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Dissertations / Theses on the topic 'Cryptography'
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Poschmann, Axel York. "Lightweight cryptography cryptographic engineering for a pervasive world." Berlin Bochum Dülmen London Paris Europ. Univ.-Verl, 2009. http://d-nb.info/996578153/04.
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Almeida, Braga Daniel de. "Cryptography in the wild : the security of cryptographic implementations." Thesis, Rennes 1, 2022. http://www.theses.fr/2022REN1S067.
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Les attaques par canaux auxiliaire sont redoutables face aux implémentations cryptographiques. Malgré les attaques passées, et la prolifération d'outils de vérification, ces attaques affectent encore de nombreuses implémentations. Dans ce manuscrit, nous abordons deux aspects de cette problématique, centrés autour de l'attaque et de la défense. Nous avons dévoilé plusieurs attaques par canaux auxiliaires microarchitecturaux sur des implémentations de protocoles PAKE. En particulier, nous avons exposé des attaques sur Dragonfly, utilisé dans la nouvelle norme Wi-Fi WPA3, et SRP, déployé dans de nombreux logiciel tels que ProtonMail ou Apple HomeKit. Nous avons également exploré le manque d'utilisation par les développeurs d'outil permettant de détecter de telles attaques. Nous avons questionné des personnes impliqués dans différents projets cryptographiques afin d'identifier l'origine de ce manque. De leur réponses, nous avons émis des recommandations. Enfin, dans l'optique de mettre fin à la spirale d'attaques-correction sur les implémentations de Dragonfly, nous avons fournis une implémentation formellement vérifiée de la couche cryptographique du protocole, dont l'exécution est indépendante des secretsSide-channel attacks are daunting for cryptographic implementations. Despite past attacks, and the proliferation of verification tools, these attacks still affect many implementations. In this manuscript, we address two aspects of this problem, centered around attack and defense. We unveil several microarchitectural side-channel attacks on implementations of PAKE protocols. In particular, we exposed attacks on Dragonfly, used in the new Wi-Fi standard WPA3, and SRP, deployed in many software such as ProtonMail or Apple HomeKit. We also explored the lack of use by developers of tools to detect such attacks. We questioned developers from various cryptographic projects to identify the origin of this lack. From their answers, we issued recommendations. Finally, in order to stop the spiral of attack-patch on Dragonfly implementations, we provide a formally verified implementation of the cryptographic layer of the protocol, whose execution is secret-independent
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Yerushalmi, Yoav. "Incremental cryptography." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42789.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 147-148).
by Yoav Yerushalmi.
M.Eng.
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Shamonin, K. E. "Quantum cryptography." Thesis, Sumy State University, 2018. http://essuir.sumdu.edu.ua/handle/123456789/66837.
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To advance most popular encryption algorithms such as public-key
encryption and signature-based schemes, methods of quantum
cryptography can be used. The main advantage of quantum cryptography is
the fact it cannot be broken by any non-quantum computers and
eavesdropping is impossible in quantum key distribution.
Fundamental quantum mechanics is used in quantum key distribution to
guarantee the safety of data transmitted. It is based on entangled pairs of
photons in E91 protocol or photon polarization states in BB84 protocol.
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Lopez, Samuel. "MODERN CRYPTOGRAPHY." CSUSB ScholarWorks, 2018. https://scholarworks.lib.csusb.edu/etd/729.
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We live in an age where we willingly provide our social security number, credit card information, home address and countless other sensitive information over the Internet. Whether you are buying a phone case from Amazon, sending in an on-line job application, or logging into your on-line bank account, you trust that the sensitive data you enter is secure. As our technology and computing power become more sophisticated, so do the tools used by potential hackers to our information. In this paper, the underlying mathematics within ciphers will be looked at to understand the security of modern ciphers.
An extremely important algorithm in today's practice is the Advanced Encryption Standard (AES), which is used by our very own National Security Agency (NSA) for data up to TOP SECRET. Another frequently used cipher is the RSA cryptosystem. Its security is based on the concept of prime factorization, and the fact that it is a hard problem to prime factorize huge numbers, numbers on the scale of 2^{2048} or larger. Cryptanalysis, the study of breaking ciphers, will also be studied in this paper. Understanding effective attacks leads to understanding the construction of these very secure ciphers.
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Minaud, Brice. "Analyse de primitives cryptographiques récentes." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S066/document.
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Dans cette thèse, nous nous intéressons à la sécurité de quelques primitives cryptographiques récentes, d’abord symétriques puis asymétriques, en passant par le modèle en boîte blanche, qui est à certains égards intermédiaire. Dans un premier temps, nous montrons l’existence de fonctions linéaires non triviales commutant avec la fonction de tour de certains chiffrements par bloc, dont découlent des attaques par auto-similarité et sous-espace invariant. Nous nous intéressons ensuite à la cryptanalyse de la structure ASASA, où deux couches non linéaires S sont imbriquées dans des couches affines A. Notre cryptanalyse structurelle permet de casser des instances de chiffrement symétrique, multivarié et en boîte blanche. En nous concentrant sur le modèle d’incompressibilité en boîte blanche, nous montrons ensuite comment réaliser un chiffrement par bloc et un générateur de clef efficaces dont la sécurité est prouvable. Finalement, du côté purement asymétrique, nous décrivons une attaque polynomiale contre une construction récente d’application multilinéaireIn this thesis, we study the security of some recent cryptographic primitives, both symmetric and asymmetric. Along the way we also consider white-box primitives, which may be regarded as a middle ground between symmetric and asymmetric cryptography. We begin by showing the existence of non-trivial linear maps commuting with the round function of some recent block cipher designs, which give rise to self-similarity and invariant subspace attacks. We then move on to the structural cryptanalysis of ASASA schemes, where nonlinear layers S alternate with affine layers A. Our structural cryptanalysis applies to symmetric, multivariate, as well as white-box instances. Focusing on the white-box model of incompressibility, we then build an efficient block cipher and key generator that offer provable security guarantees. Finally, on the purely asymmetric side, we describe a polynomial attack against a recent multilinear map proposal
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PRIYADHARSHINI, THIRUTHUVADOSS ANGELINE. "Comparison and Performance Evaluation of Modern Cryptography and DNA Cryptography." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-120103.
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In this paper, a new cryptographic method called DNA cryptography and the already existing methods of modern cryptography are studied, implemented and results are obtained. Both these cryptographic method’s results are compared and analyzed to find out the better approach among the two methods. The comparison is done in the main aspects of process running time, key size, computational complexity and cryptographic strength. And the analysis is made to find the ways these above mentioned parameters are enhancing the respective cryptographic methods and the performance is evaluated. For comparison the Triple Data Encryption Algorithm (TDEA) from the modern methods and the DNA hybridization and the chromosomes DNA indexing methods from the DNA cryptography methods are implemented and analyzed. These intended methods are dependent on the main principles of mathematical calculations and bio molecular computations. The Triple DES algorithm uses three keys. In this method the DES block cipher algorithm is utilized three times to each different block of the input data to obtain the encrypted text. And then the DES block cipher decryption algorithm is applied to the obtained cipher text three times using the same three keys and the original message is obtained. The key size is increased in Triple DES more than that of the DES which makes the algorithm more secured. In the DNA hybridization method, the original message which is referred as plain text is converted in the form of binary. This binary form of data is then compared with the randomly generated OTP key in the DNA form and the encrypted message is obtained. This obtained encrypted message is also in the form of DNA. The decryption message is carried out in reverse using the encrypted data and the OTP key and the original message is retrieved. In the DNA indexing method, the plain text which is the original message is converted to the binary form and again to the DNA form. The OTP keys are generated randomly from the public database. This OTP key and the DNA form of the plain text are compared and a random index is generated, which is the encrypted data. Decryption process is carried out in the opposite order to obtain the original plain text message. Finally, the results of DNA cryptography are compared with that of the results obtained in Triple DES algorithm and the performance is evaluated to find out the most secured and less time consuming technique. The proposed work is implemented using bio informatics toolbox in MATLAB.
