The last decade has been characterized by a rapid increase in the usage of mobile communications. One of the main aspects of mobile communications is mobility. This means that mobile phones have to switch between base station cells in order to support the uninterrupted usage of all available services within the area of the mobile network coverage. The process of switching user devices between base station cells is called a handover. Accordingly, base stations are optimized to serve mobile phones with certain moving velocities based on an area and user characteristics to better handle handovers. However, issues appear when a mobile phone starts switching rapidly between two different cells in a short period of time, referred to as ping-pong handover. These occurrences cause negative effects in terms of increased telecom operators signaling overhead and user dissatisfaction. The 3rd Generation Partnership Project (3GPP) defines a metric called ping-pong rate in order to analyze what is the most adequate base station configuration concerning different user velocities and how well base stations handle handovers. The ping-pong rate is defined as a share of ping-pong handovers in total handovers, without taking into consideration the conditions under which they occur. In this paper, the conditions under which ping-pong handovers occur are analyzed by using live, non-simulated data. Findings show that the handovers under different conditions have different probabilities to become ping-pong handovers. Furthermore, these findings are utilized for defining a new empiric metric used for evaluating the handover handling of pre-configured base stations. Consequently, the novel empiric metric provides better insights into the base station handling of handovers than the ping-pong rate defined by 3GPP.

With the everyday growth of the Internet of Things (IoT), the number of connected sensor devices increases as well, where each sensor consumes energy while being constantly online. During that time, they collect large amounts of data in short intervals leading to the collection of redundant and perhaps irrelevant data. Moreover, being commonly battery powered, sensor batteries need to be frequently replaced or recharged. The former requires smarter and less frequent data collection, while the latter being complementary to the former requires putting them to sleep while not being used in order to save energy. The focus of this article is low-cost gas sensors as they need to preheat for several minutes to reliably collect gas concentration. However, instead of waiting for a sensor to heat up, a transient, i.e., a data trend that the sensor collects while heating up is analyzed. It is shown that long short-term memory (LSTM) neural network can be used to learn and later predict the actual gas level from a part of the transient. This way, instead of being constantly online or fully preheating, the sensor needs to be turned on for only 20 s and then sleep for 120 s. With high accuracy, our approach decreases energy consumption by up to 85% compared to a system where sensors are constantly online, and more than 50% compared to a system where a sensor collects actual values instead of a part of the transient.

A plethora of organizations, companies, and foremost universities and educational institutions are using WPA2-Enterprise protocol to allow their end-users to connect to provided Wi-Fi networks. When both the provider’s and the end-user’s devices are configured properly, it is considered one of the safest Wi-Fi connection protocols with the added benefits of having a unique password for every Wi-Fi user. However, a known evil twin attack can be performed to steal users’ Wi-Fi login credentials, if the devices are not configured correctly. Considering the widespread use of Wi-Fi-enabled smartphones and rising concerns regarding users’ privacy, we focus on the privacy aspects of WPA2-Enterprise vulnerabilities mainly on the widespread Eduroam network. We show that device deanonymization is a concerning liability of many Eduroam networks. More than 87% of 1650 devices collected during a two-month test on our university are vulnerable to MAC address deanonymization attack. Furthermore, by analyzing the Eduroam Configuration Assistant Tool of 1066 different institutions around the world, 67% of exported Eduroam profiles having the Wi-Fi device reveal the user’s identity in the clear, thus linking the users with the device’s MAC address. Indeed, the analysis of the configuration profiles has been confirmed by performing the deanonymization attack on a large-scale international music festival in our country, where 70% of the devices have been vulnerable. Additionally, we showcase the psychological aspects of secure Eduroam users, where some are willing to modify secure configuration profiles to gain aspects to certain blocked features. As a result, the attacker is granted with user credentials and IMSI number and provided with access to all Eduroam-related services.

