Usable Security: Why Do We Need It? How Do We Get It?

Security experts frequently refer to people as “the weakest link in the chain” of system security. Famed hacker Kevin Mitnick revealed that he hardly ever cracked a password, because it “was easier to dupe people into revealing it” by employing a range of social engineering techniques. Often, such failures are attributed to users’ carelessness and ignorance. However, more enlightened researchers have pointed out that current security tools are simply too complex for many users, and they have made efforts to improve user interfaces to security tools. In this chapter, we aim to broaden the current perspective, focusing on the usability of security tools (or products) and the process of designing secure systems for the real-world context (the panorama) in which they have to operate. Here we demonstrate how current human factors knowledge and user-centered design principles can help security designers produce security solutions that are effective in practice

Passwords and the evolution of imperfect authentication

Theory on passwords has lagged practice, where large providers use back-end smarts to survive with imperfect technology.This is the author accepted manuscript. The final version is available from ACM via http://dx.doi.org/10.1145/269939

Secure and Usable User Authentication

Authentication is a ubiquitous task in users\u27 daily lives. The dominant form of user authentication are text passwords. They protect private accounts like online banking, gaming, and email, but also assets in organisations. Yet, many issues are associated with text passwords, leading to challenges faced by both, users and organisations. This thesis contributes to the body of research enabling secure and usable user authentication, benefiting both, users and organisations. To that end, it addresses three distinct challenges. The first challenge addressed in this thesis is the creation of correct, complete, understandable, and effective password security awareness materials. To this end, a systematic process for the creation of awareness materials was developed and applied to create a password security awareness material. This process comprises four steps. First, relevant content for an initial version is aggregated (i.e. descriptions of attacks on passwords and user accounts, descriptions of defences to these attacks, and common misconceptions about password and user account security). Then, feedback from information security experts is gathered to ensure the correctness and completeness of the awareness material. Thereafter, feedback from lay-users is gathered to ensure the understandability of the awareness material. Finally, a formal evaluation of the awareness material is conducted to ensure its effectiveness (i.e. whether the material improves participant\u27s ability to assess the security of passwords as well as password-related behaviour and decreases the prevalence of common misconceptions about password and user account security). The results of the evaluation show the effectiveness of the awareness material: it significantly improved the participants\u27 ability to assess the security of password-related behaviour as well as passwords and significantly decreased the prevalence of misconceptions about password and user account security. The second challenge addressed in this thesis is shoulder-surfing resistant text password entry with gamepads (as an example of very constrained input devices) in shared spaces. To this end, the very first investigation of text password entry with gamepads is conducted. First, the requirements of authentication in the gamepad context are described. Then, these requirements are applied to assess schemes already deployed in the gamepad context and shoulder-surfing resistant authentication schemes from the literature proposed for non-gamepad contexts. The results of this assessment show that none of the currently deployed and only four of the proposals in the literature fulfil all requirements. Furthermore, the results of the assessment also indicate a need for an empirical evaluation in order to exactly gauge the shoulder-surfing threat in the gamepad context and compare alternatives to the incumbent on-screen keyboard. Based on these results, two user studies (one online study and one lab study) are conducted to investigate the shoulder-surfing resistance and usability of three authentication schemes in the gamepad context: the on-screen keyboard (as de-facto standard in this context), the grid-based scheme (an existing proposal from the literature identified as the most viable candidate adaptable to the gamepad context during the assessment), and Colorwheels (a novel shoulder-surfing resistant authentication scheme specifically designed for the gamepad context). The results of these two user studies show that on-screen keyboards are highly susceptible to opportunistic shoulder-surfing, but also show the most favourable usability properties among the three schemes. Colorwheels offers the most robust shoulder-surfing resistance and scores highest with respect to participants\u27 intention to use it in the future, while showing more favourable usability results than the grid-based scheme. The third challenge addressed in this thesis is secure and efficient storage of passwords in portfolio authentication schemes. Portfolio authentication is used to counter capture attacks such as shoulder-surfing or eavesdropping on network traffic. While usability studies of portfolio authentication schemes showed promising results, a verification scheme which allows secure and efficient storage of the portfolio authentication secret had been missing until now. To remedy this problem, the (t,n)-threshold verification scheme is proposed. It is based on secret sharing and key derivation functions. The security as well as the efficiency properties of two variants of the scheme (one based on Blakley secret sharing and one based on Shamir secret sharing) are evaluated against each other and against a naive approach. These evaluations show that the two (t,n)-threshold verification scheme variants always exhibit more favourable properties than the naive approach and that when deciding between the two variants, the exact application scenario must be considered. Three use cases illustrate as exemplary application scenarios the versatility of the proposed (t,n)-threshold verification scheme. By addressing the aforementioned three distinct challenges, this thesis demonstrates the breadth of the field of usable and secure user authentication ranging from awareness materials, to the assessment and evaluation of authentication schemes, to applying cryptography to craft secure password storage solutions. The research processes, results, and insights described in this thesis represent important and meaningful contributions to the state of the art in the research on usable and secure user authentication, offering benefits for users, organisations, and researchers alike

