706 research outputs found

    How Push-To-Talk Makes Talk Less Pushy

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    This paper presents an exploratory study of college-age students using two-way, push-to-talk cellular radios. We describe the observed and reported use of cellular radio by the participants. We discuss how the half-duplex, lightweight cellular radio communication was associated with reduced interactional commitment, which meant the cellular radios could be used for a wide range of conversation styles. One such style, intermittent conversation, is characterized by response delays. Intermittent conversation is surprising in an audio medium, since it is typically associated with textual media such as instant messaging. We present design implications of our findings.Comment: 10 page

    Blindspot: Indistinguishable Anonymous Communications

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    Communication anonymity is a key requirement for individuals under targeted surveillance. Practical anonymous communications also require indistinguishability - an adversary should be unable to distinguish between anonymised and non-anonymised traffic for a given user. We propose Blindspot, a design for high-latency anonymous communications that offers indistinguishability and unobservability under a (qualified) global active adversary. Blindspot creates anonymous routes between sender-receiver pairs by subliminally encoding messages within the pre-existing communication behaviour of users within a social network. Specifically, the organic image sharing behaviour of users. Thus channel bandwidth depends on the intensity of image sharing behaviour of users along a route. A major challenge we successfully overcome is that routing must be accomplished in the face of significant restrictions - channel bandwidth is stochastic. We show that conventional social network routing strategies do not work. To solve this problem, we propose a novel routing algorithm. We evaluate Blindspot using a real-world dataset. We find that it delivers reasonable results for applications requiring low-volume unobservable communication.Comment: 13 Page

    The Transparency Tax

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    Transparency is critical to good governance, but it also imposes significant governance costs. Beyond a certain point, excess transparency acts as a kind of tax on the legal system. Others have noted the burdens of maximalist transparency policies on both budgets and regulatory efficiency, but they have largely ignored the deeper cost that transparency imposes: it constrains one’s ability to support the law while telling a self-serving story about what that support means. Transparency’s true tax on the law is the loss of expressive ambiguity. In order to understand this tax, this Article develops a taxonomy of transparency types. Typically, transparency means something like openness. But openness about what—the law’s obligations? The reasons for the obligations? The actors behind the law? And open to whom? These are different aspects of what we typically lump together and call “transparency,” and they present different tradeoffs. With these tradeoffs in mind, we can begin to make more informed choices about how to draw the line between maximal and minimal transparency. Of particular note is the finding that we can demand maximal transparency about the law’s obligations without incurring much of the transparency tax. This runs contrary to the soft law literature, which suggests that vagueness about obligation is less costly than the alternative. The Article concludes with a guide for thinking through future transparency tradeoffs

    CoverUp: Privacy Through Forced Participation in Anonymous Communication Networks

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    The privacy guarantees of anonymous communication networks (ACNs) are bounded by the number of participants. As a consequence, an ACN can only achieve strong privacy guarantees if it succeeds in attracting a large number of active users. Vice versa, weak privacy guarantees renders an ACN unattractive, leading to a low number of users. In this work, we show how to break this vicious circle. We develop CoverUp, a system that forces visitors of highly accessed websites to become involuntary participants of an ACN. CoverUp leverages basic browser functionality to execute server-served JavaScript code and to open remote connections to connect all website visitors to an ACN (which we instantiate by a mix server). We build two applications on top of CoverUp: an anonymous feed and a chat. We show that both achieve practical performance and strong privacy guarantees. Towards a network-level attacker, CoverUp makes voluntary and involuntary participants indistinguishable, thereby providing an anonymity set that includes all voluntary and involuntary participants (i.e., all website visitors). Given this, CoverUp provides even more than mere anonymity: the voluntary participants can hide the very intention to use the ACN. As the concept of forced participation raises ethical and legal concerns, we discuss these concerns and describe how these can be addressed

    Compressive Privacy for a Linear Dynamical System

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    We consider a linear dynamical system in which the state vector consists of both public and private states. One or more sensors make measurements of the state vector and sends information to a fusion center, which performs the final state estimation. To achieve an optimal tradeoff between the utility of estimating the public states and protection of the private states, the measurements at each time step are linearly compressed into a lower dimensional space. Under the centralized setting where all measurements are collected by a single sensor, we propose an optimization problem and an algorithm to find the best compression matrix. Under the decentralized setting where measurements are made separately at multiple sensors, each sensor optimizes its own local compression matrix. We propose methods to separate the overall optimization problem into multiple sub-problems that can be solved locally at each sensor. We consider the cases where there is no message exchange between the sensors; and where each sensor takes turns to transmit messages to the other sensors. Simulations and empirical experiments demonstrate the efficiency of our proposed approach in allowing the fusion center to estimate the public states with good accuracy while preventing it from estimating the private states accurately
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