A wireless sensor network consists of a number of sensor devices and coordinator(s) or sink(s). A coordinator collects the sensed data from the sensor devices for further processing. In such networks, sensor devices are generally powered by batteries. Since wireless transmission of packets consumes significant amount of energy, it is important for a network to adopt a medium access control (MAC) technology which is energy efficient and satisfies the communication performance requirements. Carrier sense multiple access with collision avoidance (CSMA/CA), which is a popular access technique because of its simplicity, flexibility and robustness, suffers poor throughput and energy inefficiency performance in wireless sensor networks. On the other hand, time division multiple access (TDMA) is a collision free and delay bounded access technique but suffers from the scalability problem. For this reason, this thesis focuses on design and analysis of hybrid channel access schemes which combine the strengths of both the CSMA/CA and TDMA schemes. In a hybrid CSMA/CA-TDMA scheme, the use of the CSMA/CA period and the TDMA period can be optimized to enhance the communication performance in the network. If such a hybrid channel access scheme is not designed properly, high congestion during the CSMA/CA period and wastage of bandwidth during the TDMA period result in poor communication performance in terms of throughput and energy efficiency. To address this issue, distributed and centralized channel access schemes are proposed to regulate the activities (such as transmitting, receiving, idling and going into low power mode) of the sensor devices. This regulation during the CSMA/CA period and allocation of TDMA slots reduce traffic congestion and thus improve the network performance. In this thesis work, time slot allocation methods in hybrid CSMA/CA-TDMA schemes are also proposed and analyzed to improve the network performance. Finally, such hybrid CSMA/CA-TDMA schemes are used in a cellular layout model for the multihop wireless sensor network to mitigate the hidden terminal collision problem.

Handling mobility in wireless sensor networks can pose formidable challenges in protocol design, especially, at the link layer. Since most of the proposed Medium Access Control (MAC) protocols do not accommodate mobility, a node has two options to deal with a deteriorating link: (a) to continue data transmission until the link breaks and then establishes a new link with a new relay node; or (b) to seamlessly transfer the communication to a better link parallel to the data transmission over the existing link. Different from option (a) where a node can only search for a new link after the original link disrupts, option (b) enables a node to perceive the change in the quality of a link in advance. The link quality prediction is implemented by an adaptive handover mechanism. Both approaches will inevitably introduce latency. This thesis aims to quantify and compare such latency. Specifically, it investigates the latency of packet transmission in a mobile wireless sensor network with and without the support of a handover mechanism. To start with, the thesis elaborates the effect of mobility on the performance of the existing MAC protocols, and the need to maintain an unbroken link during data transmission. To implement the handover, a target MAC protocol is required to be selected first. Since the Receiver-Initiated MAC protocol (RI-MAC) uses only short beacon and data packets during communication that substantially reduce overhearing, collision probability and data recovery cost, it is chosen as the carrier for the latency evaluation. Even though RI-MAC performs well in many aspects, it has several demerits. To address the monotonous increment in the backoff window size and to reduce the occurrence frequency of the dwell time, a burst data transmission pattern is adopted to optimize RI-MAC. With the optimization, the protocol reduces the long idle listening time that a node has to wait before data transmission, and thus, works well in a static scenario. However, due to the high probability of link disconnection, the burst data transmission does not perform well in case of mobility. For the sake of accommodating mobility, an adaptive handover mechanism is developed on top of the optimized RI-MAC. Once a node evaluates that the data packets cannot be completely transmitted before the link terminates, it will search for a new relay node while keeping communicating with the original collaborator. It is implemented by embedding a neighbor discovery request in a data packet that will be transmitted in a broadcast channel. Neighbors of the node will participate in the handover process as long as they are in an active state and their distance to the transmitter does not exceed a pre-defined threshold. As a proof-of-concept for the handover mechanism, a mathematical model is established. The transmission rate, the moving speed of human beings, the duty cycle and the network density are all taken into consideration. The analytical result shows that the communication latency decreases with an increment in the network density and the duty cycle when the handover mechanism is used, whereas the latency exhibits a reverse trend when the handover mechanism is not used. To validate the mathematics-based evaluation, the NS2 network simulator is employed. The simulation result is found to perform in accordance with the analytical result. It is asserted that the latency of packet transmission with the handover support is much less than that without the handover support. The communication latency can be saved by at least 0.28s when the handover mechanism is applied. This figure can even grow as the duty cycle and the network density increase. From this perspective, the handover mechanism is verified to improve the latency of packet transmission as far as mobility is concerned.

