Distributed Hash Tables (DHTs) are protocols and frameworks used by peer-to-peer (P2P) systems. They are used as the organizational backbone for many P2P file-sharing systems due to their scalability, fault-tolerance, and load-balancing properties. These same properties are highly desirable in a distributed computing environment, especially one that wants to use heterogeneous components. We show that DHTs can be used not only as the framework to build a P2P file-sharing service, but as a P2P distributed computing platform. We propose creating a P2P distributed computing framework using distributed hash tables, based on our prototype system ChordReduce. This framework would make it simple and efficient for developers to create their own distributed computing applications. Unlike Hadoop and similar MapReduce frameworks, our framework can be used both in both the context of a datacenter or as part of a P2P computing platform. This opens up new possibilities for building platforms to distributed computing problems. One advantage our system will have is an autonomous load-balancing mechanism. Nodes will be able to independently acquire work from other nodes in the network, rather than sitting idle. More powerful nodes in the network will be able use the mechanism to acquire more work, exploiting the heterogeneity of the network. By utilizing the load-balancing algorithm, a datacenter could easily leverage additional P2P resources at runtime on an as needed basis. Our framework will allow MapReduce-like or distributed machine learning platforms to be easily deployed in a greater variety of contexts.

An increasingly promising and widespread topic of research in distributed computing is the mobile agent paradigm: code travelling and performing computations on remote hosts in an autonomous manner. One of the biggest challenges faced by this new paradigm is security. The issue of protecting sensitive code and data carried by a mobile agent against tampering from a malicious host is particularly hard but important. Based on secure multi-party computation, a recent research direction shows the feasibility of a software-only solution to this problem, which had been deemed impossible by some researchers previously. The best result prior to this dissertation is a single-agent protocol which requires the participation of a trusted third party. Our research employs multi-agent protocols to eliminate the trusted third party, resulting in a protocol with minimum trust assumptions. This dissertation presents one of the first formal definitions of secure mobile agent computation, in which the privacy and integrity of the agent code and data as well as the data provided by the host are all protected. We present secure protocols for mobile agent computation against static, semi-honest or malicious adversaries without relying on any third party or trusting any specific participant in the system. The security of our protocols is formally proven through standard proof technique and according to our formal definition of security. Our second result is a more practical agent protocol with strong security against most real-world host attacks. The security features are carefully analyzed, and the practicality is demonstrated through implementation and experimental study on a real-world mobile agent platform. All these protocols rely heavily on well-established cryptographic primitives, such as encrypted circuits, threshold decryption, and oblivious transfer. Our study of these tools yields new contributions to the general field of cryptography. Particularly, we correct a well-known construction of the encrypted circuit and give one of the first provably secure implementations of the encrypted circuit.

Plusieurs outils ont été développé pour vérifier automatiquement les propriétés de sécurité sur des protocoles cryptographiques. Jusqu'à maintenant, la plupart de ces outils permettent de vérifier des propriétés de trace (ou propriétés d'accessibilité) tel que le secret simple ou l'authentification. Néanmoins, plusieurs propriétés de sécurité ne peuvent pas être exprimés en tant que propriété de trace, mais peuvent l'être en tant que propriété d'équivalence. L'anonymat, la non-tracabilité ou le secret fort sont des exemples classique de propriété d'équivalence. Typiquement, deux protocoles P et Q sont équivalent si les actions d'un adversaire (intrus) ne lui permettent pas de distinguer P de Q. Dans la littérature, plusieurs notions d'équivalence ont été étudiés, par exemple l'équivalence de trace ou l'équivalence observationnelle. Néanmoins, ces équivalences se relèvent être très difficiles à démontrer , d'où l'importance de développer des outils de vérification automatique efficaces de ces équivalences. Au sein de cette thèse, nous avons dans un premier temps travaillé sur une approche reposant sur des techniques de résolution de contraintes et nous avons créé un nouvel algorithme pour décider l'équivalence de trace entre deux protocoles pouvant contenir des conditionnelles avec branches "else", et pouvant également être non-déterministe. Cet algorithme a été appliqué