User’s location privacy concerns have been further raised by today’s Wi‐Fi technology omnipresence. Preferred Network Lists (PNLs) are a particularly interesting source of private location information, as devices are storing a list of previously used hotspots. Privacy implications of a disclosed PNL have been covered by numerous papers, mostly focusing on passive monitoring attacks. Nowadays, however, more and more devices no longer transmit their PNL in clear, thus mitigating passive attacks. Hidden PNLs are still vulnerable against active attacks whereby an attacker mounts a fake SSID hotspot set to one likely contained within targeted PNL. If the targeted device has this SSID in the corresponding PNL, it will automatically initiate a connection with the fake hotspot thus disclosing this information to the attacker. By iterating through different SSIDs (from a predefined dictionary) the attacker can eventually reveal a big part of the hidden PNL. Considering user mobility, executing active attacks usually has to be done within a short opportunity window, while targeting nontrivial SSIDs from user’s PNL. The existing work on active attacks against hidden PNLs often neglects both of these challenges. In this paper we propose a simple mathematical model for analyzing active SSID dictionary attacks, allowing us to optimize the effectiveness of the attack under the above constraints (limited window of opportunity and targeting nontrivial SSIDs). Additionally, we showcase an example method for building an effective SSID dictionary using top‐N recommender algorithm and validate our model through simulations and extensive real‐life tests.

Many applications from the Internet of Things (IoT) domain used in healthcare, smart homes, and cities involve a large number of interconnected wireless devices. To ensure privacy, confidentiality, and integrity of the information, devices should be initialized prior to any communication. In this paper, we present a secure initialization method for constrained IoT devices such as wireless sensors devices and/or actuators. The solution uses visible light communication (VLC) for the initial configuration of the IoT devices. The VLC system consists of a modulated light source such as a smartphone screen and a very simple photodetector. We analyze known coding and modulation techniques used for the VLC and propose BlinkComm, a differential coding technique that achieves threefold increase in transmission speed compared to existing solutions. We showed through experiments with 32 participants that the proposed solution achieves fast completion times and low error rates as well as high user satisfaction levels.

Future healthcare systems, smart homes, and similar will involve a large number of smart inter-connected wireless devices (such as wireless sensor nodes). One of the major challenges to securing these systems presents loading initial cryptographic credentials into a relatively large number of wireless devices. Furthermore, many of these technologies involve low-cost and highly interface constrained devices (lacking usual wired interfaces, displays, keypads, and alike). We propose two novel multichannel key deployment schemes for wireless networks that only require a presence of a light source device, such as a multi-touch screen (tablet or smartphone device). The first key deployment scheme is based on secret key cryptography and is suitable for interface/resource-constrained wireless devices. The second scheme assumes a strong attacker and requires the use of public key cryptography. In both our solutions, we use one-way visible light channel of multi-touch screens (flashing displays) to initialize devices in a secure, usable, and scalable way. From the user's perspective, this boils down to placing the devices on the multitouch screen after which the remaining process is fully automatized. We showed through the experiments with 48 users that our solution is user-friendly and scales linearly with the number of nodes. Copyright © 2015 John Wiley & Sons, Ltd.

Classical password/PIN-based authentication methods have proven to be vulnerable to a broad range of observation attacks (such as key-logging, video-recording or shoulder surfing attacks). In order to mitigate these attacks, a number of solutions have been proposed, most of them being cognitive authentication schemes (challenge-response protocols that require users to perform some kind of cognitive operations). In this paper, we show successful passive side-channel timing attacks on two cognitive authentication schemes, a well-known Hopper-Blum (HB) protocol and a U.S. patent Mod10 method, previously believed to be secure against observation attacks. As we show, the main security weakness of these methods comes from detectable variations in the user's cognitive load that results from cognitive operations during the authentication procedure. We carried out theoretical analysis of both Mod10 and HB methods, as well as an experimental user study of Mod10 method with 58 participants to validate the results of our timing attacks. We also propose security enhancements of these schemes aimed to mitigate the timing side-channel attacks. The proposed enhancements show the existence of a strong tradeoff between security and usability, indicating that the security of cognitive authentication schemes comes at a non-negligible usability cost (e.g., increased overall login time). For this reason, the designers of new cognitive authentication schemes should not ignore possible threats induced by side-channel timing attacks.

