Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work we present the determination of the second Hamming weight of generalized Reed- Muller codes in most cases (see Teorema 4.6). Our main reference is [13], although we have also used results from [3] and [5]. In the first chapter we describe finite fields e we show how they can be constructed. In chapter 2 we present the basics of coding theory. We define what are error correcting codes, the Hamming metric, the parameters of a code, the equivalence of codes through the concept of isometry, and we briefly present generalized Reed-Muller codes and their parameters. In chapter 3 we present some results from Grobner bases theory and the definition of Affine Cartesian codes, which generalize the generalized Reed-Muller codes. we use tools from Grobner bases theory to determine the dimension and the minimum distance of Affine Cartesian codes. We finish our work in chapter 4, with the determination of the second Hamming weight for generalized Reed-Muller codes in most cases. / Nesse trabalho apresentamos o cálculo do segundo peso de Hamming de códigos de Reed-Muller generalizados na maioria dos casos (v. Teorema 4.6). Nossa referência principal sera [13], embora tenhamos utilizado também resultados de [3] e [5]. No primeiro capítulo descrevemos os corpos finitos e mostramos como podem ser construídos. No capítulo 2 apresentamos os conceitos básicos da teoria de códigos. Nele, definimos o que são os códigos corretores de erros, a métrica de Hamming, os parâmetros de um código, a equivalência de códigos através da noção de isometria, bem como uma breve apresentação dos códigos de Reed-Muller generalizados e seus parâmetros. No capítulo 3 sao apresentados alguns resultados da teoria de Bases de Grobner e a definição dos Códigos Cartesianos Afins, que são uma generalização dos códigos de Reed-Muller generalizados. Usamos ferramentas da teoria de bases de Grobner para determinar a dimensão e distância mínima de Códigos Cartesianos Afins. Para finalizar nosso trabalho, no capítulo 4 determinamos o segundo peso de Hamming do Código de Reed-Muller generalizado na maioria dos casos. / Mestre em Matemática

