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 Resource Type:
 Conference Proceeding
 Creator:
 Seidel, Raimund, Dehne, Frank, and Klein, Rolf
 Abstract:
 Given a set S of s points in the plane, where do we place a new point, p, in order to maximize the area of its region in the Voronoi diagram of S and p? We study the case where the Voronoi neighbors of p are in convex position, and prove that there is at most one local maximum.
 Date Created:
 20021201

 Resource Type:
 Conference Proceeding
 Creator:
 Mannan, Mohammad, Barrera, David, Van Oorschot, Paul C., Lie, David, and Brown, Carson D.
 Abstract:
 Instead of allowing the recovery of original passwords, forgotten passwords are often reset using online mechanisms such as password verification questions (PVQ methods) and password reset links in email. These mechanisms are generally weak, exploitable, and force users to choose new passwords. Emailing the original password exposes the password to third parties. To address these issues, and to allow forgotten passwords to be securely restored, we present a scheme called Mercury. Its primary mode employs userlevel public keys and a personal mobile device (PMD) such as a smartphone, netbook, or tablet. A user generates a key pair on her PMD; the private key remains on the PMD and the public key is shared with different sites (e.g., during account setup). For password recovery, the site sends the (public key)encrypted password to the user's preregistered email address, or displays the encrypted password on a webpage, e.g., as a barcode. The encrypted password is then decrypted using the PMD and revealed to the user. A prototype implementation of Mercury is available as an Android application.
 Date Created:
 20120221

 Resource Type:
 Conference Proceeding
 Creator:
 Van Walderveen, Freek, Davoodi, Pooya, and Smid, Michiel
 Abstract:
 Given a set of n points in the plane, range diameter queries ask for the furthest pair of points in a given axisparallel rectangular range. We provide evidence for the hardness of designing spaceefficient data structures that support range diameter queries by giving a reduction from the set intersection problem. The difficulty of the latter problem is widely acknowledged and is conjectured to require nearly quadratic space in order to obtain constant query time, which is matched by known data structures for both problems, up to polylogarithmic factors. We strengthen the evidence by giving a lower bound for an important subproblem arising in solutions to the range diameter problem: computing the diameter of two convex polygons, that are separated by a vertical line and are preprocessed independently, requires almost linear time in the number of vertices of the smaller polygon, no matter how much space is used. We also show that range diameter queries can be answered much more efficiently for the case of points in convex position by describing a data structure of size O(n log n) that supports queries in O(log n) time.
 Date Created:
 20120515

 Resource Type:
 Conference Proceeding
 Creator:
 Cervera, Gimer, Barbeau, Michel, GarciaAlfaro, Joaquin, and Kranakis, Evangelos
 Abstract:
 The Hierarchical Optimized Link State Routing (HOLSR) protocol enhances the scalability and heterogeneity of traditional OLSRbased Mobile AdHoc Networks (MANETs). It organizes the network in logical levels and nodes in clusters. In every cluster, it implements the mechanisms and algorithms of the original OLSR to generate and to distribute control traffic information. However, the HOLSR protocol was designed with no security in mind. Indeed, it both inherits, from OLSR, and adds new security threats. For instance, the existence of misbehaving nodes can highly affect important HOLSR operations, such as the cluster formation. Cluster IDentification (CID) messages are implemented to organize a HOLSR network in clusters. In every message, the hop count field indicates to the receiver the distance in hops to the originator. An attacker may maliciously alter the hop count field. As a consequence, a receiver node may join a cluster head farther away than it appears. Then, the scalability properties in a HOLSR network is affected by an unbalanced distribution of nodes per cluster. We present a solution based on the use of hash chains to protect mutable fields in CID messages. As a consequence, when a misbehaving node alters the hop count field in a CID message, the receiver nodes are able of detecting and discarding the invalid message.
 Date Created:
 20120127

 Resource Type:
 Conference Proceeding
 Creator:
 Czyzowicz, Jurek, Opatrny, Jaroslav, Kranakis, Evangelos, Narayanan, Lata, Krizanc, Danny, Stacho, Ladislav, Urrutia, Jorge, Yazdani, Mohammadreza, and Lambadaris, Ioannis
 Abstract:
 A set of sensors establishes barrier coverage of a given line segment if every point of the segment is within the sensing range of a sensor. Given a line segment I, n mobile sensors in arbitrary initial positions on the line (not necessarily inside I) and the sensing ranges of the sensors, we are interested in finding final positions of sensors which establish a barrier coverage of I so that the sum of the distances traveled by all sensors from initial to final positions is minimized. It is shown that the problem is NP complete even to approximate up to constant factor when the sensors may have different sensing ranges. When the sensors have an identical sensing range we give several efficient algorithms to calculate the final destinations so that the sensors either establish a barrier coverage or maximize the coverage of the segment if complete coverage is not feasible while at the same time the sum of the distances traveled by all sensors is minimized. Some open problems are also mentioned.
 Date Created:
 20101213

