The Full Landscape of Robust Mean Testing: Sharp Separations between Oblivious and Adaptive Contamination

We consider the question of Gaussian mean testing, a fundamental task in high-dimensional distribution testing and signal processing, subject to adversarial corruptions of the samples. We focus on the relative power of different adversaries, and show that, in contrast to the common wisdom in robust statistics, there exists a strict separation between adaptive adversaries (strong contamination) and oblivious ones (weak contamination) for this task. Specifically, we resolve both the information-theoretic and computational landscapes for robust mean testing. In the exponential-time setting, we establish the tight sample complexity of testing $\mathcal{N}(0,I)$ against $\mathcal{N}(\alpha v, I)$, where $\|v\|_2 = 1$, with an $\varepsilon$-fraction of adversarial corruptions, to be $$\tilde{\Theta}\!\left(\max\left(\frac{\sqrt{d}}{\alpha^2}, \frac{d\varepsilon^3}{\alpha^4},\min\left(\frac{d^{2/3}\varepsilon^{2/3}}{\alpha^{8/3}}, \frac{d \varepsilon}{\alpha^2}\right)\right) \right) \,,$$ while the complexity against adaptive adversaries is $$\tilde{\Theta}\!\left(\max\left(\frac{\sqrt{d}}{\alpha^2}, \frac{d\varepsilon^2}{\alpha^4} \right)\right) \,,$$ which is strictly worse for a large range of vanishing $\varepsilon,\alpha$. To the best of our knowledge, ours is the first separation in sample complexity between the strong and weak contamination models. In the polynomial-time setting, we close a gap in the literature by providing a polynomial-time algorithm against adaptive adversaries achieving the above sample complexity $\tilde{\Theta}(\max({\sqrt{d}}/{\alpha^2}, {d\varepsilon^2}/{\alpha^4} ))$, and a low-degree lower bound (which complements an existing reduction from planted clique) suggesting that all efficient algorithms require this many samples, even in the oblivious-adversary setting.Comment: To appear in FOCS 202

Modeling Realistic Adversarial Attacks against Network Intrusion Detection Systems

The incremental diffusion of machine learning algorithms in supporting cybersecurity is creating novel defensive opportunities but also new types of risks. Multiple researches have shown that machine learning methods are vulnerable to adversarial attacks that create tiny perturbations aimed at decreasing the effectiveness of detecting threats. We observe that existing literature assumes threat models that are inappropriate for realistic cybersecurity scenarios because they consider opponents with complete knowledge about the cyber detector or that can freely interact with the target systems. By focusing on Network Intrusion Detection Systems based on machine learning, we identify and model the real capabilities and circumstances required by attackers to carry out feasible and successful adversarial attacks. We then apply our model to several adversarial attacks proposed in literature and highlight the limits and merits that can result in actual adversarial attacks. The contributions of this paper can help hardening defensive systems by letting cyber defenders address the most critical and real issues, and can benefit researchers by allowing them to devise novel forms of adversarial attacks based on realistic threat models

Securing Cloud Computations with Oblivious Primitives from Intel SGX

We are witnessing a confluence between applied cryptography and secure hardware systems in enabling secure cloud computing. On one hand, work in applied cryptography has enabled efficient, oblivious data-structures and memory primitives. On the other, secure hardware and the emergence of Intel SGX has enabled a low-overhead and mass market mechanism for isolated execution. By themselves these technologies have their disadvantages. Oblivious memory primitives carry high performance overheads, especially when run non-interactively. Intel SGX, while more efficient, suffers from numerous software-based side-channel attacks, high context switching costs, and bounded memory size. In this work we build a new library of oblivious memory primitives, which we call ZeroTrace. ZeroTrace is designed to carefully combine state-of-art oblivious RAM techniques and SGX, while mitigating individual disadvantages of these technologies. To the best of our knowledge, ZeroTrace represents the first oblivious memory primitives running on a real secure hardware platform. ZeroTrace simultaneously enables a dramatic speedup over pure cryptography and protection from software-based side-channel attacks. The core of our design is an efficient and flexible block-level memory controller that provides oblivious execution against any active software adversary, and across asynchronous SGX enclave terminations. Performance-wise, the memory controller can service requests for 4~Byte blocks in 1.2~ms and 1~KB blocks in 3.4~ms (given a 10~GB dataset). On top of our memory controller, we evaluate Set/Dictionary/List interfaces which can all perform basic operations (e.g., get/put/insert) in 1-5~ms for a 4-8~Byte block size. ZeroTrace enables secure remote computations at substantially lower overheads than other comparable state-of-the-art techniques