sur des exemples concrets comme le "Private authentification protocol" ainsi que le "E-passport protocol". Cette thèse propose également des résultats de composition pour l'équivalence de trace. En particulier, nous nous sommes intéressé à la composition parallèle de protocoles partageant certains secrets. Ainsi dans cette thèse, nous avons démontré que, sous certaines conditions, la composition parallèle de protocoles préserve les propriétés d'équivalence. Ce résultat fut appliqué au "E-passport protocol". Enfin, cette thèse présente une extension à l'outil de vérification automatique ProVerif afin de démontrer automatiquement plus de propriétés d'équivalence. Cette extension a été implémenté au sein de ProVerif ce qui a permis de démontrer la propriété d'anonymat pour le "Private authentification protocol" . / Many tools have been developed to automatically verify security properties on cryptographic protocols. But until recently, most tools focused on trace properties (or reachability properties) such as authentication and secrecy. However, many security properties cannot be expressed as trace properties, but can be written as equivalence properties. Privacy, unlinkability, and strong secrecy are typical examples of equivalence properties. Intuitively, two protocols P, Q are equivalent if an adversary can not distinguish P from Q by interacting with these processes. In the literature, several notions of equivalence were studied, e.g. trace equivalence or a stronger one, observational equivalence. However, it is often very difficult to prove by hand any of these equivalences, hence the need for efficient and automatic tools. We first worked on an approach that rely on constraint solving techniques and that is well suited for bounded number of sessions. We provided a new algorithm for deciding the trace equivalence between processes that may contain negative tests and non-determinism. We applied our results on concrete examples such as anonymity of the Private Authentication protocol and the E-passport protocol. We also investigated composition results. More precisely, we focused on parallel composition under shared secrets. We showed that under certain conditions on the protocols, the privacy type properties are preserved under parallel composition and under shared secrets. We applied our result on the e-passport protocol. At last this work presents an extension of the automatic protocol verifier ProVerif in order to prove more observational equivalences. This extension have been implemented in ProVerif and allows us to automatically prove anonymity in the private authentication protocol.

<p>Business and organizations use computer network in a greater extension than ever before, especially for business-critical use. That increase the demand of security for all systems, both against internal and external threats. The demand on the authentication method used today increases. Today they normally uses password or some kind of smart card. </p><p>I will performa literature study that will investigate the possibility to increase the security in authentication of users without the use of extra hardware. The method uses a server that stores all cryptographic keys for the user centrally to achieve stronger security. This report is based on a previous report which tested to implement this solution, in this report I will question the security of this system. I will then give an architecture proposal where this method is used to authenticate and allow cryptographic recourses for the user. </p><p>The conclusions you can get from this report is that the possibilities with comparable ease increase the security without investing in new hardware. But the solution will not be comparable by a ``smart card solution''in security levels. That means that the method described in this thesis is suitable for organizations that either do not need that strong security as smart card give or want a good solution without being forced to use some external hardware.</p>

As the next evolutionary step in digital communication systems, mobile ad hoc networks (MANETs) and their specialization like wireless sensor networks (WSNs) have been attracting much interest in both research and industry communities. In MANETs, network nodes can come together and form a network without depending on any pre-existing infrastructure and human intervention. Unfortunately, the salient characteristics of MANETs, in particular the absence of infrastructure and the constrained resources of mobile devices, present enormous challenges when designing security mechanisms in this environment. Without necessary measures, wireless communications are easy to be intercepted and activities of users can be easily traced. This thesis presents our solutions for two important aspects of securing MANETs, namely efficient key management protocols and fast implementations of cryptographic primitives on constrained devices. Due to the tight cost and constrained resources of high-volume mobile devices used in MANETs, it is desirable to employ lightweight and specialized cryptographic primitives for many security