Contrairement aux protocoles cryptographiques fondés sur la théorie des nombres, les systèmes de chiffrement basés sur les codes correcteurs d’erreurs semblent résister à l’émergence des ordinateurs quantiques. Un autre avantage de ces systèmes est que le chiffrement et le déchiffrement sont très rapides, environ cinq fois plus rapide pour le chiffrement, et 10 à 100 fois plus rapide pour le déchiffrement par rapport à RSA. De nos jours, l’intérêt de la communauté scientifique pour la cryptographie basée sur les codes est fortement motivé par la dernière annonce de la “National Institute of Standards and Technology" (NIST), qui a récemment initié le projet intitulé “Post-Quantum cryptography Project". Ce projet vise à définir de nouveaux standards pour les cryptosystèmes résistants aux attaques quantiques et la date limite pour la soumission des cryptosystèmes à clé publique est fixée pour novembre 2017. Une telle annonce motive certainement à proposer de nouveaux protocoles cryptographiques basés sur les codes, mais aussi à étudier profondément la sécurité des protocoles existants afin d’écarter toute surprise en matière de sécurité. Cette thèse suit cet ordre d’idée en étudiant la sécurité de plusieurs protocoles cryptographiques fondés sur la théorie des codes correcteurs d’erreurs. Nous avons commencé par l’étude de la sécurité d’une version modifiée du cryptosystème de Sidelnikov, proposée par Gueye et Mboup [GM13] et basée sur les codes de Reed-Muller. Cette modification consiste à insérer des colonnes aléatoires dans la matrice génératrice (ou de parité) secrète. La cryptanalyse repose sur le calcul de carrés du code public. La nature particulière des codes de Reed-Muller qui sont définis au moyen de polynômes multivariés binaires, permet de prédire les valeurs des dimensions des codes carrés calculés, puis permet de récupérer complètement en temps polynomial les positions secrètes des colonnes aléatoires. Notre travail montre que l’insertion de colonnes aléatoires dans le schéma de Sidelnikov n’apporte aucune amélioration en matière de sécurité. Le résultat suivant est une cryptanalyse améliorée de plusieurs variantes du cryptosystème GPT qui est un schéma de chiffrement en métrique rang utilisant les codes de Gabidulin. Nous montrons qu’en utilisant le Frobenius de façon appropriée sur le code public, il est possible d’en extraire un code de Gabidulin ayant la même dimension que le code de Gabidulin secret mais avec une longueur inférieure. Le code obtenu corrige ainsi moins d’erreurs que le code secret, mais sa capacité de correction d’erreurs dépasse le nombre d’erreurs ajoutées par l’expéditeur et par conséquent, un attaquant est capable de déchiffrer tout texte chiffré, à l’aide de ce code de Gabidulin dégradé. Nos résultats montrent qu’en fin de compte, toutes les techniques existantes visant à cacher la structure algébrique des codes de Gabidulin ont échoué. Enfin, nous avons étudié la sécurité du système de chiffrement de Faure-Loidreau [FL05] qui est également basé sur les codes de Gabidulin. Inspiré par les travaux précédents et, bien que la structure de ce schéma diffère considérablement du cadre classique du cryptosystème GPT, nous avons pu montrer que ce schéma est également vulnérable à une attaque polynomiale qui récupère la clé privée en appliquant l’attaque d’Overbeck sur un code public approprié. Comme exemple, nous arrivons en quelques secondes à casser les paramètres qui ont été proposés comme ayant un niveau de sécurité de 80 bits. / Contrary to the cryptosystems based on number theory, the security of cryptosystems based on error correcting codes appears to be resistant to the emergence of quantum computers. Another advantage of these systems is that the encryption and decryption are very fast, about five times faster for encryption, and 10 to 100 times faster for decryption compared to RSA cryptosystem. Nowadays, the interest of scientific community in code-based cryptography is highly motivated by the latest announcement of the National Institute of Standards and Technology (NIST). They initiated the Post-Quantum cryptography Project which aims to define new standards for quantum resistant cryptography and fixed the deadline for public key cryptographic algorithm submissions for November 2017. This announcement motivates to study the security of existing schemes in order to find out whether they are secure. This thesis thus presents several attacks which dismantle several code-based encryption schemes. We started by a cryptanalysis of a modified version of the Sidelnikov cryptosystem proposed by Gueye and Mboup [GM13] which is based on Reed-Muller codes. This modified scheme consists in inserting random columns in the secret generating matrix or parity check matrix. The cryptanalysis relies on the computation of the square of the public code. The particular nature of Reed-Muller which are defined by means of multivariate binary polynomials, permits to predict the values of the dimensions of the square codes and then to fully recover in polynomial time the secret positions of the random columns. Our work shows that the insertion of random columns in the Sidelnikov scheme does not bring any security improvement. The second result is an improved cryptanalysis of several variants of the GPT cryptosystem which is a rank-metric scheme based on Gabidulin codes. We prove that any variant of the GPT cryptosystem which uses a right column scrambler over the extension field as advocated by the works of Gabidulin et al. [Gab08, GRH09, RGH11] with the goal to resist Overbeck’s structural attack [Ove08], are actually still vulnerable to that attack. We show that by applying the Frobeniusoperator appropriately on the public key, it is possible to build a Gabidulin code having the same dimension as the original secret Gabidulin code, but with a lower length. In particular, the code obtained by this way corrects less errors than thesecret one but its error correction capabilities are beyond the number of errors added by a sender, and consequently an attacker is able to decrypt any ciphertext with this degraded Gabidulin code. We also considered the case where an isometrictransformation is applied in conjunction with a right column scrambler which has its entries in the extension field. We proved that this protection is useless both in terms of performance and security. Consequently, our results show that all the existingtechniques aiming to hide the inherent algebraic structure of Gabidulin codes have failed. To finish, we studied the security of the Faure-Loidreau encryption scheme [FL05] which is also a rank-metric scheme based on Gabidulin codes. Inspired by our precedent work and, although the structure of the scheme differs considerably from the classical setting of the GPT cryptosystem, we show that for a range of parameters, this scheme is also vulnerable to a polynomial-time attack that recovers the private key by applying Overbeck’s attack on an appropriate public code. As an example we break in a few seconds parameters with 80-bit security claim.

