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1	User Efficient Authentication Protocols with Provable Security Based on Standard Reduction and Model Checking Lin, Yi-Hui 12 September 2012 (has links) Authentication protocols are used for two parties to authenticate each other and build a secure channel over wired or wireless public channels. However, the present standards of authentication protocols are either insufficiently secure or inefficient for light weight devices. Therefore, we propose two authentication protocols for improving the security and user efficiency in wired and wireless environments, respectively. Traditionally, TLS/SSL is the standard of authentication and key exchange protocols in wired Internet. It is known that the security of TLS/SSL is not enough due to all sorts of client side attacks. To amend the client side security, multi-factor authentication is an effective solution. However, this solution brings about the issue of biometric privacy which raises public concern of revealing biometric data to an authentication server. Therefore, we propose a truly three factor authentication protocol, where the authentication server can verify their biometric data without the knowledge of users¡¦ templates and samples. In the major wireless technologies, extensible Authentication Protocol (EAP) is an authentication framework widely used in IEEE 802.11 WLANs. Authentication mechanisms built on EAP are called EAP methods. The requirements for EAP methods in WLANs authentication have been defined in RFC 4017. To achieve user efficiency and robust security, lightweight computation and forward secrecy, excluded in RFC 4017, are desired in WLAN authentication. However, all EAP methods and authentication protocols designed for WLANs so far do not satisfy all of the above properties. We will present a complete EAP method that utilizes stored secrets and passwords to verify users so that it can (1) meet the requirements of RFC 4017, (2) provide lightweight computation, and (3) allow for forward secrecy. In order to prove our proposed protocols completely, we apply two different models to examine their security properties: Bellare¡¦s model, a standard reduction based on computational model, that reduces the security properties to the computationally hard problems and the OFMC/AVISPA tool, a model checking approach based on formal model, that uses the concept of the search tree to systematically find the weaknesses of a protocol. Through adopting Bellare¡¦s model and OFMC/AVISPA tool, the security of our work is firmly established. Wireless Local Area Networks (WLANs) Wired and Wireless Security Model Checking Standard Reduction Formal Security Proofs Lightweight Devices Authentication Passwords Smart Cards Forward Secrecy Extensible Authentication Protocol (EAP) Biometric Privacy
2	Le schéma d'Even-Mansour paramétrable : preuves de sécurité à l'aide de la technique des coefficients H / The Tweakable Even-Mansour construction : security proofs with the H-coefficients technique Cogliati, Benoît-Michel 30 September 2016 (has links) Les algorithmes de chiffrement par blocs paramétrables constituent une généralisation des algorithmes de chiffrement par blocs classiques qui, en plus d'une clé et d'un message à chiffrer ou déchiffrer, admettent un paramètre additionnel, nommé tweak en anglais. Le rôle de ce paramètre additionnel est d'apporter une variabilité à l'algorithme de chiffrement, sans qu'il soit nécessaire de changer la clé ou de garder le tweak secret. Ce dernier doit également pouvoir être contrôlé par l'adversaire sans dégradation de la sécurité. Dans cette thèse nous nous intéressons à une classe particulière d'algorithmes de chiffrement par blocs, les algorithmes de chiffrement par blocs à clé alternée. Plusprécisément, nous étudions la sécurité du schéma d'Even-Mansour, qui constitue une abstraction de la structure de ces algorithmes dans le modèle de la permutation aléatoire, et cherchons à rendre ce schéma paramétrable tout en conservant de fortes garanties de sécurité. À cette fin, nous introduisons une nouvelle construction générique, baptiséeTEM, qui remplace les clés de tours de la construction d'Even-Mansour par une valeur qui dépend de la clé et du tweak, et en étudions la sécurité dans deux cas : lorsque le mixage de la clé et du tweak est linéaire ou lorsqu'il est très non-linéaire. Nos preuves de sécurité utilisent la technique des coefficients H, introduite par Jacques Patarin danssa thèse de doctorat, qui permet de transformer des problèmes cryptographiques en problèmes combinatoires sur des groupes finis. / Tweakable block ciphers are a generalization of classical