This work explores two methods for practical cryptography on mobile devices. The first method is a quantum-resistant key-exchange protocol proposed by Jao et al.. As the use of mobile devices increases, the deployment of practical cryptographic protocols designed for use on these devices is of increasing importance. Furthermore, we are faced with the possible development of a large-scale quantum computer in the near future and must take steps to prepare for this possibility. We describe the key-exchange protocol of Jao et al. and discuss their original implementation. We then describe our modifications to their scheme that make it suitable for use in mobile devices. Our code is between 18-26% faster (depending on the security level). The second is an highly optimized implementation of Miller's algorithm that efficiently computes the Optimal Ate pairing over Barreto-Naehrig curves proposed by Grewal et al.. We give an introduction to cryptographic pairings and describe the Tate pairing and its variants. We then proceed to describe Grewal et al.'s implementation of Miller's algorithm, along with their optimizations. We describe our use of hand-optimized assembly code to increase the performance of their implementation. For the Optimal Ate pairing over the BN-446 curve, our code is between 7-8% faster depending on whether the pairing uses affine or projective coordinates.

The aim of the research presented in this thesis is to investigate the use of various optimisation heuristics in the fields of automated cryptanalysis and automated cryptographic function generation. These techniques were found to provide a successful method of automated cryptanalysis of a variety of the classical ciphers. Also, they were found to enhance existing fast correlation attacks on certain stream ciphers. A previously proposed attack of the knapsack cipher is shown to be flawed due to the absence of a suitable solution evaluation mechanism. Finally, a new approach for finding highly nonlinear Boolean functions is introduced.

Made available in DSpace on 2016-12-23T14:00:40Z (GMT). No. of bitstreams: 1 FACE.pdf: 89333 bytes, checksum: 9fe2d3791aae56820ee8b6646c8b46fd (MD5) Previous issue date: 2003-06-26 / CAPES / Trata-se de uma abordagem teórica sobre Propriedade Intelectual com ênfase em Trade Secrets como barreira à entrada. Os avanços em criptologia no campo da matemática podem vir a se somar aos esforços teóricos desenvolvidos em Microeconomia em Organização Industrial. Neste contexto, a criptologia é resgatada historicamente e são apresentadas suas principais funções na Propriedade Intelectual, em especial no Trade Secrets. Questiona-se aqui: Por que as empresas criptografam seus processos produtivos? A propriedade intelectual em especial os Trade Secrets tem desempenhado importante papel, enquanto barreira à entrada na economia contemporânea? Como a criptologia e seus respectivos desenvolvimentos na matemática podem contribuir para o fortalecimento do segredo industrial? Percebe-se que apesar da presença marcante da criptografia e dos bens incorpóreos na Economia Contemporânea, ainda são escassas as análises teóricas, os estudos de caso e os bancos de dados sobre Propriedade Intelectual e principalmente, sobre Trade Secrets. Contribui ao explicitar seus conceitos e alertar para a importância de intensificação de pesquisa científica sobre o tema possibilitando, dessa forma, uma melhor compreensão da dinâmica econômica empresarial na atualidade. / This work presents a theoretical approach on intellectual property with emphasis in trade secrets as entry barriers. Progress in cryptology in the field of the mathematics can be added to the theoretical efforts developed in microeconomics in industrial organization. In this context, cryptology is rescued historically and its main functions are presented in the intellectual property, especially in trade secrets. This research questions: Why do the firms cryptograph their productive processes? Has intellectual property, especially trade secrets, been playing an important role as a barrier to entry in the contemporary economy? How can cryptology and its respective developments in mathematics contribute to the strengthening of the industrial secret? It is noticed that in spite of the outstanding presence of cryptography and of the incorporeal goods in the contemporary economy, the theoretical analyses are still scarce, as are case studies and databases on intellectual property and mainly, on trade secrets. This research contributes to explication of its concepts and warns about the importance of intensification of scientific research on this topic, in order to reach a better understanding of managerial economical dynamics at the present time.

