Mobile devices store a diverse set of private user data and have gradually become a hub to control users' other personal Internet-of-Things devices. Access control on mobile devices is therefore highly important. The widely accepted solution is to protect access by asking for a password. However, password authentication is tedious, e.g., a user needs to input a password every time she wants to use the device. Moreover, existing biometrics such as face, fingerprint, and touch behaviors are vulnerable to forgery attacks. We propose a new touch-based biometric authentication system that is passive and secure against forgery attacks. In our touch-based authentication, a user's touch behaviors are a function of some random "secret". The user can subconsciously know the secret while touching the device's screen. However, an attacker cannot know the secret at the time of attack, which makes it challenging to perform forgery attacks even if the attacker has already obtained the user's touch behaviors. We evaluate our touch-based authentication system by collecting data from 25 subjects. Results are promising: the random secrets do not influence user experience and, for targeted forgery attacks, our system achieves 0.18 smaller Equal Error Rates (EERs) than previous touch-based authentication.

The peer-review system of most academic conferences relies on the anonymity of both the authors and reviewers of submissions. In particular, with respect to the authors, the anonymity requirement is heavily disputed and pros and cons are discussed exclusively on a qualitative level. In this paper, we contribute a quantitative argument to this discussion by showing that it is possible for a machine to reveal the identity of authors of scientific publications with high accuracy. We attack the anonymity of authors using statistical analysis of multiple heterogeneous aspects of a paper, such as its citations, its writing style, and its content. We apply several multilabel, multiclass machine learning methods to model the patterns exhibited in each feature category for individual authors and combine them to a single ensemble classifier to deanonymize authors with high accuracy. To the best of our knowledge, this is the first approach that exploits multiple categories of discriminative features and uses multiple, partially complementing classifiers in a single, focused attack on the anonymity of the authors of an academic publication. We evaluate our author identification framework, deAnon, based on a real-world data set of 3894 papers. From these papers, we target 1405 productive authors that each have at least three publications in our data set. Our approach returns a ranking of probable authors for anonymous papers, an ordering for guessing the authors of a paper. In our experiments, following this ranking, the first guess corresponds to one of the authors of a paper in 39.7% of the cases, and at least one of the authors is among the top 10 guesses in 65.6% of all cases. Thus, deAnon significantly outperforms current state-of-the-art techniques for automatic deanonymization.

Sybil attacks are a fundamental threat to the security of distributed systems. Recently, there has been a growing interest in leveraging social networks to mitigate Sybil attacks. However, the existing approaches suffer from one or more drawbacks, including bootstrapping from either only known benign or known Sybil nodes, failing to tolerate noise in their prior knowledge about known benign or Sybil nodes, and not being scalable. In this paper, we aim to overcome these drawbacks. Toward this goal, we introduce SybilBelief, a semi-supervised learning framework, to detect Sybil nodes. SybilBelief takes a social network of the nodes in the system, a small set of known benign nodes, and, optionally, a small set of known Sybils as input. Then, SybilBelief propagates the label information from the known benign and/or Sybil nodes to the remaining nodes in the system. We evaluate SybilBelief using both synthetic and real-world social network topologies. We show that SybilBelief is able to accurately identify Sybil nodes with low false positive rates and low false negative rates. SybilBelief is resilient to noise in our prior knowledge about known benign and Sybil nodes. Moreover, SybilBelief performs orders of magnitudes better than existing Sybil classification mechanisms and significantly better than existing Sybil ranking mechanisms.

