Contribution à la cryptographie interactive

Nowadays, cryptography is an integral part of our daily lives. Originally intended to be used for human-to-human inter- actions, cryptography is now also used for with and between machines. In this thesis, we will present our contributions covering part of the spectrum of interactive cryptography.First, we will use cryptography as a tool for Machine Learning. We will show that a client and a server can securely interact such that the client gets his data evaluated by a model owned by the server, without learning any confidential information about the other party’s data.Next, we will extend the already existing primitive of Smooth Projective Hash Functions to make it more compliant with post-quantum cryptography, and in particular with lattices. This extension will be used as a basis for the construction of Oblivious Transfers, widely used in the Secure Multiparty Context.Finally, we will focus on lightweight cryptography, allowing technically limited devices to interact with each other while enjoying sufficient security. More precisely, we will perform a security analysis of an authenticated key exchange protocol optimized for such devices, allowing them to securely interact.De nos jours, la cryptographie fait partie intégrante de notre quotidien. Initialement destinée à être utilisée pour les interactions entre humains, elle est aujourd’hui employée pour les interactions avec et entre des machines. A travers cette thèse, nous présenterons nos diverses contributions couvrant une partie du spectre de la cryptographie interactive.Dans un premier temps, nous la verrons comme un outil au service de l’apprentissage automatique. Nous montrerons qu’elle peut permettre à un client et à un serveur d’interagir afin de faire évaluer les données du client par le modèle du serveur, sans qu’aucun d’eux n’apprenne d’informartion confidentielle au sujet de l’autre.Ensuite, nous étendrons la notion déjà existante de Smooth Projective Hash Functions pour la rendre plus compatible avec la cryptographie post-quantique, et notamment les réseaux euclidiens. Cette extension servira de base à la con- struction de Transferts Inconscients, largement déployés aujourd’hui dans le cadre de Calculs Multipartites Securisés.Finalement, nous nous intéresserons à la cryptographie à bas-coût, permettant à des appareils techniquement limités d’interagir entre eux tout en jouissant d’une sécurité suffisante. Plus précisément, nous étudierons la sécurité d’un protocole authentifié d’échange de clés optimisé pour de tels appareils, permettant d’établir une communication sécurisée entre eux

Contribution à la cryptographie interactive

Nowadays, cryptography is an integral part of our daily lives. Originally intended to be used for human-to-human inter- actions, cryptography is now also used for with and between machines. In this thesis, we will present our contributions covering part of the spectrum of interactive cryptography.First, we will use cryptography as a tool for Machine Learning. We will show that a client and a server can securely interact such that the client gets his data evaluated by a model owned by the server, without learning any confidential information about the other party’s data.Next, we will extend the already existing primitive of Smooth Projective Hash Functions to make it more compliant with post-quantum cryptography, and in particular with lattices. This extension will be used as a basis for the construction of Oblivious Transfers, widely used in the Secure Multiparty Context.Finally, we will focus on lightweight cryptography, allowing technically limited devices to interact with each other while enjoying sufficient security. More precisely, we will perform a security analysis of an authenticated key exchange protocol optimized for such devices, allowing them to securely interact.De nos jours, la cryptographie fait partie intégrante de notre quotidien. Initialement destinée à être utilisée pour les interactions entre humains, elle est aujourd’hui employée pour les interactions avec et entre des machines. A travers cette thèse, nous présenterons nos diverses contributions couvrant une partie du spectre de la cryptographie interactive.Dans un premier temps, nous la verrons comme un outil au service de l’apprentissage automatique. Nous montrerons qu’elle peut permettre à un client et à un serveur d’interagir afin de faire évaluer les données du client par le modèle du serveur, sans qu’aucun d’eux n’apprenne d’informartion confidentielle au sujet de l’autre.Ensuite, nous étendrons la notion déjà existante de Smooth Projective Hash Functions pour la rendre plus compatible avec la cryptographie post-quantique, et notamment les réseaux euclidiens. Cette extension servira de base à la con- struction de Transferts Inconscients, largement déployés aujourd’hui dans le cadre de Calculs Multipartites Securisés.Finalement, nous nous intéresserons à la cryptographie à bas-coût, permettant à des appareils techniquement limités d’interagir entre eux tout en jouissant d’une sécurité suffisante. Plus précisément, nous étudierons la sécurité d’un protocole authentifié d’échange de clés optimisé pour de tels appareils, permettant d’établir une communication sécurisée entre eux