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Nyman, Ellinor. "Cryptography : A study of modern cryptography and its mathematical methods." Thesis, Uppsala universitet, Analys och sannolikhetsteori, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-447460.
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Idrees, Zunera. "Elliptic Curves Cryptography." Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-17544.
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In the thesis we study the elliptic curves and its use in cryptography. Elliptic curvesencompasses a vast area of mathematics. Elliptic curves have basics in group theory andnumber theory. The points on elliptic curve forms a group under the operation of addition.We study the structure of this group. We describe Hasse’s theorem to estimate the numberof points on the curve. We also discuss that the elliptic curve group may or may not becyclic over finite fields. Elliptic curves have applications in cryptography, we describe theapplication of elliptic curves for discrete logarithm problem and ElGamal cryptosystem.
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Roe, Michael Robert. "Cryptography and evidence." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627396.
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Vasudevan, Prashant Nalini. "Fine-grained cryptography." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120412.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 167-180).
Fine-grained cryptography is the study of cryptographic objects that are required to be secure only against adversaries that are moderately more powerful than the honest parties. This weakening in security requirements opens up possibilities for meaningful cryptographic constructions in various settings using hardness assumptions that are considerably weaker than those used in standard cryptography. In this thesis, we study these possibilities in two different settings. First, we present functions that are hard to compute on average for algorithms running in some fixed polynomial time, assuming widely-conjectured worst-case hardness of certain problems from the study of fine-grained complexity. We also construct a proof-of-work protocol based on this hardness and certain structural properties of our functions. Second, we construct several unconditionally secure cryptographic primitives that are computable by and secure against constant-depth circuits. Under a reasonable complexity-theoretic assumption, we do the same for log-depth circuits.
by Prashant Nalini Vasudevan.
Ph. D.
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Dodis, Yevgeniy 1976. "Exposure-resilient cryptography." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/86613.
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Золотова, Світлана Григорівна, Светлана Григорьевна Золотова, Svitlana Hryhorivna Zolotova, and M. Chernyakova. "History of cryptography." Thesis, Видавництво СумДУ, 2008. http://essuir.sumdu.edu.ua/handle/123456789/16061.
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Germouty, Paul. "Identity-based cryptography." Thesis, Limoges, 2018. http://www.theses.fr/2018LIMO0041/document.
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Dans cette thèse nous étudions les possibilités que les chiffrements basés sur l’identité offrent quand ils sont utilisés dans un but différent qu’un simple chiffrement. Nous avons pu généraliser différents types de chiffrement basés sur l’identité en une nouvelle primitive nommé Downgradable Identity-based Encryption (DIBE). Nous avons trouvé un moyen générique de transformer de simple IBE en des IBE en blanc, dans le cas où l’IBE est affine nous rendons le coût de communication très faible (de linéaire à logarithmique). Ces deux primitives ont donné lieux à différentes applications : les chiffrements basés sur les attributs pour la première et le transfère inconscient pour la deuxième. Une autre application est l’utilisation d’IBE hiérarchiques pour créer des signatures à vérifieur désigné basées sur l’identité. Ensuite nous avons regardé le transfère inconscient seul et avons réussi à le généraliser en un nouveau protocole nommé Oblivious Language-based Envelope. Finalement, nous avons construit une transformation d’un protocole à un autre, d’un échange authentifié de clés par mot de passe nous avons construit un transfère inconscient. En prenant une instanciation particulière nous obtenons un protocole plus efficace que tous les précédents pour le même niveau de sécurité. La primitive chiffrement basé sur l’identité est notre outil principal pour réaliser nos constructions. Nous avons donc besoin d’une instanciation efficace de cette primitive. Nous avons utilisé celle de Blazy Kiltz et Pan à CRYPTO’14 qui est très efficace mais possède aussi une structure particulière dite affineDuring this Thesis we investigated the possibilities that Identity-based Encryption offers when used out of their original purpose. We managed to generalize a whole class of different identity-based encryption schemes into Downgradable Identity-based Encryptions. We found a generic way to construct Blind Identity-based Encryptions. These two works leads both to applications that are not a priori linked with IBE: Attribute-based Encryption from Downgradable IBE and Oblivious Transfer for Blind IBE, in the case of Affine IBE we manage to reduce the communication cost from a linear to logarithmic. As application we also find a way to use Hierarchical IBE to construct a special type of signature called Identity-based Designated Verifier Signature. We continue the research out of the context of IBE's application with Oblivious Transfer. We manage to generalize the concept of Oblivious Transfer into a new protocol called Oblivious Language-based Envelope encompassing many kind of protocols. Finally, in the image of the whole Thesis we construct Oblivious Transfer with a very different primitive called Password Authenticated Key Exchange. Surprisingly, with some optimizations this last transformation leads to a very efficient Oblivious Transfer Protocol. The Identity-based Encryption is our main basis of work, thus efficient instantiations of this primitive were the key of our own efficiency, thus we used the instanciation from the paper of Blazy et als at crypto 2014 which is efficient, tight secure and affine
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Pavlovski, Christopher John. "Applied batch cryptography." Thesis, Queensland University of Technology, 2000. https://eprints.qut.edu.au/36856/1/Christopher%20Pavlovski%20Thesis.pdf.
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The material presented in this thesis may be viewed as comprising two key parts, the first part concerns batch cryptography specifically, whilst the second deals with how this form of cryptography may be applied to security related applications such as electronic cash for improving efficiency of the protocols.
The objective of batch cryptography is to devise more efficient primitive cryptographic protocols. In general, these primitives make use of some property such as homomorphism to perform a computationally expensive operation on a collective input set. The idea is to amortise an expensive operation, such as modular exponentiation, over the input. Most of the research work in this field has concentrated on its employment as a batch verifier of digital signatures. It is shown that several new attacks may be launched against these published schemes as some weaknesses are exposed.
Another common use of batch cryptography is the simultaneous generation of digital signatures. There is significantly less previous work on this area, and the present schemes have some limited use in practical applications. Several new batch signatures schemes are introduced that improve upon the existing techniques and some practical uses are illustrated.
Electronic cash is a technology that demands complex protocols in order to furnish several security properties. These typically include anonymity, traceability of a double spender, and off-line payment features. Presently, the most efficient schemes make use of coin divisibility to withdraw one large financial amount that may be progressively spent with one or more merchants.
Several new cash schemes are introduced here that make use of batch cryptography for improving the withdrawal, payment, and deposit of electronic coins. The devised schemes apply both to the batch signature and verification techniques introduced, demonstrating improved performance over the contemporary divisible based structures. The solutions also provide an alternative paradigm for the construction of electronic cash systems.
Whilst electronic cash is used as the vehicle for demonstrating the relevance of batch cryptography to security related applications, the applicability of the techniques introduced extends well beyond this.
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Wen, Weiqiang. "Contributions to the hardness foundations of lattice-based cryptography." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN070/document.
