Dissertationen zum Thema „Cryptographie à clé secrète“
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Frixons, Paul. „Cryptographie à clé secrète et attaquant quantique dans le monde des télécommunications“. Electronic Thesis or Diss., Sorbonne université, 2022. http://www.theses.fr/2022SORUS339.
Der volle Inhalt der QuelleFor modern cryptography, the security of a system is defined as the sum of the resources required to break it. With the advent of efficient quantum computers and the new algorithmic possibilities that this opens, this amount of resource is destined to change.In this thesis, we take a step towards a better understanding of this quantum threat. After an introduction to quantum computation and cryptography, we show quantum attacks against the Legendre PRF in the setting without superposition queries and reduced quantum memory. Afterwards, we present a general way to transpose boomerang attacks into quantum attacks as well as some applications. We continue on a doubling method for block ciphers inspired by the Encrypt-Mix-Encrypt scheme and prove its security. We end by building a quantum version of the 3G/4G/5G UMTS-AKA authentication protocol before showing the security as well as the underlying primitives Milenage and TUAK
Levieil, Eric. „Contributions à l'étude cryptographique de protocoles et de primitives à clé secrète“. Paris 7, 2008. http://www.theses.fr/2008PA077077.
Der volle Inhalt der QuelleThis thesis presents four subjects in cryptography. The first one is an improvement of the BKW algorithm, which is used to solve the Learning from Parity with Noise problem. The second one is the extension to arbitrary Abelian groups of cryptanalysis methods invented in characteristic 2. We apply the results to create a secure block cipher for sequences of decimal ciphers. Then we solve the problem of multiparty computation in two particular cases; the first one could be used when the bandwith is limited, and the second one deals with rational players. We propose an efficient protocol for solving the problem of rational secret sharing for two players
Minier, Marine. „Preuves d'analyse et de sécurité en cryptologie à clé secrète“. Limoges, 2002. http://aurore.unilim.fr/theses/nxfile/default/76ab2f2d-335d-4a02-a7cb-07acf674388e/blobholder:0/2002LIMO0055.pdf.
Der volle Inhalt der QuelleThis thesis concerns, essentially, two principal aspects of symmetric cryptology
Videau, Marion. „Critères de sécurité des algorithmes de chiffrement à clé secrète“. Phd thesis, Université Pierre et Marie Curie - Paris VI, 2005. http://tel.archives-ouvertes.fr/tel-00011927.
Der volle Inhalt der Quellealgorithmes de chiffrement à clé secrète et ont été menés suivant deux
axes. Le premier concerne la sécurité des chiffrements symétriques
itératifs par blocs contre les attaques par distingueur sur le dernier
tour. Les résultats portent en particulier sur la généralisation d'une
attaque différentielle d'ordre supérieur menée sur l'algorithme
MISTY1. L'origine de cette attaque ainsi que de sa généralisation a pu
être expliquée grâce aux propriétés du spectre de Walsh des fonctions
de non-linéarité maximale utilisées. Ainsi il a été possible
d'élaborer une attaque générique sur tous les chiffrements de Feistel
à cinq tours utilisant des fonctions dont le spectre de Walsh est
divisible par une grande puissance de 2 car cette propriété permet
d'obtenir une borne supérieure sur le degré de la composition de
telles fonctions, nettement plus faible que la borne
triviale. Cette attaque suggère ainsi un nouveau critère de sécurité
qui porte sur la divisibilité du spectre de Walsh des fonctions de
tour utilisées dans les chiffrements itératifs par blocs. La deuxième
partie de la thèse porte sur l'étude des fonctions booléennes
symétriques, et en particulier sur l'existence éventuelle de
propriétés cryptographiques. À partir d'une propriété structurelle de
périodicité d'une représentation d'une fonction booléenne symétrique,
les propriétés de degré algébrique, d'équilibre, de résilience, de
critère de propagation et de non-linéarité ont été étudiées, ce qui a
permis d'améliorer les résultats existants. Par ailleurs, le calcul
explicite du spectre de Walsh des fonctions booléennes symétriques de
degré 2 et 3 a été réalisé, ainsi que la détermination de toutes les
fonctions symétriques équilibrées de degré inférieur ou égal à 7,
indépendamment du nombre de variables.
Labbe, Anna. „Conception de crypto-mémoires basées sur les algorithmes à clé secrète (DES et AES) et sur l'architecture de mémoires SRAM“. Aix-Marseille 1, 2003. http://www.theses.fr/2003AIX11046.
Der volle Inhalt der QuelleHandschuh, Helena. „Cryptanalyse et sécurité des algorithmes a clé secrète“. Paris, ENST, 1999. http://www.theses.fr/1999ENST0037.
Der volle Inhalt der QuelleCoron, Jean-Sébastien. „Cryptanalyses et preuves de sécurité de schémas à clé publique“. Palaiseau, Ecole polytechnique, 2001. http://www.theses.fr/2001EPXX0008.
Der volle Inhalt der QuelleDelerablée, Cécile. „Cryptographie dans les groupes“. Paris 7, 2009. http://www.theses.fr/2009PA077111.
Der volle Inhalt der QuelleSince the apparition of public-key cryptography, many protocols have been introduced in multi-user contexts. Those protocols involve groups of users, managed (or not) by one or several authorities. In this thesis, we focus on cryptography in groups, and study the two major primitives, which are (group) signature and (broadcast) encryption. In a first part, we present the mathematical tools and some computational problems which are usefull later, as well as the concepts of public-key signature and encryption. The second part focus on group signatures. We propose a new scheme, and a new primitive (illustrated by a new scheme), more general. Finally, we study encryption schemes in groups, usually called broadcast encryption schemes. We present three contributions about this notion. Thus we improve the efficiency of some existing schemes, and propose some new primitives, bringing new functionalities, with respect to efficiency constraints
Chevallier-Mames, Benoit. „Cryptographie à clé publique : constructions et preuves de sécurité“. Paris 7, 2006. http://www.theses.fr/2006PA077008.