This thesis describes methods of secret communication based on latin squares and their close relative, quasigroups. Different types of cryptosystems are described, including ciphers, public-key cryptosystems, and cryptographic hash functions. There is also a chapter devoted to different secret sharing schemes based on latin squares. The primary objective is to present previously described cryptosystems and secret sharing schemes in a more accessible manner, but this text also defines two new ciphers based on isotopic latin squares and reconstructs a lost proof related to row-latin squares. / Denna uppsats beskriver kryptosystem och metoder för hemlighetsdelning baserade på latinska kvadrater och det närliggande konceptet kvasigrupper. Olika sorters chiffer, både symmetriska och asymmetriska, behandlas. Dessutom finns ett kapitel tillägnat kryptografiska hashfunktioner och ett tillägnat metoder för hemlighetsdelning. Huvudsyftet är att beskriva redan existerande metoder för hemlig kommunikation på ett mer lättillgängligt sätt och med nya exempel, men dessutom återskapas ett, till synes, förlorat bevis relaterat till rad-latinska kvadrater samt beskrivs två nya chiffer baserade på isotopa latinska kvadrater.

This diploma thesis deals with certification and certification authorities, certification path PKI and principles of its validation and security. Also deals with structure of certificate itself and possible misuse of included information. Moreover, possibility of misues of third party certificates and proclamation of untrusted certificate to client's system.