block ciphers which, in addition to a key and a plaintext or a ciphertext, take an additionnal parameter called a tweak. The goal of this new parameter is to bring variability to the block cipher without needing to change the key or to keep the tweak secret. The tweak should also be adversariallycontrollable without sacrificing security. In this thesis we study a particular class of block ciphers, namely key-alternating ciphers. More precisely, we study the security of the Even-Mansour scheme, which is an abstraction of these ciphers in the random permutation model, and seek to bring tweakability to this scheme while keeping strong security guarantees. To this end, we introduce a new generic construction, dubbed TEM, which replaces the round keys from the Even-Mansour construction by a value depending on both the key and the tweak, and study its security in two cases: when the tweak and key mixing is linear or highly non-linear. Our security proofs rely on the H-coefficients technique, a technique introduced by Jacques Patarin in his PhD thesis which transforms cryptographic problems into combinatorial problems in finite groups. Cryptographie symétrique Preuves de sécurité Au-Delà de la borne des anniversaires Construction d'Even-Mansour Indistinguabilité Symmetric cryptography Security proofs Beyond the birthday bound Tweakable block ciphers Even-Mansour construction Indistinguishability 005.82
3	Key establishment : proofs and refutations Choo, Kim-Kwang Raymond January 2006 (has links) We study the problem of secure key establishment. We critically examine the security models of Bellare and Rogaway (1993) and Canetti and Krawczyk (2001) in the computational complexity approach, as these models are central in the understanding of the provable security paradigm. We show that the partnership definition used in the three-party key distribution (3PKD) protocol of Bellare and Rogaway (1995) is flawed, which invalidates the proof for the 3PKD protocol. We present an improved protocol with a new proof of security. We identify several variants of the key sharing requirement (i.e., two entities who have completed matching sessions, partners, are required to accept the same session key). We then present a brief discussion about the key sharing requirement. We identify several variants of the Bellare and Rogaway (1993) model. We present a comparative study of the relative strengths of security notions between the several variants of the Bellare-Rogaway model and the Canetti-Krawczyk model. In our comparative study, we reveal a drawback in the Bellare, Pointcheval, and Rogaway (2000) model with the protocol of Abdalla and Pointcheval (2005) as a case study. We prove a revised protocol of Boyd (1996) secure in the Bellare-Rogaway model. We then extend the model in order to allow more realistic adversary capabilities by incorporating the notion of resetting the long-term compromised key of some entity. This allows us to detect a known weakness of the protocol that cannot be captured in the original model. We also present an alternative protocol that is efficient in both messages and rounds. We prove the protocol secure in the extended model. We point out previously unknown flaws in several published protocols and a message authenticator of Bellare, Canetti, and Krawczyk (1998) by refuting claimed proofs of security. We also point out corresponding flaws in their existing proofs. We propose fixes to these protocols and their proofs. In some cases, we present new protocols with full proofs of security. We examine the role of session key construction in key establishment protocols, and demonstrate that a small change to the way that session keys are constructed can have significant benefits. Protocols that were proven secure in a restricted Bellare-Rogaway model can then be proven secure in the full model. We present a brief discussion on ways to construct session keys in key establishment protocols and also prove the protocol of Chen and Kudla (2003) secure in a less restrictive Bellare-Rogaway model. To complement the computational complexity approach, we provide a formal specification and machine analysis of the Bellare-Pointcheval-Rogaway model using an automated model checker, Simple Homomorphism Verification Tool (SHVT). We demonstrate that structural flaws in protocols can be revealed using our framework. We reveal previously unknown flaws in the unpublished preproceedings version of the protocol due to Jakobsson and Pointcheval (2001) and several published protocols with only heuristic security arguments. We conclude this thesis with a listing of some open problems that were encountered in the study. authentication communications security computational complexity computer security cryptographic protocols cryptography DiffieHellman-based protocols formal methods formal specification and verification identity-based protocols key agreement protocols key distribution key establishment protocols key exchange protocols key transport protocols password-based protocols proofs of security provable security provably-secure protocols security proofs