In many emerging applications, data streams are monitored in a network environment. Due to limited communication bandwidth and other resource constraints, a critical and practical demand is to online compress data streams continuously with quality guarantee. Although many data compression and digital signal processing methods have been developed to reduce data volume, their super-linear time and more-than-constant space complexity prevents them from being applied directly on data streams, particularly over resource-constrained sensor networks. In this thesis, we tackle the problem of online quality guaranteed compression of data streams using fast linear approximation (i.e., using line segments to approximate a time series). Technically, we address two versions of the problem which explore quality guarantees in different forms. We develop online algorithms with linear time complexity and constant cost in space. Our algorithms are optimal in the sense that they generate the minimum number of segments that approximate a time series with the required quality guarantee. To meet the resource constraints in sensor networks, we also develop a fast algorithm which creates connecting segments with very simple computation. The low cost nature of our methods leads to a unique edge on the applications of massive and high speed streaming environment, low bandwidth networks, and heavily constrained nodes in computational power (e.g., tiny sensor nodes). We implement and evaluate our methods in the application of an acoustic wireless sensor network.

Sensor networks are innovative wireless networks consisting of a large number of low-cost, resource-constrained sensor nodes that collect, process, and transmit data in a distributed and collaborative way. There are numerous applications for wireless sensor networks, and security is vital for many of them. However, sensor nodes suffer from many constraints, including low computation capability, small memory, limited energy resources, susceptibility to physical capture, and the lack of infrastructure, all of which impose formidable security challenges and call for innovative approaches. In this thesis, we present our research results on three important aspects of securing sensor networks: lightweight entity authentication, distributed node clone detection, and secure data aggregation. As the technical core of our lightweight authentication proposals, a special type of circulant matrix named circulant-P2 matrix is introduced. We prove the linear independence of matrix vectors, present efficient algorithms on matrix operations, and explore other important properties. By combining circulant-P2 matrix with the learning parity with noise problem, we develop two one-way authentication protocols: the innovative LCMQ protocol, which is provably secure against all probabilistic polynomial-time attacks and provides remarkable performance on almost all metrics except one mild requirement for the verifier's computational capacity, and the HB$^C$ protocol, which utilizes the conventional HB-like authentication structure to preserve the bit-operation only computation requirement for both participants and consumes less key storage than previous HB-like protocols without sacrificing other performance. Moreover, two enhancement mechanisms are provided to protect the HB-like protocols from known attacks and to improve performance. For both protocols, practical parameters for different security levels are recommended. In addition, we build a framework to extend enhanced HB-like protocols to mutual authentication in a communication-efficient fashion. Node clone attack, that is, the attempt by adversaries to add one or more nodes to the network by cloning captured nodes, imposes a severe threat to wireless sensor networks. To cope with it, we propose two distributed detection protocols with difference tradeoffs on network conditions and performance. The first one is based on distributed hash table, by which a fully decentralized, key-based caching and checking system is constructed to deterministically catch cloned nodes in general sensor networks. The protocol performance of efficient storage consumption and high security level is theoretically deducted through a probability model, and the resulting equations, with necessary adjustments for real application, are supported by the simulations. The other is the randomly directed exploration protocol, which presents notable communication performance and minimal storage consumption by an elegant probabilistic directed forwarding technique along with random initial direction and border determination. The extensive experimental results uphold the protocol design and show its efficiency on communication overhead and satisfactory detection probability. Data aggregation is an inherent requirement for many sensor network applications, but designing secure mechanisms for data aggregation is very challenging because the aggregation nature that requires intermediate nodes to process and change messages, and the security objective to prevent malicious manipulation, conflict with each other to a great extent. To fulfill different challenges of secure data aggregation, we present two types of approaches. The first is to provide cryptographic integrity mechanisms for general data aggregation. Based on recent developments of homomorphic primitives, we propose three integrity schemes: a concrete homomorphic MAC construction, homomorphic hash plus aggregate MAC, and homomorphic hash with identity-based aggregate signature, which provide different tradeoffs on security assumption, communication payload, and computation cost. The other is a substantial data aggregation scheme that is suitable for a specific and popular class of aggregation applications, embedded with built-in security techniques that effectively defeat outside and inside attacks. Its foundation is a new data structure---secure Bloom filter, which combines HMAC with Bloom filter. The secure Bloom filter is naturally compatible with aggregation and has reliable security properties. We systematically analyze the scheme's performance and run extensive simulations on different network scenarios for evaluation. The simulation results demonstrate that the scheme presents good performance on security, communication cost, and balance.