Der volle Inhalt der QuelleThe public key cryptography concept, proposed by Whitfield Diffie et Martin Hellman, changed the cryptology world. After the description of first heuristically secure schemes, thé formalization of models and security notions has allowed the emergency of provable security. After some reminds about cryptography and security reduction, we propose new signature and encryption schemes, with some advantages over the existing Systems. Indeed, we propose two new signature schemes with a security proof in the random oracle model, and expose a new signature scheme which features a provable security in the standard model. All of these schemes feature both tight security and the possible use of coupons. Next, we describe a new encryption scheme, based on a new cryptographical problem. We also give another look to the universel paddings, and show how to obtain tight security for identity-based encryption schemes. In the last part of this thesis, we deal with the physical security of cryptographical software. We propose notably new efficient countermeasures against simple side-channel attacks (SPA) and differentiel side-channel attacks (DPA)
Gérard, Benoît. „Cryptanalyses statistiques des algorithmes de chiffrement à clef secrète“. Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00577229.
Der volle Inhalt der QuelleBultel, Xavier. „Mécanismes de délégation pour les primitives de cryptographie à clé publique“. Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC100.
Der volle Inhalt der QuelleJaulmes, Eliane. „Analyse de sécurité des schémas cryptographiques“. Palaiseau, Ecole polytechnique, 2003. http://www.theses.fr/2003EPXX0016.
Der volle Inhalt der QuelleIonica, Sorina. „Algorithmique des couplages et cryptographie“. Versailles-St Quentin en Yvelines, 2010. http://www.theses.fr/2010VERS0013.
Der volle Inhalt der QuellePairings were used in cryptography for the first time to transform the elliptic curve discrete logarithm problem into a discrete logarithm problem in the finite field. Later on, it was shown that pairings could be used to build cryptosystems. In this thesis we propose the use of pairings in the study of isogeny volcanoes and the use of isogenies for efficient implementation of pairings. Isogeny volcanoes are graphs whose vertices are elliptic curves and whose edges are l-isogenies. Algorithms allowing to travel on these graphs were developed by Kohel in his thesis (1996) and later on, by Fouquet and Morain (2001). However, up to now, no method was known, to predict, before taking a step on the volcano, the direction of this step. Given a point P of order l on the elliptic curve, we develop a method to decide whether the subgroup generated by P is the kernel of a horizontal isogeny, a descending or an ascending one. Our method, which consists mainly in the computation of a small number of pairings, is very efficient and gives, in most cases, simple algorithms, allowing to navigate on the volcano. The second part of this thesis focuses on the implementation of pairings on elliptic curves in Edwards form. Using an isogeny of degree 4 from the Edwards curve to an elliptic curve in Weierstrass form, we gave the first efficient implementation of Miller's algorithm on Edwards curves. Our method has performances similar to implementations of the same algorithm on the Weierstrass form of an elliptic curve
Canteaut, Anne. „Analyse et conception de chiffrements à clef secrète“. Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2006. http://tel.archives-ouvertes.fr/tel-00095980.
Der volle Inhalt der Quelletrès largement répandus car ils sont les seuls à atteindre les débits
de chiffrement requis par la plupart des applications et à permettre
une mise en oeuvre sous forme d'un circuit de taille
raisonnable. Dans ce contexte, les travaux présentés dans ce mémoire
ont pour objet la conception de nouvelles attaques sur les algorithmes
symétriques et leur formalisation afin de mettre en évidence les
propriétés structurelles qui les rendent opérationnelles. Cette
approche conduit à de nouveaux critères de conception et à la
construction d'objets qui permettent de leur résister de manière
certaine. Cette étude s'articule notamment autour de l'idée que, pour
résister de manière sûre aux cryptanalyses connues et pour atteindre
de bonnes performances, un chiffrement symétrique doit utiliser des
objets aux propriétés exceptionnelles, dont la structure algébrique
forte ouvre paradoxalement une brèche exploitable dans une nouvelle
attaque. Ce principe est ici décliné pour les deux familles
d'algorithmes symétriques, les chiffrements à flot et les chiffrements
par blocs.
Fuchsbauer, Georg. „Cryptographie dans les groupes“. Paris 7, 2010. http://www.theses.fr/2010PA077121.
Der volle Inhalt der QuelleWe advocate modular design of cryptographic primitives and give building blocks to achieve this efficiently. This thesis introduces two new primitives called automorphic signatures and commuting signatures and verifiable encryption, and illustrates their usefulness by giving numerous applications. Automorphic signatures are digital signatures whose verification keys lie in the message space; messages and signatures consist of elements of a bilinear group, and verification is done by evaluating a set of pairing-product equations. These signatures, of which we provide practical instantiations under appropriate assumptions, make a perfect counterpart to the efficient proof System by Groth and Sahai. Together, they enables us to give thé first efficient instantiations of round-optimal blind signatures and anonymous proxy signatures, as well as a new fully secure group-signature scheme. Commuting signatures extend verifiably encrypted signatures as follows: in addition to encrypting a signature so that the validity of the plaintext can be verified, the signer can do so even if the message to sign is encrypted (and unknown); thus signing and encrypting commute. Our instantiation combines automorphic signatures with Groth-Sahai proofs, of which we show a series of useful properties. As an application, we give the first instantiation of delegatable anonymous credentials with non-interactive (and thus concurrently secure) issuing and delegation. Our scheme is also significantly more efficient than previous ones. All our constructions are proved secure in the standard model under non-interactive assumptions
Izabachène, Malika. „L' anonymat dans les protocoles cryptographiques“. Paris 7, 2009. http://www.theses.fr/2009PA077182.