The quest to replace passwords: A framework for comparative evaluation of web authentication schemes

Abstract—We evaluate two decades of proposals to replace text passwords for general-purpose user authentication on the web using a broad set of twenty-five usability, deployability and security benefits that an ideal scheme might provide. The scope of proposals we survey is also extensive, including password management software, federated login protocols, graphical password schemes, cognitive authentication schemes, one-time passwords, hardware tokens, phone-aided schemes and biometrics. Our comprehensive approach leads to key insights about the difficulty of replacing passwords. Not only does no known scheme come close to providing all desired benefits: none even retains the full set of benefits that legacy passwords already provide. In particular, there is a wide range from schemes offering minor security benefits beyond legacy passwords, to those offering significant security benefits in return for being more costly to deploy or more difficult to use. We conclude that many academic proposals have failed to gain traction because researchers rarely consider a sufficiently wide range of real-world constraints. Beyond our analysis of current schemes, our framework provides an evaluation methodology and benchmark for future web authentication proposals. Keywords-authentication; computer security; human computer interaction; security and usability; deployability; economics; software engineering. I

Access Control In and For the Real World

Access control is a core component of any information-security strategy. Researchers have spent tremendous energy over the past forty years defining abstract access-control models and proving various properties about them. However, surprisingly little attention has been paid to how well these models work in real socio-technical systems (i.e., real human organizations). This dissertation describes the results of two qualitative studies (involving 52 participants from four companies, drawn from the financial, software, and healthcare sectors) and observes that the current practice of access control is dysfunctional at best. It diagnoses the broken assumptions that are at the heart of this dysfunction, and offers a new definition of the access-control problem that is grounded in the requirements and limitations of the real world