Herta Müller represents physical suffering and repression in her works, often reflecting on the regime of Nicolae Ceaușescu, and her constant interest in language and reflexivity towards writing have led her to develop sophisticated metaphors that she uses to illuminate language and its functioning under such subjugation. With reference to her fiction and non-fiction, I demonstrate how she uses concrete ideas to understand linguistic phenomena. She evokes injury, destruction, force, life, space, touch, silence, and other bodily experiences to make sense of language in the condition of suffering from social oppression. Drawing on conceptual metaphor theory within the framework of cognitive literary studies, I argue that Müller both relies on and estranges the ways in which people speak and think about language. Language is imagined differently depending on the circumstances and in close relationship with various sensory experiences. The complexity of the relationship between language and thought problematises the process of metaphor building and makes it difficult to identify its key aspects across different contexts and sensory modalities. Müller’s tropes are easy to experience, but difficult to analyse. The idea of language does not exist as a stable concept and is regularly reimagined in her texts; but its meaning is not arbitrary and depends on bodily experience. While Müller evokes such experience to understand language in the condition of suffering, she can also use linguistic concepts to elucidate more abstract ideas. Language can be regarded as an abstract or concrete phenomenon depending on the relevant bodily, linguistic, and cultural contexts. This project contributes to the study of Müller’s poetics as well as to the literary critical interpretation of embodied cognition, and develops the use of conceptual metaphor theory for literary analysis. It also seeks to develop understanding of the role of bodily experience in the metaphorical conceptualisation of language.

<p>En säker informationskanal med hög överföringskvalitet krävs i dessa dagar när informationsöverföringen ökar för varje år som går. Det finns olika sätt att skapa detta. Antingen genom att se till att överföringsmediet är av mycket hög kvalitet eller att skapa en skyddsmekanism som gör att de överföringsfel som kan uppstå kan detekteras och även korrigeras om man önskar detta. Denna uppsats handlar om detta, att kunna detektera och korrigera fel. Denna gren inom matematiken kallas kodningsteori.</p><p>Uppsatsen presenterar grunden för kodningsteorin, för att sedan presentera några vanligt förekommande kodningsalgoritmer, Hamming koder, BCH koder, Reed-Solomon. Jag går in på djupet av en av de absolut äldsta kodningsalgoritmerna, en kod som presenterades 1954 av David E. Muller, något senare presenterade en annan föregångare inom kodningsteori, Irving S. Reed, en avkodningsalgoritm för Mullers kod. Denna kod blev känd under namnet Reed-Muller kod.</p><p>Jag presenterar teorin bakom Reed-Muller kod och hur ett Reed-Muller kodord skapas med hjälp av teorin. Jag visar också hur man avkodar Reed-Muller kod med hjälp av olika algoritmer där Irving S. Reeds algoritm står i centrum. För att testa kodning och avkodning i simulerad verklighet används datorprogrammet Matlab. Slutligen presenteras hur kodnings- och avkodningsalgoritmer kan skapas med hjälp av grindnät.</p>