Sensor technologies are vital today in gathering information about certain environments and wireless sensor networks are getting more widespread use everyday. These networks are characterized by a number of sensor nodes deployed in the field for the observation of some phenomena. Due to the limited battery capacity in sensor nodes, energy efficiency is a major and challenging problem in such power-constrained networks. Some of the network design parameters have a direct impact on the network&rsquo / s lifetime. These parameters have to be chosen in such a way that the network use its energy resources efficiently. This thesis studies these parameters that should be selected according to certain trade offs with respect to the network&rsquo / s lifetime. In this work, these trade offs have been investigated and illustrated in detail in various combinations. To achieve this goal, a special simulation tool has been designed and implemented in this work that helps in analyzing the effects of the selected parameters on sensor network&rsquo / s lifetime. OMNeT++, a discrete event simulator, provides the framework for the sensor network simulator&rsquo / s development. Ultimately, results of extensive computational tests are presented, which may be helpful in guiding the sensor network designers in optimally selecting the network parameters for prolonged lifetime.

This thesis investigates inkjet-printed flexible antennas fabricated on paper substrates as a system-level solution for ultra-low-cost and mass production of RF structures. These modules are designed for the UHF Radio Frequency Identification (RFID) Tags and Wireless Sensor Nodes (WSN); however the approach could be easily extended to other microwave and wireless applications. Chapter 1 serves as an introduction to RFID technology and its capabilities while listing the major challenges that could potentially hinder RFID practical implementation. Chapter 2 discusses the benefits of using paper as a substrate for high-frequency applications, reporting its very good electrical/dielectric performance up to at least 1 GHz. The dielectric properties are studied by using the microstrip ring resonator. Brief discussion on Liquid Crystal Polymer (LCP) is also given in this chapter. Chapter 3 gives details about the inkjet printing technology, including the characterization of the conductive ink, which consists of nano-silver-particles, while highlighting the importance of this technology as a fast and simple fabrication technique especially on flexible organic (e.g.LCP) or paper-based substrates. Chapter 4 focuses on antenna designs. Four examples are given to provide: i) matching techniques to complex IC impedance, ii) proof of concept of inkjet printing on paper substrate through measurement results, iii) demonstration of a fully-integrated wireless sensor modules on paper and show a 2D sensor integration with an RFID tag module on paper. Chapter 5 concludes the thesis by explaining the importance of this work in creating a first step towards an environmentally friendly generation of "green" RF electronics and modules.

