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Дисертації з теми "Chiffrement de groupe":
Barthoulot, Anaïs. "Chiffrement avancé pour le partage de données sensibles." Electronic Thesis or Diss., Limoges, 2023. http://www.theses.fr/2023LIMO0067.
Data, including private information, plays a pivotal role in our daily lives today. Current research predominantly focuses on data storage, with an emphasis on the ability to securely process data even when it is encrypted. However, beyond mere preservation, data must also be shared in various ways: either among an individual and a group of individuals, sometimes bound by common characteristics defining sharing rules, or simply between two individuals. Currently, these different modes of sharing are not yet well-mastered, either due to their high performance cost or limited functionalities. This thesis delves into various encryption schemes tailored for sharing sensitive data, proposing new constructions. Firstly, we investigate two cryptographic primitives: identity-based encryption schemes with wildcards and cryptographic accumulators, which serve as a starting point for our new constructions. Regarding identity-based encryption schemes with wildcards, we introduce a new security property and propose two new instantiations, one of which satisfies this new security property that we have defined. For cryptographic accumulators, we present a new type of accumulator, an improved scheme compared to the state of the art, and a second scheme illustrating our new functionality. We also introduce a new security property for this primitive and raise numerous questions concerning various properties of the latter. Finally, we explore the construction of encryption schemes suited for data sharing using the two aforementioned primitives. We propose a generic construction of a group encryption scheme (including "augmented" group encryption) based on identity-based encryption schemes with wildcards. With our instantiations of the primitive, we achieve a new group encryption scheme that enhances the state of the art by offering adaptive security rather than just selective, while preserving the efficiency of the best schemes due to a constant ciphertext size. For "augmented" group encryption schemes, the combination of one of our instantiations of identity-based encryption schemes with wildcards and our generic construction enables us to obtain a new scheme, the first to guarantee adaptive security in the standard model. Unfortunately, in terms of efficiency, our scheme is no more efficient than a "trivial" solution. However, thanks to our generic constructions, an enhancement of the underlying primitive will contribute to improving "augmented" group encryption schemes. We also propose an attribute-based encryption scheme using our new type of accumulators. This scheme is the first to offer a constant size for the secret key and ciphertext, regardless of the number of attributes in the scheme, while guaranteeing adaptive security. However, this efficiency comes at the cost of an exponential size for the public key, and our construction, relying on specific features of our new accumulator instantiation with pairings, cannot be generalized. Finally, through a concrete use case, we introduce a novel approach to access control using identity-based encryption schemes with wildcards
Chridi, Najah. "Contributions à la vérification automatique de protocoles de groupes." Phd thesis, Université Henri Poincaré - Nancy I, 2009. http://tel.archives-ouvertes.fr/tel-00417290.
Bien que beaucoup de travaux aient été dédiés pour les protocoles classiques comme le protocole de Needham-Schroeder, très peu de travaux s'adressent à la classe des protocoles de groupe dont les caractéristiques principales sont : les propriétés de sécurité spécifiques qu'ils doivent satisfaire, et le nombre arbitraire des participants qu'ils impliquent.
Cette thèse comprend deux contributions principales. La première traite la première caractéristique des protocoles de groupe.
Pour cela, nous avons défini un modèle appelé modèle de services que nous avons utilisé pour proposer une stratégie de recherche d'attaques se basant sur la résolution de contraintes. L'approche proposée a permis de retrouver d'anciennes attaques et d'en découvrir de nouvelles sur quelques protocoles de groupe. Certaines attaques ont aussi pu être généralisées pour couvrir le cas de $n$ participants. La deuxième contribution principale de cette thèse consiste à définir un modèle synchrone qui généralise les modèles standards de protocoles en permettant les listes non bornées à l'intérieur des messages. Ceci est assuré par l'introduction d'un nouvel opérateur appelé $mpair$ qui représente une liste construite sur un même patron. Dans ce modèle étendu, nous avons proposé une procédure de décision pour une classe particulière des protocoles de groupe appelée classe de protocoles bien-tagués avec clefs autonomes, en présence d'un intrus actif et avec des clefs composées.