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La cryptographie sur les réseaux est l’une des approches les plus compétitives pour protéger la confidentialité, dans les applications actuelles et l’ère post-quantique. Le problème central qui sert de fondement de complexité de la cryptographie sur réseaux est Learning with Errors (LWE). Il consiste à résoudre un système d’équations bruité, linéaire et surdéterminé. Ce problème est au moins aussi difficile que les problèmes standards portant sur les réseaux, tels que le décodage à distance bornée (BDD pour Bounded Distance Decoding) et le problème du vecteur le plus court unique (uSVP pour unique Shortest Vector Problem). Tous ces problèmes sont conjecturés difficiles à résoudre, même avec un ordinateur quantique de grande échelle. En particulier, le meilleur algorithme connu pour résoudre ces problèmes, BKZ, est très coûteux. Dans cette thèse, nous étudions les relations de difficulté entre BDD et uSVP, la difficulté quantique de LWE et les performances pratiques de l’algorithme BKZ. Tout d’abord, nous donnons une relation de difficulté plus étroite entre BDD et uSVP. Plus précisément, nous améliorons la réduction de BDD à uSVP d’un facteur √2, comparément à celle de Lyubashevsky et Micciancio. Ensuite, Nous apportons un nouvel élément à la conjecture que LWE est quantiquement difficile. Concrètement, nous considérons une version relâchée de la version quantique du problème du coset dièdral et montrons une équivalence computationnelle entre LWE et ce problème. Enfin, nous proposons un nouveau simulateur pour BKZ. Dans ce dernier travail, nous proposons le premier simulateur probabiliste pour BKZ, qui permet de prévoir le comportement pratique de BKZ très précisémentLattice-based cryptography is one of the most competitive candidates for protecting privacy, both in current applications and post quantum period. The central problem that serves as the hardness foundation of lattice-based cryptography is called the Learning with Errors (LWE). It asks to solve a noisy equation system, which is linear and over-determined modulo q. Normally, we call LWE problem as an average-case problem as all the coefficients in the equation system are randomly chosen modulo q. The LWE problem is conjectured to be hard even wtih a large scale quantum computer. It is at least as hard as standard problems defined in the lattices, such as Bounded Distance Decoding (BDD) and unique Shortest Vector Problem (uSVP). Finally, the best known algorithm for solving these problems is BKZ, which is very expensive. In this thesis, we study the quantum hardness of LWE, the hardness relations between the underlying problems BDD and uSVP, and the practical performance of the BKZ algorithm. First, we give a strong evidence of quantum hardness of LWE. Concretely, we consider a relaxed version of the quantum version of dihedral coset problem and show an computational equivalence between LWE and this problem. Second, we tighten the hardness relation between BDD and uSVP. More precisely, We improve the reduction from BDD to uSVP by a factor √2, compared to the one by Lyubashevsky and Micciancio. Third, we propose a more precise simulator for BKZ. In the last work, we propose the first probabilistic simulotor for BKZ, which can pridict the practical behavior of BKZ very precisely
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Kosek, Amy. "An Exploration of Mathematical Applications in Cryptography." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1428944810.
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Bultel, Xavier. "Mécanismes de délégation pour les primitives de cryptographie à clé publique." Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC100.
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Bisson, Gaetan. "Endomorphism Rings in Cryptography." Phd thesis, Institut National Polytechnique de Lorraine - INPL, 2011. http://tel.archives-ouvertes.fr/tel-00609211.
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La cryptographie est devenue indispensable afin de garantir la sécurité et l'intégrité des données transitant dans les réseaux de communication modernes. Ces deux dernières décennies, des cryptosystèmes très efficaces, sûr et riches en fonctionnalités ont été construits à partir de variétés abéliennes définies sur des corps finis. Cette thèse contribue à certains aspects algorithmiques des variétés abéliennes ordinaires touchant à leurs anneaux d'endomorphismes. Cette structure joue un rôle capital dans la construction de variétés abéliennes ayant de bonnes propriétés. Par exemple, les couplages ont récemment permis de créer de nombreuses primitives cryptographiques avancées ; construire des variétés abéliennes munies de couplages efficaces nécessite de choisir des anneaux d'endomorphismes convenables, et nous montrons qu'un plus grand nombre de tels anneaux peut être utilisé qu'on ne pourrait croire. Nous nous penchons aussi le problème inverse qu'est celui du calcul de l'anneau d'endomorphisme d'une variété abélienne donnée, et qui possède en outre plusieurs applications pratiques. Précédemment, les meilleures méthodes ne résolvaient ce problème qu'en temps exponentiel ; nous concevons ici plusieurs algorithmes de complexité sous-exponentielle pour le résoudre dans le cas ordinaire. Pour les courbes elliptiques, nous algorithmes sont très efficaces, ce que nous démontrons en attaquant des problèmes de grande taille, insolvables jusqu'à ce jour. De plus, nous bornons rigoureusement la complexité de notre algorithme sous l'hypothèse de Riemann étendue. En tant que sous-routine alternative, nous nous considérons aussi une généralisation du problème du sac à dos dans les groupes finis, et montrons comment il peut être résolu en utilisant peu de mémoire. Enfin, nous généralisons notre méthode aux variétés abélienne de dimension supérieure, ce qui nécessite davantage d'hypothèses heuristiques. Concrètement, nous développons une bibliothèque qui permet d'évaluer des isogénies entre variétés abéliennes ; en utilisant cet outil important dans notre algorithme, nous appliquons notre méthode généralisée à des exemples illustratifs et de tailles jusqu'à présent inatteignables.
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Alexander, Nicholas Charles. "Algebraic Tori in Cryptography." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1154.
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Communicating bits over a network is expensive. Therefore, cryptosystems that transmit as little data as possible are valuable. This thesis studies several cryptosystems that require significantly less bandwidth than conventional analogues. The systems we study, called torus-based cryptosystems, were analyzed by Karl Rubin and Alice Silverberg in 2003 [RS03]. They interpreted the XTR [LV00] and LUC [SL93] cryptosystems in terms of quotients of algebraic tori and birational parameterizations, and they also presented CEILIDH, a new torus-based cryptosystem. This thesis introduces the geometry of algebraic tori, uses it to explain the XTR, LUC, and CEILIDH cryptosystems, and presents torus-based extensions of van Dijk, Woodruff, et al. [vDW04, vDGP+05] that require even less bandwidth. In addition, a new algorithm of Granger and Vercauteren [GV05] that attacks the security of torus-based cryptosystems is presented. Finally, we list some open research problems.
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Déchène, Isabelle. "Generalized Jacobians in cryptography." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100347.
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Groups where the discrete logarithm problem (DLP) is believed to be intractable have proved to be inestimable building blocks for cryptographic applications. They are at the heart of numerous protocols such as key agreements, public-key cryptosystems, digital signatures, identification schemes, publicly verifiable secret sharings, hash functions and bit commitments. The search for new groups with intractable DLP is therefore of great importance. The study of such a candidate, the so-called generalized Jacobians, is the object of this dissertation. The motivation for this work came from the observation that several practical discrete logarithm-based cryptosystems, such as ElGamal, the Elliptic and Hyperelliptic Curve Cryptosystems, XTR, the Lucas-based cryptosystem LUC as well as the torus-based cryptosystem CEILIDH can all naturally be reinterpreted in terms of generalized Jacobians. We next provide, from a cryptographic point of view, a global description of this family of algebraic groups that highlights their potential for applications. Our main contribution is then to introduce a new public-key cryptosystem based on the simplest non-trivial generalized Jacobian of an elliptic curve. This work thus provides the first concrete example of a semi-abelian variety suitable for DL-based cryptography.
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Inamori, Hitoshi. "Security in quantum cryptography." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393459.
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Gray, Sean. "Quantum Entanglement and Cryptography." Thesis, Uppsala universitet, Teoretisk fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-227085.
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In this paper the features of quantum systems which lay the foundation of quantum entanglement are studied. General properties of entangled states are discussed, including their entropy and relation to Bell's inequality. Applications of entanglement, namely quantum teleportation and quantum cryptography, are also considered.
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Park, Sunoo. "Cryptography for societal benefit." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118099.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 331-349).
The deployment of cryptography in society has a range of effects that are not always evident when studying cryptography as a technological construct in isolation. This observation suggests a number of natural research directions that examine cryptography as an instrument of societal influence; that is, as a technological construct in conjunction with its societal effects. This thesis presents the results of six papers spanning the three broad contexts listed next. - Institutional accountability Cryptography can enhance transparency and accountability of institutions seeking public trust, such as governmental agencies, judicial systems, and election infrastructure. - Individual empowerment in oppressive environments Cryptography can empower individuals to communicate securely and undetectably and to preserve their anonymity, even in hostile environments. - Incentivizing collaboration Cryptography can facilitate collaboration between rational -- possibly selfish and/or competing -- parties in a way that is beneficial to all participants, by providing credible guarantees of secrecy and correct protocol execution to mutually distrustful parties.
by Sunoo Park.