This thesis studies cooperative sensing and transmission in the context ofwireless sensor networks (WSNs). We especially focus on two means of cooperative sensing and transmission, namely, distributed source coding and relaying. We consider systems where the usefulness of the measured data is dependent on how old the data is and we therefore need low-delay transmission schemes. At first sight, the low-delay criterion may seem to be of little relevance, but it is this aspect in particular that distinguishes this thesis from many of the existing communication theoretic results, which often are asymptotic in the block lengths. The thesis is composed of an introductory part, discussing the fundamentals of communication theory and how these are related to the requirements of WSNs, followed by a part where the results of the thesis are reported in Papers A-H. Papers A-D study different scenarios for distributed source-channel coding. In Paper A, we consider transmission of correlated continuous sources and propose an iterative algorithm for designing simple and energy-efficient sensor nodes. In particular the cases of the binary symmetric channel as well as the additive white Gaussian noise channel are studied. In Paper B, the work is extended to channels with interference and it is shown that also in this case there can be significant power savings by performing a joint optimization of the system.Papers C and D use a more structured approach and propose side-information-aware source-channel coding strategies using lattices and sinusoids. In Paper E, we apply the methods we have used in joint source-channel coding to the famous Witsenhausen counterexample. By using a relatively simple iterative algorithm, we are able to demonstrate the best numerical performance known to date. For the case of systems with relays, we study the transmission of a continuous Gaussian source and the transmission of an uniformly distributed discrete source. In both situations, we propose algorithms to design low-delay source-channel and relay mappings. By studying the structure of the optimized source-channel and relay mappings, we provide useful insights into how the optimized systems work. These results are reported in Papers F and G. In Paper H, we finally consider sum-MSE minimization for the Gaussian multiple-input, multiple-output broadcast channel. By using recently discovered properties of this problem, we derive a closed-form expression for the optimal power allocation in the two-user scenario and propose a conceptually simple and efficient algorithm that handles an arbitrary number of users. Throughout the thesis we show that there are significant gains if the parts of the system are jointly optimized for the source and channel statistics. All methods that are considered in this thesis yield very low coding and decoding delays. In general, nonlinear mappings outperform linear mappings for problems where there is side-information available. Another contribution of this thesis is visualization of numerically optimized systems that can be used as inspiration when structured low-delay systems are designed. / The author changed name from Johannes Karlsson to Johannes Kron in January 2011. QC 20110512

The battery driven nature of wireless sensor networks, combined with the need of extended lifetime mandates that energy efficiency is a metric with high priority. In the current thesis we explore and compare the energy dissipation of di fferent processor architectures and how it is associated with performance and area requirements. The processor architectures are di erentiated based on the datapath length (16-bit, 32-bit, 64-bit and 128-bit) and the corresponding size of the data memories. Our study focuses on AES algorithm, and the indicated processor architectures support AES forward encryption, CCM (32/64/128), CBC (32/64/128) and CTR common modes of operation. In each processor architecture the instruction set is extended to increase the efficiency of the system. / -

Η παρούσα διπλωματική έχει ως στόχο την παρουσίαση και ανάπτυξη ενός πλήρους πληροφοριακού συστήματος που είναι δυνατόν η εφαρμογή του στο πραγματικό κόσμο να καθιστά ένα σπίτι ως «έξυπνο». Ο σκοπός της δημιουργίας του συστήματος αυτού είναι η μέτρηση και η καταχώρηση των συνθηκών που επικρατούν σε ένα χώρο και ο εντοπισμός κινήσεων που γίνονται μέσα σε αυτόν ώστε να εκτελεστούν κάποιες λειτουργίες αυτόματα. Το εν λόγω πληροφοριακό σύστημα αποτελείται από έναν κεντρικό υπολογιστή ο οποίος συνδέεται με ένα δίκτυο από διάφορους αισθητήρες, με μια βάση δεδομένων και έχει δυνατότητα επικοινωνίας με κινητό τηλέφωνο μέσω 3G δικτύου ώστε να υπάρχει απομακρυσμένη πρόσβαση σε όλες τις λειτουργίες. Έτσι η ανάπτυξη και η παρουσίαση αυτού του συστήματος δίνει τη δυνατότητα δημιουργίας ενός έξυπνου σπιτιού με εξατομικευμένες προδιαγραφές και δυνατότητα επέκτασης του συστήματος. Εν κατακλείδι, η παρούσα διπλωματική εργασία, θέλει να αναδείξει την ευκολία, την απλότητα, την ευελιξία, αλλά και την χρησιμότητα που έχει ένα έξυπνο σπίτι. Παρουσιάζει ουσιαστικά την καρδιά του έξυπνου σπιτιού, ποιες είναι οι βασικές του μονάδες, πώς λειτουργούν και πώς αλληλεπιδρούν μεταξύ τους. / This Thesis aims at presenting and developing a complete system which can apply in the real world to make a home "smart." The purpose of creating this system is the measurement and recording of conditions of the house (humidity, temperature, light density etc) and monitor movements inside restricted areas in order to automate and trigger different operations. This information system consists of a central computer which is connected to a network of several sensors, a database and is also capable of remote access with mobile phone via 3G network. Thus the development and presentation of this system enables the creation of a smart home with personalized specifications and scalability of the system. In conclusion, this thesis wants to demonstrate the ease, simplicity, flexibility, and the utility a smart home has. Presents the heart of the smart house, what are the basic units, how they work and how they interact.

