士(経済学) / 甲第22948号 / 経博第623号 / 新制||経||294(附属図書館) / 京都大学大学院経済学研究科経済学専攻 / (主査)教授 諸富 徹, 教授 矢野 剛, 教授 劉 徳強 / 学位規則第4条第1項該当 / Doctor of Economics / Kyoto University / DFAM

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / This thesis defines collusion broadly as play in a repeated game which differs from play in a one shot game. The analysis of collusion is an important part of many branches of economics. In industrial organization, for example, if collusion were not present then we could restrict investigation to the study of oligopolistic and competitive markets. Another important part of modern economic theory is the analysis of situations where there exists some ldnd of privileged information. Game theorists would say that in such a scenario there exists incomplete information. The predominant theme of the three essays composing this thesis is the study of repeated games under incomplete information. Typically, repeated game analyses have assumed the presence of complete information. However, many examples of repeated interaction must be treated in an incomplete information scenario. Auctions, the subject of the first essay, are the most natural example of this. The goal of this study is to understand how bidders collude in auctions. The main innovation is an explicit treatment of the repeated nature of the game to endogenize the threats necessary to support non competitive behavior. This analysis yields several testable implications about the behavior of colluding agents in auctions which are not apparent from the few models which have studied collusion in auctions from a static point of view. Nearly every model constructed to study collusion makes predictions which are at odds with accepted stylized facts. The most prominent of these paradoxes is the stability which theoretical models predict yet empirical and allegorical evidence rejects. This is the subject of the second essay. Incomplete information takes the form of how players evaluate future payoffs. This is an important detail because future payoffs are the only tool a cartel can use to enforce the play of collusive equilibria. The developed model imposes that patience is private information and heterogeneous and develops predictions which contrast strongly with accepted models of collusion. The predictions of the model are supported with discussion of some empirical evidence on cartels. The third essay develops a model which can have sociological as well as economic applications, in that it studies how rational agents form surplus creating partnerships in a repeated, incomplete information environment. Previous work has assumed an exogenous production technology which partners use to create this surplus. Furthermore an agents type, which affects surplus creation, has always been assumed to be observable. This essay studies matching with an endogenous production technology, in the sense that the surplus is a function of the level of collusion which can be supported. Collusion can be supported to varying degree based upon the type (patience, or discount factor) of each agent in the partnership. A special attention is turned to contrasting the implications of the model in the presence of complete as opposed to incomplete information.

Charles University in Prague Faculty of Social Sciences Institute of Economic Studies MASTER THESIS An Experimental Test of Design Alternatives for Spectrum Auctions with Communication Channels Author: Bc. Jindřich Matoušek Supervisor: PhDr. Lubomír Cingl Academic Year: 2013/2014 Abstract The multi-unit auction mechanisms are one of the most important instruments used for the allocation of spectrum licenses, airport time slots, delivery routes, networking or furniture allocation. This thesis experimentally examines the attributes of complex multi-unit auction mechanisms (Simultaneous Multi-Round Auction and its combinatorial extension Simultaneous Multi-Round Package Bidding) in the presence of an opportunity to collude among the bidding participants due to a provision of a simple communication channel - a chat window. The results suggest that in our parameter setting, the combinatorial bidding format does not bring higher efficiency. Interestingly, allowing for communication increases efficiency in both examined auction formats. Bidders are able to split the auctioned goods in a collusive agreement, which results in a better allocation compared to the auction formats without the communication channel. Combinatorial bidding on packages probably makes the decision-making problem of bidders hard to process...

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La théorie de l'agence a offert une analyse approfondie des conditions sous lesquelles les incitations parviennent à réconcilier les intérêts divergents du principal et de l'agent. Les essais présentés dans cette thèse évaluent la pertinence empirique de ces résultats face à l'intervention d'une tierce partie dans trois situations-types : le comportement de corruption, les choix de pratique des médecins spécialistes et la demande de travail au noir