Le chiffrement homomorphe est une branche de la cryptologie, dans laquelle les schémas de chiffrement offrent la possibilité de faire des calculs sur les messages chiffrés, sans besoin de les déchiffrer. L’intérêt pratique de ces schémas est dû à l’énorme quantité d'applications pour lesquels ils peuvent être utilisés. En sont un exemple le vote électronique, les calculs sur des données sensibles, comme des données médicales ou financières, le cloud computing, etc..Le premier schéma de chiffrement (complètement) homomorphe n'a été proposé qu'en 2009 par Gentry. Il a introduit une technique appelée bootstrapping, utilisée pour réduire le bruit des chiffrés : en effet, dans tous les schémas de chiffrement homomorphe proposés, les chiffrés contiennent une petite quantité de bruit, nécessaire pour des raisons de sécurité. Quand on fait des calculs sur les chiffrés bruités, le bruit augmente et, après avoir évalué un certain nombre d’opérations, ce bruit devient trop grand et, s'il n'est pas contrôlé, risque de compromettre le résultat des calculs.Le bootstrapping est du coup fondamental pour la construction des schémas de chiffrement homomorphes, mais est une technique très coûteuse, qu'il s'agisse de la mémoire nécessaire ou du temps de calcul. Les travaux qui on suivi la publication de Gentry ont eu comme objectif celui de proposer de nouveaux schémas et d’améliorer le bootstrapping pour rendre le chiffrement homomorphe faisable en pratique. L’une des constructions les plus célèbres est GSW, proposé par Gentry, Sahai et Waters en 2013. La sécurité du schéma GSW se fonde sur le problème LWE (learning with errors), considéré comme difficile en pratique. Le bootstrapping le plus rapide, exécuté sur un schéma de type GSW, a été proposé en 2015 par Ducas et Micciancio. Dans cette thèse on propose une nouvelle variante du schéma de chiffrement homomorphe de Ducas et Micciancio, appelée TFHE.Le schéma TFHE améliore les résultats précédents, en proposant un bootstrapping plus rapide (de l'ordre de quelques millisecondes) et des clés de bootstrapping plus petites, pour un même niveau de sécurité. TFHE utilise des chiffrés de type TLWE et TGSW (scalaire et ring) : l’accélération du bootstrapping est principalement due à l’utilisation d’un produit externe entre TLWE et TGSW, contrairement au produit externe GSW utilisé dans la majorité des constructions précédentes.Deux types de bootstrapping sont présentés. Le premier, appelé gate bootstrapping, est exécuté après l’évaluation homomorphique d’une porte logique (binaire ou Mux) ; le deuxième, appelé circuit bootstrapping, peut être exécuté après l’évaluation d’un nombre d'opérations homomorphiques plus grand, pour rafraîchir le résultat ou pour le rendre compatible avec la suite des calculs.Dans cette thèse on propose aussi de nouvelles techniques pour accélérer l’évaluation des calculs homomorphiques, sans bootstrapping, et des techniques de packing des données. En particulier, on présente un packing, appelé vertical packing, qui peut être utilisé pour évaluer efficacement des look-up table, on propose une évaluation via automates déterministes pondérés, et on présente un compteur homomorphe appelé TBSR qui peut être utilisé pour évaluer des fonctions arithmétiques.Pendant les travaux de thèse, le schéma TFHE a été implémenté et il est disponible en open source.La thèse contient aussi des travaux annexes. Le premier travail concerne l’étude d’un premier modèle théorique de vote électronique post-quantique basé sur le chiffrement homomorphe, le deuxième analyse la sécurité des familles de chiffrement homomorphe dans le cas d'une utilisation pratique sur le cloud, et le troisième ouvre sur une solution différente pour le calcul sécurisé, le calcul multi-partite. / Fully homomorphic encryption is a new branch of cryptology, allowing to perform computations on encrypted data, without having to decrypt them. The main interest of homomorphic encryption schemes is the large number of practical applications for which they can be used. Examples are given by electronic voting, computations on sensitive data, such as medical or financial data, cloud computing, etc..The first fully homomorphic encryption scheme has been proposed in 2009 by Gentry. He introduced a new technique, called bootstrapping, used to reduce the noise in ciphertexts: in fact, in all the proposed homomorphic encryption schemes, the ciphertexts contain a small amount of noise, which is necessary for security reasons. If we perform computations on noisy ciphertexts, the noise increases and, after a certain number of operations, the noise becomes to large and it could compromise the correctness of the final result, if not controlled.Bootstrapping is then fundamental to construct fully homomorphic encryption schemes, but it is very costly in terms of both memory and time consuming.After Gentry’s breakthrough, the presented schemes had the goal to propose new constructions and to improve bootstrapping, in order to make homomorphic encryption practical. One of the most known schemes is GSW, proposed by Gentry, Sahai et Waters in 2013. The security of GSW is based on the LWE (learning with errors) problem, which is considered hard in practice. The most rapid bootstrapping on a GSW-based scheme has been presented by Ducas and Micciancio in 2015. In this thesis, we propose a new variant of the scheme proposed by Ducas and Micciancio, that we call TFHE.The TFHE scheme improves previous results, by performing a faster bootstrapping (in the range of a few milliseconds) and by using smaller bootstrapping keys, for the same security level. TFHE uses TLWE and TGSW ciphertexts (both scalar and ring): the acceleration of bootstrapping is mainly due to the replacement of the internal GSW product, used in the majority of previous constructions, with an external product between TLWE and TGSW.Two kinds of bootstrapping are presented. The first one, called gate bootstrapping, is performed after the evaluation of a homomorphic gate (binary or Mux); the second one, called circuit bootstrapping, can be executed after the evaluation of a larger number of homomorphic operations, in order to refresh the result or to make it compatible with the following computations.In this thesis, we also propose new techniques to improve homomorphic computations without bootstrapping and new packing techniques. In particular, we present a vertical packing, that can be used to efficiently evaluate look-up tables, we propose an evaluation via weighted deterministic automata, and we present a homomorphic counter, called TBSR, that can be used to evaluate arithmetic functions.During the thesis, the TFHE scheme has been implemented and it is available in open source.The thesis contains also ancillary works. The first one concerns the study of the first model of post-quantum electronic voting based on fully homomorphic encryption, the second one analyzes the security of homomorphic encryption in a practical cloud implementation scenario, and the third one opens up about a different solution for secure computing, multi-party computation.

This thesis presents a computationally efficient cryptosystem based on chaotic continuous-interval cellular automata (CCA). This cryptosystem increases data protection as demonstrated by its flexibility to encrypt/decrypt information from distinct sources (e.g., text, sound, and images). This cryptosystem has the following enhancements over the previous chaos-based cryptosystems: (i) a mathematical model based on a new chaotic CCA strange attractor, (ii) integration of modules containing dynamical systems to generate complex sequences, (iii) generation of an unlimited number of keys due to the features of chaotic phenomena obtained through CCA, which is an improvement over previous symmetric cryptosystems, and (iv) a high-quality concealment of the cryptosystem strange attractor. Instead of using differential equations, a process of mixing chaotic sequences obtained from CCA is also introduced. As compared to other recent approaches, this mixing process provides a basis to achieve higher security by using a higher degree of complexity for the encryption/decryption processes. This cryptosystem is tested through the following three methods: (i) a stationarity test based on the invariance of the first ten statistical moments, (ii) a polyscale test based on the variance fractal dimension trajectory (VFDT) and the spectral fractal dimension (SFD), and (iii) a surrogate data test. This cryptosystem secures data from distinct sources, while leaving no patterns in the ciphertexts. This cryptosystem is robust in terms of resisting attacks that: (i) identify a chaotic system in the time domain, (ii) reconstruct the chaotic attractor by monitoring the system state variables, (iii) search the system synchronization parameters, (iv) statistical cryptanalysis, and (v) polyscale cryptanalysis.