HASH(0x3b6160c)

This paper reports two attacks on Undercover, a human authentication scheme against passive observers proposed at CHI 2008. The first attack exploits nonuniform human behavior in responding to authentication challenges and the second one is based on information leaked from authentication challenges or responses visible to the attacker. The second attack can be generalized to break two alternative Undercover designs presented at Pervasive 2009. All the attacks exploit design flaws of the Undercover implementations.

Despite years of intensive research, the main deterrents of widely deploying secure communication between wireless nodes remains the cumbersome key setup process. In this paper, we address this problem and we introduce Integrity (I) regions, a novel security primitive that enables message authentication in wireless networks without the use of preestablished or precertified keys. Integrity regions are based on the verification of entity proximity through time-of-arrival ranging techniques. IRegions can be efficiently implemented with ultrasonic ranging, in spite of the fact that ultrasound ranging techniques are vulnerable to distance enlargement and reduction attacks. We further show how IRegions can be used for key establishment in mobile peer-to-peer wireless networks and we propose a novel automatic key establishment approach, largely transparent to users, by leveraging on IRegions and nodes' mobility. We analyze our proposals against a multitude of security threats and we validate our findings via extensive simulations.

Peer-to-peer (P2P) architectures are gaining increasing popularity in disseminating content to a large number of nodes. In this paper, we show that small coalitions between peers can further enhance the performance of current P2P architectures. Small coalitions bridge the gap between inefficient non-cooperative and fully cooperative architectures by establishing a robust tradeoff between the complexity and performance of the resource distribution process. Owing to their small size, small coalitions are inherently resilient to the churn in existing P2P systems and embed natural incentives for peers to self-organize in order to improve their download times. We evaluate several coalition strategies analytically and empirically via simulations and we show that our solutions considerably improve the download performance in current P2P systems.

In this paper, we study the problem of efficient medium access control (MAC) among cognitive radio devices that are equipped with multiple radios and thus are capable of transmitting simultaneously at different frequencies (channels). We assume that radios contend on each channel using the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. We study two MAC problems: (i) the allocation of the available channels among radios, and (ii) the optimal usage of each allocated channel by the radios occupying it. Both problems are studied in a game-theoretic setting, where devices aim to selfishly maximize their share of the available bandwidth. As for the first problem, we show that the “price of anarchy” is close to 1, that is, Nash equilibria imply nearly system optimal allocations of the available channels. For the second problem, we design a game such that it admits a unique Nash equilibrium that is is both fair and Pareto-optimal. Furthermore, we propose simple mechanisms that enable selfish cognitive radio devices not only to coordinate efficiently on the available channels but also to optimally use every single allocated channel.

We consider the following problem: how can two devices that do not share any secrets establish a shared secret key over a wireless radio channel in the presence of a communication jammer? An inherent challenge in solving this problem is that known anti-jamming techniques (e.g.,frequency hopping or direct-sequence spread spectrum) which should support device communication during the key establishment require that the devices share a secret spreading key (or code) prior to the start of their communication. This requirement creates a circular dependency between anti-jamming spread-spectrum communication and key establishment, which has so far not been addressed. In this work, we propose an Uncoordinated Frequency Hopping (UFH) scheme that breaks this dependencyand enables key establishment in the presence of a communication jammer. We perform a detailed analysis of our UFH scheme and show its feasibility, both in terms of execution time and resource requirements.