applications. Motivated by the design of the well-known Enigma machine, we present a novel ultra-lightweight cryptographic algorithm, referred to as Hummingbird, for resource-constrained devices. Hummingbird can provide the designed security with small block size and is resistant to the most common attacks such as linear and differential cryptanalysis. Furthermore, we also present efficient software implementations of Hummingbird on 4-, 8- and 16-bit microcontrollers from Atmel and Texas Instruments as well as efficient hardware implementations on the low-cost field programmable gate arrays (FPGAs) from Xilinx, respectively. Our experimental results show that after a system initialization phase Hummingbird can achieve up to 147 and 4.7 times faster throughput for a size-optimized and a speed-optimized software implementation, respectively, when compared to the state-of-the-art ultra-lightweight block cipher PRESENT on the similar platforms. In addition, the speed optimized Hummingbird encryption core can achieve a throughput of 160.4 Mbps and the area optimized encryption core only occupies 253 slices on a Spartan-3 XC3S200 FPGA device. Bilinear pairings on the Jacobians of (hyper-)elliptic curves have received considerable attention as a building block for constructing cryptographic schemes in MANETs with new and novel properties. Motivated by the work of Scott, we investigate how to use efficiently computable automorphisms to speed up pairing computations on two families of non-supersingular genus 2 hyperelliptic curves over prime fields. Our findings lead to new variants of Miller's algorithm in which the length of the main loop can be up to 4 times shorter than that of the original Miller's algorithm in the best case. We also generalize Chatterjee et al.'s idea of encapsulating the computation of the line function with the group operations to genus 2 hyperelliptic curves, and derive new explicit formulae for the group operations in projective and new coordinates in the context of pairing computations. Efficient software implementation of computing the Tate pairing on both a supersingular and a non-supersingular genus 2 curve with the same embedding degree of k = 4 is investigated. Combining the new algorithm with known optimization techniques, we show that pairing computations on non-supersingular genus 2 curves over prime fields use up to 55.8% fewer field operations and run about 10% faster than supersingular genus 2 curves for the same security level. As an important part of a key management mechanism, efficient key revocation protocol, which revokes the cryptographic keys of malicious nodes and isolates them from the network, is crucial for the security and robustness of MANETs. We propose a novel self-organized key revocation scheme for MANETs based on the Dirichlet multinomial model and identity-based cryptography. Firmly rooted in statistics, our key revocation scheme provides a theoretically sound basis for nodes analyzing and predicting peers' behavior based on their own observations and other nodes' reports. Considering the difference of malicious behaviors, we proposed to classify the nodes' behavior into three categories, namely good behavior, suspicious behavior and malicious behavior. Each node in the network keeps track of three categories of behavior and updates its knowledge about other nodes' behavior with 3-dimension Dirichlet distribution. Based on its own analysis, each node is able to protect itself from malicious attacks by either revoking the keys of the nodes with malicious behavior or ceasing the communication with the nodes showing suspicious behavior for some time. The attack-resistant properties of the resulting scheme against false accusation attacks launched by independent and collusive adversaries are also analyzed through extensive simulations. In WSNs, broadcast authentication is a crucial security mechanism that allows a multitude of legitimate users to join in and disseminate messages into the networks in a dynamic and authenticated way. During the past few years, several public-key based multi-user broadcast authentication schemes have been proposed in the literature to achieve immediate authentication and to address the security vulnerability intrinsic to μTESLA-like schemes. Unfortunately, the relatively slow signature verification in signature-based broadcast authentication has also incurred a series of problems such as high energy consumption and long verification delay. We propose an efficient technique to accelerate the signature verification in WSNs through the cooperation among sensor nodes. By allowing some sensor nodes to release the intermediate computation results to their neighbors during the signature verification, a large number of sensor nodes can accelerate their signature verification process significantly. When applying our faster signature verification technique to the broadcast authentication in a 4×4 grid-based WSN, a quantitative performance analysis shows that our scheme needs 17.7%~34.5% less energy and runs about 50% faster than the traditional signature verification method.