4	Itérations chaotiques pour la sécurité de l'information dissimulée / Chaotic iterations for the Hidden Information Security Friot, Nicolas 05 June 2014 (has links) Les systèmes dynamiques discrets, œuvrant en itérations chaotiques ou asynchrones, se sont avérés être des outils particulièrement intéressants à utiliser en sécurité informatique, grâce à leur comportement hautement imprévisible, obtenu sous certaines conditions. Ces itérations chaotiques satisfont les propriétés de chaos topologiques et peuvent être programmées de manière efficace. Dans l’état de l’art, elles ont montré tout leur intérêt au travers de schémas de tatouage numérique. Toutefois, malgré leurs multiples avantages, ces algorithmes existants ont révélé certaines limitations. Cette thèse a pour objectif de lever ces contraintes, en proposant de nouveaux processus susceptibles de s’appliquer à la fois au domaine du tatouage numérique et au domaine de la stéganographie. Nous avons donc étudié ces nouveaux schémas sur le double plan de la sécurité dans le cadre probabiliste. L’analyse de leur biveau de sécurité respectif a permis de dresser un comparatif avec les autres processus existants comme, par exemple, l’étalement de spectre. Des tests applicatifs ont été conduits pour stéganaliser des processus proposés et pour évaluer leur robustesse. Grâce aux résultats obtenus, nous avons pu juger de la meilleure adéquation de chaque algorithme avec des domaines d’applications ciblés comme, par exemple, l’anonymisation sur Internet, la contribution au développement d’un web sémantique, ou encore une utilisation pour la protection des documents et des donnés numériques. Parallèlement à ces travaux scientifiques fondamentaux, nous avons proposé plusieurs projets de valorisation avec pour objectif la création d’une entreprise de technologies innovantes. / Discrete dynamical systems by chaotic or asynchronous iterations have proved to be highly interesting toolsin the field of computer security, thanks to their unpredictible behavior obtained under some conditions. Moreprecisely, these chaotic iterations possess the property of topological chaos and can be programmed in anefficient way. In the state of the art, they have turned out to be really interesting to use notably through digitalwatermarking schemes. However, despite their multiple advantages, these existing algorithms have revealedsome limitations. So, these PhD thesis aims at removing these constraints, proposing new processes whichcan be applied both in the field of digital watermarking and of steganography. We have studied these newschemes on two aspects: the topological security and the security based on a probabilistic approach. Theanalysis of their respective security level has allowed to achieve a comparison with the other existing processessuch as, for example, the spread spectrum. Application tests have also been conducted to steganalyse and toevaluate the robustness of the algorithms studied in this PhD thesis. Thanks to the obtained results, it has beenpossible to determine the best adequation of each processes with targeted application fields as, for example,the anonymity on the Internet, the contribution to the development of the semantic web, or their use for theprotection of digital documents. In parallel to these scientific research works, several valorization perspectiveshave been proposed, aiming at creating a company of innovative technology. Dissimulation d'informations Étalement de spectre Exposant de Lyapunov Internet Iterations chaotiques Modèles mathématiques Preuve de sécurité Protection des documents numériques Robustesse Sécurité informatique Sécurité des données Sécurité topologique Stéganalyse Stéganographie Stégo-sécurité Syqstèlesss dynamiques discrets Tatouage numérique Tests applicatifs Théorie du chaos Topologie Vie privée Application tests Chaotiques iterations; Chaos theory Computer security Data hiding Data security Digital Watermarking Discret dynamycal systems Internet Lyapunov exponent Mathematics models Privacy Protection of digital documents Robustness Security proofs Spread spectrum Steganalysis Steganography Stego-security Topological security Topology 005.8

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