Les caractéristiques de l'offre de gaz en Europe et les spécificités du marché gazier ont conduit les régulateurs à adopter des régulations asymétriques, prenant la forme de gas release et d'objectifs de pertes de parts de marché. Les expériences empiriques montrent, en accord avec la théorie économique, que ces mesures rendent des concurrents actifs sur le marché et ne découragent pas les investissements. En terme de concurrence, les effets sont plus mitigés. Certains effets positifs trouvent certainement leur cause dans la croissance de la consommation qui est parfois exponentielle ou le développement des infrastructures d'importation et de transport. Ces mesures peuvent cependant favoriser les comportements collusifs, les stratégies d'écrémage ou de « reverse cherry picking », ainsi que des entrées inefficaces, rendues possibles car le concurrent est protégé pour une période de temps donnée. Un gas release crée une relation commerciale entre l'opérateur historique et son concurrent, ainsi qu'un système de contraintes sur les capacités de chacun. Les stratégies de prix ou de quantités sont alors modifiées. Les prix d'équilibre sont plus volatils et peuvent s'éloigner nettement du « mark-u p » de concurrence. De même, les stratégies d'un modèle de COURNOT se complexifient. L'opérateur historique, si les quantités rétrocédées sont fortes et ses approvisionnements faibles, peut laisser augmenter volontairement ses coûts pour accroître ses profits. Cette stratégie d'augmentation des coûts des rivaux est d'autant plus possible que le prix de rétrocession est proche de ses coûts d'approvisionnement. Elle ne détériore pas le surplus des consommateurs mais diminue le bien-être. Le régulateur peut restaurer l'incitation à l'efficacité en fixant une proportion rétrocédée en fonction du niveau des approvisionnements observé. Cette proportion ne doit pas être trop faible pour faire bénéficier le marché de l'incitation à l'efficacité de l'opérateur historique et des ventes plus importantes des deux opérateurs. Dans un même temps, une proportion trop élevée accentue les possibilités d'augmentation des coûts des rivaux ou de collusion.