Tucker, Ida. "Chiffrement fonctionnel et signatures distribuées fondés sur des fonctions de hachage à projection, l'apport des groupes de classe." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEN054.
One of the current challenges in cryptographic research is the development of advanced cryptographic primitives ensuring a high level of confidence. In this thesis, we focus on their design, while proving their security under well-studied algorithmic assumptions.My work grounds itself on the linearity of homomorphic encryption, which allows to perform linear operations on encrypted data. Precisely, I built upon the linearly homomorphic encryption scheme introduced by Castagnos and Laguillaumie at CT-RSA'15. Their scheme possesses the unusual property of having a prime order plaintext space, whose size can essentially be tailored to ones' needs. Aiming at a modular approach, I designed from their work technical tools (projective hash functions, zero-knowledge proofs of knowledge) which provide a rich framework lending itself to many applications.This framework first allowed me to build functional encryption schemes; this highly expressive primitive allows a fine grained access to the information contained in e.g., an encrypted database. Then, in a different vein, but from these same tools, I designed threshold digital signatures, allowing a secret key to be shared among multiple users, so that the latter must collaborate in order to produce valid signatures. Such signatures can be used, among other applications, to secure crypto-currency wallets. Significant efficiency gains, namely in terms of bandwidth, result from the instantiation of these constructions from class groups. This work is at the forefront of the revival these mathematical objects have seen in cryptography over the last few years
Marjane, Abdelaziz. "Conception Vectorielle de Registre à rétroaction avec retenue sur les corps finis." Phd thesis, Université Paris-Nord - Paris XIII, 2011. http://tel.archives-ouvertes.fr/tel-00680021.
Arfaoui, Ghada. "Conception de protocoles cryptographiques préservant la vie privée pour les services mobiles sans contact." Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2013/document.
The increasing number of worldwide mobile platforms and the emergence of new technologies such as the NFC (Near Field Communication) lead to a growing tendency to build a user's life depending on mobile phones. This context brings also new security and privacy challenges. In this thesis, we pay further attention to privacy issues in NFC services as well as the security of the mobile applications private data and credentials namely in Trusted Execution Environments (TEE). We first provide two solutions for public transport use case: an m-pass (transport subscription card) and a m-ticketing validation protocols. Our solutions ensure users' privacy while respecting functional requirements of transport operators. To this end, we propose new variants of group signatures and the first practical set-membership proof that do not require pairing computations at the prover's side. These novelties significantly reduce the execution time of such schemes when implemented in resource constrained environments. We implemented the m-pass and m-ticketing protocols in a standard SIM card: the validation phase occurs in less than 300ms whilst using strong security parameters. Our solutions also work even when the mobile is switched off or the battery is flat. When these applications are implemented in TEE, we introduce a new TEE migration protocol that ensures the privacy and integrity of the TEE credentials and user's private data. We construct our protocol based on a proxy re-encryption scheme and a new TEE model. Finally, we formally prove the security of our protocols using either game-based experiments in the random oracle model or automated model checker of security protocols
Pierrot, Cécile. "Le logarithme discret dans les corps finis." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066495.