Der volle Inhalt der QuelleAnonymity arises in several situations : the technological revolution of the Internet has strengthened its prominency, especially when networking websites store private information on users. The goal of this thesis is to review and elaborate anonymous mechanisms to establish an appropriate trade-off between the information leakage, efficiency and security. Firstly, we present a state-of-the-art of the techniques used for the design of anonymous protocols. Then, we focus on identity-based encryption, a primitive that simplifies certificates' management. We give a new definition of anonymity in this setting. We also consider anonymous schemes with revocable anonymity and consider subliminal channel attacks. We propose an efficient scheme and prove its security in a model that we intro-duce. Finally, we address anonymity in Passord-Based Key-Exchange (PAKE) protocols, where a user wants to establish a common session key with a server. We consider security of PAKE protocols in the two-or three-player setting, enhancing adversarial behaviors while keeping the user's identity private, which precisely consists in an application of our new definition of anonymity
Lefranc, David. „Authentification asymétrique à bas coût et vérification assistée par ordinateur“. Caen, 2005. http://www.theses.fr/2005CAEN2024.
Der volle Inhalt der QuelleAmblard, Zoé. „Cryptographie quantique et applications spatiales“. Thesis, Limoges, 2016. http://www.theses.fr/2016LIMO0113.
Der volle Inhalt der QuelleThis thesis in collaboration with Thales Alenia Space studies quantum cryptographic protocols for n parties in dimension d. We first analyze the family of Bell inequalities called homogeneous Bell inequalities introduces by François Arnault in [1] and we construct several theoretical tools for a better understanding of these inequalities. With these tools, we show how to implement the measurements required to test these inequalities by using optical devices calleds multiport beamsplitters and described by Zukowski et al. in [2]. We use these devices to construct new cryptographic protocols in dimension d called hdDEB which we describe in [3]. Then, we study advantages and drawbacks of the use of quantum cryptography to protect satellite links in a noisy environment. We consider several scenarios with LEO satellites and, for each of them, we conclude about the interest of using Quantum Key Distribution protocols
Vial, prado Francisco. „Contributions to design and analysis of Fully Homomorphic Encryption schemes“. Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLV107/document.
Der volle Inhalt der QuelleFully Homomorphic Encryption schemes allow public processing of encrypted data. Since the groundbreaking discovery of the first FHE scheme in 2009 by Craig Gentry, an impressive amount of research has been conducted to improve efficiency, achieve new levels of security, and describe real applications and connections to other areas of cryptography. In this Dissertation, we first give a detailed account on research these past years. Our contributions include a key-recovery attack on the ideal lattices FHE scheme and a new conception of hierarchic encryption, avoiding at some extent betrayal between users while maintaining the flexibility of FHE. We also describe some implementations. This research was done in the Laboratoire de Mathématiques de Versailles, under supervision of Prof. Louis Goubin
Perret, Ludovic. „Étude d'outils algébriques et combinatoires pour la cryptographie à clef publique“. Université de Marne-la-Vallée, 2005. http://www.theses.fr/2005MARN0250.
Der volle Inhalt der QuellePlantard, Thomas. „Arithmétique modulaire pour la cryptographie“. Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2005. http://tel.archives-ouvertes.fr/tel-00112121.
Der volle Inhalt der QuelleCette thèse se divise en quatre parties.
La première partie est une introduction à la cryptographie à clé publique. Cette thèse ayant pour objectif d'améliorer les calculs modulaires, nous commençons par présenter dans quels contextes la cryptographie nécessite une arithmétique modulaire efficace. Les principaux protocoles (de ECC ou RSA) ont des besoins en arithmétiques modulaires.
La deuxième partie est un état de l'art sur les différents algorithmes existants pour effectuer une arithmétique modulaire complète : addition, inversion et multiplication. Nous y répertorions aussi les différentes classes de moduli existantes. Celle ci sont utilisées en particulier pour l'implantation des protocoles d'ECC.
Dans la troisième partie, nous proposons un nouveau système de représentation. Nous y exposons les outils algorithmiques pour effectuer une arithmétique optimisée pour une classe de moduli, ainsi que ceux nécessaires à une arithmétique modulaire pour tous les autres moduli.
Dans la dernière partie, nous regroupons plusieurs résultats concernant l'arithmétique modulaire pour de "petits" moduli. Nous proposons un algorithme de multiplication modulaire pour modulo variable, une amélioration des changements de base pour le RNS ainsi qu'une algorithmique basée sur une table mémoire.
Biswas, Bhaskar. „Implementational aspects of code-based cryptography“. Palaiseau, Ecole polytechnique, 2010. http://pastel.archives-ouvertes.fr/docs/00/52/30/07/PDF/thesis.pdf.
Der volle Inhalt der QuelleSur la plateforme de thèses en ligne Tel on trouve le résumé suivant : We present the implementation details of Hybrid McEliece Encryption Scheme (HyMES), a improved version of the original McEliece scheme developed with Nicolas Sendrier. We present a modified version of the original scheme (which we call hybrid). It has two modifications, the first increases the information rate by putting some data in the error pattern. The second reduces the public key size by making use of a generator matrix in systematic form. We will show that the same security reduction as for the original system holds. We then describe the key generation, the encryption and the decryption algorithms and their implementation. Finally we will give some computation time for various parameters, compare them with the best known attacks, and discuss the best trade-offs. The idea of McEliece scheme is to hide the structure of the code by means of a transformation of the generator matrix. The transformed generator matrix becomes the public key and the secret key is the structure of the Goppa code together with the transformation parameters. The security relies on the fact that the decoding problem for general linear code is NP-complete. While the RSA public-key cryptosystem has become most widely used, McEliece cryptosystem has not been quite as successful. Partly because of the large public key, which impose less problem with the advance in hardware today. Our aim has been to implement a fairly fast and concise software implementation that may be used as a reference benchmark. We present the algorithmic details of our implementation as well. That is to specify the algorithms we use and the way we use them. The whole project is freely available at http://www-roc. Inria. Fr/secret/CBCrypto/index. Php?pg=hymes
Koussa, Eliane. „Analysis and design of post-quantum cryptographic algorithms : PKP-based signature scheme and ultra-short multivariate signatures“. Electronic Thesis or Diss., université Paris-Saclay, 2020. http://www.theses.fr/2020UPASG027.