Financial intermediaries are recognized to promote the efficiency of resource allocation by mitigating problems of incentives, asymmetric information and contract incompleteness. The role played by financial intermediaries is perceived so crucial that these institutions have received all over the world the greatest attention of regulators. Differences in regulatory regimes as well as in the real economies have produced a large variety in the characteristics of financial sectors and of individual intermediaries. In particular, in different places and times it is possible to observe banking sectors more or less competitive, populated by credit intermediaries of different sizes and with different levels of specialization. This variety of institutions raises interesting questions about the features of a well functioning financial intermediation sector. These questions have inspired an important body of economic literature which, however, is still inconclusive in many aspects. This dissertation includes three studies all intending to contribute in this direction. Chapter 2 Recent empirical works have found evidence consistent with larger banks having lower incentives to collect soft information and, in particular, to lend to small firms which are typically regarded as relatively opaque borrowers. Another market segment affected by relatively high levels of opaqueness is that of long-term loans and the reason is that, as emphasized in the corporate finance literature, short-term maturities are useful for the purpose of screening and monitoring investment projects. It is therefore interesting to assess whether large and small banks differ in their propensity to issue long-term loans, a type of investigation which has not been conducted yet. The reason why small and large banks might be expected to have a different propensity to issue long-term loans has to do with two notions. First, the effectiveness of a short-term maturity as a screening and monitoring device is preserved only if parties anticipate that, when payments are due, the lender will not be willing to extend the maturity, otherwise the initial short-term loan is de facto a long-term one. The problem may rise if the liquidation of insolvent firms produces lower payoffs than their refinancing: under these circumstances, as suggested by theories on renegotiation, liquidation is not implemented no matter what is written on the contract (parties can easily avoid the inefficiency that would result from liquidation, for example by simply granting a new loan). Second, at a more specific level theories on renegotiation suggest that the ability to commit to not extend thematurity decreases with bank size.1 Small banks are therefore predicted to issue shorter-term loans and to make a better selection of projects. The results are consistent with this prediction. Controlling for other characteristics of both the demand- and the supply-side as well as for the type of guarantee supplied, small banks have lower proportions of long-term loans to total loans and lower proportions of non performing loans to total loans. It should be pointed out that this does not imply that small banks are necessarily more efficient since short-term maturities also have costs; in particular, short-term maturities can interfere with the incentives of good types by inducing short-termism (the inflation of shortterm results at the expenses of total profitability). Moreover, beyond the ability to commit other supply-side features are shown to be relevant in the determination of the maturity, at least with specific classes borrowers. In particular, the findings are also consistent with the presence of economies of scale in lending at long maturities to firms in more technical and innovative industries. Since providing the right incentives to high quality entrepreneurs and to firms in innovative sectors is more likely to be a priority in more advanced countries, a policy implication is that these economies need more the presence of large credit institutions and the more so if venture capital and stock market are of limited size. Chapter 3 As already emphasized, theories on renegotiation suggest that the ability of banks to commit to a given course of action is an important factor for efficiency and that such ability depends on observable characteristics, like bank size. An important aspect which has not been analyzed in the theoretical literature is the effect that competition among banks exert on their ability to commit. The theoretical model presented in chapter 3 tries to provide an answer to this question. More specifically, the model studies the effects of competition among banks when these are subject to dynamic commitment problems which may result in excess refinancing of insolvent borrowers (soft budget constraint) as well as in excess termination of profitable ones (ratchet effect and short-termism). The building assumption is that, because of priority schemes and relationship lending, competition is harsher for new lending than for lending to ongoing projects. The main conclusion is that there exists a trade-off between the benefits that competition brings by disciplining low quality borrowers and the costs implied by worsening the incentives of good ones. The model also allows to look at the effects of competition on stability. This is done in two ways by looking at the extent to which competition interferes with the procyclicality of the banking sector and by studying if competition may eliminate or add inefficient equilibria. The main policy implication is that the optimal level of competition of a banking system is positively related to the quality of the underlying economy. If taken together, the results of chapters 2 and 3 also provide a theory about local or regional banks which is not based on any aprioristic assumption about the technology of these type of intermediaries. As long as these institutions can be seen as banks with a relatively high market power and a relatively small size (they are often important players at a local level although of limited size), both chapters 2 and 3 suggest that these intermediaries can more easily commit to a tough stance at the refinancing stage, with positive effects on their ability to screen out bad projects but with negative effects on their ability to incentivize good types and to fund more technical and innovative firms. In other words, these institutions might promote growth at earlier stages of development, although they are not sufficient to address the incentive issues of more advanced economies. Interestingly, this interpretation of the role of local banks is totally distinct from the traditional one which is based on the aprioristic assumption that these banks are good in doing relationship lending. Chapter 4 Conflicts of interest of economic institutions carrying out a variety of functions are considered a widespread phenomenon severely limiting the efficiency that can be achieved. These worries are often taken as justification for regulations imposing transparency requirements or tougher measures like separation of functions. At the same time, contract theory suggests that the effects of opportunistic behavior can be limited by adopting appropriate incentive schemes. The third study, chapter 4, tries to understand from a theoretical point of view to what extent the use of incentive schemes can address the distortions posed by the presence of conflicts of interest. The universal bank is regarded as a (common) agent serving different clients with potentially conflicting interests: for example, it may buy assets on behalf of investors and sell assets on behalf of issuing firms. The clients offer incentive schemes to the bank and they behave non-cooperatively. The bank decides a level of effort and, when firewalls are absent, a level of collusion, modelled as a costly and unproductive redistribution of wealth among the clients (for example, the banks can at no cost sell the securities it is underwriting to the funds it manages and can do so at the price it likes). Firewalls are defined as all legal or economic devices imposing a real separation of functions and therefore preventing the bank from colluding as specified above. The main conclusion is that in the absence of firewalls the equilibrium incentive schemes are steeper. This means that the equilibrium level of effort is higher and may compensate the (ex post) inefficiency of collusion. In other words, not only appropriate incentive schemes can eliminate the distortions posed by conflicts of interest but, at least in principle, their presence may even be necessary for efficiency (this happens if effort is a public good for the two principals so that the allocation without firewalls is characterized by under-provision of effort). At the same time, the allocation without firewalls is shown to be the least efficient in the presence of one naive player who does not recognize the existence of the conflict of interest. As long as transparency requirements can be considered tools to improve market participants’ sophistication, these results suggest why and how this type of regulation can work. Moreover, the model allows to draw conclusions about the desirability of tougher regulation prescribing a more or less neat separation of functions. With sophisticated economic agents, who can address the distortions posed by conflicts of interest by choosing appropriate incentive schemes, separation of functions is unnecessary or even detrimental for efficiency. On the other hand, more or less powerful firewalls are desirable if market participants are not considered sufficiently sophisticated to be able to react to the presence of conflicts of interest and if transparency requirements cannot increase their sophistication. In few words, the optimal regulation of conflicts of interest is softer in situations involving professionals who are more likely to realize and to react by choosing an appropriate incentive scheme or, more generally, for institutions operating in advanced economies where the average level of market participants sophistication is higher.