Algebraic attacks constitute an effective class of cryptanalytic attacks which have come up recently. In algebraic attacks, the relations between the input, output and the key are expressed as a system of equations and then solved for the key. The main idea is in obtaining a system of equations which is solvable using reasonable amount of resources. The new approaches proposed in this work and experimental studies on the existing algebraic attacks on stream ciphers will be presented. In the first attack on filter generator, the input-output relations are expressed in conjunctive normal form. The system of equations is then solved using modified Zakrevskij technique. This was one of the earliest algebraic attacks on the nonlinear filter generator. In the second attack, we relaxed the constraint on algebraic attack that the entire system description be known and the output sequence extension problem where the filter function is unknown is considered. We modeled the problem as a multivariate interpolation problem and solved it. An advantage of this approach is that it can be adapted to work for noisy output sequences where as the existing algebraic attacks expect the output sequence to be error free. Adding memory to filter/combiner function increases the degree of system of equations and finding low degree equations in this case is computeintensive. The method for computing low degree relations for combiners with memory was applied to the combiner in E0 stream cipher. We found that the relation given in literature [Armknecht and Krause] was incorrect. We obtained the correct equation and verified its correctness. A time-data size trade off attack for clock controlled filter generator was developed. The time complexity and the data requirements are in between the two approaches used in literature. A recent development of algebraic attacks - the Cube attack was studied. Cube attack on variants of Trivium were proposed by Dinur and Shamir where linear equations in key bits were obtained by combining equations for output bit for same key and a set of Initialization Vectors (IVs). We investigated the effectiveness of the cube attack on Trivium. We showed that the linear equations obtained were not general and hence the attack succeeds only for some specific values of IVs. A reason for the equations not being general is given and a modification to the linear equation finding step suggested.

<p>Despite the rapid development of adversarial attacks on machine learning models, many types of new adversarial examples remain unknown. Undiscovered types of adversarial attacks pose a</p><p>serious concern for the safety of the models, which raises the issue about the effectiveness of current adversarial robustness evaluation. Image semantic segmentation is a practical computer</p><p>vision task. However, segmentation networks’ robustness under adversarial attacks receives insufficient attention. Recently, machine learning researchers started to focus on generating</p><p>adversarial examples beyond the norm-bound restriction for segmentation neural networks. In this thesis, a simple and efficient method: AdvDRIT is proposed to synthesize unconstrained controllable adversarial images leveraging conditional-GAN. Simple CGAN yields poor image quality and low attack effectiveness. Instead, the DRIT (Disentangled Representation Image Translation) structure is leveraged with a well-designed loss function, which can generate valid adversarial images in one step. AdvDRIT is evaluated on two large image datasets: ADE20K and Cityscapes. Experiment results show that AdvDRIT can improve the quality of adversarial examples by decreasing the FID score down to 40% compared to state-of-the-art generative models such as Pix2Pix, and also improve the attack success rate 38% compared to other adversarial attack methods including PGD.</p>

Deep Neural Networks (DNNs) are ubiquitous and span a variety of applications ranging from image classification and facial recognition to medical image analysis and real-time object detection. As DNN models become more sophisticated and complex, the computational cost of training these models becomes a burden. For this reason, outsourcing the training process has been the go-to option for many DNN users. Unfortunately, this comes at the cost of vulnerability to backdoor attacks. These attacks aim at establishing hidden backdoors in the DNN such that it performs well on clean samples but outputs a particular target label when a trigger is applied to the input. Current backdoor attacks generate triggers in the spatial domain; however, as we show in this work, it is not the only domain to exploit and one should always "check the other doors". To the best of our knowledge, this work is the first to propose a pipeline for generating a spatially dynamic (changing) and invisible (low norm) backdoor attack in the frequency domain. We show the advantages of utilizing the frequency domain for creating undetectable and powerful backdoor attacks through extensive experiments on various datasets and network architectures. Unlike most spatial domain attacks, frequency-based backdoor attacks can achieve high attack success rates with low poisoning rates and little to no drop in performance while remaining imperceptible to the human eye. Moreover, we show that the backdoored models (poisoned by our attacks) are resistant to various state-of-the-art (SOTA) defenses, and so we contribute two possible defenses that can successfully evade the attack. We conclude the work with some remarks regarding a network’s learning capacity and the capability of embedding a backdoor attack in the model.

In this dissertation, we study an important problem of security in wireless networks. We study different attacks and defense strategies in general and more specifically jamming attacks. We begin the dissertation by providing a tutorial introducing the operations research community to the various types of attacks and defense strategies in wireless networks. In this tutorial, we give examples of mathematical programming models to model jamming attacks and defense against jamming attacks in wireless networks. Later we provide a comprehensive taxonomic classification of the various types of jamming attacks and defense against jamming attacks. The classification scheme will provide a one stop location for future researchers on various jamming attack and defense strategies studied in literature. This classification scheme also highlights the areas of research in jamming attack and defense against jamming attacks which have received less attention and could be a good area of focus for future research. In the next chapter, we provide a bi-level mathematical programming model to study jamming attack and defense strategy. We solve this using a game-theoretic approach and also study the impact of power level, location of jamming device, and the number of transmission channels available to transmit data on the attack and defense against jamming attacks. We show that by increasing the number of jamming devices the throughput of the network drops by at least 7%. Finally we study a special type of jamming attack, flow-jamming attack. We provide a mathematical programming model to solve the location of jamming devices to increase the impact of flow-jamming attacks on wireless networks. We provide a Benders decomposition algorithm along with some acceleration techniques to solve large problem instances in reasonable amount of time. We draw some insights about the impact of power, location and size of the network on the impact of flow-jamming attacks in wireless networks.