Inspired by unidirectional error detecting codes that are used in situations where only one kind of bit errors are possible (e.g., it is possible to change a bit "0" into a bit "1", but not the contrary), we propose integrity codes (I-codes) for a radio communication channel, which enable integrity protection of messages exchanged between entities that do not hold any mutual authentication material (i.e. public keys or shared secret keys). The construction of I-codes enables a sender to encode any message such that if its integrity is violated in transmission over a radio channel, the receiver is able to detect it. In order to achieve this, we rely on the physical properties of the radio channel and on unidirectional error detecting codes. We analyze in detail the use of I-codes on a radio communication channel and we present their implementation on a wireless platform as a "proof of concept". We further introduce a novel concept called "authentication through presence", whose broad applications include broadcast authentication, key establishment and navigation signal protection. We perform a detailed analysis of the security of our coding scheme and we show that it is secure within a realistic attacker model.

In this work, we propose and analyze a new approach for securing localization and location verification in wireless networks based on hidden and mobile base stations. Our approach enables secure localization with a broad spectrum of localization techniques: ultrasonic or radio, based on received signal strength or signal time of flight. Through several examples we show how this approach can be used to secure node-centric and infrastructure-centric localization schemes. We further show how this approach can be applied to secure localization in mobile ad-hoc and sensor networks.

Channel allocation was extensively studied in the framework of cellular networks. But the emergence of new system concepts, such as cognitive radio systems, has brought this topic into the focus of research again. In this paper, we study in detail the problem of competitive multi-radio multi-channel allocation in wireless networks. We study the existence of Nash equilibria in a static game and we conclude that, in spite of the non-cooperative behavior of such devices, their channel allocation results in a load-balancing solution. In addition, we consider the fairness properties of the resulting channel allocations and their resistance to the possible coalitions of a subset of players. Finally, we present three algorithms that achieve a load-balancing Nash equilibrium channel allocation; each of them using a different set of available information.

In each country today, cellular networks operate on carefully separated frequency bands. This separation is imposed by the regulators of the given country to avoid interference between these networks. But, the separation is only valid within the borders of a country, hence the operators are left on their own to resolve cross-border interference of their cellular networks. In this paper, we focus on the scenario of two operators, each located on one side of the border. We assume that they want to fine-tune the emitting power of the pilot signals (i.e., beacon signals) of their base stations. This operation is crucial, because the pilot signal power determines the number of users they can attract and hence the revenue they can obtain. In the case of no power costs, we show that there exists a motivation for the operators to be strategic, meaning to fine-tune the pilot signal powers of their base stations. In addition, we study Nash equilibrium conditions in an empirical model and investigate the efficiency of the Nash equilibria for different user densities. Finally, we modify our game model to take power costs into account. The game with power costs corresponds to the well-known prisoner's dilemma: The players are still motivated to adjust their pilot powers, but their strategic behavior leads to a sub-optimal Nash equilibrium.

We propose SecNav, a new protocol for securing wireless navigation systems. This protocol secures localization and time synchronization in wireless networks by relying on devices' awareness of presence in the power-range (coverage area) of navigation stations. We perform a detailed security analysis of SecNav and show that, compared to existing secure navigation approaches, it prevents the widest range of attacks on navigation. Our implementation of SecNav, using 802.11b devices, shows that this scheme can be efficiently implemented with existing technologies.

Due to their very nature, wireless sensor networks are probably the category of wireless networks most vulnerable to "radio channel jamming"-based denial-of-service (DoS) attacks. An adversary can easily mask the events that the sensor network should detect by stealthily jamming an appropriate subset of the nodes; in this way, he prevents them from reporting what they are sensing to the network operator. Therefore, even if an event is sensed by one or several nodes (and the sensor network is otherwise fully connected), the network operator cannot be informed on time. We show how the sensor nodes can exploit channel diversity in order to create wormholes that lead out of the jammed region, through which an alarm can be transmitted to the network operator. We propose three solutions. The first is based on wired pairs of sensors, the second relies on frequency hopping, and the third is based on a novel concept called uncoordinated channel hopping. We develop appropriate mathematical models to study the proposed solutions

Abstract — Until recently, the problem of localization in wireless networks has been mainly studied in a nonadversarial setting. Only recently, a number of solutions have been proposed that aim to detect and prevent attacks on localization systems. In this work, we propose a new approach to secure localization based on hidden and mobile base stations. Our approach enables secure localization with a broad spectrum of localization techniques: ultrasonic or radio, based on received signal strength or signal time of flight. Through several examples we show how this approach can be used to secure nodecentric and infrastructure-centric localization schemes. We further show how this approach can be applied to secure localization in sensor networks. I.