There has been considerable success in developing strategies to detect insider threats in information systems based on what one might call the random object access model or ROA. This approach models illegitimate users as ones who randomly access records. The goal is to use statistics, machine learning, knowledge of workflows and other techniques to support an anomaly detection framework that finds such users. In this paper we introduce and study a random topic access model or RTA aimed at users whose access may be illegitimate but is not fully random because it is focused on common semantic themes. We argue that this model is appropriate for a meaningful range of attacks and develop a system based on topic summarization that is able to formalize the model and provide anomalous user detection effectively for it. To this end, we use healthcare as an example and propose a framework for evaluating the ability to recognize various types of random users called random topic access detection or RTAD. Specifically, we utilize a combination of Latent Dirichlet Allocation (LDA), for feature extraction, a k-nearest neighbor (k-NN) algorithm for outlier detection and evaluate the ability to identify different adversarial types. We validate the technique in the context of hospital audit logs where we show varying degrees of success based on user roles and the anticipated characteristics of attackers. In particular, it was found that RTAD exhibits strong performance for roles are described by a few topics, but weaker performance when users are more topic-agnostic.

The overall network traffic patterns generated by today's smartphones result from the typically large and diverse set of installed applications. In addition to the traffic generated by the user, most applications generate characteristic traffic from their background activities, such as periodic update requests or server synchronisation. Although the encryption of transmitted data in 3G networks prevents an eavesdropper from analysing the content, periodic traffic patterns leak side-channel information like timing and data volume. In this work, we extract such side-channel features from network traffic generated from the most popular applications, such as Facebook, WhatsApp, Skype, Dropbox, and others, and evaluate whether they can be used to reliably identify a smartphone. By computing fingerprints from approx,6,hours of background traffic, we show that 15 minutes of monitored traffic suffice to reliably identify a smartphone based on its behavioural fingerprint with a success probability of 90%.

We investigate whether a classifier can continuously authenticate users based on the way they interact with the touchscreen of a smart phone. We propose a set of 30 behavioral touch features that can be extracted from raw touchscreen logs and demonstrate that different users populate distinct subspaces of this feature space. In a systematic experiment designed to test how this behavioral pattern exhibits consistency over time, we collected touch data from users interacting with a smart phone using basic navigation maneuvers, i.e., up–down and left–right scrolling. We propose a classification framework that learns the touch behavior of a user during an enrollment phase and is able to accept or reject the current user by monitoring interaction with the touch screen. The classifier achieves a median equal error rate of 0% for intrasession authentication, 2%–3% for intersession authentication, and below 4% when the authentication test was carried out one week after the enrollment phase. While our experimental findings disqualify this method as a standalone authentication mechanism for long-term authentication, it could be implemented as a means to extend screen-lock time or as a part of a multimodal biometric authentication system.

Role mining tackles the problem of finding a role-based access control (RBAC) configuration, given an access-control matrix assigning users to access permissions as input. Most role-mining approaches work by constructing a large set of candidate roles and use a greedy selection strategy to iteratively pick a small subset such that the differences between the resulting RBAC configuration and the access control matrix are minimized. In this article, we advocate an alternative approach that recasts role mining as an inference problem rather than a lossy compression problem. Instead of using combinatorial algorithms to minimize the number of roles needed to represent the access-control matrix, we derive probabilistic models to learn the RBAC configuration that most likely underlies the given matrix. Our models are generative in that they reflect the way that permissions are assigned to users in a given RBAC configuration. We additionally model how user-permission assignments that conflict with an RBAC configuration emerge and we investigate the influence of constraints on role hierarchies and on the number of assignments. In experiments with access-control matrices from real-world enterprises, we compare our proposed models with other role-mining methods. Our results show that our probabilistic models infer roles that generalize well to new system users for a wide variety of data, while other models’ generalization abilities depend on the dataset given.