Ph. D.
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Fournier, Jacques Jean-Alain Michael. "Vector microprocessors for cryptography." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613318.
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Дядечко, Алла Миколаївна, Алла Николаевна Дядечко, Alla Mykolaivna Diadechko, and V. V. Kontchevich. "Security pitfalls in cryptography." Thesis, Видавництво СумДУ, 2010. http://essuir.sumdu.edu.ua/handle/123456789/18334.
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A cryptographic system can only be as strong as the encryption algorithms, digital signature algorithms, one-way hash functions, and massage authentication codes it relies on.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/18334
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Delman, Bethany. "Genetic algorithms in cryptography /." Link to online version, 2003. https://ritdml.rit.edu/dspace/handle/1850/263.
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Goldenberg, David. "Adaptive learning and cryptography." W&M ScholarWorks, 2010. https://scholarworks.wm.edu/etd/1539623564.
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Significant links exist between cryptography and computational learning theory. Cryptographic functions are the usual method of demonstrating significant intractability results in computational learning theory as they can demonstrate that certain problems are hard in a representation independent sense. On the other hand, hard learning problems have been used to create efficient cryptographic protocols such as authentication schemes, pseudo-random permutations and functions, and even public key encryption schemes.;Learning theory / coding theory also impacts cryptography in that it enables cryptographic primitives to deal with the issues of noise or bias in their inputs. Several different constructions of "fuzzy" primitives exist, a fuzzy primitive being a primitive which functions correctly even in the presence of "noisy", or non-uniform inputs. Some examples of these primitives include error-correcting blockciphers, fuzzy identity based cryptosystems, fuzzy extractors and fuzzy sketches. Error correcting blockciphers combine both encryption and error correction in a single function which results in increased efficiency. Fuzzy identity based encryption allows the decryption of any ciphertext that was encrypted under a "close enough" identity. Fuzzy extractors and sketches are methods of reliably (re)-producing a uniformly random secret key given an imperfectly reproducible string from a biased source, through a public string that is called the "sketch".;While hard learning problems have many qualities which make them useful in constructing cryptographic protocols, such as their inherent error tolerance and simple algebraic structure, it is often difficult to utilize them to construct very secure protocols due to assumptions they make on the learning algorithm. Due to these assumptions, the resulting protocols often do not have security against various types of "adaptive" adversaries. to help deal with this issue, we further examine the inter-relationships between cryptography and learning theory by introducing the concept of "adaptive learning". Adaptive learning is a rather weak form of learning in which the learner is not expected to closely approximate the concept function in its entirety, rather it is only expected to answer a query of the learner's choice about the target. Adaptive learning allows for a much weaker learner than in the standard model, while maintaining the the positive properties of many learning problems in the standard model, a fact which we feel makes problems that are hard to adaptively learn more useful than standard model learning problems in the design of cryptographic protocols. We argue that learning parity with noise is hard to do adaptively and use that assumption to construct a related key secure, efficient MAC as well as an efficient authentication scheme. In addition we examine the security properties of fuzzy sketches and extractors and demonstrate how these properties can be combined by using our related key secure MAC. We go on to demonstrate that our extractor can allow a form of related-key "hardening" for protocols in that, by affecting how the key for a primitive is stored it renders that protocol immune to related key attacks.
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Chakraborty, Kaushik. "Cryptography with spacetime constraints." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066194/document.
Full textAbstract:
Dans cette thèse,nous étudions comment exploiter des contraintes spatio-temporelles,notamment le principe d'impossibilité de transmission supraluminique,dans le but de créer des primitives cryptographiques sûres,par exemple la vérification de position ou la "mise en gage de bit''(bit commitment). D'après le principe d'impossibilité de transmission supraluminique,aucun vecteur physique d'information ne peut voyager plus vite que la vitesse de la lumière. Ce principe entraîne une contrainte sur le temps de communication entre deux points éloignés. Ce délai dans le transfert d'information peut être utilisé comme une contrainte temporelle interdisant la communication. En cryptographie multi-agents,il est connu que l'hypothèse de non-communication entre les agents permet de réaliser de manière sécurisée de nombreuses primitives comme la "mise en gage de bit'' et l'un des buts de cette thèse est de comprendre à quel point les contraintes spatio-temporelles peuvent être exploitèes pour simuler des scénarios de non-communication. Dans la première partie de cette thèse nous étudions comment utiliser une contrainte de non-communication pour essayer de vérifier la position d'une personne.Dans la dernière partie,nous nous penchons sur deux exemples de protocoles de ``mise en gage de bit'' relativistes afin d'en étudier la sécurité contre des adversaires classiques. Pour conclure cette thèse,nous mentionnons quelques problèmes ouverts intéréssants. Ces problèmes ouverts peuvent être très utiles pour comprendre le rôle de contraintes spatio-temporelles,par exemple de l'impossibilité de transmission supraluminique,dans la conception de primitives cryptographiques parfaitement sûresIn this thesis we have studied how to exploit relativistic constraints such as the non-superluminal signalling principle to design secure cryptographic primitives like position-verification and bit commitment. According to non-superluminal signalling principle, no physical carrier of information can travel faster than the speed of light. This put a constraint on the communication time between two distant stations. One can consider this delay in information transfer as a temporal non-communication constraint. Cryptographic primitives like bit-commitment, oblivious transfer can be implemented with perfect secrecy under such non-communication assumption between the agents. The first part of this thesis has studied how non-signalling constraints can be used for secure position verification. Here, we have discussed about a strategy which can attack any position verification scheme. In the next part of this thesis we have discussed about the nonlocal games, relevant for studying relativistic bit commitment protocols. We have established an upper bound on the classical value of such family of games. The last part of this thesis discusses about two relativistic bit commitment protocols and their security against classical adversaries. We conclude this thesis by giving a brief summary of the content of each chapter and mentioning interesting open problems. These open problems can be very useful for better understanding of the role of spacetime constraints such as non-superluminal signalling in designing perfectly secure cryptographic primitives
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Chakraborty, Kaushik. "Cryptography with spacetime constraints." Electronic Thesis or Diss., Paris 6, 2017. http://www.theses.fr/2017PA066194.
Full textAbstract:
Dans cette thèse,nous étudions comment exploiter des contraintes spatio-temporelles,notamment le principe d'impossibilité de transmission supraluminique,dans le but de créer des primitives cryptographiques sûres,par exemple la vérification de position ou la "mise en gage de bit''(bit commitment). D'après le principe d'impossibilité de transmission supraluminique,aucun vecteur physique d'information ne peut voyager plus vite que la vitesse de la lumière. Ce principe entraîne une contrainte sur le temps de communication entre deux points éloignés. Ce délai dans le transfert d'information peut être utilisé comme une contrainte temporelle interdisant la communication. En cryptographie multi-agents,il est connu que l'hypothèse de non-communication entre les agents permet de réaliser de manière sécurisée de nombreuses primitives comme la "mise en gage de bit'' et l'un des buts de cette thèse est de comprendre à quel point les contraintes spatio-temporelles peuvent être exploitèes pour simuler des scénarios de non-communication. Dans la première partie de cette thèse nous étudions comment utiliser une contrainte de non-communication pour essayer de vérifier la position d'une personne.Dans la dernière partie,nous nous penchons sur deux exemples de protocoles de ``mise en gage de bit'' relativistes afin d'en étudier la sécurité contre des adversaires classiques. Pour conclure cette thèse,nous mentionnons quelques problèmes ouverts intéréssants. Ces problèmes ouverts peuvent être très utiles pour comprendre le rôle de contraintes spatio-temporelles,par exemple de l'impossibilité de transmission supraluminique,dans la conception de primitives cryptographiques parfaitement sûresIn this thesis we have studied how to exploit relativistic constraints such as the non-superluminal signalling principle to design secure cryptographic primitives like position-verification and bit commitment. According to non-superluminal signalling principle, no physical carrier of information can travel faster than the speed of light. This put a constraint on the communication time between two distant stations. One can consider this delay in information transfer as a temporal non-communication constraint. Cryptographic primitives like bit-commitment, oblivious transfer can be implemented with perfect secrecy under such non-communication assumption between the agents. The first part of this thesis has studied how non-signalling constraints can be used for secure position verification. Here, we have discussed about a strategy which can attack any position verification scheme. In the next part of this thesis we have discussed about the nonlocal games, relevant for studying relativistic bit commitment protocols. We have established an upper bound on the classical value of such family of games. The last part of this thesis discusses about two relativistic bit commitment protocols and their security against classical adversaries. We conclude this thesis by giving a brief summary of the content of each chapter and mentioning interesting open problems. These open problems can be very useful for better understanding of the role of spacetime constraints such as non-superluminal signalling in designing perfectly secure cryptographic primitives
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Klembalski, Katharina. "Cryptography and number theory in the classroom -- Contribution of cryptography to mathematics teaching." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-80390.