TOWARDS PRIVACY-PRESERVING AND ROBUST WEB OVERLAYS

Ph.DDOCTOR OF PHILOSOPH

Signaling and Reciprocity:Robust Decentralized Information Flows in Social, Communication, and Computer Networks

Complex networks exist for a number of purposes. The neural, metabolic and food networks ensure our survival, while the social, economic, transportation and communication networks allow us to prosper. Independently of the purposes and particularities of the physical embodiment of the networks, one of their fundamental functions is the delivery of information from one part of the network to another. Gossip and diseases diffuse in the social networks, electrochemical signals propagate in the neural networks and data packets travel in the Internet. Engineering networks for robust information flows is a challenging task. First, the mechanism through which the network forms and changes its topology needs to be defined. Second, within a given topology, the information must be routed to the appropriate recipients. Third, both the network formation and the routing mechanisms need to be robust against a wide spectrum of failures and adversaries. Fourth, the network formation, routing and failure recovery must operate under the resource constraints, either intrinsic or extrinsic to the network. Finally, the autonomously operating parts of the network must be incentivized to contribute their resources to facilitate the information flows. This thesis tackles the above challenges within the context of several types of networks: 1) peer-to-peer overlays – computers interconnected over the Internet to form an overlay in which participants provide various services to one another, 2) mobile ad-hoc networks – mobile nodes distributed in physical space communicating wirelessly with the goal of delivering data from one part of the network to another, 3) file-sharing networks – networks whose participants interconnect over the Internet to exchange files, 4) social networks – humans disseminating and consuming information through the network of social relationships. The thesis makes several contributions. Firstly, we propose a general algorithm, which given a set of nodes embedded in an arbitrary metric space, interconnects them into a network that efficiently routes information. We apply the algorithm to the peer-to-peer overlays and experimentally demonstrate its high performance, scalability as well as resilience to continuous peer arrivals and departures. We then shift our focus to the problem of the reliability of routing in the peer-to-peer overlays. Each overlay peer has limited resources and when they are exhausted this ultimately leads to delayed or lost overlay messages. All the solutions addressing this problem rely on message redundancy, which significantly increases the resource costs of fault-tolerance. We propose a bandwidth-efficient single-path Forward Feedback Protocol (FFP) for overlay message routing in which successfully delivered messages are followed by a feedback signal to reinforce the routing paths. Internet testbed evaluation shows that FFP uses 2-5 times less network bandwidth than the existing protocols relying on message redundancy, while achieving comparable fault-tolerance levels under a variety of failure scenarios. While the Forward Feedback Protocol is robust to message loss and delays, it is vulnerable to malicious message injection. We address this and other security problems by proposing Castor, a variant of FFP for mobile ad-hoc networks (MANETs). In Castor, we use the same general mechanism as in FFP; each time a message is routed, the routing path is either enforced or weakened by the feedback signal depending on whether the routing succeeded or not. However, unlike FFP, Castor employs cryptographic mechanisms for ensuring the integrity and authenticity of the messages. We compare Castor to four other MANET routing protocols. Despite Castor's simplicity, it achieves up to 40% higher packet delivery rates than the other protocols and recovers at least twice as fast as the other protocols in a wide range of attacks and failure scenarios. Both of our protocols, FFP and Castor, rely on simple signaling to improve the routing robustness in peer-to-peer and mobile ad-hoc networks. Given the success of the signaling mechanism in shaping the information flows in these two types of networks, we examine if signaling plays a similar crucial role in the on-line social networks. We characterize the propagation of URLs in the social network of Twitter. The data analysis uncovers several statistical regularities in the user activity, the social graph, the structure of the URL cascades as well as the communication and signaling dynamics. Based on these results, we propose a propagation model that accurately predicts which users are likely to mention which URLs. We outline a number of applications where the social network information flow modelling would be crucial: content ranking and filtering, viral marketing and spam detection. Finally, we consider the problem of freeriding in peer-to-peer file-sharing applications, when users can download data from others, but never reciprocate by uploading. To address the problem, we propose a variant of the BitTorrent system in which two peers are only allowed to connect if their owners know one another in the real world. When the users know which other users their BitTorrent client connects to, they are more likely to cooperate. The social network becomes the content distribution network and the freeriding problem is solved by leveraging the social norms and reciprocity to stabilize cooperation rather than relying on technological means. Our extensive simulation shows that the social network topology is an efficient and scalable content distribution medium, while at the same time provides robustness to freeriding

Putin's Grand Strategy: Russia's Campaign of Controlled Instability in Ukraine and Beyond