Android and Facebook provide third-party applications with access to users' private data and the ability to perform potentially sensitive operations (e.g., post to a user's wall or place phone calls). As a security measure, these platforms restrict applications' privileges with permission systems: users must approve the permissions requested by applications before the applications can make privacy-or security-relevant API calls. However, recent studies have shown that users often do not understand permission requests and are unsure of which permissions are typical for applications. As a first step towards simplifying permission systems, we cluster a corpus of 188,389 Android applications and 27,029 Facebook applications to find patterns in permission requests. Using a method for Boolean matrix factorization to find overlapping clusters of permissions, we find that Facebook permission requests follow a clear structure that can be fitted well with only five patterns, whereas Android applications demonstrate more complex permission requests. We also find that low-reputation applications often deviate from the permission request patterns that we identified for high-reputation applications, which suggests that permission request patterns can be indicative of user satisfaction or application quality.

The USA is witnessing a heavy debate about the influence of political campaign contributions and votes cast on the floor of the United States Congress. We contribute quantitative arguments to this predominantly qualitative discussion by analyzing a dataset of political campaign contributions. We validate that the campaign donations of politicians are mainly influenced by his or her political power and affiliation to a political party. Approaching the question of whether donations influence votes, we employ supervised learning techniques to classify how a politician will vote based solely upon from whom he or she received donations. The statistical significance of the results are assessed within the context of the debate currently surrounding campaign finance reform. Our experimental findings exhibit a large predictive power of the donations, demonstrating high informativeness of the donations with respect to voting outcomes. However, observing the slightly superior accuracy of the party line as a predictor, a causal relationship between donations and votes cannot be identified.

Truncated Singular Value Decomposition (SVD) calculates the closest rank-k approximation of a given input matrix. Selecting the appropriate rank k defines a critical model order choice in most applications of SVD. To obtain a principled cut-off criterion for the spectrum, we convert the underlying optimization problem into a noisy channel coding problem. The optimal approximation capacity of this channel controls the appropriate strength of regularization to suppress noise. In simulation experiments, this information theoretic method to determine the optimal rank competes with state-of-the art model selection techniques.

There have been many approaches proposed for role mining. However, the problems solved often differ due to a lack of consensus on the formal definition of the role mining problem. In this paper, we provide a detailed analysis of the requirements for role mining, the existing definitions of role mining, and the methods used to assess role mining results. Given basic assumptions on how access-control configurations are generated, we propose a novel definition of the role mining problem that fulfills the requirements that real-world enterprises typically have. In this way, we recast role mining as a prediction problem.

Role mining algorithms address an important access control problem: configuring a role-based access control system. Given a direct assignment of users to permissions, role mining discovers a set of roles together with an assignment of users to roles. The results should closely agree with the direct assignment. Moreover, the roles should be understandable from the business perspective in that they reflect functional roles within the enterprise. This requires hybrid role mining methods that work with both direct assignments and business information from the enterprise.

Conventional clustering methods typically assume that each data item belongs to a single cluster. This assumption does not hold in general. In order to overcome this limitation, we propose a generative method for clustering vectorial data, where each object can be assigned to multiple clusters. Using a deterministic annealing scheme, our method decomposes the observed data into the contributions of individual clusters and infers their parameters. Experiments on synthetic Boolean data show that our method achieves higher accuracy in the source parameter estimation and superior cluster stability compared to state-of-the-art approaches. We also apply our method to an important problem in computer security known as role mining. Experiments on real-world access control data show performance gains in generalization to new employees against other multi-assignment methods. In challenging situations with high noise levels, our approach maintains its good performance, while alternative state-of-the-art techniques lack robustness.

Role Engineering is a security-critical task for systems using role-based access control (RBAC). Different role-mining approaches have been proposed that attempt to automatically infer appropriate roles from existing user-permission assignments. However, these approaches are mainly combinatorial and lack an underlying probabilistic model of the domain. We present the first probabilistic model for RBAC. Our model defines a general framework for expressing user permission assignments and can be specialized to different domains by limiting its degrees of freedom with appropriate constraints. For one practically important instance of this framework, we show how roles can be inferred from data using a state-of-the-art machine-learning algorithm. Experiments on both randomly generated and real-world data provide evidence that our approach not only creates meaningful roles but also identifies erroneous user-permission assignments in given data.