Full textAbstract:
Cryptography fascinates people of all generations and is increasingly presented as an example for the relevance and application of the mathematical sciences. Indeed, many principles of modern cryptography can be described at a secondary school level. In this context, the mathematical background is often only sparingly shown. In the worst case, giving mathematics this character of a tool reduces the application of mathematical insights to the message ”cryptography contains math”. This paper examines the question as to
what else cryptography can offer to mathematics education. Using the RSA cryptosystem and related content, specific mathematical competencies are highlighted that complement standard teaching, can be taught with cryptography as an example, and extend and deepen key mathematical concepts.
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Rossi, Mélissa. "Extended security of lattice-based cryptography." Electronic Thesis or Diss., Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLE050.
Full textAbstract:
La cryptographie fondée sur les réseaux euclidiens représente une alternative prometteuse à la cryptographie asymétrique utilisée actuellement, en raison de sa résistance présumée à un ordinateur quantique universel. Cette nouvelle famille de schémas asymétriques dispose de plusieurs atouts parmi lesquels de fortes garanties théoriques de sécurité, un large choix de primitives et, pour certains de ses représentants, des performances comparables aux standards actuels. Une campagne de standardisation post-quantique organisée par le NIST est en cours et plusieurs schémas utilisant des réseaux euclidiens font partie des favoris. La communauté scientifique a été encouragée à les analyser car ils pourraient à l'avenir être implantés dans tous nos systèmes. L'objectif de cette thèse est de contribuer à cet effort. Nous étudions la sécurité de ces nouveaux cryptosystèmes non seulement au sens de leur résistance à la cryptanalyse en ''boîte noire'' à l'aide de moyens de calcul classiques, mais aussi selon un spectre plus large de modèles de sécurité, comme les attaques quantiques, les attaques supposant des failles d'utilisation, ou encore les attaques par canaux auxiliaires. Ces différents types d’attaques ont déjà été largement formalisés et étudiés par le passé pour des schémas asymétriques et symétriques pré-quantiques. Dans ce mémoire, nous analysons leur application aux nouvelles structures induites par les réseaux euclidiens. Notre travail est divisé en deux parties complémentaires : les contremesures et les attaques. La première partie regroupe nos contributions à l'effort actuel de conception de nouvelles protections algorithmiques afin de répondre aux nombreuses publications récentes d’attaques par canaux auxiliaires. Les travaux réalisés en équipe auxquels nous avons pris part on abouti à l'introduction de nouveaux outils mathématiques pour construire des contre-mesures algorithmiques, appuyées sur des preuves formelles, qui permettent de prévenir systématiquement les attaques physiques et par analyse de temps d'exécution. Nous avons ainsi participé à la protection de plusieurs schémas de signature fondés sur les réseaux euclidiens comme GLP, BLISS, qTesla ou encore Falcon. Dans une seconde partie consacrée à la cryptanalyse, nous étudions dans un premier temps de nouvelles attaques qui tirent parti du fait que certains schémas de chiffrement à clé publique ou d'établissement de clé peuvent échouer avec une faible probabilité. Ces échecs sont effectivement faiblement corrélés au secret. Notre travail a permis d’exhiber des attaques dites « par échec de déchiffrement » dans des modèles de failles d'utilisation ou des modèles quantiques. Nous avons d'autre part introduit un outil algorithmique de cryptanalyse permettant d’estimer la sécurité du problème mathématique sous-jacent lorsqu’une information partielle sur le secret est donnée. Cet outil s’est avéré utile pour automatiser et améliorer plusieurs attaques connues comme des attaques par échec de déchiffrement, des attaques classiques ou encore des attaques par canaux auxiliairesLattice-based cryptography is considered as a quantum-safe alternative for the replacement of currently deployed schemes based on RSA and discrete logarithm on prime fields or elliptic curves. It offers strong theoretical security guarantees, a large array of achievable primitives, and a competitive level of efficiency. Nowadays, in the context of the NIST post-quantum standardization process, future standards may ultimately be chosen and several new lattice-based schemes are high-profile candidates. The cryptographic research has been encouraged to analyze lattice-based cryptosystems, with a particular focus on practical aspects. This thesis is rooted in this effort. In addition to black-box cryptanalysis with classical computing resources, we investigate the extended security of these new lattice-based cryptosystems, employing a broad spectrum of attack models e.g. quantum, misuse, timing or physical attacks. Accounting that these models have already been applied to a large variety of pre-quantum asymmetric and symmetric schemes before, we concentrate our efforts on leveraging and addressing the new features introduced by lattice structures. Our contribution is twofold: defensive, i.e. countermeasures for implementations of lattice-based schemes and offensive, i.e. cryptanalysis. On the defensive side, in view of the numerous recent timing and physical attacks, we wear our designer's hat and investigate algorithmic protections. We introduce some new algorithmic and mathematical tools to construct provable algorithmic countermeasures in order to systematically prevent all timing and physical attacks. We thus participate in the actual provable protection of the GLP, BLISS, qTesla and Falcon lattice-based signatures schemes. On the offensive side, we estimate the applicability and complexity of novel attacks leveraging the lack of perfect correctness introduced in certain lattice-based encryption schemes to improve their performance. We show that such a compromise may enable decryption failures attacks in a misuse or quantum model. We finally introduce an algorithmic cryptanalysis tool that assesses the security of the mathematical problem underlying lattice-based schemes when partial knowledge of the secret is available. The usefulness of this new framework is demonstrated with the improvement and automation of several known classical, decryption-failure, and side-channel attacks
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Roux-Langlois, Adeline. "Lattice - Based Cryptography - Security Foundations and Constructions." Thesis, Lyon, École normale supérieure, 2014. http://www.theses.fr/2014ENSL0940/document.