Ένα ασύρματο δίκτυο αισθητήρων αποτελείται από χωρικά κατανεμημένες αυτόνομες συσκευές, οι οποίες χρησιμοποιούν αισθητήρες για την συνεργατική παρακολούθηση φυσικών και περιβαλλοντικών συνθηκών. Ένας κόμβος ενός δικτύου αισθητήρων συνήθως αποτελείται από ένα μικροελεγκτή, ένα ραδιο-πομποδέκτη, μια πηγή ενέργειας, η οποία συχνά είναι μια μπαταρία και διαφόρων ειδών αισθητήρες (π.χ. θερμοκρασίας, υγρασίας, φωτεινότητας). Τα ασύρματα δίκτυα αισθητήρων προσφέρουν οικονομικά βιώσιμες λύσεις σε ποικίλες εφαρμογές. Δίκτυα τέτοιου τύπου δραστηριοποιούνται σε βιοιατρικές, στρατιωτικές, βιομηχανικές εφαρμογές καθώς και εφαρμογές παρακολούθησης του φυσικού περιβάλλοντος. Επιπλέον, τα δίκτυα αισθητήρων είναι κλειδί για τη δημιουργία έξυπνων χώρων που ενθέτουν τεχνολογία πληροφορίας στα καθημερινά περιβάλλοντα εργασίας και κατοικίας. Λόγω της χρήσης τέτοιων δικτύων σε περιβάλλοντα που ανταλλάσσονται ευαίσθητες πληροφορίες, δημιουργούνται θέματα ασφάλειας και μυστικότητας. Χαρακτηριστικά των διαφόρων εφαρμογών όπως η λειτουργία σε αντίξοα περιβάλλοντα, η ελλιπής γνώση της τοπολογίας του δικτύου, οι δυνατότητες αυτο-οργάνωσης και αυτόματης διόρθωσης λειτουργιών και η λειτουργία χωρίς ανθρώπινη επιτήρηση καθιστούν τη διατήρηση της ασφάλειας μια μεγάλη πρόκληση. Ένας κλάδος που παρέχει λύσεις σε προβλήματα ασφαλείας είναι αυτός της κρυπτογραφίας. Η κρυπτογραφία είναι μια καλά εδραιωμένη επιστημονική περιοχή, με πρωτόκολλα και πρότυπα τα οποία τυγχάνουν ευρείας αναγνώρισης. Παρόλα αυτά, η χρήση τους σε περιβάλλοντα περιορισμένων πόρων όπως αυτά των ασυρμάτων δικτύων αισθητήρων, απαιτεί προσαρμογές. Η απαίτηση αυτή προκύπτει λόγω των ιδιαίτερων χαρακτηριστικών των δικτύων αυτών και των κόμβων που τα απαρτίζουν όπως η χαμηλή υπολογιστική ισχύς, οι περιορισμένες δυνατότητες αποθήκευσης και η περιορισμένη διαθέσιμη ενέργεια καθώς και η επικοινωνία ασύρματης φύσης που υιοθετείται. Ένα επιπλέον πρόβλημα που παρουσιάζεται στα ασύρματα δίκτυα αισθητήρων, είναι η ετερογένεια. Οι συσκευές αισθητήρων που παράγονται από τη βιομηχανία σήμερα, έχουν διαφορετικές υπολογιστικές δυνατότητες και εκτελούν διαφορετικά λειτουργικά συστήματα. Κάποιες αποτελούνται από μικροεπεξεργαστές 8-bit και έχουν ελάχιστη ποσότητα μνήμης RAM, ενώ άλλες έχουν πολύ μεγάλη υπολογιστική δύναμη και μπορούν να εκτελέσουν desktop λειτουργικά συστήματα όπως Linux. Έτσι, ενώ είναι σχετικά εύκολο να αναπτύξει κανείς μια εφαρμογή για μια συγκεκριμένη πλατφόρμα, είναι πολύ δύσκολο να γράψει γενικό κώδικα ανεξάρτητο της πλατφόρμας μεταγλώτισσης. Έτσι, υπάρχοντες υλοποιημένοι αλγόριθμοι και εφαρμογές πρέπει να τροποποιούνται κατάλληλα για να μπορούν να προσαρμοστούν σε διαφορετικά περιβάλλοντα ανάπτυξης. Μια απάντηση στο παραπάνω πρόβλημα δίνει η βιβλιοθήκη Wiselib η οποία προσφέρει ένα προγραμματιστικό περιβάλλον για την ανάπτυξη γενικών αλγορίθμων που έχουν ως στόχο την εκτέλεσή τους σε ετερογενή δίκτυα αισθητήρων. Σκοπός της παρούσας διπλωματικής εργασίας είναι να προσφέρει λύσεις στα δύο προαναφερθέντα προβλήματα, ανάπτυσσοντας κρυπτογραφικούς αλγόριθμους για ετερογενή ασύρματα δίκτυα αισθητήρων. Για την επίτευξη του σκοπού αυτού, αναπτύσουμε μια κρυπτογραφική βιβλιοθήκη στο προγραμματιστικό περιβάλλον της Wiselib, μιας γενικής βιβλιοθήκης αλγορίθμων για ετερογενή δίκτυα αισθητήρων. Η Wiselib είναι υλοποιημένη σε C++ και με χρήση τεχνικών όπως τα πρότυπα και οι inline συναρτήσεις, επιτρέπει τη συγγραφή γενικού κώδικα ο οποίος αναλύεται και δεσμεύεται κατά τη διαδικασία