Der volle Inhalt der QuelleThe construction of large quantum computers would endanger most of the public-key cryptographic schemes in use today. Therefore, there is currently a large research effort to develop new post-quantum secure schemes. In particular, we are interested in post-quantum cryptographic schemes whose security relies on the hardness of solving some mathematical problems such as thePermuted Kernel Problem (PKP) and the Hidden Field Equations (HFE). This work investigates first the complexity of PKP. And after a thorough analysis of the State-of-theart attacks of PKP, we have been able to update some results that were not accurate, and to provide an explicit complexity formula which allows us to identify hard instances and secure sets of parameters of this problem. PKP was used in 1989 to develop the first Zero-Knowledge Identification Scheme (ZK-IDS) that has an efficient implementation on low-cost smart cards. In a second step, we optimize the PKP-based ZK-IDS and then we introduce PKP-DSS:a Digital Signature Scheme based on PKP. We construct PKP-DSS from the ZK-IDS based on PKP by using the traditional Fiat-Shamir (FS) transform that converts Identification schemes into Signature schemes. We develop a constant time implementation of PKP-DSS. It appears that our scheme is very competitive with other post-quantum FS signature schemes. Since that PKP is an NP-Complete problem and since there are no known quantum attacks for solving PKP significantly better than classical attacks, we believe that our scheme is post-quantum secure. On the other hand, we study multivariate public-key signature schemes that provide“ultra”-short signatures. We first analyze the most known attacks against multivariate signatures, and then define the minimal parameters that allow ultra-short signature. We also design some specific newmodes of operations in order to avoid particular attacks.Second, we provide various explicit examples of ultra-short signature schemes that are based on variants of HFE. We present parameters for several level of classical security: 80, 90, 100 bits in addition to 128, 192, and 256 bits; foreach level, we propose different choices of finite fields
Laguillaumie, Fabien. „Signatures à vérification contrôlée basées sur des applications bilinéaires : conception et analyse de sécurité“. Caen, 2005. http://www.theses.fr/2005CAEN2008.
Der volle Inhalt der QuelleFossier, Simon. „Mise en oeuvre et évaluation de dispositifs de cryptographie quantique à longueur d'onde télécom“. Paris 11, 2009. http://www.theses.fr/2009PA112188.
Der volle Inhalt der QuelleQuantum Key Distribution (QKD) is defined as the distribution of a common secret key between two distant parties, the unconditionnal security of this distribution being ensured by the laws of quantum physics and informations theroy. We have designed a complete QKD demonstrator, based on protocol in which information is encoded on continous variables of light, namely the quadratures of the electromagnetic field. The system is entirely composed of standard components from the telecommunication industry, allowing Alice, to generate the required coherent states of light and to modulate them, and Bob to measure these states using a pulsed, shot-noise limited homodyne detector. Moreover, we have developed a set of software which manages the entire key distribution process ; on the one hand, the quantum transmission and the feed-back controls required for a correct stability ; on the other hand, the extraction of secret keys from the data shared after the transmission. The system has been integrated in rack cases, so as to perform a true-scale demonstration within a OKD network, which was deployed on standard fibers installed in Vienna (Austria). During this demonstration, our systems has operated continuously for 57 hours, with an average key rate of 8 kbit/s. Finally, we have explored various possibilities of improvement for the system, through a new QKD protocol and the use of optical amplifiers
Chaulet, Julia. „Etude de cryptosystèmes à clé publique basés sur les codes MDPC quasi-cycliques“. Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066064.pdf.
Der volle Inhalt der QuelleConsidering the McEliece cryptosystem using quasi-cylcic MDPC (Moderate Density Parity Check matrix) codes allows us to build a post-quantum encryption scheme with nice features. Namely, it has reasonable key sizes and both encryption and decryption are performed using binary operations. Thus, this scheme seems to be a good candidate for embedded and lightweight implementations. In this case, any information obtained through side channels can lead to an attack. In the McEliece cryptosystem, the decryption process essentially consists in decoding. As we consider the use of an iterative and probabilistic algorithm, the number of iterations needed to decode depends on the instance considered and some of it may fail to be decoded. These behaviors are not suitable because they may be used to extract information about the secrets. One countermeasure could be to bound the number of encryptions using the same key. Another solution could be to employ a constant time decoder with a negligible decoding failure probability, that is to say which is about the expected security level of the cryptosystem. The main goal of this thesis is to present new methods to analyse decoder behavior in a cryptographic context.Second, we explain why a McEliece encryption scheme based on polar code does not ensure the expected level of security. To do so, we apply new techniques to resolve the code equivalence problem. This allows us to highlight several common properties shared by Reed-Muller codes and polar codes. We introduce a new family of codes, named decreasing monomial codes, containing both Reed-Muller and polar codes. These results are also of independent interest for coding theory
Chevalier, Céline. „Etude de protocoles cryptographiques à base de mots de passe“. Paris 7, 2009. http://www.theses.fr/2009PA077183.