Full textAbstract:
La cryptographie reposant sur les réseaux Euclidiens est une branche récente de la cryptographie dans laquelle la sécurité des primitives repose sur la difficulté présumée de certains problèmes bien connus dans les réseaux Euclidiens. Le principe de ces preuves est de montrer que réussir une attaque contre une primitive est au moins aussi difficile que de résoudre un problème particulier, comme le problème Learning With Errors (LWE) ou le problème Small Integer Solution (SIS). En montrant que ces problèmes sont au moins aussi difficiles à résoudre qu'un problème difficile portant sur les réseaux, présumé insoluble en temps polynomial, on en conclu que les primitives construites sont sûres. Nous avons travaillé sur l'amélioration de la sécurité et des constructions de primitives cryptographiques. Nous avons étudié la difficulté des problèmes SIS et LWE et de leurs variantes structurées sur les anneaux d'entiers de corps cyclotomiques, et les modules libres sur ceux-ci. Nous avons montré d'une part qu'il existe une preuve de difficulté classique pour le problème LWE (la réduction existante de Regev en 2005 était quantique), d'autre part que les variantes sur les modules sont elles-aussi difficiles. Nous avons aussi proposé deux nouvelles variantes de signatures de groupe dont la sécurité repose sur SIS et LWE. L'une est la première reposant sur les réseaux et ayant une taille et une complexité poly-logarithmique en le nombre d'utilisateurs. La seconde construction permet de plus la révocation d'un membre du groupe. Enfin, nous avons amélioré la taille de certains paramètres dans le travail sur les applications multilinéaires cryptographiques de Garg, Gentry et HaleviLattice-based cryptography is a branch of cryptography exploiting the presumed hardness of some well-known problems on lattices. Its main advantages are its simplicity, efficiency, and apparent security against quantum computers. The principle of the security proofs in lattice-based cryptography is to show that attacking a given scheme is at least as hard as solving a particular problem, as the Learning with Errors problem (LWE) or the Small Integer Solution problem (SIS). Then, by showing that those two problems are at least as hard to solve than a hard problem on lattices, presumed polynomial time intractable, we conclude that the constructed scheme is secure.In this thesis, we improve the foundation of the security proofs and build new cryptographic schemes. We study the hardness of the SIS and LWE problems, and of some of their variants on integer rings of cyclotomic fields and on modules on those rings. We show that there is a classical hardness proof for the LWE problem (Regev's prior reduction was quantum), and that the module variants of SIS and LWE are also hard to solve. We also give two new lattice-based group signature schemes, with security based on SIS and LWE. One is the first lattice-based group signature with logarithmic signature size in the number of users. And the other construction allows another functionality, verifier-local revocation. Finally, we improve the size of some parameters in the work on cryptographic multilinear maps of Garg, Gentry and Halevi in 2013
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Prest, Thomas. "Gaussian sampling in lattice-based cryptography." Thesis, Paris, Ecole normale supérieure, 2015. http://www.theses.fr/2015ENSU0045/document.
Full textAbstract:
Bien que relativement récente, la cryptographie à base de réseaux euclidiens s’est distinguée sur de nombreux points, que ce soit par la richesse des constructions qu’elle permet, par sa résistance supposée à l’avènement des ordinateursquantiques ou par la rapidité dont elle fait preuve lorsqu’instanciée sur certaines classes de réseaux. Un des outils les plus puissants de la cryptographie sur les réseaux est le Gaussian sampling. À très haut niveau, il permet de prouver qu’on connaît une base particulière d’un réseau, et ce sans dévoiler la moindre information sur cette base. Il permet de réaliser une grande variété de cryptosystèmes. De manière quelque peu surprenante, on dispose de peu d’instanciations pratiques de ces schémas cryptographiques, et les algorithmes permettant d’effectuer du Gaussian sampling sont peu étudiés. Le but de cette thèse est de combler le fossé qui existe entre la théorie et la pratique du Gaussian sampling. Dans un premier temps, nous étudions et améliorons les algorithmes existants, à la fois par une analyse statistique et une approche géométrique. Puis nous exploitons les structures sous-tendant de nombreuses classes de réseaux, ce qui nous permet d’appliquer à un algorithme de Gaussian sampling les idées de la transformée de Fourier rapide, passant ainsi d’une complexité quadratique à quasilinéaire. Enfin, nous utilisons le Gaussian sampling en pratique et instancions un schéma de signature et un schéma de chiffrement basé sur l’identité. Le premierfournit des signatures qui sont les plus compactes obtenues avec les réseaux à l’heure actuelle, et le deuxième permet de chiffrer et de déchiffrer à une vitesse près de mille fois supérieure à celle obtenue en utilisant un schéma à base de couplages sur les courbes elliptiquesAlthough rather recent, lattice-based cryptography has stood out on numerous points, be it by the variety of constructions that it allows, by its expected resistance to quantum computers, of by its efficiency when instantiated on some classes of lattices. One of the most powerful tools of lattice-based cryptography is Gaussian sampling. At a high level, it allows to prove the knowledge of a particular lattice basis without disclosing any information about this basis. It allows to realize a wide array of cryptosystems. Somewhat surprisingly, few practical instantiations of such schemes are realized, and the algorithms which perform Gaussian sampling are seldom studied. The goal of this thesis is to fill the gap between the theory and practice of Gaussian sampling. First, we study and improve the existing algorithms, byboth a statistical analysis and a geometrical approach. We then exploit the structures underlying many classes of lattices and apply the ideas of the fast Fourier transform to a Gaussian sampler, allowing us to reach a quasilinearcomplexity instead of quadratic. Finally, we use Gaussian sampling in practice to instantiate a signature scheme and an identity-based encryption scheme. The first one yields signatures that are the most compact currently obtained in lattice-based cryptography, and the second one allows encryption and decryption that are about one thousand times faster than those obtained with a pairing-based counterpart on elliptic curves
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Scerri, Guillaume. "Proof of security protocols revisited." Thesis, Cachan, Ecole normale supérieure, 2015. http://www.theses.fr/2015DENS0002/document.
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Avec la généralisation d'Internet, l'usage des protocoles cryptographiques est devenu omniprésent. Étant donné leur complexité et leur l'aspect critique, une vérification formelle des protocoles cryptographiques est nécessaire.Deux principaux modèles existent pour prouver les protocoles. Le modèle symbolique définit les capacités de l'attaquant comme un ensemble fixe de règles, tandis que le modèle calculatoire interdit seulement a l'attaquant derésoudre certain problèmes difficiles. Le modèle symbolique est très abstrait et permet généralement d'automatiser les preuves, tandis que le modèle calculatoire fournit des garanties plus fortes.Le fossé entre les garanties offertes par ces deux modèles est dû au fait que le modèle symbolique décrit les capacités de l'adversaire alors que le modèle calculatoire décrit ses limitations. En 2012 Bana et Comon ont proposé unnouveau modèle symbolique dans lequel les limitations de l'attaquant sont axiomatisées. De plus, si la sémantique calculatoire des axiomes découle des hypothèses cryptographiques, la sécurité dans ce modèle symbolique fournit desgaranties calculatoires.L'automatisation des preuves dans ce nouveau modèle (et l'élaboration d'axiomes suffisamment généraux pour prouver un grand nombre de protocoles) est une question laissée ouverte par l'article de Bana et Comon. Dans cette thèse nous proposons une procédure de décision efficace pour une large classe d'axiomes. De plus nous avons implémenté cette procédure dans un outil (SCARY). Nos résultats expérimentaux montrent que nos axiomes modélisant la sécurité du chiffrement sont suffisamment généraux pour prouver une large classe de protocolesWith the rise of the Internet the use of cryptographic protocols became ubiquitous. Considering the criticality and complexity of these protocols, there is an important need of formal verification.In order to obtain formal proofs of cryptographic protocols, two main attacker models exist: the symbolic model and the computational model. The symbolic model defines the attacker capabilities as a fixed set of rules. On the other hand, the computational model describes only the attacker's limitations by stating that it may break some hard problems. While the former is quiteabstract and convenient for automating proofs the later offers much stronger guarantees.There is a gap between the guarantees offered by these two models due to the fact the symbolic model defines what the adversary may do while the computational model describes what it may not do. In 2012 Bana and Comon devised a new symbolic model in which the attacker's limitations are axiomatised. In addition provided that the (computational semantics) of the axioms follows from the cryptographic hypotheses, proving security in this symbolic model yields security in the computational model.The possibility of automating proofs in this model (and finding axioms general enough to prove a large class of protocols) was left open in the original paper. In this thesis we provide with an efficient decision procedure for a general class of axioms. In addition we propose a tool (SCARY) implementing this decision procedure. Experimental results of our tool shows that the axioms we designed for modelling security of encryption are general enough to prove a large class of protocols
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Paindavoine, Marie. "Méthodes de calculs sur les données chiffrées." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1009/document.