En säker informationskanal med hög överföringskvalitet krävs i dessa dagar när informationsöverföringen ökar för varje år som går. Det finns olika sätt att skapa detta. Antingen genom att se till att överföringsmediet är av mycket hög kvalitet eller att skapa en skyddsmekanism som gör att de överföringsfel som kan uppstå kan detekteras och även korrigeras om man önskar detta. Denna uppsats handlar om detta, att kunna detektera och korrigera fel. Denna gren inom matematiken kallas kodningsteori. Uppsatsen presenterar grunden för kodningsteorin, för att sedan presentera några vanligt förekommande kodningsalgoritmer, Hamming koder, BCH koder, Reed-Solomon. Jag går in på djupet av en av de absolut äldsta kodningsalgoritmerna, en kod som presenterades 1954 av David E. Muller, något senare presenterade en annan föregångare inom kodningsteori, Irving S. Reed, en avkodningsalgoritm för Mullers kod. Denna kod blev känd under namnet Reed-Muller kod. Jag presenterar teorin bakom Reed-Muller kod och hur ett Reed-Muller kodord skapas med hjälp av teorin. Jag visar också hur man avkodar Reed-Muller kod med hjälp av olika algoritmer där Irving S. Reeds algoritm står i centrum. För att testa kodning och avkodning i simulerad verklighet används datorprogrammet Matlab. Slutligen presenteras hur kodnings- och avkodningsalgoritmer kan skapas med hjälp av grindnät.

The purpose of this master thesis was to investigate how effiecient the extractionof radiofrequency quality metrics from digital video broadcast (DVB) streamscan become using software defined radio. Software defined radio (SDR) is a fairlynew technology that offers you the possibility of very flexible receivers and transmitters where it is possible to upgrade the modulation and demodulation overtime. Agama is interested in SDR for use in the Agama Analyzer, a widely deployedmonitoring probe running on top of standard services. Using SDR, Agama coulduse that in all deployments, such as DVB by cable/terrestrial/satellite (DVBC/T/S), which would simplify logistics. This thesis is an implementation of a SDR to be able to receive DVB-C. TheSDR must perform a number of adaptive algorithms in order to prevent the received symbols from being significantly different from the transmitted ones. Themain parts of the SDR include timing recovery, carrier recovery and equalization.Timing recovery performs synchronization between the transmitted and receivedsymbols and the carrier recovery performs synchronization between the carrierwave of the transmitter and the local oscillator in the receiver. The thesis discusses various methods to perform the different types of synchronizations andequalizations in order to find the most suitable methods.

Submitted by (ana.araujo@ufrpe.br) on 2016-07-07T12:58:08Z No. of bitstreams: 1 Juliana Katia da Silva.pdf: 2299995 bytes, checksum: 786d6f38a091474c4b7f97d00ef069a9 (MD5) / Made available in DSpace on 2016-07-07T12:58:08Z (GMT). No. of bitstreams: 1 Juliana Katia da Silva.pdf: 2299995 bytes, checksum: 786d6f38a091474c4b7f97d00ef069a9 (MD5) Previous issue date: 2009-02-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The understanding of the central mechanisms favouring sex and recombination in real populations is one of the fundamental issues in evolutionary biology. Based on a previous stochastic formulation to the study of sex, here we aim to investigate the conditions under which epistasis favours the fixation of the sexual mode of reproduction in a given population. Besides, we try to identify the evolutionary forces which contribute to this process. Our model considers a finite population model which assumes the existence of a recombination modifier allele which can activate the recombination mechanism. We have found that sex is very little favoured in a scenario of antagonistic epistasis, and this advantage only takes place in a narrow range of values of the selection coefficient, sd. On the other hand, synergistic epistasis favours recombination in a very broad domain. However, the major mechanism contributing to the spreading of the modifier allele depends on the range of values of sd. At large sd background selection favours recombination since it increases the efficacy of selection, while at low sd Muller’s ratchet is the leading mechanism. / O entendimento dos mecanismos centrais que favorecem o sexo e a recombinação nas populações é um das questões fundamentais, e que ainda se encontra indefinida, na Biologia Evolucionária. Diversos modelos e teorias têm sido propostos de forma a melhor compreender a predominância do sexo e recombinação na natureza. Uma teoria de sucesso deve ser capaz de mostrar que existem mecanismos que contrabalanceiem os custos imediatos associados à reprodução sexuada. Aqui nesta dissertação de mestrado fazemos uma extensão de um modelo estocástico para o estudo do sexo, de forma agora a verificarmos em que condições a epistasia (interação entre genes) favorece a fixação do modo de reprodução sexuado, e que mecanismos evolucionários contribuem para isto. Consideramos um modelo de população finita que assume a existência de um alelo modificador de recombinação que é então inserido em uma população inicialmente assexuada. O destino desse alelo é então analisado. Verificamos que o sexo é pouco favorecido quando consideramos o relevo com epistasia antagonística, tornando-se vantajoso em um pequeno intervalo de valores do parâmetro seletivo sd. Já no caso da epistasia sinergística, observamos uma grande vantagem para a recombinação em duas regiões distintas: uma para pequenos valores de sd, e neste caso é a Catraca de Muller o mecanismo responsável pela vantagem; e na segunda região para grandes valores de sd, o mecanismo responsável é o efeito Hill-Robertson, em que a recombinação atua de forma a aumentar a eficácia da seleção purificadora.