Der volle Inhalt der QuelleA fundamental property fulfilled by cryptography is the creation of secure communication channels, which guarantee authentication, integrity and confidentiality of the data transfered. Authentication, which allows several users to be convinced of the identities of their interlocutors, is generally nothing but a preliminary step to the proper communication, and is often coupled with the generation of a secret session key, which then enables the encryption of the following messages. We focus here on a particular type of authentication, based on passwords. We first recall the different security frameworks, as well as the existing protocols, particularly insisting on the new framework of universal composability. We show next that two variants of existing protocols remain secure in this context, under strong security hypothesis, and in the random oracle and ideal cipher models. In a third step, we extend the smooth hash functions to obtain a protocol with an equivalent level of security, but this time in the standard model. This protocol does not output a bitstring anymore, but a random group element. We then present a randomness ex-tractor from such a group element, to obtain a random bitstring. Finally, we show how to extend the use of passwords to public key primitives, by defining the new notion of distributed cryptography from passwords
Debraize, Blandine. „Méthodes de cryptanalyse pour les schémas de chiffrement symétrique“. Versailles-St Quentin en Yvelines, 2008. http://www.theses.fr/2008VERS0044.
Der volle Inhalt der QuelleSymmetric ciphers are designed to protect the confidentiality of data. To study the security of these ciphers, we will adopt two points of view in this thesis, that we combine in some cases : algebraic methods and guess-and-determine attacks. In a first part, we recall some useful notions about symmetric ciphers and Gröbner bases. In a second part we propose and analyse algorithms allowing to perform practical simulations of algebraic attacks on a PC. The third part is dedicated to algebraic cryptanalysis of block ciphers. We use the practical algorithms of Part 2 on toy ciphers to show that the use of several plaintextciphertext pairs can lead to significant improvements in the complexity of algebraic attacks. We also propose a theoretical contribution about the algebraic immunity of certain types of S-boxes. Finally in a fourth part, we analyse the security of some stream ciphers. We first test and develop a previous analysis on the standardized Snow 2. 0. To reach this goal, we study the algebraic immunity of the modular addition. Secondly we go further into the knowledge about decimation operators, by proposing new cryptanalyses on the Self- Shrinking Generator, the Bit-Search Generator and the optimal components like the ABSG
Tran, Christophe. „Formules d'addition sur les jacobiennes de courbes hyperelliptiques : application à la cryptographie“. Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S153/document.
Der volle Inhalt der QuelleIn this thesis, I study two different aspects of elliptic and hyperelliptic curves based cryptography.In the first part, I confront two methods of pairings computation, whose original feature is that they are not based the traditional Miller algorithm. Therefore, in [42], K. Stange computed Tate pairings on elliptic curves using a new tool, the elliptic nets. Y. Uchida and S. Uchiyama generalized these objects to hyperelliptic case ([47]), but they gave an algorithm for pairing computation only for the genus 2 case. My first work in this thesis was to give this algorithm for the general case. Meanwhile, D. Lubicz and D. Robert gave in [28] an other pairing computation method, based on theta functions. The second result of my thesis is the reunification of these two methods : I show that the recurrence equation which is the basis of nets theory is a consequence of the addition law of theta functions used in the Lubicz and Robert’s algorithm. In the second part, I study the index calculus algorithm attacking the elliptic and hyperelliptic curve discrete logarithm problem. In the elliptic case, one of the main steps of this attack requires the Semaev polynomials. I reconstruct these polynomials using Weierstrass sigma function, with the purpose of giving their first hyperelliptic generalization
Chaulet, Julia. „Etude de cryptosystèmes à clé publique basés sur les codes MDPC quasi-cycliques“. Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066064/document.
Der volle Inhalt der QuelleConsidering the McEliece cryptosystem using quasi-cylcic MDPC (Moderate Density Parity Check matrix) codes allows us to build a post-quantum encryption scheme with nice features. Namely, it has reasonable key sizes and both encryption and decryption are performed using binary operations. Thus, this scheme seems to be a good candidate for embedded and lightweight implementations. In this case, any information obtained through side channels can lead to an attack. In the McEliece cryptosystem, the decryption process essentially consists in decoding. As we consider the use of an iterative and probabilistic algorithm, the number of iterations needed to decode depends on the instance considered and some of it may fail to be decoded. These behaviors are not suitable because they may be used to extract information about the secrets. One countermeasure could be to bound the number of encryptions using the same key. Another solution could be to employ a constant time decoder with a negligible decoding failure probability, that is to say which is about the expected security level of the cryptosystem. The main goal of this thesis is to present new methods to analyse decoder behavior in a cryptographic context.Second, we explain why a McEliece encryption scheme based on polar code does not ensure the expected level of security. To do so, we apply new techniques to resolve the code equivalence problem. This allows us to highlight several common properties shared by Reed-Muller codes and polar codes. We introduce a new family of codes, named decreasing monomial codes, containing both Reed-Muller and polar codes. These results are also of independent interest for coding theory
Traoré, Karim Jacques. „Monnaie électronique“. Caen, 2001. http://www.theses.fr/2001CAEN2063.
Der volle Inhalt der QuelleMazloum, Taghrid. „Analyse et modélisation du canal radio pour la génération de clés secrètes“. Electronic Thesis or Diss., Paris, ENST, 2016. http://www.theses.fr/2016ENST0012.
Der volle Inhalt der QuelleNowadays, the security of ubiquitous wireless communications becomes more and more a crucial requirement. Even though data is widely protected via symmetric ciphering keys, a well-known difficulty is the generation and distribution of such keys. In the recent years therefore, a set of works have addressed the exploitation of inherent characteristics of the fading propagation channel for security. In particular, secret keys could be generated from the wireless channel, considered as a shared source of randomness, available merely to a pair of communicating entities. ln the present dissertation, we are interested in the approach of secret key generation (SKG) from wireless channels, especially in relating the radio channel properties to the generated keys quality. We first develop a stochastic channel model, focusing on the security with respect to the eavesdropper side, which shows a residual channel memory weil beyond a few wavelengths distance (spatially nonstationary scenarios). Then, we analyze the channel degrees of freedom (DoF) and their impact on the SKG performance in different channel conditions, especially by considering more realistic channels in both outdoor and indoor environments (respectively through simulated ray tracing data and through measurements). The results show that, even for moderately wide band (such as standardized in IEEE 802.11), the sole frequency DOF or its association with the spatial DOF is often enough for generating long keys, provided an efficient quantization method of the complex channel coefficients is used
Trinh, Viet Cuong. „Sécurité et efficacité des schémas de diffusion de données chiffrés“. Paris 8, 2013. http://octaviana.fr/document/181103516#?c=0&m=0&s=0&cv=0.