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L'annonce de l'essor du chiffrement des données se heurte à celle de l'avènement du "big data". Il n'est maintenant plus suffisant d'envoyer et de recevoir des données, il faut pouvoir les analyser, les exploiter ou encore les partager à grande échelle. Or, les données à protéger sont de plus en plus nombreuses, notamment avec la prise de conscience de l'impact qu'ont les nouvelles technologies (smartphones, internet of things, cloud,...) sur la vie privée des utilisateurs. En rendant ces données inaccessibles, le chiffrement bloque a priori les fonctionnalités auxquelles les utilisateurs et les fournisseurs de service sont habitués. Pour rétablir ces fonctionnalités, il est nécessaire de savoir calculer des fonctions de données chiffrées, et cette thèse explore plusieurs pistes dans ce sens. Dans une première partie, nous nous intéressons au chiffrement totalement homomorphe qui permet de réaliser des calculs arbitraires sur les données chiffrées. Ce type de chiffrement est cependant particulièrement coûteux, notamment à cause de l'appel souvent nécessaire à une procédure très coûteuse : le réamorçage. Nous prouvons ici que minimiser le nombre de réamorçages est un problème NP-complet et donnons une méthode pratique pour approximer ce minimum. Dans une seconde partie, nous étudions des schémas dédiés à une fonctionnalité donnée. Le premier cas d'usage considéré est celui de la déduplication vérifiable de données chiffrées. Il s'agit pour un serveur de stockage externe d'être assuré qu'il ne conserve qu'un seul exemplaire de chaque fichier, même si ceux-ci sont chiffrés, ce qui lui permet d'optimiser l'usage de ses ressources mémoires. Ensuite, nous proposons un schéma de chiffrement cherchable permettant de détecter des intrusions dans un réseau de télécommunications chiffrés. En effet, le travail d'inspection du réseau par des moteurs d'analyse est actuellement entravé par la croissance du trafic chiffré. Les résultats obtenus permettent ainsi d'assurer la confidentialité des échanges tout en garantissant l'absence d'intrusions malveillantes dans le traficNowadays, encryption and services issued of ``big data" are at odds. Indeed, encryption is about protecting users privacy, while big data is about analyzing users data. Being increasingly concerned about security, users tend to encrypt their sensitive data that are subject to be accessed by other parties, including service providers. This hinders the execution of services requiring some kind of computation on users data, which makes users under obligation to choose between these services or their private life. We address this challenge in this thesis by following two directions.In the first part of this thesis, we study fully homomorphic encryption that makes possible to perform arbitrary computation on encrypted data. However, this kind of encryption is still inefficient, and this is due in part to the frequent execution of a costly procedure throughout evaluation, namely the bootstrapping. Thus, efficiency is inversely proportional to the number of bootstrappings needed to evaluate functions on encrypted data. In this thesis, we prove that finding such a minimum is NP-complete. In addition, we design a new method that efficiently finds a good approximation of it. In the second part, we design schemes that allow a precise functionality. The first one is verifiable deduplication on encrypted data, which allows a server to be sure that it keeps only one copy of each file uploaded, even if the files are encrypted, resulting in an optimization of the storage resources. The second one is intrusion detection over encrypted traffic. Current encryption techniques blinds intrusion detection services, putting the final user at risks. Our results permit to reconcile users' right to privacy and their need of keeping their network clear of all intrusion
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Makarov, Vadim. "Quantum cryptography and quantum cryptanalysis." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1473.
Full textAbstract:
This doctoral thesis summarizes research in quantum cryptography done at the Department of Electronics and Telecommunications at the Norwegian University of Science and Technology (NTNU) from 1998 through 2007.
The opening parts contain a brief introduction into quantum cryptography as well as an overview of all existing single photon detection techniques for visible and near infrared light. Then, our implementation of a fiber optic quantum key distribution (QKD) system is described. We employ a one-way phase coding scheme with a 1310 nm attenuated laser source and a polarization-maintaining Mach-Zehnder interferometer. A feature of our scheme is that it tracks phase drift in the interferometer at the single photon level instead of employing hardware phase control measures. An optimal phase tracking algorithm has been developed, implemented and tested. Phase tracking accuracy of +-10 degrees is achieved when approximately 200 photon counts are collected in each cycle of adjustment. Another feature of our QKD system is that it uses a single photon detector based on a germanium avalanche photodiode gated at 20 MHz. To make possible this relatively high gating rate, we have developed, implemented and tested an afterpulse blocking technique, when a number of gating pulses is blocked after each registered avalanche. This technique allows to increase the key generation rate nearly proportionally to the increase of the gating rate. QKD has been demonstrated in the laboratory setting with only a very limited success: by the time of the thesis completion we had malfunctioning components in the setup, and the quantum bit error rate remained unstable with its lowest registered value of about 4%.
More than half of the thesis is devoted to various security aspects of QKD. We have studied several attacks that exploit component imperfections and loopholes in optical schemes. In a large pulse attack, settings of modulators inside Alice's and Bob's setups are read out by external interrogating light pulses, without interacting with quantum states and without raising security alarms. An external measurement of phase shift at Alice's phase modulator in our setup has been demonstrated experimentally. In a faked states attack, Eve intercepts Alice's qubits and then utilizes various optical imperfections in Bob's scheme to construct and resend light pulses in such a way that Bob does not distinguish his detection results from normal, whereas they give Bob the basis and bit value chosen at Eve's discretion. Construction of such faked states using several different imperfections is discussed. Also, we sketch a practical workflow of breaking into a running quantum cryptolink for the two abovementioned classes of attacks. A special attention is paid to a common imperfection when sensitivity of Bob's two detectors relative to one another can be controlled by Eve via an external parameter, for example via the timing of the incoming pulse. This imperfection is illustrated by measurements on two different single photon detectors. Quantitative results for a faked states attack on the Bennett-Brassard 1984 (BB84) and the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocols using this imperfection are obtained. It is shown how faked states can in principle be constructed for quantum cryptosystems that use a phase-time encoding, the differential phase shift keying (DPSK) and the Ekert protocols. Furthermore we have attempted to integrate this imperfection of detectors into the general security proof for the BB84 protocol. For all attacks, their applicability to and implications for various known QKD schemes are considered, and countermeasures against the attacks are proposed.
The thesis incorporates published papers [J. Mod. Opt. 48, 2023 (2001)], [Appl. Opt. 43, 4385 (2004)], [J. Mod. Opt. 52, 691 (2005)], [Phys. Rev. A 74, 022313 (2006)], and [quant-ph/0702262].
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Kirlar, Baris Bulent. "Elliptic Curve Pairing-based Cryptography." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612613/index.pdf.
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In this thesis, we explore the pairing-based cryptography on elliptic curves from the theoretical and implementation point of view. In this respect, we first study so-called pairing-friendly elliptic curves used in pairing-based cryptography. We classify these curves according to their construction methods and study them in details.
Inspired of the work of Koblitz and Menezes, we study the elliptic curves in the form $y^{2}=x^{3}-c$ over the prime field $F_{q}$ and compute explicitly the number of points $#E(mathbb{F}_{q})$. In particular, we show that the elliptic curve $y^{2}=x^{3}-1$ over $mathbb{F}_{q}$ for the primes $q$ of the form $27A^{2}+1$ has an embedding degree $k=1$ and belongs to Scott-Barreto families in our classification. Finally, we give examples of those primes $q$ for which the security level of the pairing-based cryptographic protocols on the curve $y^{2}=x^{3}-1$ over $mathbb{F}_{q}$ is equivalent to 128-, 192-, or 256-bit AES keys.
From the implementation point of view, it is well-known that one of the most important part of the pairing computation is final exponentiation. In this respect, we show explicitly how the final exponentiation is related to the linear recurrence relations. In particular, this correspondence gives that finding an algoritm to compute final exponentiation is equivalent to finding an algorithm to compute the $m$-th term of the associated linear recurrence relation. Furthermore, we list all those work studied in the literature so far and point out how the associated linear recurrence computed efficiently.
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Lydersen, Lars Vincent van de Wiel. "Practical security of quantum cryptography." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13856.