The prevalence of cloud storage has yielded significant benefits to consumers. Trusted Exe- cution Environments (TEEs) have been introduced to protect program execution and data in the cloud. However, an attacker targeting the cloud storage server through side-channel attacks can still learn some data in TEEs. This data retrieval is possible through the monitor- ing and analysis of the encrypted ciphertext as well as a program's memory access patterns. As the attacks grow in complexity and accuracy, innovative protection methods must be de- signed to secure data. This thesis proposes and implements an ORAM controller primitive in TEE and protects it from all potential side-channel attacks. This thesis presents two vari- ations, each with two different encryption methods designed to mitigate attacks targeting both memory access patterns and ciphertext analysis. The latency for enabling this protec- tion is calculated and proven to be 75.86% faster overall than the previous implementation on which this thesis is based. / Master of Science / Cloud storage and computing has become ubiquitous in recent times, with usage rising ex- ponentially over the past decade. Cloud Service Providers also offer Confidential Computing services for clients requiring data computation which is encrypted and protected from the service providers themselves. While these services are protected against attackers directly looking to access secure data, they are still vulnerable against attacks which only observe, but do not interfere. Such attacks monitor a client's memory access pattern or the encrypted data in the server and can obtain sensitive information including encryption keys. This work proposes and implements an Oblivious RAM design which safeguards against the aforemen- tioned attacks by using a mix of confidential computing in hardware and special algorithms designed to randomize the client's data access patterns. The evaluation of this work shows a significant increase in performance over previous works in this domain while using the latest technology in confidential computing.

The present study was designed to test the efficacy of a bibliotherapy-relapse prevention (BT-RP) program for panic attacks in which the active BT-RP condition was compared to a waiting-list control condition. Prior to the administration of the six-month BT-RP program, all participants completed an initial BT intervention (Febbraro, 1997) based on the book Coping with Panic (Clum, 1990). The BT-RP program was designed to: (a) review major components of the initial intervention; (b) increase practice of panic coping skills and therapeutic self-exposure; (c) enhance social support for panic recovery; (d) teach cognitive restructuring skills related to relapse prevention; (e) provide a protocol to follow in the event of a setback; and (f) reduce overall levels of stress. Brief monthly phone contacts were included in the BT-RP condition. Thirty-six participants, 17 in the BT-RP condition and 19 in the WL control condition, completed the study. A 2 (Treatment condition: BT-RP versus WL control) X 2 (Time: Pre-BT-RP assessment versus Post-BT-RP assessment) mixed-model research design was used to analyze the results. Results indicted significant reductions from pre- to post-treatment in the BT-RP condition for panic cognitions, anticipatory anxiety, agoraphobic avoidance, and depression, but not in the WL condition. When statistically controlling for initial levels of these variables via analyses of covariance (ANCOVAs), significant post-treatment differences in the expected direction emerged for these four dependent measure and for state anxiety. In addition, the BT-RP group reported significantly fewer panic attacks during the six-month course of the treatment trial than the WL control group on a measure of retrospective recall of full-blown panic attacks. There was also a statistically significant proportional between-group difference in terms of clinically significant improvement for full-blown panic attacks and agoraphobic avoidance in favor of the BT-RP group. However, no significant between-group differences emerged for the maintenance of initial treatment gains for panic frequency, panic symptoms, panic cognitions, anticipatory anxiety, or agoraphobic avoidance. Results of the present study are discussed in the framework of benefits of the present BT-RP program, limitations of the findings, recommendations for future research in this area, and implications for BT treatments in general. / Ph. D.

Treatment outcome studies investigating potential treatments for panic disorder invariably begin with a lengthy assessment designed to determine whether a potential subject meets criteria for the disorder. Through the process of assessment, subject are usually given some form of feedback about their condition, if only to tell them they meet criteria to enter the study. Assessment and feedback are thought to have therapeutic effects and empirical evidence is beginning to document this (Bien, Miller, & Tonigan, 1993; Finn & Tonsager, 1992). To date, there have been no studies that investigate the effects of assessment plus feedback or assessment alone on individuals with panic attacks. This study investigated whether assessment or assessment plus feedback produced any differential effects on panic attack sufferers. Seventy participants were randomly assigned to one of four groups: 1) assessment with mailed feedback (n=17); 2) assessment with face-to-face feedback (n=14); 3) assessment with no feedback (n=19); and 4) no assessment or feedback (n=20). Assessment consisted of completing a composite self-report instrument that asks about frequency of panic attacks and panic-related symptomatology. Feedback was standardized and computer generated but individualized based on scores on the assessment measure. All groups completed the outcome measures and between group differences were examined. No statistically significant differences were found between these four groups on any dependent measure. However, for a smaller subset of participants (N=35) who had at least one full panic attack at pre-assessment, a significant reduction in frequency of combined (full plus limited-symptom) panic attacks was seen pre to post, F(1,32)=7.47, p<.01, with a marginally significant two-way interaction of Time and Condition, F(2,32)=3.12, p<.06. Basically, both feedback groups showed a reduction in panic attacks while the assessment only condition remained the same. / Master of Science

