20 research outputs found
Catalepsie par chlorpromazine chez le rat normal ou chez le rat rendu arthritique par adjuvant de Freund
La catalepsie par chlorpromazine est moins prononcĂ©e chez le Rat rendu arthritique par adjuvant de Fhkvxd que chez lâanimal sain
Generation of protocols in multi-user cases
Dans cette thĂšse, nous utilisons des protocoles cryptographiques existants afin dâen proposer de nouveaux ou avec de nouvelles propriĂ©tĂ©s intĂ©ressantes.Nous avons tout dâabord proposer un protocole de signature Ă base dâattributs Ă partir dâun chiffrement basĂ© sur lâidentitĂ©. La sĂ©curitĂ© de cette construction est prouvĂ©e sous une hypothĂšse classique. Par la suite, nous proposons une signature en blanc en tour optimal et de taille constante grĂące Ă la mĂ©thode de construction de Fischlin et des preuves non-interactives Ă divulgation nulle de connaissance. De plus, cette signature est prouvĂ©e sĂ»re sous une hypothĂšse classique. En rĂ©sultat annexe, nous proposons une signature sur chiffrĂ© randomizable de taille constante est Ă©galement prĂ©sentĂ©e et prouvĂ©e sous la mĂȘme hypothĂšse.Ensuite, nous introduisons un nouveau protocole de chiffrement basĂ© sur lâidentitĂ© (IBE) qui permet a un traceur, avec une clĂ© associĂ© Ă une identitĂ©, de filtrer tout les chiffrĂ©s envoyĂ© Ă cette identitĂ© prĂ©cise (et seulement celle-ci).Finalement nous proposons un protocole de signature Ă trois parties prouvĂ©e sĂ»r sous des hypothĂšses standards. Cette construction utilise diffĂ©rents outils tels que des SPHF ou la signature asymĂ©trique de Waters.In this thesis, we use building blocks to propose new one or with new interesting properties. First, we propose a attribute-based designated verifier signature thanks to an IBE. Security properties are proven under usual hypothesis. Then, we introduce our round-optimal constant-size blind signature thanks to Fischlin framework and NIZK. As a side result, we propose a constant-size signature on randomizable ciphertexts. Then, we introduce a new IBE which allows a tracer, given a tracing key associated to an identity, to filter all the ciphertexts that are sent to this specific identity (and only those). Two applications of this protocols are proposed. We show that our modification doesnât alter the security of IBE. Finally, we present a threshold signature between an user, a token and a server thanks to different building blocks like SPHF or assymetric Waters signature. The security of the construction is proven under regular assumptions like CDH+ or DDH
Généralisation des protocoles en cas multi-utilisateurs
In this thesis, we use building blocks to propose new one or with new interesting properties. First, we propose a attribute-based designated verifier signature thanks to an IBE. Security properties are proven under usual hypothesis. Then, we introduce our round-optimal constant-size blind signature thanks to Fischlin framework and NIZK. As a side result, we propose a constant-size signature on randomizable ciphertexts. Then, we introduce a new IBE which allows a tracer, given a tracing key associated to an identity, to filter all the ciphertexts that are sent to this specific identity (and only those). Two applications of this protocols are proposed. We show that our modification doesnât alter the security of IBE. Finally, we present a threshold signature between an user, a token and a server thanks to different building blocks like SPHF or assymetric Waters signature. The security of the construction is proven under regular assumptions like CDH+ or DDH.Dans cette thĂšse, nous utilisons des protocoles cryptographiques existants afin dâen proposer de nouveaux ou avec de nouvelles propriĂ©tĂ©s intĂ©ressantes.Nous avons tout dâabord proposer un protocole de signature Ă base dâattributs Ă partir dâun chiffrement basĂ© sur lâidentitĂ©. La sĂ©curitĂ© de cette construction est prouvĂ©e sous une hypothĂšse classique. Par la suite, nous proposons une signature en blanc en tour optimal et de taille constante grĂące Ă la mĂ©thode de construction de Fischlin et des preuves non-interactives Ă divulgation nulle de connaissance. De plus, cette signature est prouvĂ©e sĂ»re sous une hypothĂšse classique. En rĂ©sultat annexe, nous proposons une signature sur chiffrĂ© randomizable de taille constante est Ă©galement prĂ©sentĂ©e et prouvĂ©e sous la mĂȘme hypothĂšse.Ensuite, nous introduisons un nouveau protocole de chiffrement basĂ© sur lâidentitĂ© (IBE) qui permet a un traceur, avec une clĂ© associĂ© Ă une identitĂ©, de filtrer tout les chiffrĂ©s envoyĂ© Ă cette identitĂ© prĂ©cise (et seulement celle-ci).Finalement nous proposons un protocole de signature Ă trois parties prouvĂ©e sĂ»r sous des hypothĂšses standards. Cette construction utilise diffĂ©rents outils tels que des SPHF ou la signature asymĂ©trique de Waters
Hardware security without secure hardware: How to decrypt with a password and a server
ISSN:0304-397
Hardware security without secure hardware: How to decrypt with a password and a server
International audienceHardware security tokens have now been used for several decades to store cryptographic keys. When deployed, the security of the corresponding schemes fundamentally relies on the tamper-resistance of the tokens â a very strong assumption in practice. Moreover, even secure tokens, which are expensive and cumbersome, can often be subverted.We introduce a new cryptographic primitive called Encryption schemes with Password-protected Assisted Decryption (EPAD schemes), in which a user's decryption key is shared between a user device (or token) on which no assumption is made, and an online server. The user shares a human-memorizable password with the server. To decrypt a ciphertext, the user launches, from a public computer, a distributed protocol with the device and the server, authenticating herself to the server with her password (unknown to the device); in such a way that her secret key is never reconstructed during the interaction. We propose a strong security model which guarantees that (1) for an efficient adversary to infer any information about a user's plaintexts, it must know her password and have corrupted her device (secrecy is guaranteed if only one of the two conditions is fulfilled), (2) the device and the server are unable to infer any information about the ciphertexts they help to decrypt (even though they could together reconstruct the secret key), and (3) the user is able to verify that the device and the server both performed the expected computations. These EPAD schemes are in the password-only model, meaning that the user is not required to remember a trusted public key, and her password remains safe even if she is led to interact with a wrong server and a malicious device.We then give a practical pairing-based EPAD scheme. Our construction is provably secure under standard computational assumptions, using non-interactive proof systems which can be efficiently instantiated in the standard security model, i.e., without relying on the random oracle heuristic