Inspired by unidirectional error detecting codes that are used in situations where only one kind of bit errors are possible (e.g., it is possible to change a bit "0" into a bit "1", but not the contrary), we propose integrity codes (I-codes) for a radio communication channel, which enable integrity protection of messages exchanged between entities that do not hold any mutual authentication material (i.e. public keys or shared secret keys). The construction of I-codes enables a sender to encode any message such that if its integrity is violated in transmission over a radio channel, the receiver is able to detect it. In order to achieve this, we rely on the physical properties of the radio channel. We analyze in detail the use of I-codes on a radio communication channel and we present their implementation on a Mica2 wireless sensor platform as a "proof of concept". We finally introduce a novel concept called "authentication through presence" that can be used for several applications, including for key establishment and for broadcast authentication over an insecure radio channel. We perform a detailed analysis of the security of our coding scheme and we show that it is secure with respect to a realistic attacker model.

We present a set of simple techniques for key establishment over a radio link in peer-to-peer networks. Our approach is based on the Diffie-Hellmankey agreement protocol, which is known to be vulnerable to the "man-in-the-middle" attack if the two users involved in the protocol do not share any authenticated information about each other (e.g., public keys, certificates, passwords,shared keys, etc.) prior to the protocol execution. In this paper, we solve the problem by leveraging on the natural ability of users to authenticate each other by visual and verbal contact. We propose three techniques. The first is based on visual comparison of short strings, the second on distance bounding, and the third on integrity codes; in each case, the users do not need to enter any password or other data, nor do they need physical or infrared connectivity between their devices. We base our analysis on a well-established methodology that leads us to a rigorous modularization and a thorough robustness proof of our proposal.

CSMA/CA protocols rely on the random deferment of packet transmissions. Like most other protocols, CSMA/CA was designed with the assumption that the nodes would play by the rules. This can be dangerous, since the nodes themselves control their random deferment. Indeed, with the higher programmability of the network adapters, the temptation to tamper with the software or firmware is likely to grow; by doing so, a user could obtain a much larger share of the available bandwidth at the expense of other users. We use a game-theoretic approach to investigate the problem of the selfish behavior of nodes in CSMA/CA networks, specifically geared towards the most widely accepted protocol in this class of protocols, IEEE 802.11. We characterize two families of Nash equilibria in a single stage game, one of which always results in a network collapse. We argue that this result provides an incentive for cheaters to cooperate with each other. Explicit cooperation among nodes is clearly impractical. By applying the model of dynamic games borrowed from game theory, we derive the conditions for the stable and optimal functioning of a population of cheaters. We use this insight to develop a simple, localized and distributed protocol that successfully guides multiple selfish nodes to a Pareto-optimal Nash equilibrium.

In all-wireless networks a crucial problem is to minimize energy consumption, as in most cases the nodes are battery-operated. We focus on the problem of power-optimal broadcast, for which it is well known that the broadcast nature of the radio transmission can be exploited to optimize energy consumption. Several authors have conjectured that the problem of power-optimal broadcast is NP-complete. We provide here a formal proof, both for the general case and for the geometric one; in the former case, the network topology is represented by a generic graph with arbitrary weights, whereas in the latter a Euclidean distance is considered. We then describe a new heuristic, Embedded Wireless Multicast Advantage. We show that it compares well with other proposals and we explain how it can be distributed.