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On the applicability of short key asymmetric cryptography in low power wireless sensor networks
(2016)
The growing popularity of Wireless Sensor Networks (WSN) makes the spectrum of their applications very wide. A great number of the application areas like health monitoring or military applications require a high level of security and dependability from the wireless sensor network. Solving these issues can be supported by providing cryptographic solutions into WSN applications. Since the WSNs mainly consist of low power devices, cryptographic solutions ideal for WSNs should provide computationally lightweight security mechanisms producing small data packets and ensuring confidentiality. Cryptographic mechanisms that have both these features are considered in this thesis, which main objective is the analysis of the applicability of the short key elliptic curve cryptography in WSN environments. Reduced key lengths require modification of the standard ECC security algorithms to provide authentication and also a novel solution for a cryptographic secure pseudo-random number generator. The proposed solution is based on the standard ECC, but it differs in several aspects. The main difference is that the parameters of the used elliptic curve have to be kept secret. This is due to the fact that solving the Discreet Logarithm Problem (DLP) for such short parameters can be done in short time. Additionally, using shorter parameters for the underlying elliptic curves excludes also the use of standard hash functions, what mainly influences the mechanisms for generating the digital signature. Hash functions require large input values and produce relatively large output data that is inapplicable in the shortECC environment. Thus, within this thesis a modified version of standard Elliptic Curves Digital Signature Algorithm is proposed, which does not require any hash function. The shortECC needs pseudo-random numbers in the encryption and the digital signature protocols, but since it operates on numbers that are significantly shorter than the ones used by other cryptographic approaches, pseudo-random number generators for standard approaches are not suitable for shortECC. Thus, the new pseudo-random number generator not involving any additional hardware besides the modules available on the used test platform and operating on 32-bit long integers, is proposed. The randomness of the numbers generated by the proposed algorithm and their applicability for cryptographic purposes was evaluated using the NIST test suites. The shortECC approach was also subjected to cryptanalysis in order to proof its security and determine the circumstances and constraints for its application.
Drahtlose eingebettete Systeme haben vielfältige Anwendungsmöglichkeiten, sei es im Internet der Dinge oder in Sensornetzen. Diese Systeme sollen dabei ohne Eingriff von außen eine hohe Laufzeit erreichen. Die Energieversorgung und der Verbrauch spielen dabei entscheidende Rollen, sind jedoch Varianzen unterworfen. Sollen Wartungsintervalle oder Lebenszeitziele erreicht werden, ist deshalb ein dynamisches Energiemanagement unabdingbar.
In dieser Doktorarbeit wird ein solcher Ansatz vorgestellt, umgesetzt und evaluiert. Im Gegensatz zu existierenden Ansätzen werden Varianzen auf allen drei Ebenen des Managements (Energieversorgung, Energieverbrauch und Energieverwaltung) adressiert. Für die Energieversorgung wird eine Batterieüberwachung vorgestellt, welche eine Steuerung des Verbrauchs ohne komplexe Berechnung des Ladezustands ermöglicht. Der Verbrauch des Systems wird durch einen Software-basierten Ansatz feingranular ermittelt und bezieht Varianzen durch Änderungen der Spannung und der Effizienz von Spannungswandlern ein. Die Verwaltung und Zuordnung der Energie zu Anwendungszielen erfolgt mittels dynamischer Energiebudgets und bietet verschiedene Strategien, um auf Änderungen des Bedarfs adäquat reagieren zu können.