61 research outputs found

    Analisys of frequency-correlation properties of multipath channel for encyprion key generation using samples of differential phase

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    © 2018 IEEE. Wireless Key Generation exploits randomness of fast fading of a multipath radio channel to create identical copies of a shared encryption key at two communication nodes. A promising way for creating a highly secure key is use of samples of differential phase, which allows to overcome short-term instability of frequency standards and to make key generation devices smaller. This study examines frequency-correlation properties of the multipath channel to justify a feasibility of encryption keys generation with the differential phase method. By computer simulation, frequency autocorrelation functions of the envelope and carrier phase of a multipath radio signal are obtained, and estimates of the channel coherence bandwidth are made for a typical urban propagation environment. For random variations of the differential phase of a two-sine probe signal, a probability distribution is analyzed, its uniformity tests are done, and estimates of Shannon entropy at various frequency separations of the two probing tones are made. An effect of the line-of-sight wave and the number of multipaths on the channel frequency-correlation function and on probabilistic properties of the differential phase is considered

    Key Exchange at the Physical Layer

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    Establishing a secret communication between two parties requires both legal parties to share a private key. One problem consists of finding a way to establish a shared secret key without the availability of a secure channel. One method uses the reciprocity and multipath interference properties of the wireless channel for this purpose. We analyze this technique in the following three aspects: vulnerabilities and attacks, improvements to the protocol and experimental validation

    Reliable high-data rate body-centric wireless communication

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    Analyse et modélisation du canal radio pour la génération de clés secrètes

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    Nowadays, the security of ubiquitous wireless communications becomes more and more a crucial requirement. Even though data is widely protected via symmetric ciphering keys, a well-known difficulty is the generation and distribution of such keys. In the recent years therefore, a set of works have addressed the exploitation of inherent characteristics of the fading propagation channel for security. In particular, secret keys could be generated from the wireless channel, considered as a shared source of randomness, available merely to a pair of communicating entities. ln the present dissertation, we are interested in the approach of secret key generation (SKG) from wireless channels, especially in relating the radio channel properties to the generated keys quality. We first develop a stochastic channel model, focusing on the security with respect to the eavesdropper side, which shows a residual channel memory weil beyond a few wavelengths distance (spatially nonstationary scenarios). Then, we analyze the channel degrees of freedom (DoF) and their impact on the SKG performance in different channel conditions, especially by considering more realistic channels in both outdoor and indoor environments (respectively through simulated ray tracing data and through measurements). The results show that, even for moderately wide band (such as standardized in IEEE 802.11), the sole frequency DOF or its association with the spatial DOF is often enough for generating long keys, provided an efficient quantization method of the complex channel coefficients is used.La sécurité des communications sans fil omniprésentes devient, ces dernières années, de plus en plus une exigence incontournable. Bien que la cryptographie symétrique assure largement la confidentialité des données, la difficulté concerne la génération et la distribution de clés secrètes. Récemment, des études indiquent que les caractéristiques inhérentes du canal de propagation peuvent être exploitées afin de consolider la sécurité. En particulier, le canal radio fournit en effet une source d'aléa commune à deux utilisateurs à partir de laquelle des clés secrètes peuvent être générées. Dans la présente dissertation, nous nous intéressons au processus de génération de clés secrètes (SKG), tout en reliant les propriétés du canal radio à la qualité des clés générées. D'abord nous développons un modèle du canal stochastique, traitant la sécurité du point de vue de l'espion, qui montre une mémoire de canal résiduelle bien au-delà d'une distance de quelques longueurs d'onde (scénarios spatialement non-stationnaires). Ensuite, nous exploitons les degrés de liberté (DOF) du canal et analysons leur impact sur la performance de SKG dans différentes conditions, tout en considérant des canaux plus réalistes en environnements extérieur et intérieur (respectivement grâce à des données déterministes simulées et à des mesures). Les résultats montrent que, même pour des bandes modérées (comme standardisées dans la norme IEEE 802.11), le seul DoF de fréquence ou de son association avec le DoF spatial est souvent suffisant pour générer des longues clés, à condition d'utiliser une méthode efficace de quantification des coefficients complexes du canal

    Occupancy Detection using Wireless Sensor Network in Indoor Environment

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    Occupancy detection plays an important role in many smart buildings such as reducing building energy usage by controlling heating, ventilation and air conditioning (HVAC) systems, monitoring systems and managing lighting systems, tracking people in hospitals for medical issues, advertising to people in malls, and to search and rescue missions. The global positioning system (GPS) is used most widely as a localization system but highly inaccurate for indoor applications. The indoor environment is difficult to handle because along with the loss of signals, privacy is a major concern. Indoor tracking has many aspects in common with sensor localization in Wireless Sensor Networks (WSN). The contribution of this work is the demonstration of a nonintrusive approach to detect an occupancy in a building using wireless sensor networks to detect energy from cell phones in a secure facility and perform indoor localization based on the minimum mean square error (MMSE). To estimate the occupancy, the detected cellular signals information such as signal amplitude, frequency, power and detection time is sent to a fusion server, matched the detected signals by time and channel information, performed localization to estimate a location, and finally estimated the occupancy of rooms in a building from the estimated locations