 Resource Type:
 Conference Proceeding
 Creator:
 Barbeau, Michel, Kranakis, Evangelos, and GarciaAlfaro, Joaquin
 Abstract:
 The design and implementation of security threat mitigation mechanisms in RFID systems, specially in lowcost RFID tags, are gaining great attention in both industry and academia. One main focus of research interests is the authentication and privacy techniques to prevent attacks targeting the insecure wireless channel of these systems. Cryptography is a key tool to address these threats. Nevertheless, strong hardware constraints, such as production costs, power consumption, time of response, and regulations compliance, makes the use of traditional cryptography in these systems a very challenging problem. The use of lowoverhead procedures becomes the main approach to solve these challenging problems where traditional cryptography cannot fit. Recent results and trends, with an emphasis on lightweight techniques for addressing critical threats against lowcost RFID systems, are surveyed.
 Date Created:
 20100503

 Resource Type:
 Conference Proceeding
 Creator:
 Kranakis, Evangelos, Krizanc, Danny, Narayanan, Lata, and Keane, Michael
 Abstract:
 Delay (or disruption) tolerant sensor networks may be modeled as Markovian evolving graphs [1]. We present experimental evidence showing that considering multiple (possibly not shortest) paths instead of one fixed (greedy) path can decrease the expected time to deliver a packet on such a network by as much as 65 per cent depending on the probability that an edge exists in a given time interval. We provide theoretical justification for this result by studying a special case of the Markovian evolving grid graph. We analyze a natural algorithm for routing on such networks and show that it is possible to improve the expected time of delivery by up to a factor of two depending upon the probability of an edge being up during a time step and the relative positions of the source and destination. Furthermore we show that this is optimal, i.e., no other algorithm can achieve a better expected running time. As an aside, our results give high probability bounds for Knuth's toilet paper problem [11].
 Date Created:
 20091201

 Resource Type:
 Conference Proceeding
 Creator:
 He, Meng, Dillabaugh, Craig, Zeh, Norbert, and Maheshwari, Anil
 Date Created:
 20091201

 Resource Type:
 Conference Proceeding
 Creator:
 Krizanc, D., Yazdani, M., Stacho, L., Narayanan, L., Lambadaris, Ioannis, Opatrny, J., Czyzowicz, J., Kranakis, Evangelos, and Urrutia, J.
 Abstract:
 We consider n mobile sensors located on a line containing a barrier represented by a finite line segment. Sensors form a wireless sensor network and are able to move within the line. An intruder traversing the barrier can be detected only when it is within the sensing range of at least one sensor. The sensor network establishes barrier coverage of the segment if no intruder can penetrate the barrier from any direction in the plane without being detected. Starting from arbitrary initial positions of sensors on the line we are interested in finding final positions of sensors that establish barrier coverage and minimize the maximum distance traversed by any sensor. We distinguish several variants of the problem, based on (a) whether or not the sensors have identical ranges, (b) whether or not complete coverage is possible and (c) in the case when complete coverage is impossible, whether or not the maximal coverage is required to be contiguous. For the case of n sensors with identical range, when complete coverage is impossible, we give linear time optimal algorithms that achieve maximal coverage, both for the contiguous and noncontiguous case. When complete coverage is possible, we give an O(n 2) algorithm for an optimal solution, a linear time approximation scheme with approximation factor 2, and a (1∈+∈ε) PTAS. When the sensors have unequal ranges we show that a variation of the problem is NPcomplete and identify some instances which can be solved with our algorithms for sensors with unequal ranges.
 Date Created:
 20091019

 Resource Type:
 Conference Proceeding
 Creator:
 Barbeau, Michel and Laurendeau, Christine
 Abstract:
 Increasingly ubiquitous wireless technologies require novel localization techniques to pinpoint the position of an uncooperative node, whether the target be a malicious device engaging in a security exploit or a lowbattery handset in the middle of a critical emergency. Such scenarios necessitate that a radio signal source be localized by other network nodes efficiently, using minimal information. We propose two new algorithms for estimating the position of an uncooperative transmitter, based on the received signal strength (RSS) of a single target message at a set of receivers whose coordinates are known. As an extension to the concept of centroid localization, our mechanisms weigh each receiver's coordinates based on the message's relative RSS at that receiver, with respect to the span of RSS values over all receivers. The weights may decrease from the highest RSS receiver either linearly or exponentially. Our simulation results demonstrate that for all but the most sparsely populated wireless networks, our exponentially weighted mechanism localizes a target node within the regulations stipulated for emergency services location accuracy.
 Date Created:
 20090928