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.

EN: Jaspers came to philosophy from medicine and psychology. Unique personal situation, authentic life experience, unrepeatable faithful self-respect turned psychopathologist Jaspers from psychiatric physiology of soul to the thesis of ciphers of transcendence, borderline, edge and horizon. He constituted his own pattern of the thinker not only as an explaining teacher, but also as co-creator of original ethics, based on deep comprehension of the other, importance of encompassing communication between man and man. First section of my work deals with the concept of Border. Our attitudes and picture of the universe and its evaluation are limited by borders. The holistic complex being remains behind the horizon The second part is dedicated to border-line situation as an phenomenon of possibility, as seen from the point of view of Jaspers own existence, as presented in his Philosophy, including commentary based on new translations by Vaclav Nemec Closing part deals with existential communication and holistic transition from possible to new horizons of transcendence. My interpretation of chosen excerpts comes mostly from "Psychologie der Weltanschauungen." Quotations appear in my own translation.

EN: Jaspers came to philosophy from medicine and psychology. Unique personal situation, authentic life experience, unrepeatable faithful self-respect turned psychopathologist Jaspers from psychiatric physiology of soul to the thesis of ciphers of transcendence, borderline, edge and horizon. He constituted his own pattern of the thinker not only as an explaining teacher, but also as co-creator of original ethics, based on deep comprehension of the other, importance of encompassing communication between man and man. First section of my work deals with the concept of Border. Our attitudes and picture of the universe and its evaluation are limited by borders. The holistic complex being remains behind the horizon The second part is dedicated to border-line situation as an phenomenon of possibility, as seen from the point of view of Jaspers own existence, as presented in his Philosophy, including commentary based on new translations by Vaclav Nemec Closing part deals with existential communication and holistic transition from possible to new horizons of transcendence. My interpretation of chosen excerpts comes mostly from "Allgemeine Psychopathologie" "Psychologie der Weltanschauungen." Quotations appear in my own translation. KEY WORDS: Prophetic philosophy, philosophy as treatment of world opinion,...

This diploma’s thesis discourses the cryptographic systems and ciphers, whose function, usage and practical implementation are analysed. In the first chapter basic cryptographic terms, symmetric and asymetric cryptographic algorithms and are mentioned. Also usage and reliability are analysed. Following chapters mention substitution, transposition, block and stream ciphers, which are elementary for most cryptographic algorithms. There are also mentioned the modes, which the ciphers work in. In the fourth chapter are described the principles of some chosen cryptographic algorithms. The objective is to make clear the essence of the algorithms’ behavior. When describing some more difficult algorithms the block scheme is added. At the end of each algorithm’s description the example of practical usage is written. The chapter no. five discusses the hardware implementation. Hardware and software implementation is compared from the practical point of view. Several design instruments are described and different hardware design programming languages with their progress, advantages and disadvantages are mentioned. Chapter six discourses the hardware implementation design of chosen ciphers. Concretely the design of stream cipher with pseudo-random sequence generator is designed in VHDL and also in Matlab. As the second design was chosen the block cipher GOST, which was designed in VHDL too. Both designs were tested and verified and then the results were summarized.