    MedLAN: Compact mobile computing system for wireless information access in emergency hospital wards

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    This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.As the need for faster, safer and more efficient healthcare delivery increases, medical consultants seek new ways of implementing a high quality telemedical system, using innovative technology. Until today, teleconsultation (the most common application of Telemedicine) was performed by transferring the patient from the Accidents and Emergency ward, to a specially equipped room, or by moving large and heavy machinery to the place where the patient resided. Both these solutions were unpractical, uneconomical and potentially dangerous. At the same time wireless networks became increasingly useful in point-of-care areas such as hospitals, because of their ease of use, low cost of installation and increased flexibility. This thesis presents an integrated system called MedLAN dedicated for use inside the A&E hospital wards. Its purpose is to wirelessly support high-quality live video, audio, high-resolution still images and networks support from anywhere there is WLAN coverage. It is capable of transmitting all of the above to a consultant residing either inside or outside the hospital, or even to an external place, thorough the use of the Internet. To implement that, it makes use of the existing IEEE 802.11b wireless technology. Initially, this thesis demonstrates that for specific scenarios (such as when using WLANs), DICOM specifications should be adjusted to accommodate for the reduced WLAN bandwidth. Near lossless compression has been used to send still images through the WLANs and the results have been evaluated by a number of consultants to decide whether they retain their diagnostic value. The thesis further suggests improvements on the existing 802.11b protocol. In particular, as the typical hospital environment suffers from heavy RF reflections, it suggests that an alternative method of modulation (OFDM) can be embedded in the 802.11b hardware to reduce the multipath effect, increase the throughput and thus the video quality sent by the MedLAN system. Finally, realising that the trust between a patient and a doctor is fundamental this thesis proposes a series of simple actions aiming at securing the MedLAN system. Additionally, a concrete security system is suggested, that encapsulates the existing WEP security protocol, over IPSec