This thesis presents a computationally efficient cryptosystem based on chaotic continuous-interval cellular automata (CCA). This cryptosystem increases data protection as demonstrated by its flexibility to encrypt/decrypt information from distinct sources (e.g., text, sound, and images). This cryptosystem has the following enhancements over the previous chaos-based cryptosystems: (i) a mathematical model based on a new chaotic CCA strange attractor, (ii) integration of modules containing dynamical systems to generate complex sequences, (iii) generation of an unlimited number of keys due to the features of chaotic phenomena obtained through CCA, which is an improvement over previous symmetric cryptosystems, and (iv) a high-quality concealment of the cryptosystem strange attractor. Instead of using differential equations, a process of mixing chaotic sequences obtained from CCA is also introduced. As compared to other recent approaches, this mixing process provides a basis to achieve higher security by using a higher degree of complexity for the encryption/decryption processes. This cryptosystem is tested through the following three methods: (i) a stationarity test based on the invariance of the first ten statistical moments, (ii) a polyscale test based on the variance fractal dimension trajectory (VFDT) and the spectral fractal dimension (SFD), and (iii) a surrogate data test. This cryptosystem secures data from distinct sources, while leaving no patterns in the ciphertexts. This cryptosystem is robust in terms of resisting attacks that: (i) identify a chaotic system in the time domain, (ii) reconstruct the chaotic attractor by monitoring the system state variables, (iii) search the system synchronization parameters, (iv) statistical cryptanalysis, and (v) polyscale cryptanalysis.

Made available in DSpace on 2014-12-17T15:47:44Z (GMT). No. of bitstreams: 1 SamuelOA.pdf: 1023593 bytes, checksum: 651d5e25960d6664c54a1e7690f2acb6 (MD5) Previous issue date: 2007-08-06 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / In this work, we propose a multi agent system for digital image steganalysis, based on the poliginic bees model. Such approach aims to solve the problem of automatic steganalysis for digital media, with a case study on digital images. The system architecture was designed not only to detect if a file is suspicious of covering a hidden message, as well to extract the hidden message or information regarding it. Several experiments were performed whose results confirm a substantial enhancement (from 67% to 82% success rate) by using the multi-agent approach, fact not observed in traditional systems. An ongoing application using the technique is the detection of anomalies in digital data produced by sensors that capture brain emissions in little animals. The detection of such anomalies can be used to prove theories and evidences of imagery completion during sleep provided by the brain in visual cortex areas / Neste trabalho, propomos um sistema multi-agentes para estegan?lise em imagens digitais, baseado na met?fora das abelhas polig?nicas. Tal abordagem visa resolver o problema da estegan?lise autom?tica de m?dias digitais, com estudo de caso para imagens digitais. A arquitetura do sistema foi projetada n?o s? para detectar se um arquivo ? ou n?o suspeito de possuir uma mensagem oculta em si, como tamb?m para extrair essa mensagem ou informa??es acerca dela. Foram realizados v?rios experimentos cujos resultados confirmam uma melhoria substancial (de 67% para 82% de acertos) com o uso da abordagem multi-agente, fato n?o observado em outros sistemas tradicionais. Uma aplica??o atualmente em andamento com o uso da t?cnica ? a detec??o de anomalias em dados digitais produzidos por sensores que captam emiss?es cerebrais em pequenos animais. A detec??o de tais anomalias pode ser usada para comprovar teorias e evidencias de complementa??o do imageamento durante o sono, provida pelo c?rebro nas ?reas visuais do c?rtex cerebral

The Master thesis is an introduction to cryptology. The Thesis describe cryptosystems and selects one ideal cypher for low-power microcontroler. In thesis provides manual for instal development program COde Composer Studio, basic implementation of selected cryptosystem with small numbers and suggestion for implementation selected cyptosystem with big numbers.