No / This book provides a contemporary month-by-month analysis of events in Iraq since May 2005 and assesses how they impact on other countries including Afghanistan, Iran and the wider Middle East. The book charts a tumultuous period in the conflict, including a wider international perspective on the terrorist attacks in London and Sharm al Sheik, and an assessment of how US public opinion has changed as the war drags on. It brings together Paul Rogers' international security monthly briefings as published on the Oxford Research Group website between May 2005 - April 2006, and concludes with a commentary on the significance of the year's events, and an analysis of the current situation. This is the third ORG International Security Report. We have also published reports in 2004 and 2005.

Anxiety may be experienced in a variety of response modes. There is evidence to suggest that panic disordered individuals differ from individuals with other anxiety diagnoses in that they experience a greater increase in somatic symptoms and catastrophic cognitions. Further it has been suggested that panic disordered individuals, as compared to other anxiety disordered individuals, experience greater global anxiety and depression. The present study compared the total scores of 93 disordered subjects on the Symptom Assessment Questionnaire and the Cognitions Assessment Questionnaire and found that both questionnaires discriminated panic disordered subjects from non-panic disordered subjects. The two questionnaires also discriminated subjects with panic attacks from subjects without panic attacks. Item analyses were conducted on both questionnaires in order to identify specific items which differentiated panic disordered subjects from non-panic disordered subjects and subjects with panic attacks from subjects without panic attacks. Factor analyses were conducted on both questionnaires, resulting in the identification of somatic and cognitive factors salient to the phenomenon of panic. In general, the identified factors supported and expanded upon the panic symptoms listed in DSM-III. Finally, two widely used measures of anxiety and depression were administered to subjects. Panickers scored higher than Non-panickers on measures of state-anxiety, trait-anxiety, and depression. The Panic Disordered Group scored higher than the Non-Panic Disordered Group on the depression scale. However, the Panic Disordered Group scored no differently from the NonPanic Disordered on the state-anxiety and trait-anxiety inventories, suggesting that the presence of panic attacks in all anxiety diagnostic groups weakened the ability of the tradition anxiety measures to distinguish between the comparison groups. / M.S.

In recent years, machine learning (ML) has been explored and employed in many fields. However, there are growing concerns about the robustness of machine learning models. These concerns are further amplified in security-critical applications — attackers can manipulate the inputs (i.e., adversarial examples) to cause machine learning models to make a mistake, and it's very challenging to obtain a large amount of attackers' data. These make applying machine learning in security-critical applications difficult. In this dissertation, we present several approaches to robustifying three machine learning based security applications. First, we start from adversarial examples in image recognition. We develop a method to generate robust adversarial examples that remain effective in the physical domain. Our core idea is to use an image-to-image translation network to simulate the digital-to-physical transformation process for generating robust adversarial examples. We further show these robust adversarial examples can improve the robustness of machine learning models by adversarial retraining. The second application is bot detection. We show that the performance of existing machine learning models is not effective if we only have the limit attackers' data. We develop a data synthesis method to address this problem. The key novelty is that our method is distribution aware synthesis, using two different generators in a Generative Adversarial Network to synthesize data for the clustered regions and the outlier regions in the feature space. We show the detection performance using 1% of attackers' data is close to existing methods trained with 100% of the attackers' data. The third component of this dissertation is phishing detection. By designing a novel measurement system, we search and detect phishing websites that adopt evasion techniques not only at the page content level but also at the web domain level. The key novelty is that our system is built on the observation of the evasive behaviors of phishing pages in practice. We also study how existing browsers defenses against phishing websites that impersonate trusted entities at the web domain. Our results show existing browsers are not yet effective to detect them. / Doctor of Philosophy / Machine learning (ML) is computer algorithms that aim to identify hidden patterns from the data. In recent years, machine learning has been widely used in many fields. The range of them is broad, from natural language to autonomous driving. However, there are growing concerns about the robustness of machine learning models. And these concerns are further amplified in security-critical applications — Attackers can manipulate their inputs (i.e., adversarial examples) to cause machine learning models to predict wrong, and it's highly expensive and difficult to obtain a huge amount of attackers' data because attackers are rare compared to the normal users. These make applying machine learning in security-critical applications concerning. In this dissertation, we seek to build better defenses in three types of machine learning based security applications. The first one is image recognition, by developing a method to generate realistic adversarial examples, the machine learning models are more robust for defending against adversarial examples by adversarial retraining. The second one is bot detection, we develop a data synthesis method to detect malicious bots when we only have the limit malicious bots data. For phishing websites, we implement a tool to detect domain name impersonation and detect phishing pages using dynamic and static analysis.