As the next evolutionary step in digital communication systems, mobile ad hoc networks (MANETs) and their specialization like wireless sensor networks (WSNs) have been attracting much interest in both research and industry communities. In MANETs, network nodes can come together and form a network without depending on any pre-existing infrastructure and human intervention. Unfortunately, the salient characteristics of MANETs, in particular the absence of infrastructure and the constrained resources of mobile devices, present enormous challenges when designing security mechanisms in this environment. Without necessary measures, wireless communications are easy to be intercepted and activities of users can be easily traced. This thesis presents our solutions for two important aspects of securing MANETs, namely efficient key management protocols and fast implementations of cryptographic primitives on constrained devices. Due to the tight cost and constrained resources of high-volume mobile devices used in MANETs, it is desirable to employ lightweight and specialized cryptographic primitives for many security applications. Motivated by the design of the well-known Enigma machine, we present a novel ultra-lightweight cryptographic algorithm, referred to as Hummingbird, for resource-constrained devices. Hummingbird can provide the designed security with small block size and is resistant to the most common attacks such as linear and differential cryptanalysis. Furthermore, we also present efficient software implementations of Hummingbird on 4-, 8- and 16-bit microcontrollers from Atmel and Texas Instruments as well as efficient hardware implementations on the low-cost field programmable gate arrays (FPGAs) from Xilinx, respectively. Our experimental results show that after a system initialization phase Hummingbird can achieve up to 147 and 4.7 times faster throughput for a size-optimized and a speed-optimized software implementation, respectively, when compared to the state-of-the-art ultra-lightweight block cipher PRESENT on the similar platforms. In addition, the speed optimized Hummingbird encryption core can achieve a throughput of 160.4 Mbps and the area optimized encryption core only occupies 253 slices on a Spartan-3 XC3S200 FPGA device. Bilinear pairings on the Jacobians of (hyper-)elliptic curves have received considerable attention as a building block for constructing cryptographic schemes in MANETs with new and novel properties. Motivated by the work of Scott, we investigate how to use efficiently computable automorphisms to speed up pairing computations on two families of non-supersingular genus 2 hyperelliptic curves over prime fields. Our findings lead to new variants of Miller's algorithm in which the length of the main loop can be up to 4 times shorter than that of the original Miller's algorithm in the best case. We also generalize Chatterjee et al.'s idea of encapsulating the computation of the line function with the group operations to genus 2 hyperelliptic curves, and derive new explicit formulae for the group operations in projective and new coordinates in the context of pairing computations. Efficient software implementation of computing the Tate pairing on both a supersingular and a non-supersingular genus 2 curve with the same embedding degree of k = 4 is investigated. Combining the new algorithm with known optimization techniques, we show that pairing computations on non-supersingular genus 2 curves over prime fields use up to 55.8% fewer field operations and run about 10% faster than supersingular genus 2 curves for the same security level. As an important part of a key management mechanism, efficient key revocation protocol, which revokes the cryptographic keys of malicious nodes and isolates them from the network, is crucial for the security and robustness of MANETs. We propose a novel self-organized key revocation scheme for MANETs based on the Dirichlet multinomial model and identity-based cryptography. Firmly rooted in statistics, our key revocation scheme provides a theoretically sound basis for nodes analyzing and predicting peers' behavior based on their own observations and other nodes' reports. Considering the difference of malicious behaviors, we proposed to classify the nodes' behavior into three categories, namely good behavior, suspicious behavior and malicious behavior. Each node in the network keeps track of three categories of behavior and updates its knowledge about other nodes' behavior with 3-dimension Dirichlet distribution. Based on its own analysis, each node is able to protect itself from malicious attacks by either revoking the keys of the nodes with malicious behavior or ceasing the communication with the nodes showing suspicious behavior for some time. The attack-resistant properties of the resulting scheme against false accusation attacks launched by independent and collusive adversaries are also analyzed through extensive simulations. In WSNs, broadcast authentication is a crucial security mechanism that allows a multitude of legitimate users to join in and disseminate messages into the networks in a dynamic and authenticated way. During the past few years, several public-key based multi-user broadcast authentication schemes have been proposed in the literature to achieve immediate authentication and to address the security vulnerability intrinsic to μTESLA-like schemes. Unfortunately, the relatively slow signature verification in signature-based broadcast authentication has also incurred a series of problems such as high energy consumption and long verification delay. We propose an efficient technique to accelerate the signature verification in WSNs through the cooperation among sensor nodes. By allowing some sensor nodes to release the intermediate computation results to their neighbors during the signature verification, a large number of sensor nodes can accelerate their signature verification process significantly. When applying our faster signature verification technique to the broadcast authentication in a 4×4 grid-based WSN, a quantitative performance analysis shows that our scheme needs 17.7%~34.5% less energy and runs about 50% faster than the traditional signature verification method.