Der volle Inhalt der QuelleIn this thesis, we work on the domain of broadcast encryption and tracing traitors. Our contributions can be divided into three parts. We first recall the three tracing models: non-black-box tracing model, single-key black box tracing model, and general black box tracing model. While the last model is the strongest model, the two former models also cover many practical scenarios. We propose an optimal public key traitor tracing scheme in the two first models. We then consider two new advanced attacks (pirate evolution attack and Pirates 2. 0) which were proposed to point out some weaknesses of the schemes in the subset-cover framework, or more generally of combinatorial schemes. Since these schemes have been widely implemented in practice, it is necessary to find some counter-measures to these two types of attacks. In the second contribution, we build two schemes which are relatively efficient and which resist well these two types of attacks. In the last contribution, we study a generalized model for broadcast encryption which we call multi-channel broadcast encryption. In this context, the broadcastor can encrypt several messages to several target sets “at the same time”. This covers many scenarios in practice such as in pay-TV systems in which providers have to send various contents to different groups of users. We propose an efficient scheme with constant size ciphertext
Castagnos, Guilhem. „Quelques schémas de cryptographie asymétrique probabiliste“. Limoges, 2006. http://aurore.unilim.fr/theses/nxfile/default/958eca82-7e39-4d46-a25a-734a4af7ba9f/blobholder:0/2006LIMO0025.pdf.
Der volle Inhalt der QuelleIn this thesis, we build, in a generic way, several families of probabilistic trapdoor functions. First, a family of homomorphic trapdoor functions which generalize, among others, the Paillier cryptosystem, and then two others families of trapdoor functions, built from deterministic trapdoor functions. We consider then several finite groups in order to use these trapdoor functions: quotients of Z, elliptic curves over Z/nZ (with n odd integer), for which we give a complete set of addition formulæ, and another finite group, not widely used in cryptography, the group of norm 1 elements of a quadratic field modulo n. We describe several cryptosystems, using the corresponding trapdoor functions in these groups, together with an analysis of their security and their complexity. With quotients of Z and elliptic curves, we get some cryptosystems yet described in the past few years. Using quadratic fields quotients, we propose several new efficient probabilistic schemes
Dubois, Vivien. „Cryptanalyse de Schémas Multivariés“. Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00811529.
Der volle Inhalt der QuelleZapalowicz, Jean-Christophe. „Sécurité des générateurs pseudo-aléatoires et des implémentations de schémas de signature à clé publique“. Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S103/document.
Der volle Inhalt der QuelleIn this thesis, we are interested in the security of pseudorandom number generators and of implementations of signature schemes. Regarding the signature schemes, we propose, in the case of a widespread implementation of RSA, various fault attacks which apply to any padding function. In addition we present a proven secure infective countermeasure to protect the RSA--PSS scheme against some non-random faults. Furthermore we study the ECDSA scheme coupled with the GLV/GLS speed-up techniques. Depending on the implementations, we prove either the good distribution of the used nonce, or that it has a bias, thereby enabling an attack. Finally we develop a tool for automatically finding fault attacks given an implementation and a fault policy, which is successfully applied to some RSA and ECDSA implementations. Regarding pseudorandom number generators, we study the nonlinear ones and improve some attacks by reducing the information available to the adversary. We also are interested in the security of the Micali-Schnorr generator through various attacks and a statistical study of its security assumption. Finally we propose a cryptanalysis of any public-key scheme based on the factorization or the discrete logarithm when the secret key is generated using a linear generator
Lodewyck, Jérôme. „Dispositif de distribution quantique de clé avec des états cohérents à longueur d'onde télécom“. Paris 11, 2006. https://pastel.archives-ouvertes.fr/tel-00130680v2.
Der volle Inhalt der QuelleBecker, Anja. „The representation technique : application to hard problems in cryptography“. Versailles-St Quentin en Yvelines, 2012. http://www.theses.fr/2012VERS0025.
Der volle Inhalt der QuelleThe focus of this thesis is an algorithmic technique to solve the random, hard subset-sum problem and the distance-decoding problem in a random linear code. The subset-sum problem provides an alternative to other hard problems used in cryptography (e. G. , factoring or the discrete logarithm problem). Its description is simple and the computation of sums of integers is an easy task. Furthermore, no polynomial-time quantum algorithm for solving general knapsacks is known. One can construct one-way functions, pseudo-random generators and private-key encryption schemes from the hardness assumption of the average-case problem. Also some cryptosystems based on lattice problems are provably as secure as the difficulty of the average-case subset-sum problem. Decoding problems can be seen as a vectorial subset-sum problem. Of particular interest is the bounded-distance-decoding problem in a random code. It permits public-key encryption, digital signatures, identification schemes and hash-functions. We present different generic algorithmic tools to solve the above problems. By use of our extended representation technique, we obtain an algorithm of exponentially lower asymptotic running time than previous approaches for the hardest case of a random subset-sum problem. We show that the technique can be applied to the domain of code-based cryptography. This results in improved information-set decoding that solves the distance-decoding problem for random linear codes. The new algorithm is asymptotically faster by an exponential factor
Sanders, Olivier. „Conception et optimisation de mécanismes cryptographique anonymes“. Thesis, Paris, Ecole normale supérieure, 2015. http://www.theses.fr/2015ENSU0027/document.