μεταγλώττισσης χωρίς να δημιουργείται πλεονασμός μνήμης ή υπολογισμού. Λόγω των απαιτήσεων ασφαλείας που δημιουργούνται από τις εφαρμογές δικτύων αισθητήρων καθώς και των περιορισμένων υπολογιστικών πόρων, η κρυπτογραφική μας βιβλιοθήκη παρέχει αλγορίθμους τόσο συμμετρικής όσο και ασυμμετρικής κρυπτογραφίας. Οι αλγόριθμοι ασυμμετρικής κρυπτογραφίας βασίζονται στην κρυπτογραφία ελλειπτικών καμπυλών. Οι ελλειπτικές καμπύλες αποτελούν ένα ιδανικό σύστημα για ανάπτυξη κρυπτογραφίας δημοσίου κλειδιού σε ενσωματωμένα περιβάλλοντα τα οποία υστερούν σε επεξεργαστική ισχύ, μνήμη και ενέργεια. Αυτό ισχύει διότι τα συστήματα ελλειπτικών καμπυλών προσφέρουν το ίδιο επίπεδο ασφάλειας με άλλα κρυπτοσυστήματα (π.χ. RSA) με χρήση πολύ μικρότερου μεγέθους κλειδιών. Έτσι, συνολικά η βιβλιοθήκη μας παρέχει τους εξής αλγορίθμους: τον αλγόριθμο συμμετρικής κρυπτογράφησης AES, τον αλγόριθμο κατακερματισμού SHA-1, το σχήμα συμφωνίας κλειδιών Diffie Hellman (ECDH), τον αλγόριθμο ασυμμετρικής κρυπτογράφησης ECIES και το σχήμα ψηφιακής υπογραφής ECDSA. Για την ανάλυση της απόδοσης της κρυπτογραφικής μας βιβλιοθήκης γίνεται πειραματική αξιολόγηση (χρόνος εκτέλεσης, ενέργεια,μέγεθος μεταφρασμένου κώδικα) των παραπάνω αλγορίθμων σε δύο συσκευές ( iSense, TelosB) με διαφορετικές επεξεργαστικές δυνατότητες (16 MHz, 8 MHz) που τρέχουν διαφορετικά λειτουργικά συστήματα (iSense OS, Contiki Sky). Το γεγονός ότι αξιολογήσαμε τους κρυπτογραφικούς αλγορίθμους σε δύο συσκευές διαφορετικών δυνατοτήτων και περιβαλλόντων ανάπτυξης, αποδεικνύει τη γενικότητα της υλοποίησης μας.Τέλος, για να αποδείξουμε την ευκολία χρήσης των υλοποιημένων αλγορίθμων παρουσιάζουμε τρεις εφαρμογές δικτύων αισθητήρων που τους χρησιμοποιούνε. Πιο συγκεκριμένα, επιδεικνύουμε πως οι κρυπτογραφικοί αλγόριθμοι μπορούν να συνδυαστούν με αλγορίθμους δρομολόγησης και ομαδοποίησης που παρέχει η βιβλιοθήκη Wiselib, με αποτέλεσμα να δημιουργηθούν ασφαλείς εφαρμογές δικτύων αισθητήρων. / A wireless sensor network consists of spatially distributed autonomous devices, that use sensors in order to cooperatively monitor natural and environmental conditions. A wireless sensor network node typically consists of a micro-processor, a radio transceiver, an energy source (usually a battery) and various kinds of sensors that measure different environmental conditions (e.g. temperature, humidity, lightness). Wireless sensor networks are economically viable solutions to various applications. Networks of this type are used in biomedical, military, industrial as well as in applications that monitor the natural environment. Moreover, sensor networks are a key for the creation of smart spaces that introduce information technology in everyday environments like those of home and work. Because sensor networks are typically deployed in environments where sensitive information is communicated, security and privacy issues arise. Application characteristics like deployment in adverse environments, the incomplete knowledge of the network topology, the possibility of self-organization and the operation without human surveillance make the maintenance of security a big challenge. Cryptography is a science field that provides solutions to security problems. Cryptography is a well established science field that has provided protocols and standards of wide acceptance. However, the use of such protocols and standards in resource constrained environments, like those of sensor networks, requires changes and adaptations. This