Security Analysis of the EDHOC protocol

Ephemeral Diffie-Hellman Over COSE (EDHOC) aims at being a very compact and lightweight authenticated Diffie-Hellman key exchange with ephemeral keys. It is expected to provide mutual authen- tication, forward secrecy, and identity protection, with a 128-bit security level.A formal analysis has already been proposed at SECRYPT ’21, on a former version, leading to some improvements, in the ongoing evaluation process by IETF. Unfortunately, while formal analysis can detect some misconceptions in the protocol, it cannot evaluate the actual security level.In this paper, we study the last version. Without complete breaks, we anyway exhibit attacks in 2^64 operations, which contradict the expected 128-bit security level. We thereafter propose improvements, some of them being at no additional cost, to achieve 128-bit security for all the security properties (i.e. key privacy, mutual authentication, and identity- protection)

Security Analysis of Improved EDHOC Protocol

International audienceEphemeral Diffie-Hellman Over COSE (EDHOC) aims at being a very compact and lightweight authenticated Diffie-Hellman key exchange with ephemeral keys. It is expected to provide mutual authentication, forward secrecy, and identity protection, with a 128-bit security level.A formal analysis has already been proposed at SECRYPT ’21, on a former version, leading to some improvements, in the ongoing evaluation process by IETF. Unfortunately, while formal analysis can detect some vulnerabilities in the protocol, it cannot evaluate the actual security level.In this paper, we study the protocol as it appeared in version 15. Without complete breaks, we anyway exhibit attacks in 2^64 operations, which contradict the expected 128-bit security level. We thereafter propose improvements, some of them being at no additional cost, to achieve 128-bit security for all the security properties (i.e. key privacy, mutual authentication, and identity-protection)

Post-Quantum and UC-secure Oblivious Transfer from SPHF with Grey Zone

International audienceOblivious Transfer (OT) is a major primitive for secure multiparty computation. Indeed, combined with symmetric primitives along with garbled circuits, it allows any secure function evaluation between two parties. In this paper, we propose a new approach to build OT protocols. Interestingly, our new paradigm features a security analysis in the Universal Composability (UC) framework and may be instantiated from post-quantum primitives. In order to do so, we define a new primitive named Smooth Projective Hash Function with Grey Zone (SPHFwGZ) which can be seen as a relaxation of the classical Smooth Projective Hash Functions, with a subset of the words for which one cannot claim correctness nor smoothness: the grey zone. As a concrete application, we provide two instantiations of SPHFwGZ respectively based on the Diffie-Hellman and the Learning With Errors (LWE) problems. Hence, we propose a quantum-resistant OT protocol with UC-security in the random oracle model

Post-Quantum and UC-secure Oblivious Transfer from SPHF with Grey Zone

International audienceOblivious Transfer (OT) is a major primitive for secure multiparty computation. Indeed, combined with symmetric primitives along with garbled circuits, it allows any secure function evaluation between two parties. In this paper, we propose a new approach to build OT protocols. Interestingly, our new paradigm features a security analysis in the Universal Composability (UC) framework and may be instantiated from post-quantum primitives. In order to do so, we define a new primitive named Smooth Projective Hash Function with Grey Zone (SPHFwGZ) which can be seen as a relaxation of the classical Smooth Projective Hash Functions, with a subset of the words for which one cannot claim correctness nor smoothness: the grey zone. As a concrete application, we provide two instantiations of SPHFwGZ respectively based on the Diffie-Hellman and the Learning With Errors (LWE) problems. Hence, we propose a quantum-resistant OT protocol with UC-security in the random oracle model

Post-Quantum Oblivious Transfer from Smooth Projective Hash Functions with Grey Zone

Oblivious Transfer (OT) is a major primitive for secure multiparty computation. Indeed, combined with symmetric primitives along with garbled circuits, it allows any secure function evaluation between two parties. In this paper, we propose a new approach to build OT protocols. Interestingly, our new paradigm features a security analysis in the Universal Composability (UC) framework and may be instantiated from post-quantum primitives. In order to do so, we define a new primitive named Smooth Projective Hash Function with Grey Zone (SPHFwGZ) which can be seen as a relaxation of the classical Smooth Projective Hash Functions, with a subset of the words for which one cannot claim correctness nor smoothness: the grey zone. As a concrete application, we provide two instantiations of SPHFwGZ respectively based on the Diffie-Hellman and the Learning With Errors (LWE) problems. Hence, we propose a quantum-resistant OT protocol with UC-security in the random oracle model

Secure Decision Forest Evaluation

International audienceDecision forests are classical models to efficiently make decision on complex inputs with multiple features. While the global structure of the trees or forests is public, sensitive information have to be protected during the evaluation of some client inputs with respect to some server model. Indeed, the comparison thresholds on the server side may have economical value while the client inputs might be critical personal data. In addition, soundness is also important for the receiver. In our case, we will consider the server to be interested in the outcome of the model evaluation so that the client should not be able to bias it. In this paper, we propose a new offline/online protocol between a client and a server with a constant number of rounds in the online phase, with both privacy and soundness against malicious clients. CCS Concepts: • Security and Privacy → Cryptography

Posterior fossa tumors in children: Radiological tips & tricks in the age of genomic tumor classification and advance MR technology

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