Submitted by (ana.araujo@ufrpe.br) on 2016-08-09T13:23:57Z No. of bitstreams: 1 Oscar Felipe Falcao Raposo.pdf: 947805 bytes, checksum: 8fe5720f628d5178eea9572acc985b50 (MD5) / Made available in DSpace on 2016-08-09T13:23:57Z (GMT). No. of bitstreams: 1 Oscar Felipe Falcao Raposo.pdf: 947805 bytes, checksum: 8fe5720f628d5178eea9572acc985b50 (MD5) Previous issue date: 2006-10-24 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / We investigate the evolution of asexual populations subject to a large supply of deleterious mutations such that Muller’s ratchet operates. In this regime, the accumulation of deleterious mutations takes place continuously with the resulting loss of the least-loaded class of individuals. In the current work, we study the effect of the supply of beneficial mutations on the ratchet’s speed. We also examine how the rate of substitution of favorable mutations as well as the mean selective effect of favorable mutations that reach fixation is compared to those assuming a population at equilibrium. We observe that under Muller’s ratchet, the rate of fixation of advantageous mutations is higher than that predicted for an equilibrium population. The difference between the rate supposing an equilibrium regime and that for the non-equilibrium case becomes larger as we increase the rate of deleterious mutations. On the other hand, the mean selective effect of beneficial mutations that reach fixation is smaller than the expected value for the equilibrium situation. / Nós investigamos a evolução das populações assexuadas sujeita à ocorrência de um fluxo contínuo de mutações deletérias, onde a Catraca de Muller opera. Neste regime, a acumulação de mutações deletérias ocorre continuamente com a conseqüente perda da classe de indivíduos mais adaptados. Na nossa dissertação nós estudamos o efeito das mutações benéficas na velocidade da catraca. Nós examinamos como a taxa de substituição das mutações benéficas como também o efeito seletivo médio das mutações favoráveis que alcançam a fixação é comparada àquelas que supõem uma população em equilíbrio. Nós observamos que sob o regime de não-equilíbrio, a taxa de fixação das mutações vantajosas é mais elevada do que aquela estimada para uma população em equilíbrio. A diferença entre a taxa que supõe um regime de equilíbrio e aquela para um regime de não-equilíbrio torna-se maior quando aumentamos a taxa de mutações deletérias. Por outro lado, o efeito seletivo médio das mutações benéficas que alcançam a fixação é menor do que o valor previsto para a situação de equilíbrio.

En produktiv ambivalens som lar absurd slapstick forenes med dypt gravalvor i et spill mellom abstrakt og konkret. Gjennom mine arbeider forsøker jeg blande sammen eller sette ulike referanser opp mot hverandre og med dette frammane en følelse av tvetydighet som jeg ofte opplever/A productive ambivalence that allows absurd slapstick to come together with the gravely serious in a play between the abstract and the concrete. Through my works I try to blend or contrast different references and thereby evoke a feeling of ambiguity that I often experience.

No description available.