Cloud computing has been developed rapidly in recent years, and offers novel concepts and innovations in computer use. One application of cloud computing is that people can designate a proxy to help them to execute a number of tasks in certain situations instead of undertaking all tasks themselves. With this application, people can benefit from the proxy; however, some information is revealed to the proxy, such as their activities, and private data. That is, the proxy is aware of the actions of people through delegation processes, and proxy re-encryption which is a cryptographic primitive has been proposed to solve this problem. In the proxy re-encryption system, when a user (e.g., Alice) wants to send a ciphertext that is encrypted by her secret key and stored in the cloud to another user (e.g., Bob), she can designate a proxy to transform the ciphertext into a different ciphertext that can be decrypted by Bob¡¦s private key. Based on attribute-based encryption and proxy re-encryption, we propose attribute-based proxy re-encryption with bilinear pairing. Furthermore, in the proposed scheme, third paries cannot decrypt the ciphertext if they do no have matching attributes, regardless of being helped by proxy. Finally, we offer security proofs to demonstrate that the proposed scheme satisfies the essential requirements of attribute-based encryption schemes and proxy re-encryption schemes.

This thesis examines verifiability and receipt freeness in cryptographic voting protocols in detail and points out the contradiction between these requirements. Firstly, an extensive electronic voting requirement set is clearly defined, and then the voting dilemma is described. This is followed by a suggestion of an applicable solution to overcome the voting dilemma by introducing Predefined Fake Vote (PreFote) scheme. Based on a comprehensive literature review, a classification of the existing privacy preserving approaches and a taxonomy of the existing cryptographic voting protocols extending the previous studies are provided. Thereby, a complete and secure cryptographic voting protocol satisfying all electronic voting security requirements at the same time seems non-existent. Hence, an alternative privacy preserving approach is highly needed. Pseudo-Voter Identity (PVID) scheme, proposed in the present study, is a practical and low cost one. The PVID scheme is based on RSA blind signature, and it allows recasting without sacrificing uniqueness. Furthermore, this study proposes a dynamic ballot mechanism including an extension with PreFotes. This study, wherein the PVID scheme and extended dynamic ballots with PreFotes are employed, proposes a practical, complete and secure cryptographic voting protocol over a network for large scale elections, which fulfils all of the electronic voting security requirements: privacy, eligibility, uniqueness, fairness, uncoercibility, receipt-freeness, individual verifiability and accuracy. Lastly, a method to analyse voting systems based on security requirements is suggested, and a detailed analysis of the proposed protocol, which uses this method, concludes this study.