Supporting users in password authentication with persuasive design

Activities like text-editing, watching movies, or managing personal finances are all accomplished with web-based solutions nowadays. The providers need to ensure security and privacy of user data. To that end, passwords are still the most common authentication method on the web. They are inexpensive and easy to implement. Users are largely accustomed to this kind of authentication but passwords represent a considerable nuisance, because they are tedious to create, remember, and maintain. In many cases, usability issues turn into security problems, because users try to work around the challenges and create easily predictable credentials. Often, they reuse their passwords for many purposes, which aggravates the risk of identity theft. There have been numerous attempts to remove the root of the problem and replace passwords, e.g., through biometrics. However, no other authentication strategy can fully replace them, so passwords will probably stay a go-to authentication method for the foreseeable future. Researchers and practitioners have thus aimed to improve users' situation in various ways. There are two main lines of research on helping users create both usable and secure passwords. On the one hand, password policies have a notable impact on password practices, because they enforce certain characteristics. However, enforcement reduces users' autonomy and often causes frustration if the requirements are poorly communicated or overly complex. On the other hand, user-centered designs have been proposed: Assistance and persuasion are typically more user-friendly but their influence is often limited. In this thesis, we explore potential reasons for the inefficacy of certain persuasion strategies. From the gained knowledge, we derive novel persuasive design elements to support users in password authentication. The exploration of contextual factors in password practices is based on four projects that reveal both psychological aspects and real-world constraints. Here, we investigate how mental models of password strength and password managers can provide important pointers towards the design of persuasive interventions. Moreover, the associations between personality traits and password practices are evaluated in three user studies. A meticulous audit of real-world password policies shows the constraints for selection and reuse practices. Based on the review of context factors, we then extend the design space of persuasive password support with three projects. We first depict the explicit and implicit user needs in password support. Second, we craft and evaluate a choice architecture that illustrates how a phenomenon from marketing psychology can provide new insights into the design of nudging strategies. Third, we tried to empower users to create memorable passwords with emojis. The results show the challenges and potentials of emoji-passwords on different platforms. Finally, the thesis presents a framework for the persuasive design of password support. It aims to structure the required activities during the entire process. This enables researchers and practitioners to craft novel systems that go beyond traditional paradigms, which is illustrated by a design exercise.Heutzutage ist es möglich, mit web-basierten Lösungen Texte zu editieren, Filme anzusehen, oder seine persönlichen Finanzen zu verwalten. Die Anbieter müssen hierbei Sicherheit und Vertraulichkeit von Nutzerdaten sicherstellen. Dazu sind Passwörter weiterhin die geläufigste Authentifizierungsmethode im Internet. Sie sind kostengünstig und einfach zu implementieren. NutzerInnen sind bereits im Umgang mit diesem Verfahren vertraut jedoch stellen Passwörter ein beträchtliches Ärgernis dar, weil sie mühsam zu erstellen, einzuprägen, und verwalten sind. Oft werden Usabilityfragen zu Sicherheitsproblemen, weil NutzerInnen Herausforderungen umschiffen und sich einfach zu erratende Zugangsdaten ausdenken. Daneben verwenden sie Passwörter für viele Zwecke wieder, was das Risiko eines Identitätsdiebstals weiter erhöht. Es gibt zahlreiche Versuche die Wurzel des Problems zu beseitigen und Passwörter zu ersetzen, z.B. mit Biometrie. Jedoch kann bisher kein anderes Verfahren sie vollkommen ersetzen, so dass Passwörter wohl für absehbare Zeit die Hauptauthentifizierungsmethode bleiben werden. ExpertInnen aus Forschung und Industrie haben sich deshalb zum Ziel gefasst, die Situation der NutzerInnen auf verschiedene Wege zu verbessern. Es existieren zwei Forschungsstränge darüber wie man NutzerInnen bei der Erstellung von sicheren und benutzbaren Passwörtern helfen kann. Auf der einen Seite haben Regeln bei der Passworterstellung deutliche Auswirkungen auf Passwortpraktiken, weil sie bestimmte Charakteristiken durchsetzen. Jedoch reduziert diese Durchsetzung die Autonomie der NutzerInnen und verursacht Frustration, wenn die Anforderungen schlecht kommuniziert oder übermäßig komplex sind. Auf der anderen Seite stehen nutzerzentrierte Designs: Hilfestellung und Überzeugungsarbeit sind typischerweise nutzerfreundlicher wobei ihr Einfluss begrenzt ist. In dieser Arbeit erkunden wir die potenziellen Gründe für die Ineffektivität bestimmter Überzeugungsstrategien. Von dem hierbei gewonnenen Wissen leiten wir neue persuasive Designelemente für Hilfestellung bei der Passwortauthentifizierung ab. Die Exploration von Kontextfaktoren im Umgang mit Passwörtern basiert auf vier Projekten, die sowohl psychologische Aspekte als auch Einschränkungen in der Praxis aufdecken. Hierbei untersuchen wir inwiefern Mental Modelle von Passwortstärke und -managern wichtige Hinweise auf das Design von persuasiven Interventionen liefern. Darüber hinaus werden die Zusammenhänge zwischen Persönlichkeitsmerkmalen und Passwortpraktiken in drei Nutzerstudien untersucht. Eine gründliche Überprüfung von Passwortregeln in der Praxis zeigt die Einschränkungen für Passwortselektion und -wiederverwendung. Basierend auf der Durchleuchtung der Kontextfaktoren erweitern wir hierauf den Design-Raum von persuasiver Passworthilfestellung mit drei Projekten. Zuerst schildern wir die expliziten und impliziten Bedürfnisse in punkto Hilfestellung. Daraufhin erstellen und evaluieren wir eine Entscheidungsarchitektur, welche veranschaulicht wie ein Phänomen aus der Marketingpsychologie neue Einsichten in das Design von Nudging-Strategien liefern kann. Im Schlussgang versuchen wir NutzerInnen dabei zu stärken, gut merkbare Passwörter mit Hilfe von Emojis zu erstellen. Die Ergebnisse zeigen die Herausforderungen und Potenziale von Emoji-Passwörtern auf verschiedenen Plattformen. Zuletzt präsentiert diese Arbeit ein Rahmenkonzept für das persuasive Design von Passworthilfestellungen. Es soll die benötigten Aktivitäten während des gesamten Prozesses strukturieren. Dies erlaubt ExpertInnen neuartige Systeme zu entwickeln, die über traditionelle Ansätze hinausgehen, was durch eine Designstudie veranschaulicht wird