Cryptography is the study of techniques for secure communication in the presence of third parties, also called adversaries. Such techniques are detailed in cryptosystems, explaining how to securely encode and decode messages. They are designed around computational hardness assumptions related to mathematical properties, making such algorithms hard to break in practice by any adversary. These protocols are based on the computational difficulty of various problems which often come from number theory, such as integer factorization or discrete logarithms computations. This manuscript focuses on the discrete logarithm problem in finite fields and revolves around three axes.First we detail classical results about the problem without any consideration to the target group. We deal with complexity classes and some general methods that do not need any information on the group.The study of the discrete logarithm problem in finite fields starts with small characteristic ones. The aim is to present a Frobenius representation algorithm that leads to the current discrete logarithm record in characteristic 3.For medium or large characteristics finite fields, another approach is required. The multiple number field sieve reaches the best asymptotic heuristic complexities for this double range of characteristics. We also introduce the notion of nearly sparse matrices. Designing a new algorithm dedicated to explicitly give the kernel of such a matrix eases in practice the linear algebra step of any variant of the number field sieve
Ragab, Hassen Hani. "Key management for content access control in hierarchical environments." Compiègne, 2007. http://www.theses.fr/2007COMP1718.
Lots of applications, ranging from interactive online games to business corporations and government departments, and from multi-layered data streaming to databases access control, require ensuring that its users respect some access control restrictions. Content access control in hierarchies (CACH) consists in ensuring, using cryptographic techniques, that the users access application resources to which they are entitled. Content access control is generally ensured by encrypting the system resources and giving the keys to users having access to them. Generating and managing those keys is a crucial requirement for the deployment of content access control systems. Moreover, large scale hierarchies with highly dynamic users present serious scalability issues for key management. In this thesis, we deal with key management for content access control. We start by defining building blocks of key management for CACH. Then, we study the existing key management solutions and classify them into two categories -namely, the dependent keys and independent keys approaches - and propose a key management framework for each category. We further propose a generic model to represent independent-keys key management schemes and use this model to define lower bounds on the key management overhead. Then, we propose a new independent-keys key management scheme and prove that it is optimal by showing that it reaches the overhead lower bounds. The optimality of this scheme constitutes one of the most important results of our thesis. Thereafter, we propose new efficient dependent-keys key management schemes and evaluate them by simulations and Markov process modelling. At last, we propose a variant of our schemes allowing to define trade-offs on the performance criteria. We show that this variant offers a means to define very interesting overhead trade-offs
Pierrot, Cécile. "Le logarithme discret dans les corps finis." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066495/document.
Cryptography is the study of techniques for secure communication in the presence of third parties, also called adversaries. Such techniques are detailed in cryptosystems, explaining how to securely encode and decode messages. They are designed around computational hardness assumptions related to mathematical properties, making such algorithms hard to break in practice by any adversary. These protocols are based on the computational difficulty of various problems which often come from number theory, such as integer factorization or discrete logarithms computations. This manuscript focuses on the discrete logarithm problem in finite fields and revolves around three axes.First we detail classical results about the problem without any consideration to the target group. We deal with complexity classes and some general methods that do not need any information on the group.The study of the discrete logarithm problem in finite fields starts with small characteristic ones. The aim is to present a Frobenius representation algorithm that leads to the current discrete logarithm record in characteristic 3.For medium or large characteristics finite fields, another approach is required. The multiple number field sieve reaches the best asymptotic heuristic complexities for this double range of characteristics. We also introduce the notion of nearly sparse matrices. Designing a new algorithm dedicated to explicitly give the kernel of such a matrix eases in practice the linear algebra step of any variant of the number field sieve
Книги з теми "Chiffrement de groupe":
Steinwandt, Rainer, and Maria Isabel Gonzalez Vasco. Group Theoretic Cryptography. Taylor & Francis Group, 2015.
Vasco, Maria Isabel, Spyros Magliveras, and Rainer Steinwandt. Group Theoretic Cryptography. Taylor & Francis Group, 2012.
Steinwandt, Rainer, and Maria Isabel Gonzalez Vasco. Group Theoretic Cryptography. Taylor & Francis Group, 2015.
Vasco, Maria Isabel, Spyros Magliveras, and Rainer Steinwandt. Group Theoretic Cryptography (Chapman & Hall/Crc Cryptography and Network Security Series). Chapman & Hall/CRC, 2008.
Halldórsson, Guðmundur Jón. Apache Accumulo for Developers. Packt Publishing, 2013.