Die Dissertation erläutert, wie ein Anonymisierungsdienst zu gestalten ist, so daß er für den durchschnittlichen Internetnutzer benutzbar ist. Ein Schwerpunkt dabei war die Berücksichtigung einer möglichst holistischen Sichtweise auf das Gesamtsystem "Anonymisierungsdienst". Es geht daher um die ingenieurmäßige Berücksichtigung der vielschichtigen Anforderungen der einzelnen Interessengruppen. Einige dieser Anforderungen ergeben sich aus einem der zentralen Widersprüche: auf der einen Seite die Notwendigkeit von Datenschutz und Privatheit für den Einzelnen, auf der anderen Seite die ebenso notwendige Überwachbarkeit und Zurechenbarkeit, etwa für die Strafverfolgung. Die Dissertation beschäftigt sich mit dem Aufzeigen und Entwickeln von technischen Möglichkeiten, die zur Lösung dieses Widerspruches herangezogen werden können.

The aim of this work is to show the effectiveness of techniques that allow a user to maintain its privacy and anonymity while participating in real word scenario. Users need to communicate with each other in many situations in order to share information. This creates the danger of the user’s privacy being breached and it can discourage users from taking active participation in any information sharing task. There are many real scenarios or application where users want to remain anonymous while having their communication secured. This is so in vehicular communication systems. Group signatures are versatile cryptographic tools that are suitable when we need security and privacy protection. A group signature scheme allows members of a group to sign messages on behalf of the group. Any receiver can verify the message validity but cannot discover the identity of the sender from the signed message or link two or more messages from the same signer. However, the identity of the signer can be discovered by an authority using a signed message. For this reason, Group Signature schemes were proposed in the context of vehicular communication systems. In this context, communication and computation overheads are critical. Thus, the focus of this thesis is to implement and compare different group signature schemes in terms of overhead introduced due to processing cost, and analytically evaluate their suitability for vehicular communication scenarios.

Internet has become a great part of our daily routines giving us the ability to perform various actions in many aspects of our personal and social life. The new available opportunities provided with the Internet enhancement have opened a great space for improvement in our lives but they have also provided space for new types of criminal behaviour to occur. Cyberbullying and cyberstalking are part of the wide range of criminal behaviors performed through an online device. The presence of online criminal behavior is accompanied by the increase on the online victimization rates. The aim of this paper is to explain online victimization performed through cyberbullying and cyberstalking based on the theories of routine activity, social learning and victim precipitation.The results show that online victimization is closely connected with the daily routines that individuals have accompanied by the interactions and associations that are performed during our social life who also influence the practise of online victimization. Anonymity is a commonly found factor almost always present and plays an important role on explaining the behavior itself for both the offender and the victim's side. Overall the findings show that both online offenders and online victims of cyberbullying and cyberstalking are given more engagement opportunities in the criminal act due to the constant usage and the inclusion of online devices in theor daily routines. The above accompanied with the anonymity and opportunity provided by cyberspace ease the " performance" of cyber victimization.

Denna text diskuterar antagonistisk graffiti i Pompeji ur ett rumsligt perspektiv för att analysera spridningen av graffiti. Texten ämnar även att undersöka ifall det är vanligare att skriva förolämpande graffiti på specifika platser i staden. Ytterligare ett mål med uppsatsen är att undersöka ifall modern teoribildning kan bidra till en bättre förståelse av graffitins spridning genom disinhibitionsteorin. Antik graffiti jämförs med moderna beteenden online och kring graffiti. Graffitin verkar skrivas på platser där den är synlig av andra människor och den är vanlig på både privata och offentliga byggnader. Disinhibition kan vara en möjlig förklaringsmodell angående förolämpande graffiti orsakad av exempelvis anonymitet. / This text discusses antagonistic graffiti in Pompeii from a spatial perspective to analyse the spread of graffiti. The text also aims to study whether it is more common to write offensive graffiti in certain areas of the city. Another goal with this thesis is to study whether modern sociological theory can help understand the spread of graffiti through the disinhibition theory. Ancient graffiti is compared to modern behaviours online and around graffiti. Graffiti seems to be written in places where it could be seen by other people, and it is common on both private and public buildings. Disinhibition could be a possible explanatory model when discussing offensive graffiti caused by, for example, anonymity.