This thesis addresses the great lengths to which Vladimir Putin and the Russian Federation have gone to foster “controlled instability” in the former Soviet Union. It is said that those who do not learn from history are doomed to repeat it, and with Western policy makers who appear unwilling to act on intelligence regarding Russian actions as well as incontrovertible evidence of Putin’s aggressive strategy, this Western failure to learn has contributed significantly to a repeat of various Russian behaviors during past conflicts. Russian actions pose a clear and present danger to the stability of the global community. Because many of the current events are not yet published in texts or are classified, the author has had to depend heavily upon open-source references from the internet to provide key events as they chronologically happened, particularly when analyzing the crisis in Ukraine. In writing the thesis, my observations have been validated by Russia’s recent incursion into Syria to fortify the Russian leadership’s interests as a result of the continued inaction of Western policy makers. As a result, we will see significant additional instances of controlled instability from Russia in the future

Race, Ethnicity and Nuclear War

Ranging across novels and poetry, critical theory and film, comics and speeches, Race, Ethnicity and Nuclear War: Representations of Nuclear Weapons and Post-Apocalyptic Worlds explores how writers, thinkers, and filmmakers have answered the following question: are nuclear weapons ‘white’? Race, Ethnicity and Nuclear War listens to voices from around the Anglophone world and the debates followed do not only take place on the soil of the nuclear powers. Filmmakers and writers from the Caribbean, Australia, and India take up positions shaped by their specific place in the decolonizing world and their particular experience of nuclear weapons. The texts considered in Race, Ethnicity and Nuclear War encompass the many guises of representations of nuclear weapons. New thoughts are offered on the major texts that SF scholars often return to, such as Philip Wylie’s Tomorrow! and Pat Frank’s Alas Babylon, and a host of little known and under-researched texts are scrutinized too

The psychological battlefield : Lord Kitchener’s middle-class volunteers in the Great War