    Towards reliable communication in low-power wireless body area networks

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    Es wird zunehmend die Ansicht vertreten, dass tragbare Computer und Sensoren neue Anwendungen in den Bereichen Gesundheitswesen, personalisierte Fitness oder erweiterte Realität ermöglichen werden. Die am Körper getragenen Geräte sind dabei mithilfe eines Wireless Body Area Network (WBAN) verbunden, d.h. es wird drahtlose Kommunikation statt eines drahtgebundenen Kanals eingesetzt. Der drahtlose Kanal ist jedoch typischerweise ein eher instabiles Kommunikationsmedium und die Einsatzbedingungen von WBANs sind besonders schwierig: Einerseits wird die Kanalqualität stark von den physischen Bewegungen der Person beeinflusst, andererseits werden WBANs häufig in lizenzfreien Funkbändern eingesetzt und sind daher Störungen von anderen drahtlosen Geräten ausgesetzt. Oft benötigen WBAN Anwendungen aber eine zuverlässige Datenübertragung. Das erste Ziel dieser Arbeit ist es, ein besseres Verständnis dafür zu schaffen, wie sich die spezifischen Einsatzbedingungen von WBANs auf die intra-WBAN Kommunikation auswirken. So wird zum Beispiel analysiert, welchen Einfluss die Platzierung der Geräte auf der Oberfläche des menschlichen Körpers und die Mobilität des Benutzers haben. Es wird nachgewiesen, dass während regelmäßiger Aktivitäten wie Laufen die empfangene Signalstärke stark schwankt, gleichzeitig aber Signalstärke-Spitzen oft einem regulären Muster folgen. Außerdem wird gezeigt, dass in urbanen Umgebungen die Effekte von 2.4 GHz Radio Frequency (RF) Interferenz im Vergleich zu den Auswirkungen von fading (Schwankungen der empfangenen Signalstärke) eher gering sind. Allerdings führt RF Interferenz dazu, dass häufiger Bündelfehler auftreten, d.h. Fehler zeitlich korrelieren. Dies kann insbesondere in Anwendungen, die eine geringe Übertragungslatenz benötigen, problematisch sein. Der zweite Teil dieser Arbeit beschäftigt sich mit der Analyse von Verfahren, die potentiell die Zuverlässigkeit der Kommunikation in WBANs erhöhen, ohne dass wesentlich mehr Energie verbraucht wird. Zunächst wird der Trade-off zwischen Übertragungslatenz und der Zuverlässigkeit der Kommunikation analysiert. Diese Analyse basiert auf einem neuen Paket-Scheduling Algorithmus, der einen Beschleunigungssensor nutzt, um die WBAN Kommunikation auf die physischen Bewegungen der Person abzustimmen. Die Analyse zeigt, dass unzuverlässige Kommunikationsverbindungen oft zuverlässig werden, wenn Pakete während vorhergesagter Signalstärke-Spitzen gesendet werden. Ferner wird analysiert, inwiefern die Robustheit gegen 2.4 GHz RF Interferenz verbessert werden kann. Dazu werden zwei Verfahren betrachtet: Ein bereits existierendes Verfahren, das periodisch einen Wechsel der Übertragungsfrequenz durchführt (channel hopping) und ein neues Verfahren, das durch RF Interferenz entstandene Bitfehler reparieren kann, indem der Inhalt mehrerer fehlerhafter Pakete kombiniert wird (packet combining). Eine Schlussfolgerung ist, dass Frequenzdiversität zwar das Auftreten von Bündelfehlern reduzieren kann, dass jedoch die statische Auswahl eines Kanals am oberen Ende des 2.4 GHz Bandes häufig schon eine akzeptable Abhilfe gegen RF Interferenz darstellt.There is a growing belief that wearable computers and sensors will enable new applications in areas such as healthcare, personal fitness or augmented reality. The devices are attached to a person and connected through a Wireless Body Area Network (WBAN), which replaces the wires of traditional monitoring systems by wireless communication. This comes, however, at the cost of turning a reliable communication channel into an unreliable one. The wireless channel is typically a rather unstable medium for communication and the conditions under which WBANs have to operate are particularly harsh: not only is the channel strongly influenced by the movements of the person, but WBANs also often operate in unlicensed frequency bands and may therefore be exposed to a significant amount of interference from other wireless devices. Yet, many envisioned WBAN applications require reliable data transmission. The goals of this thesis are twofold: first, we aim at establishing a better understanding of how the specific WBAN operating conditions, such as node placement on the human body surface and user mobility, impact intra-WBAN communication. We show that during periodic activities like walking the received signal strength on an on-body communication link fluctuates strongly, but signal strength peaks often follow a regular pattern. Furthermore, we find that in comparison to the effects of fading 2.4 GHz Radio Frequency (RF) interference causes relatively little packet loss - however, urban 2.4 GHz RF noise is bursty (correlated in time), which may be problematic for applications with low latency bounds. The second goal of this thesis is to analyze how communication reliability in WBANs can be improved without sacrificing a significant amount of additional energy. To this end, we first explore the trade-off between communication latency and communication reliability. This analysis is based on a novel packet scheduling algorithm, which makes use of an accelerometer to couple WBAN communication with the movement patterns of the user. The analysis shows that unreliable links can often be made reliable if packets are transmitted at predicted signal strength peaks. In addition, we analyze to what extent two mechanisms can improve robustness against 2.4 GHz RF interference when adopted in a WBAN context: we analyze the benefits of channel hopping, and we examine how the packet retransmission process can be made more efficient by using a novel packet combining algorithm that allows to repair packets corrupted by RF interference. One of the conclusions is that while frequency agility may decrease "burstiness" of errors the static selection of a channel at the upper end of the 2.4 GHz band often already represents a good remedy against RF interference

    Secure short-range communications

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    Analysts predict billions of everyday objects will soon become ``smart’\u27 after designers add wireless communication capabilities. Collectively known as the Internet of Things (IoT), these newly communication-enabled devices are envisioned to collect and share data among themselves, with new devices entering and exiting a particular environment frequently. People and the devices they wear or carry may soon encounter dozens, possibly hundreds, of devices each day. Many of these devices will be encountered for the first time. Additionally, some of the information the devices share may have privacy or security implications. Furthermore, many of these devices will have limited or non-existent user interfaces, making manual configuration cumbersome. This situation suggests that devices that have never met, nor shared a secret, but that are in the same physical area, must have a way to securely communicate that requires minimal manual intervention. In this dissertation we present novel approaches to solve these short-range communication issues. Our techniques are simple to use, secure, and consistent with user intent. We first present a technique called Wanda that uses radio strength as a communication channel to securely impart information onto nearby devices. We focus on using Wanda to introduce new devices into an environment, but Wanda could be used to impart any type of information onto wireless devices, regardless of device type or manufacturer. Next we describe SNAP, a method for a single-antenna wireless device to determine when it is in close physical proximity to another wireless device. Because radio waves are invisible, a user may believe transmissions are coming from a nearby device when in fact the transmissions are coming from a distant adversary attempting to trick the user into accepting a malicious payload. Our approach significantly raises the bar for an adversary attempting such a trick. Finally, we present a solution called JamFi that exploits MIMO antennas and the Inverse-Square Law to securely transfer data between nearby devices while denying more distant adversaries the ability to recover the data. We find JamFi is able to facilitate reliable and secure communication between two devices in close physical proximity, even though they have never met nor shared a key
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