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The peculiar properties of quantum mechanics enable possibilities not allowed by classical physics. In particular, two parties can generate a random, secret key at a distance, even though an eavesdropper can do anything permitted by the laws of physics. Measuring the quantum properties of the signals generating the key, would ultimately change them, and thus reveal the eavesdropper’s presence. This exchange of a random, secret key is known as quantum cryptography. Quantum cryptography can be, and has been proven unconditionally secure using perfect devices. However, when quantum cryptography is implemented, one must use components available with current technology. These are usually imperfect. Although the security of quantum cryptography has been proven for components with certain imperfections, the question remains: can quantum cryptography be implemented in a provable, unconditionally secure way, using components available with current technology? This thesis contains both a theoretical, and an experimental contribution to the answer of this question. On the experimental side, components used in, and complete quantum cryptography systems have been carefully examined for security loopholes. In particular, it turned out that two commercial quantum cryptography systems contained loopholes, which would allow an eavesdropper to capture the full secret key, without exposing her presence. Furthermore, this detector control attack could be implemented with current technology. The attack is applicable against a variety of quantum cryptography implementations and protocols. The theoretical contribution consists of security proofs for quantum cryptography in a very general setting. Precisely, the security is proven with arbitrary individual imperfections in the source and detectors. These proofs should make it possible to use a wide array of imperfect devices in implementations of quantum cryptography. Finally, a secure detection scheme is proposed, immune to the detector control attack and compatible with those security proofs. Therefore, if this scheme is implemented correctly, it offers provable security.
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Muecke, Innes. "Greyscale and colour visual cryptography." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0017/MQ48283.pdf.
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Živić, Nataša. "Joint channel coding and cryptography." Aachen Shaker, 2007. http://d-nb.info/99003707X/04.
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Weir, J. P. "Visual cryptography and its applications." Thesis, Queen's University Belfast, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557852.
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" In this thesis, a number of new schemes are presented which address current problems and shortcomings within the area of visual cryptography. Visual cryptography provides a very powerful means by which a secret, in the form of a digital image, can be distributed (encoded) into two or more pieces known as shares. When these shares are xeroxed onto transparencies and superimposed exactly together, the original secret can be recovered (decoded) without the necessity for computation. Traditionally, visual cryptography allows effective and efficient sharing of a single secret between a number of trusted parties. One aspect of the research within this thesis specifically addresses the issues of embedding more than two secrets within a set of two shares. Alignment poses a further problem. The placement of the shares must be specific. In order to ease ali~ent, the techniques developed within this thesis for sharing multiple secrets relaxes this restriction. The result is a scheme in which the shares can be superimposed upon one another in a multitude of positions and alignment styles which enables multiple secret recovery. Applications of visual cryptography are also examined and presented. This is an area within visual cryptography that has had very little attention in terms of research. The primary focus of the work presented within this thesis concentrates on applications of visual cryptography in real world scenarios. For such a simple and effective method of sharing secrets, practical applications are as yet, limited. A number of novel uses for visual cryptography are presented that use theoretical techniques in a practical way.
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Grundy, Dan. "Concepts and calculation in cryptography." Thesis, University of Kent, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498823.
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Longrigg, Jonathan James. "Aspects of Braid group cryptography." Thesis, University of Newcastle Upon Tyne, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492947.
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Miller, Justin C. "The security of quantum cryptography." Honors in the Major Thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/340.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Arts and Sciences
Mathematics
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Lütkenhaus, Norbert. "Generalised measurements and quantum cryptography." Thesis, University of Strathclyde, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443856.
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Hutchinson, Aaron. "Algorithms in Elliptic Curve Cryptography." Thesis, Florida Atlantic University, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10980188.
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Elliptic curves have played a large role in modern cryptography. Most notably, the Elliptic Curve Digital Signature Algorithm (ECDSA) and the Elliptic Curve Diffie-Hellman (ECDH) key exchange algorithm are widely used in practice today for their efficiency and small key sizes. More recently, the Supersingular Isogeny-based Diffie-Hellman (SIDH) algorithm provides a method of exchanging keys which is conjectured to be secure in the post-quantum setting. For ECDSA and ECDH, efficient and secure algorithms for scalar multiplication of points are necessary for modern use of these protocols. Likewise, in SIDH it is necessary to be able to compute an isogeny from a given finite subgroup of an elliptic curve in a fast and secure fashion.
We therefore find strong motivation to study and improve the algorithms used in elliptic curve cryptography, and to develop new algorithms to be deployed within these protocols. In this thesis we design and develop d-MUL, a multidimensional scalar multiplication algorithm which is uniform in its operations and generalizes the well known 1-dimensional Montgomery ladder addition chain and the 2-dimensional addition chain due to Dan J. Bernstein. We analyze the construction and derive many optimizations, implement the algorithm in software, and prove many theoretical and practical results. In the final chapter of the thesis we analyze the operations carried out in the construction of an isogeny from a given subgroup, as performed in SIDH. We detail how to efficiently make use of parallel processing when constructing this isogeny.
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Ozturk, Erdinc. "Low Power Elliptic Curve Cryptography." Digital WPI, 2005. https://digitalcommons.wpi.edu/etd-theses/691.
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This M.S. thesis introduces new modulus scaling techniques for transforming a class of primes into special forms which enable efficient arithmetic. The scaling technique may be used to improve multiplication and inversion in finite fields. We present an efficient inversion algorithm that utilizes the structure of a scaled modulus. Our inversion algorithm exhibits superior performance to the Euclidean algorithm and lends itself to efficient hardware implementation due to its simplicity. Using the scaled modulus technique and our specialized inversion algorithm we develop an elliptic curve processor architecture. The resulting architecture successfully utilizes redundant representation of elements in GF(p) and provides a low-power, high speed, and small footprint specialized elliptic curve implementation. We also introduce a unified Montgomery multiplier architecture working on the extension fields GF(p), GF(2) and GF(3). With the increasing research activity for identity based encryption schemes, there has been an increasing need for arithmetic operations in field GF(3). Since we based our research on low-power and small footprint applications, we designed a unified architecture rather than having a seperate hardware for GF{3}. To the best of our knowledge, this is the first time a unified architecture was built working on three different extension fields.
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Staffas, Rebecca. "Post-quantum Lattice-based Cryptography." Thesis, KTH, Matematik (Avd.), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188022.
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In a future full of quantum computers, new foundations for asymmetric cryptography are needed. We study the theoretical foundations for lattice-based cryptography as well as the current state on cryptographic attacks against them. We then turn our attention to signature systems and especially the system BLISS from 2013. We give an overview of the BLISS protocol and its security, and analyse its object sizes and resistance to attacks. We find that BLISS does not provide as high security as initially claimed. We then propose modifications to BLISS in order to allow for freer choices of dimension and modulus. We also propose novel implementation tricks and accommodate for these in the protocol. We call our modified system REBLISS and propose parameter sets. Our performance measurements suggest that this is a good alternative to BLISS.Med framtiden full av kvantdatorer behövs nya fundament för asymmetrisk kryptografi. Vi undersöker den teoretiska basen för gitterbaserad kryptografi och kartlägger även tillhörande kryptografiska attacker. Vi riktar sedan in oss mot signaturalgoritmer och speciellt protokollet BLISS från 2013. Vi presenterar en översikt över protokollet och dess säkerhet. Vi analyserar också storlekarna på tillhörande objekt och motståndskraften mot attacker. Vi finner att BLISS inte kan uppvisa så hög säkerhet som tidigare har påståtts. Vi föreslår sedan förändringar i BLISS för att tillåta ett friare val av dimension och primtal. Vi föreslår innovativa trick för en snabbare implementation och gör plats för dessa i algoritmerna. Vår modifierade algoritm får namnet REBLISS och vi föreslår nya uppsättningar av systemparametrar. Våra prestandamätningar visar att detta är ett bra alternativ till BLISS.
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Rudenko. "THE MAIN FEATURES OF CRYPTOGRAPHY." Thesis, Київ 2018, 2018. http://er.nau.edu.ua/handle/NAU/33893.
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