Anonymous communications networks help to solve the real and important problem of enabling users to communicate privately over the Internet. However, by doing so, they also introduce an entirely new problem: How can service providers on the Internet---such as websites, IRC networks and mail servers---allow anonymous access while protecting themselves against abuse by misbehaving anonymous users? Recent research efforts have focused on using anonymous blacklisting systems (also known as anonymous revocation systems) to solve this problem. As opposed to revocable anonymity systems, which enable some trusted third party to deanonymize users, anonymous blacklisting systems provide a way for users to authenticate anonymously with a service provider, while enabling the service provider to revoke access from individual misbehaving anonymous users without revealing their identities. The literature contains several anonymous blacklisting systems, many of which are impractical for real-world deployment. In 2006, however, Tsang et al. proposed Nymble, which solves the anonymous blacklisting problem very efficiently using trusted third parties. Nymble has inspired a number of subsequent anonymous blacklisting systems. Some of these use fundamentally different approaches to accomplish what Nymble does without using third parties at all; so far, these proposals have all suffered from serious performance and scalability problems. Other systems build on the Nymble framework to reduce Nymble's trust assumptions while maintaining its highly efficient design. The primary contribution of this thesis is a new anonymous blacklisting system built on the Nymble framework---a nimbler version of Nymble---called Nymbler. We propose several enhancements to the Nymble framework that facilitate the construction of a scheme that minimizes trust in third parties. We then propose a new set of security and privacy properties that anonymous blacklisting systems should possess to protect: 1) users' privacy against malicious service providers and third parties (including other malicious users), and 2) service providers against abuse by malicious users. We also propose a set of performance requirements that anonymous blacklisting systems should meet to maximize their potential for real-world adoption, and formally define some optional features in the anonymous blacklisting systems literature. We then present Nymbler, which improves on existing Nymble-like systems by reducing the level of trust placed in third parties, while simultaneously providing stronger privacy guarantees and some new functionality. It avoids dependence on trusted hardware and unreasonable assumptions about non-collusion between trusted third parties. We have implemented all key components of Nymbler, and our measurements indicate that the system is highly practical. Our system solves several open problems in the anonymous blacklisting systems literature, and makes use of some new cryptographic constructions that are likely to be of independent theoretical interest.

Smart environments provide users with a large number of new services that will improve their lives, however, they also have the potential for collecting staggering amounts of personal information, which, if misused, poses a multitude of privacy threats to users ranging from identification, tracking, stalking, monitoring and profiling. Consequently, the users’ right to informational self-determination is at stake in smart environments. Usable Privacy-Enhancing Identity Management (PE-IdM) can re-establish user control by offering users a selection of meaningful privacy preference settings that they could choose from. However, different privacy trade-offs need to be considered and managed for the configuration of the identity management system as well as cultural privacy aspects influencing user's privacy preferences. Guidelines for usable management of privacy settings that address varying end user preferences for control and privacy conflicting goals are needed.   The objective of this thesis is to explore approaches for enforcing usable PE-IdM for smart environments, with a focus on vehicular ad hoc networks (VANETs). To that end, we unravel the technical state of the art regarding the problem space and solutions, as well as investigating users’ privacy preferences cross-culturally in Sweden and South Africa. We elicit requirements for achieving usable PE-IdM, which are based on usable configuration options, offering suitable selectable privacy settings that will cater for the needs and preferences of users with different cultural backgrounds.

The amount of personal identifiable information that people distribute over different online services has grown rapidly and considerably over the last decades. This has led to increased probabilities for identity theft, profiling and linkability attacks, which can in turn not only result in a threat to people’s personal dignity, finances, and many other aspects of their lives, but also to societies in general. Methods and tools for securing people’s online activities and protecting their privacy on the Internet, so called Privacy Enhancing Technologies (PETs), are being designed and developed. However, these technologies are often seen by ordinary users as complicated and disruptive of their primary tasks.   In this licentiate thesis, I investigate the usability aspects of three main privacy and security enhancing mechanisms. These mechanisms have the goal of helping and encouraging users to protect their privacy on the Internet as they engage in some of the steps necessary to complete a digital transaction. The three mechanisms, which have been investigated within the scope of different research projects, comprise of (1) graphical visualizations of service providers’ privacy policies and user-friendly management and matching of users’ privacy preferences “on the fly”, (2) methods for helping users create appropriate mental models of the data minimization property of anonymous credentials, and (3) employing touch-screen biometrics as a method to authenticate users into mobile devices and verify their identities during a digital transaction.   Results from these investigations suggest that these mechanisms can make digital transactions privacy-friendly and secure while at the same time delivering convenience and usability for ordinary users.

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When you are browsing websites, third-party resources record your online habits; such tracking can be considered an invasion of privacy. It was previously unknown how many third-party resources, trackers and tracker companies are present in the different classes of websites chosen: globally popular websites, random samples of .se/.dk/.com/.net domains and curated lists of websites of public interest in Sweden. The in-browser HTTP/HTTPS traffic was recorded while downloading over 150,000 websites, allowing comparison of HTTPS adaption and third-party tracking within and across the different classes of websites. The data shows that known third-party resources including known trackers are present on over 90% of most classes, that third-party hosted content such as video, scripts and fonts make up a large portion of the known trackers seen on a typical website and that tracking is just as prevalent on secure as insecure sites. Observations include that Google is the most widespread tracker organization by far, that content is being served by known trackers may suggest that trackers are moving to providing services to the end user to avoid being blocked by privacy tools and ad blockers, and that the small difference in tracking between using HTTP and HTTPS connections may suggest that users are given a false sense of privacy when using HTTPS. / <p>Source code, datasets, and a video recording of the presentation is available on the master's thesis website.</p>