Der volle Inhalt der QuelleNew technologies offer greater convenience for end-users but usually at the cost of a loss in terms of privacy, which is often underestimated by the latter. For example, knowledge by a third party of the information related to a transaction is far from insignificant since it may reveal intimate details such as whereabouts, religious beliefs or health status.In this thesis, we are interested in cryptographic technics allowing to reconcile both security requirements and user’s privacy. In a first part, we will focus on two specific cases: anonymous payment and anonymous authentication. We propose new constructions, improving the efficiency of state-of-the-art solutions, which make all the features of these primitives more accessible for practical applications. We provide a detailed security analysis for each scheme, proving that they achieve the expected properties under reasonable assumptions.However, to fulfill the strong technical constraints of these use cases, it may be necessary to optimize these constructions which are usually rather complex. To this end, we propose in a second part, new solutions to improve the efficiency of most common operations and algorithms. Each of these contributions is not restricted to anonymous systems and thus may be of independent interest
Le, Quoc Cuong. „Autour des réseaux quantiques et des modèles de relais pour la clé quantique“. Phd thesis, Télécom ParisTech, 2009. http://pastel.archives-ouvertes.fr/pastel-00006239.
Der volle Inhalt der QuelleLe, Quoc Cuong. „Autour des réseaux quantiques et des modèles de relais pour la clé quantique“. Phd thesis, Paris, ENST, 2009. https://pastel.hal.science/pastel-00006239.
Der volle Inhalt der QuelleIQuantum Key Distribution (QKD) is a technology that ensures, in theory, the inviolability of the transmitted key. However, some practical implementation problems remain open, especially on increasing the range of QKD's application. The objective of this thesis is to answer twocorrelated questions: (1) how to build large QKD networks, (2) how to secure QKD key relays. We have proposed, at the first stage, a model to ensure the security of key transmission in a large QKD network by using a stochastic routing. The effectiveness of this method is demonstrated by using percolation theory. In a second stage, we explored the safety of QKD relays and arrive to propose four new models to expand the range of QKD
Furon, Teddy. „Application du tatouage numérique à la protection de copie“. Paris, ENST, 2002. http://www.theses.fr/2002ENST0014.
Der volle Inhalt der QuelleWe consider in this thesis the use of digital watermarking in the copy protection framework for consumer electronics devices. We describe first the copy protection issue. Then, we build the global system with elementary securityparts such as encryption and digital signature. Yet, contrary to common approaches, the role of the watermark hasbeen reduced to the minimum: it is only a flag warning the devices that the content is protected. It is a kind ofsecond line of defence. Watermarking for copy protection is difficult due to two facts: the protected contents arewatermarked with the same key and the pirates have access to a watermark detector. Three kinds of attacks stemfrom these facts: the watermarked contents only attack, the original/watermarked contents attack and the chosenwatermarked contents attack. Even if we manage to reduced the capacity to one bit, the choice of a watermarkingtechnique is still difficult: an analysis shows that classical spread spectrum techniques do not provide a sufficientlyhigh level of security for this application. This is the reason why we invent a new class of methods known asasymmetric watermarking. This provides high security level but requires a bigger amount of data to detect thewatermark. To boost the detector, we take advantage of the side information at the embedding stage to optimisethe watermark detection. This gives birth to another new method so-called JANIS. For a small loss in the securitylevel, the detector is much more efficient. To conclude, these new methods may justify the Kerckhoffs principle in watermarking for copy protection
Urvoy, De Portzamparc Frédéric. „Sécurités algébrique et physique en cryptographie fondée sur les codes correcteurs d'erreurs“. Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066106/document.
Der volle Inhalt der QuelleCode-based cryptography, introduced by Robert McEliece in 1978, is a potential candidate to replace the asymetric primitives which are threatened by quantum computers. More generral, it has been considered secure for more than thirty years, and allow very vast encryption primitives. Its major drawback lies in the size of the public keys. For this reason, several variants of the original McEliece scheme with keys easier to store were proposed in the last years.In this thesis, we are interested in variants using alternant codes with symmetries and wild Goppa codes. We study their resistance to algebraic attacks, and reveal sometimes fatal weaknesses. In each case, we show the existence of hidden algebraic structures allowing to describe the secret key with non-linear systems of multivariate equations containing fewer variables then in the previous modellings. Their resolutions with Gröbner bases allow to find the secret keys for numerous instances out of reach until now and proposed for cryptographic purposes. For the alternant codes with symmetries, we show a more fondamental vulnerability of the key size reduction process. Prior to an industrial deployment, it is necessary to evaluate the resistance to physical attacks, which target device executing a primitive. To this purpose, we describe a decryption algorithm of McEliece more resistant than the state-of-the-art.Code-based cryptography, introduced by Robert McEliece in 1978, is a potential candidate to replace the asymetric primitives which are threatened by quantum computers. More generral, it has been considered secure for more than thirty years, and allow very vast encryption primitives. Its major drawback lies in the size of the public keys. For this reason, several variants of the original McEliece scheme with keys easier to store were proposed in the last years.In this thesis, we are interested in variants using alternant codes with symmetries and wild Goppa codes. We study their resistance to algebraic attacks, and reveal sometimes fatal weaknesses. In each case, we show the existence of hidden algebraic structures allowing to describe the secret key with non-linear systems of multivariate equations containing fewer variables then in the previous modellings. Their resolutions with Gröbner bases allow to find the secret keys for numerous instances out of reach until now and proposed for cryptographic purposes. For the alternant codes with symmetries, we show a more fondamental vulnerability of the key size reduction process. Prior to an industrial deployment, it is necessary to evaluate the resistance to physical attacks, which target device executing a primitive. To this purpose, we describe a decryption algorithm of McEliece more resistant than the state-of-the-art
Siad, Amar. „Protocoles de génération des clés pour le chiffrement basé sur de l'identité“. Paris 8, 2012. http://www.theses.fr/2012PA083660.