applies due to the special characteristics of such networks and the devices that consist them, e.g. the restricted processing power, the limited storage possibility and energy as well as the wireless nature of communication. A second problem that arises in wireless sensor networks is that of heterogeneity. The nodes produced by the industry today have different processing possibilities and execute various operating systems. Some nodes consist of 8-bit micro-processors that offer tiny amounts of RAM memory, whereas others are produced with 32-bit processors that can even execute desktop operating systems like Linux. Thus, while it is easy for a developer to implement a platform specific application, it is quite difficult to write some generic platform independent code. In order to re-use implemented applications and algorithms in different development environments a programmer has to make adaptations and changes according to the new platform specifications. A solution to this problem is provided by Wiselib. Wiselib offers an development environment suitable for the implementation of generic algorithms that can be compiled and executed on heterogenous wireless sensor networks. The objective of this work is to provide solutions to the aforementioned sensor network problems (security, heterogeneity). For this reason, we develop a cryptographic library on the generic program environment of Wiselib, a generic algorithm library for heterogenous sensor networks. Wiselib is implemented in C++ and employing advanced techniques, like templates and inline functions, it allows writing of generic code that can be allocated and resolved during compilation without producing computation or memory overhead. Due to the security requirements imposed by the sensor network applications and the resource restrictions by the sensor nodes, our cryptographic library provides symmetric as well as asymmetric cryptographic algorithms. The public key algorithms are based on elliptic curve cryptography. Elliptic curves consist an ideal system for the development of public key cryptography in resource constrained environments that offer restricted computation power, memory and energy. That is because elliptic curve cryptosystems offer the same level of security with other public key cryptosystems (e.g. RSA), using much smaller key sizes. Thus, in total our cryptographic library provides the following algorithms: the symmetric encryption algorithm AES, the hash algorithm SHA-1, the key agreement scheme Diffie Hellman (ECDH), the public key encryption algorithm ECIES and the signature scheme ECDSA. In order to evaluate the performance of our cryptographic library we experimentally test (in terms of execution time, compiled code size, energy consumption) its algorithms on two devices (iSense, TelosB) with different processing possibilities (16 MHz, 8 MHz) that execute different operating systems (iSense OS, Contiki Sky). The fact that we evaluated the cryptographic algorithms on two different devices with unlike capabilities and that execute different operating systems proves that our implementation is generic. Finally, in order to prove the ease of use of the implemented cryptographic algorithms we present three sensor network applications that employ them. More precisely, we show how our cryptographic algorithms can be combined with routing and clustering algorithms (provided by Wiselib), resulting in secure sensor network applications.