Breaking the anonymity of different wireless users with the purpose of decreasing internet crime rates is addressed in this thesis by considering radiometric identification techniques. Minute imperfections and non-idealities in the different transmitter components, especially the inherent nonlinearity in power amplifiers, result in variations in their Volterra series representations which could be utilized as a signature. For a two user scenario, signal processing algorithms based on generalized likelihood ratio test(GLRT) and the classical likelihood ratio test are introduced and the resulting receiver decision rules and performance curves are presented. These algorithms consider the high signal to noise ratio(SNR) case where we have available the input samples completely at the receiver which is a practical assumption for most cases. Volterra series are widely used in behavioral modeling of power amplifiers. To validate the existence of these variations in the Volterra series representation of power amplifiers, process variations are introduced as major sources. The plausibility of our techniques are justified by deriving and comparing the Volterra coefficients for the fast and slow process corners. Finally,an information theoretic framework is presented where the amount of mutual information of the output about the Volterra coefficients represents the amount of anonymity taken from users. Here, some results for the low SNR case are presented to prove the achievability of some information about individual systems using our hardware anonymity breaking techniques.

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Humans’ emotions have the ability to take over, which might end up with responses inappropriate to the situation. The solution to inappropriate responses is to have a better awareness. Great team-work, calm employees, and rational decision making are all qualities that derive benefit from emotional self-awareness. However, studies show that only 36 percent can identify their emotions as they happen. This paper takes on the opportunity to raise emotional self-awareness by designing a prototype that enables the users to reflect and anonymously share their emotion through an audience response system. Forty-eight participants, in various group sizes, did within-subjects tests. They started by writing down their answer to the question: How do you feel?. They later answered through the prototype. Whether or not the participants managed to be more specific through the prototype was measured, as well as their perceived anonymity. The results revealed that the prototype was useful in both helping the users to learn emotion definitions and further specify their emotion. In regards to the perceived anonymity, it showed that the design was favoring a larger group size around 20 participants.

More than two-and-a-half million people currently use the Tor network to communicate anonymously via the Internet and gain access to online media that are not accessible using standard Internet technology. This sphere of communication can be described as the hidden web. In part because this phenomenon is very recent, the subject has scarcely been studied in the social sciences. It is therefore the purpose of this paper to answer four fundamental questions: What is the hidden web? What characterises the communication sphere of the hidden web in contrast to the “normal Internet”? Which reasons can be identified to explain the development of the hidden web as a new communication sphere? And, finally, what is the social significance of the hidden web? / Über zweieinhalb Millionen Menschen nutzen gegenwärtig das Tor Network, um anonym über das Internet zu kommunizieren und Zugriff auf Online-Medien zu erhalten, die mit gewöhnlicher Internettechnik nicht nutzbar ist. Diese Kommunikationssphäre kann als Hidden Web bezeichnet werden. Unter anderem weil es sich um ein sehr junges Phänomen handelt, liegen bisher nahezu keine sozialwissenschaftlichen Erkenntnisse zu dem Thema vor. Dementsprechend werden hier vier grundlegende Fragen beantwortet: Was ist das Hidden Web? Welche Eigenschaften weist die Kommunikationssphäre des Hidden Web im Vergleich zum „normalen“ Internet auf? Welche Gründen lassen sich identifizieren, die die Entstehung des Hidden Web als neue Kommunikationssphäre erklären können? Und welche gesellschaftliche Bedeutung kommt dem Hidden Web schließlich zu?