Der volle Inhalt der QuelleIdentity-Based Encryption suffers from the problem of trust in the key generation authority PKG (Private Key Generator), which results in the ability of this authority to produce and distribute, without the knowledge a genuine user, multiple private-keys or multiple copies of a single key. This problem makes the deployment of these systems limited to areas where trust in the PKG must have a fairly high level. An important and natural question is to ask how can we reduce the trust one should have in the PKG. In this thesis, after conducting a development of the state of the art on the subject, we answer this question by studying this problem in its theoretical and practical aspects. On the theoretical stage, we present constructions of distributed cryptographic protocols that reduce the trust to its lowest level never reached before. We develop protocols for private-key generation in different security models while presenting real-world applications using these new protocols in the setting of searchable encryption. Furthermore, we develop necessary infrastructures needed for the deployment of our protocols. In practical terms, we implement KGLib: the first complete, efficient and modular library which brings together the most known techniques for private-key generation for identity-based cryptosystems. This library aims at providing robust tools designed in a modular and reusable way to allow easy implementation and rapid prototyping of the latest results coming from theoretical cryptography
Chen, Yuanmi. „Réduction de réseau et sécurité concrète du chiffrement complètement homomorphe“. Paris 7, 2013. http://www.theses.fr/2013PA077242.
Der volle Inhalt der QuelleThe popularity of lattice-based cryptography has significantly increased in the past few years with the discovery of new spectacular functionalities such as fully-homomorphic encryption and (indistinguishability) obfuscation. It has become crucial to be able to analyze the concrete security of lattice-based cryptosystems, in order to select their parameters and to assess their practical performances. In a first part, we present a theoretical analysis and concrete improvements to the so-called BKZ reduction, which is considered tô be the most efficient lattice reduction algorithm in practice for high dimensions. We begin by studying the main subroutine of BKZ, enumeration, and we extend the analysis of pruned enumeration by Gama, Nguyen and Regev (EUROCRYPT 2010). Next, we improve the BKZ algorithm by using several techniques, such as pruned enumeration, pre-processing and abort. And we discuss how to select BKZ parameters efficiently. Based on numerous experiments, we present a simulation algorithm to predict the output quality of BKZ reduction. This allows us to revise the security estimates of numerous lattice-based cryptosystems, and explain how to solve SVP by enumeration as efficiently as possible, based on the state-of-the-art. In a second part, we present a new algorithm for the approximate greatest common divisor problem, using a time/memory trade-off. This provides a better concrete attack on the fully-homomorphic encryption scheme proposed by Coron, Mandal, Naccache and Tibouchi (CRYPTO 2011). It also has other applications in cryptanalysis
Mazloum, Taghrid. „Analyse et modélisation du canal radio pour la génération de clés secrètes“. Thesis, Paris, ENST, 2016. http://www.theses.fr/2016ENST0012/document.
Der volle Inhalt der QuelleNowadays, the security of ubiquitous wireless communications becomes more and more a crucial requirement. Even though data is widely protected via symmetric ciphering keys, a well-known difficulty is the generation and distribution of such keys. In the recent years therefore, a set of works have addressed the exploitation of inherent characteristics of the fading propagation channel for security. In particular, secret keys could be generated from the wireless channel, considered as a shared source of randomness, available merely to a pair of communicating entities. ln the present dissertation, we are interested in the approach of secret key generation (SKG) from wireless channels, especially in relating the radio channel properties to the generated keys quality. We first develop a stochastic channel model, focusing on the security with respect to the eavesdropper side, which shows a residual channel memory weil beyond a few wavelengths distance (spatially nonstationary scenarios). Then, we analyze the channel degrees of freedom (DoF) and their impact on the SKG performance in different channel conditions, especially by considering more realistic channels in both outdoor and indoor environments (respectively through simulated ray tracing data and through measurements). The results show that, even for moderately wide band (such as standardized in IEEE 802.11), the sole frequency DOF or its association with the spatial DOF is often enough for generating long keys, provided an efficient quantization method of the complex channel coefficients is used
Eynard, Julien. „Approche arithmétique RNS de la cryptographie asymétrique“. Electronic Thesis or Diss., Paris 6, 2015. http://www.theses.fr/2015PA066107.
Der volle Inhalt der QuelleThis thesis is at the crossroads between cryptography and computer arithmetic. It deals with enhancement of cryptographic primitives with regard to computation acceleration and protection against fault injections through the use of residue number systems (RNS) and their associated arithmetic. So as to contribute to secure the modular multiplication, which is a core operation for many asymmetric cryptographic primitives, a new modular reduction algorithm supplied with fault detection capability is presented. A formal proof guarantees that faults affecting one or more residues during a modular reduction are well detected. Furthermore, this approach is generalized to an arithmetic dedicated to non-prime finite fields Fps . Afterwards, RNS are used in lattice-based cryptography area. The aim is to exploit acceleration properties enabled by RNS, as it is widely done for finite field arithmetic. As first result, a new version of Babai’s round-off algorithm based on hybrid RNS-MRS representation is presented. Then, a new and specific acceleration technique enables to create a full RNS algorithm computing a close lattice vector
Lepoint, Tancrède. „Conception and implémentation de cryptographie à base de réseaux“. Phd thesis, Ecole Normale Supérieure de Paris - ENS Paris, 2014. http://tel.archives-ouvertes.fr/tel-01069864.
Der volle Inhalt der QuelleHufschmitt, Emeline. „Signatures pour l'anonymat fondées sur les couplages et applications“. Phd thesis, Université de Caen, 2007. http://tel.archives-ouvertes.fr/tel-00258773.
Der volle Inhalt der QuelleDunand, Clément. „Autour de la cryptographie à base de tores algébriques“. Phd thesis, Université Rennes 1, 2010. http://tel.archives-ouvertes.fr/tel-00569448.
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