One of the most basic properties expected from block ciphers and hash functions is passing statistical randomness testing, as they are supposed to behave like random mappings. Previously, testing of AES candidate block ciphers was done by using the statistical tests defined in the NIST Test Suite. As some of the tests in this suite require long sequences, data sets are formed by concatenating the outputs of the algorithms obtained from various input types. However, the nature of block cipher and hash function algorithms necessitates devising tests and test parameters focused particularly on short sequences, therefore we propose a package of statistical randomness tests which produce reliable results for short sequences and test the outputs of the algorithms directly rather than concatenations. Moreover, we propose an alternative method to evaluate the test results and state the required computations of related probabilities for the new evaluation method. We also propose another package of statistical tests which are designed basing on certain cryptographic properties of block ciphers and hash functions to evaluate their randomness, namely the cryptographic randomness testing. The packages are applied to the AES finalists, and produced more precise results than those obtained in similar applications. Moreover, the packages are also applied to SHA-3 second round candidate algorithms.

Η επιστήμη της τεχνολογίας αυξάνεται ραγδαία μέρα με τη μέρα. Δυστυχώς όμως όλες αυτές οι νέες τεχνολογικές τάσεις μπορεί να κρύβουν δυσάρεστες «εκπλήξεις». Τα τελευταία χρόνια οι ασύρματες επικοινωνίες έχουν γίνει ένα πολύ σημαντικό κομμάτι της καθημερινότητάς μας. Εμπιστευόμαστε τις ασύρματες συσκευές μας και τις εταιρίες που τις παρέχουν. Ωστόσο, ερωτήματα όπως πόσο ασφαλείς μπορεί να είναι οι συσκευές μας ή οι ασύρματες επικοινωνίες μας δημιουργούνται κάθε μέρα. Παράλληλα με αυτά τα ερωτήματα, εμφανίζονται και τα Hardware Trojans. Τα Hardware Trojans είναι μέρος αυτών των καινούριων τάσεων και αποτελούν ένα πολύ σοβαρό πρόβλημα στο πεδίο των ολοκληρωμένων κυκλωμάτων. Μέχρι σήμερα έχουν γίνει ποικίλες μελέτες, χρησιμοποιώντας διαφορετικές στρατηγικές, Trojans και μεθόδους ανίχνευσης. Στη συγκεκριμένη διπλωματική εργασία παρουσιάζουμε ένα σύστημα ανίχνευσης για Hardware Trojans σε ολοκληρωμένα κυκλώματα ασύρματης κρυπτογράφησης (wireless cryptographic integrated circuit). Περιγράφεται η διαρροή των μυστικών πληροφοριών μέσω ασύρματης επικοινωνίας, χρησιμοποιώντας την τεχνική των ολοκληρωμένων κυκλωμάτων μικτού σήματος (mixed-signal integrated circuits). Δημιουργήθηκαν δύο διαφορετικά Hardware Trojans, τα οποία εισήχθησαν στο αρχικό μας σύστημα, τα οποία βέβαια δεν αλλάζουν τη λειτουργικότητά του. Παρ’ όλ’ αυτά, μπορούν να διαρρεύσουν μυστικές πληροφορίες του συστήματος. Παρουσιάζεται λοιπόν πως είναι δυνατόν να ανιχνευτεί ένα Trojan επιτυχώς μέσω διαφορετικών στατιστικών μετρήσεων που αφορούν τη συχνότητα και το πλάτος του ασύρματου σήματος μετάδοσης. / Technology grows so rapidly day by day. Unfortunately, all these new technological trends may hide unpleasant “surprises”. In recent years wireless communications have become an important part of our everyday life. We rely on our wireless devices and the companies who provide them. However, questions like how safe can our devices be or how secure can our wireless communications be, rise up almost every day. In parallel with these questions, the appearance of Hardware Trojans rise up too. Hardware Trojans are part of these new trends and they have become a serious issue in the field of integrated circuits. Various studies have been done till today, using different strategies, Trojans and detection methods. At this dissertation it is presented a Hardware Trojan detection framework in wireless cryptographic integrated circuit. Τhe leak of secret information through wireless communication is described, using the technic of mixed-signal integrated circuits. There are two Hardware Trojans created and inserted to the original system, which do not change the functionality of the system, but can leak secret information from it. It is presented how a Trojan can be successfully detected through different statistic measurements which are related to the frequency and amplitude of the wireless transmission signal.