The work presented in this document in an account of my work as a PhD student at LIX, Ecole Polytechnique, in the COMETE team under the supervision of Catuscia Palamidessi. During these studies, I have been in interested in the various aspects of concurrency covered by the COMETE team activities. The initial goal of my thesis was to investigate the aspects related to process calculi based formalisms to express and analyze Security Protocols. The ultimate goal was to makes some advances towards the automatic verification of security properties. In particular, I was interested in information-hiding protocols which require no cryptography, but normally use randomized mechanisms and therefore exhibit probabilistic behavior. Information hiding protocols are used typically in networks, and they are run by parties that reside in different locations of the system, and therefore interact asynchronously. The first work that I did was to try to give a correct meaning to the various notions of formal asynchronous communications used in various models, in particular between the field of concurrency and the field of distributed computing, where this was a recurrent question. These results are presented in the first part of this document. Being interested in the formal aspects of information-hiding problems, I took part in the preparation of the journal version of [BP09], and started preparing an automated probabilistic anonymity checker based on the formalism presented in this document. This lead to an initial draft of an implementation presented in http://vamp.gforge.inria.fr/. The formalism for this analysis is presented in the fourth part of this document. Another aspect of the verification of information hiding properties is that it requires to compute the probabilities of the possible outcomes for each scheduler. For this reason, this application quickly turned out to be highly inefficient. However, in an asynchronous system, a lot of transitions are confluent, which means that when evaluating a process, it is only necessary to choose one of the two confluent branches. Hence, I have worked on formalizing the possible optimizations based on the possible confluent computations. This work is presented in the second part of the document. Another interesting aspects of probabilistic protocols is the possibility to con- sider infinite runs. By doing such consideration, it is possible to verify the correction of some probabilistic protocols. For instance, in the case of the Crowds routing protocol, presented in Section 5.3, the protocol is considered correct because the probability of running into an infinite execution is null, hence the message will eventually be delivered. For this reason, I got interested in extending the meaning of a asynchronous probabilistic computations to the case of an infinite execution. As a matter of fact, the combination of infinite computation, confluence and probability is not easy to treat in the general case. The problem of confluence in concurrency is solved in an elegant way in an asyn- chronous paradigm called Concurrent Constraint Programming (CCP). Hence, I decided to study infinite computations in a probabilistic version of CCP. The problem, however, is that the meaning of the result of an infinite probabilistic computation was still an open problem also in that context. Hence, I studied a possible way to define this result, using the notion of valuations and sober spaces, and applied it to give a denotational semantics to probabilistic CCP, including infinite computations. This work is presented in the third part of the document. I have chosen a specific order for the various parts of this document that follows the various formal models that are used, in order to present each result along with the corresponding formalism. * In the first and second parts, I present the formal concurrent models, and in the particular asynchronous ones. * In the third part, I present the probabilistic CCP. This part also presents mathematic structures for the representation of infinite probabilistic executions. * Eventually, an application of both asynchronous and probabilistic models to the case of probabilistic information hiding is presented in the fourth part.

Denna studie har som mål att ge en inblick i varför och hur Internetanvändare nyttjar Tor Browser och The Dark Web. Nätverket och webbläsaren förknippas ofta med illegal verksamhet, men även med yttrandefrihet och anonymitet. Vi vill undersöka hur användandet av dessa ser ut och skapa en förståelse kring varför individer väljer att vända sig dit. Detta görs med hjälp av kvalitativa intervjuer med sammanlagt nio personer som använder sig av nätverket och webbläsaren. Intervjuerna har genomförts på forumen Flashback Forum, Quora och Reddit genom sajternas privata chattfunktioner. Materialet har sedan analyserats med hjälp av det teoretiska perspektivet Uses and Gratification för att synliggöra vilka sociala och psykologiska behov som tillgodoses genom användandet. Studiens resultat visade att merparten av de intervjuade vände sig till Tor Browser och The Dark Web eftersom att de, i förstahand, var intresserade av illegal verksamhet och använde nätverket samt webbläsaren för att få tillgång till materialet, men även för att göra det svårare för myndigheter att spåra deras aktivitet online. Användandet grundade sig, i andrahand, i ett intresse för yttrandefrihet och anonymitet och det var även dessa ämnen som gjorde att användarna fortsatte att återvända till Tor Browser och The Dark Web.