Tämä tutkielma tarkastelee brittiläisen keskiluokan sotilaiden psykologista kokemusta vapaaehtoisina sotilaina Kitchenerin armeijassa ensimmäisen maailmansodan aikaan. Tämän tutkielman tarkoitus on selvittää, miten sota vaikutti sotilaisiin, ja miksi he reagoivat siihen tutkielman selvittämin tavoin. Tutkielmassa kysymystä tarkastellaan sotilaiden näkökulmasta neljän sodan aspektin kautta, jotka ovat; armeijaorganisaatio, aseveljet, tappaminen ja kuolemanuhka. Motivaatio tutkielman takana oli ymmärryksen lisääminen näiden sotilaiden kokemuksesta sen jälkeen, kun he olivat vapaaehtoisina liittyneet maailman ensimmäiseen teolliseen sotaan. Kitchenerin armeija oli siviilisotilaiden armeija, ja se perustettiin täydentämään olemassaolevan brittiarmeijan rivejä, jotta valtio kykenisi jatkamaan sodankäyntiä. Sekä historiallista ja psykologista tutkimuskirjallisuutta on hyödynnetty tutkielman alkuperäislähteiden tulkinnoissa. Tutkielmassa käytetyt alkuperäislähteet ovat kirjeitä ja päiväkirjoja rintamalta, ja näiden lähteiden kautta tutkielmassa pyritään ymmärtämään ja analysoimaan niitä kokemuksia, jotka sotilaat ovat itse sanelleet. Alkuperäislähteiden lähiluku tutkimuskirjallisuuteen perustuvalla analyysilla oli tämän tutkimuksen ensisijainen metodi, johon sen johtopäätökset perustuvat. Tutkielman teoreettinen viitekehys ja siitä johtuva analyysi tukee siis vahvasti myös psykologiseen tutkimuskirjallisuuteen ja sen konsepteihin. Sotilaiden kokemusten kontekstualisoimiseen laajempaan kulttuuriseen kontekstiinsa ja vallitsevaan ajanjaksoon käytettiin maskuliinisuuden konseptia aikalaisen britti-keskiluokan kulttuurissa. Psykologisista käsitteistä tärkeimmät käsittelevät ryhmäkäyttäytymistä ja stressireaktioita, jotka tunnustetaan psykologian tutkimuksessa useimmiten defensseinä ja elämänhallinnan valineinä. Siinä missä defenssit käsitetään usein alitajuisina mielen reaktioina mahdollisesti stressiä lisäävään informaatioon, elämänhallinnan välineet ovat ainakin osittain tietoisia ja henkilön itsensä ylläpitämiä. Elämänhallinnan keinoin henkilö yrittää aktiivisesti pidättäytyä kivuliaaksi tiedetyn kohtaamiselta, samalla kun defenssit vastaavat samoihin ärsykkeisiin automaattisesti. Tutkielman johtopäätökset implikoivat, että sotilaan sosiaalinen konteksti ennen sotaa vaikutti osin heidän kokemuksiinsa sodasta sekä ennen, että jälkeen armeijaan liittymisen. Sotilaiden kulttuurillinen konteksti tarjosi heille viitekehyksen sekä heidän sisäistetyille arvoilleen, että käyttäytymiskulttuurille juoksuhaudoissa. Tulokset viittaavat myös siihen, että siinä missä jokaisen sotilaan sotakokemus oli osaltaan hyvin yksilöllinen, olivat monet sen piirteistä kulttuurisesti ja psykologisesti informoituja ja täten ollen edes jokseenkin ennustettavissa. Tutkimuksen viiteryhmän sisältä voisi löytää siis johdonmukaisuuksia, jotka edelleen voisivat ymmärrettyinä auttaa modernin sodankäynnin kokemusta vastaavanlaisissa kenttäympäristöissä laajemmassakin perspektiivissä.This Master's Thesis concerns the British middle-class soldiers' psychological experience as volunteers in Kitchener's army during the Great War. The purpose of this study is to discover how the war affected the soldiers, and why they reacted to it the way they did. It approaches this question by focusing on four aspects of the war from the soldier's perspective, namely: the military organization, his brothers in arms, the act of killing, and the threat of dying. The motivation behind this study was to better understand the experience of these soldiers after they voluntarily joined the world’s first industrial war. Kitchener's army was an army of civilian soldiers, drafted to fill in the ranks of the British army, so that it could properly take part in the war. Through using both relevant historical literature and psychological research as aid, the study uses primary sources in the form of letters and diaries from the trenches to understand and draw conclusions of the experiences personally recounted by the soldiers. The methods with which the study was conducted was through the close-reading of the sources combined with the reading and reviewing of relevant research literature to draw appropriate conclusions. The theoretical framework and subsequent analysis of the sources thus relies heavily on psychological concepts. The concept of masculinity in the contemporary middle-class culture was used to contextualize the soldiers’ experience in their historical timeframe and social niche. Meanwhile, the key psychological terms used in this study in reference to group behavior and stress responses are concepts recognized on the field of psychological research either as defense or coping mechanisms. Where defense mechanisms are commonly understood as unconscious and automatic reactions of the mind to potentially stressful information, coping mechanisms are at least partially consciously driven and maintained by the person themselves to help them refrain from having to face and process the information which they know to be painful. The conclusions of this study imply that the soldier’s social background influenced their war experience both before and after joining the war, giving them a frame of reference for both their set of values and their code of conduct which they drew upon as they adjusted to the life in the trenches. What this study’s results also imply is that while the soldiers had distinctly individual experiences of their own, they were characterized by a set of culturally and psychologically guided features, which hold within themselves a level of predictability. These conclusions suggest that though each experience of soldiers in war is unique, there are broader patterns of behavior within the context of modern warfare, which if understood, could better help predict and understand the behavior of soldiers in comparable circumstances

Novel deceptions: historical illusionism in contemporary American fiction

This study investigates the subject of illusionism in contemporary American fiction. A recurrent yet under-examined theme, the history of stage magic in the U.S. suggests how an earlier age domesticated the seeming sorcery of market capitalism, credit, limitless self-(re)making, and ethnic vanishing. Such conditions provide antecedents and analogues for the writing of fiction in a world of digitalized knowledge, work, identity, and financialization. Self-reflexively illusionist fiction today represents itself ambivalently as magical entertainment. Is its function to mesmerize audiences or alert them to ideological sleight-of-hand? If the enchantments of literary art screen the machinations of power, how do novelists preserve fiction's capacity to inspire wonder, affective experience, and ethical commitment? Chapter One argues that Cormac McCarthy's Blood Meridian presents illusionism as integral to imperialism and commodification, as well as to its own artistry. McCarthy indicates the instrumentalization of aesthetics under late capitalism yet seeks through moments of enchantment to transcend it. Chapter Two shows that in Mr. Vertigo by Paul Auster and In the Lake of the Woods by Tim O'Brien, fiction’s "magic" lies in transcending social differences and inspiring empathy, but that the historical residue of racism in American illusionism obstructs the effort to imagine otherness. Both novels reframe the worth of fiction as therapeutic. Chapter Three argues that the figure of Harry Houdini embodies literature's status as primarily entertainment, inspiring wonder rather than critique. Michael Chabon's Kavalier & Clay celebrates escapistry, but seeks through Houdini to restore a utopian dimension to entertainment.2017-11-04T00:00:00