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Gordon S.D.,Columbia University | Katz J.,University of Maryland College Park | Kolesnikov V.,Alcatel - Lucent | Krell F.,Columbia University | And 3 more authors.
Proceedings of the ACM Conference on Computer and Communications Security | Year: 2012

Traditional approaches to generic secure computation begin by representing the function f being computed as a circuit. If f depends on each of its input bits, this implies a protocol with complexity at least linear in the input size. In fact, linear running time is inherent for non-trivial functions since each party must "touch" every bit of their input lest information about the other party's input be leaked. This seems to rule out many applications of secure computation (e.g., database search) in scenarios where inputs are huge. Adapting and extending an idea of Ostrovsky and Shoup, we present an approach to secure two-party computation that yields protocols running in sublinear time, in an amortized sense, for functions that can be computed in sublinear time on a random-access machine (RAM). Moreover, each party is required to maintain state that is only (essentially) linear in its own input size. Our approach combines generic secure two-party computation with oblivious RAM (ORAM) protocols. We present an optimized version of our approach using Yao's garbled-circuit protocol and a recent ORAM construction of Shi et al. We describe an implementation of our resulting protocol, and evaluate its performance for obliviously searching a database with over 1 million entries. Our implementation outperforms off-the-shelf secure-computation protocols for databases containing more than 218 entries. Copyright © 2012 ACM. Source

Sun Y.,Huawei | Jover R.P.,and curity Research Center | Wang X.,Columbia University
IEEE Transactions on Wireless Communications | Year: 2012

Femtocell networks, consisting of a conventional macro cellular deployment and overlaying femtocells, forming a hierarchical cell structure, constitute an attractive solution to improving the macrocell capacity and coverage. However, the inter- and intra-tier interferences in such systems can significantly reduce the capacity and cause an unacceptably high level of outage. This paper treats the uplink interference problem in orthogonal frequency-division multiple-access (OFDMA)-based femtocell networks with partial cochannel deployment. We first propose an inter-tier interference mitigation strategy without the femtocell users power control by forcing the femto-interfering macrocell users to use only some dedicated subcarriers. The non-interfering macrocell users, on the other hand, can use either the dedicated subcarriers, or the shared subcarriers which are also used by the femtocell users. We then propose subcarrier allocation schemes based on the auction algorithm for macrocell users and femtocell users, respectively, to independently mitigate the intra-tier interference. The proposed interference mitigation scheme for femtocell networks offers significant performance improvement over the existing methods by substantially reducing the inter- and intra-tier inferences in the system. © 2012 IEEE. Source

Mathur S.,and curity Research Center | Miller R.,Rutgers University | Varshavsky A.,AT&T | Trappe W.,Rutgers University | Mandayam N.,Rutgers University
MobiSys'11 - Compilation Proceedings of the 9th International Conference on Mobile Systems, Applications and Services and Co-located Workshops | Year: 2011

Forming secure associations between wireless devices that do not share a prior trust relationship is an important problem. This paper presents ProxiMate, a system that allows wireless devices in proximity to securely pair with one another autonomously by generating a common cryptographic key directly from their shared time-varying wireless environment. The shared key synthesized by ProxiMate can be used by the devices to authenticate each others' physical proximity and then to communicate confidentially. Unlike traditional pairing approaches such as Diffie-Hellman, ProxiMate is secure against a computationally unbounded adversary and its computational complexity is linear in the size of the key. We evaluate ProxiMate using an experimental prototype built using an open-source software-defined platform and demonstrate its effectiveness in generating common secret bits. We further show that it is possible to speed up secret key synthesis by monitoring multiple RF sources simultaneously or by shaking together the devices that need to be paired. Finally, we show that ProxiMate is resistant to even the most powerful attacker who controls the public RF source used by the legitimate devices for pairing. © 2011 ACM. Source

Juma A.,Mozilla Corporation | Vahlis Y.,and curity Research Center | Yung M.,Columbia University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Understanding and modeling leakage in the context of cryptographic systems (connecting physical protection of keys and cryptographic operation) is an emerging area with many missing issues and hard to understand aspects. In this work we initiate the study of leakage out of cryptographic devices when the operation is inherently replicated in multiple locations. This setting (allowing the adversary access to leakage at different locations) arises naturally in cases like protocols, where different parties activate the same cryptographic function, or in the case of a global service providers (like cloud operators) which need to replicate the cryptographic function to allow for accessible and responsive services. We specifically deal with the theoretical setting of "leakage resilient cryptography," (modeling leakage as a bound associated with algorithmic steps), and in the most general model of continual leakage on memory, randomness (and thus computation) with periods of operation and refresh of private keys between them. We first investigate public-key cryptography, and construct a multi-location leakage resilient signature scheme (with unbounded number of locations) with optimal (i.e., total n (1 - o(1)) leakage) in a period, and O(log n) leakage during updates (n is the key size). The new crucial issue behind our scheme is how to maintain leakage at each location at the level of key leakage in the single location variant, even under parallel adaptive leakage at the different locations. We then construct a shared-symmetric-key authenticated session protocol that is resilient to leakage on both the sender and the receiver, and tolerates O(log n) bits of leakage per computation. We construct and utilize a single-location pseudorandom generator which is the first to tolerate continual leakage with only an efficient pseudorandom function as a primitive component. This protocol highlights the importance of protocol level "per message synchronization" against leakage adversaries. Interestingly, the construction is secure in spite of the entire randomness used in the refresh processes being publicly available. © 2012 International Association for Cryptologic Research. Source

Giura P.,and curity Research Center | Murynets I.,and curity Research Center | Jover R.P.,and curity Research Center | Vahlis Y.,Bionym Inc.
CODASPY 2014 - Proceedings of the 4th ACM Conference on Data and Application Security and Privacy | Year: 2014

The increased popularity of mobile devices widens opportunities for a user either to lose the device or to have the device stolen and compromised. At the same time, user interaction with a mobile device generates a unique set of features such as dialed numbers, timestamps of communication activities, contacted base stations, etc. This work proposes several methods to identify the user based on her communications history. Specifically, the proposed methods detect an abnormality based on the behavior fingerprint generated by a set of features from the network for each user session. We present an implementation of such methods that use features from real SMS, and voice call records from a major tier 1 cellular operator. This can potentially trigger a rapid reaction upon an unauthorized user gaining control of a lost or stolen terminal, preventing data compromise and device misuse. The proposed solution can also detect background malicious traffic originated by, for example, a malicious application running on the mobile device. Our experiments with annonymized data from 10,000 users, representing over 14 million SMS and voice call detail records, show that the proposed methods are scalable and can continuously identify millions of mobile users while preserving data privacy, and achieving low false positives and high misuse detection rates with low storage and computation overhead. Copyright 2014 ACM. Source

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