Made available in DSpace on 2014-06-12T17:40:37Z (GMT). No. of bitstreams: 2 arquivo7039_1.pdf: 1009362 bytes, checksum: 625b48f5d5a3de823ef461b914c02a80 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2003 / Desde a criação do padrão de cifragem de dados DES (Data Encryption Standard) em 1978, cifras iterativas de chave secreta baseadas em redes de Feistel têm sido construídas, visando a aumentar a segurança das informações armazenadas e transmitidas em ambientes de comunicações inseguros. Tais cifras, além de apresentarem, em geral, um alto nível de resistência a ataques criptoanalíticos, permitem implementações eficientes em diferentes plataformas, sendo portanto uma alternativa muito atraente para a proteção de grandes massas de dados. Uma das técnicas mais eficientes para criptoanalisar esse tipo de cifra é a chamada Criptoanálise Diferencial, introduzida em 1990 por Biham e Shamir. Este trabalho tem como objetivo apresentar um estudo da técnica de Criptoanálise Diferencial, bem como demonstrar uma aplicação da mesma na criptoanálise do criptosistema de chave secreta Blowfish, introduzido por Schneier em 1994. Inicialmente o trabalho aborda os principais aspectos matemáticos relacionados com a criptografia de chave secreta e, em seguida, apresenta uma introdução à área de Segurança de Dados, discorrendo sobre aspectos importantes da mesma, tais como criptografia de chave secreta e de chave pública. Além disso, são também descritos os cripto-sistemas de chave secreta DES, RC5, IDEA e Blowfish. A técnica da Criptoanálise Diferencial é então considerada em detalhes, onde são examinados os conceitos mais importantes da mesma, tais como as noções de pares diferenciais e características, entre outros. Uma aplicação da técnica é então apresentada, na avaliação do grau de segurança da cifra de bloco Blowfish

Šiame darbe supažindinama su kriptografija, jos istorija, pagrindiniais kriptografijos principais, šifravimo algoritmų tipais, jų taikymo sritimis, privalumais bei trūkumais. Taip pat apibrėžiamos pagrindinės sąvokos ir terminai, išvardinti kriptoanalitinių atakų tipai ir reikalavimai kriptosistemoms. Svarstoma, ar egzistuoja absoliučiai patikimi šifravimo algoritmai. Trumpai aprašomi pagrindiniai šifravimo būdai ir kriptoanalitiniai metodai. Darbe yra nagrinėjami blokiniai (DES, GOST, LOKI 91, SAFER K-64, FEAL–8, Blowfish, AES (Rijndael)) šifravimo algoritmai, išaiškinama jų svarba kriptografijoje, išsamiai aprašoma jų struktūra, atsparumas kriptoanalizei, išaiškinami privalumai bei trūkumai. Nagrinėjami algoritmų taikymų ypatumai, galimybės, apribojimai. Analizuojami algoritm��� atsparumo kriptoanalizei kriterijai, jų svarba bei algoritmų patikimumo priežastys. Išnagrinėjus esamus blokinius šifravimo algoritmus, buvo atliktas jų tarpusavio palyginimas. Nustatyta, kad šifravimo algoritmo patikimumas priklauso nuo atsparumo kriptoanalitiniams metodams, rakto ilgio, algoritmo architektūros. Išaiškinami pagrindiniai algoritmų privalumai: realizavimo lankstumas, kintamas rakto ilgis, numatantis algoritmo ilgaamžiškumą. Taip pat nurodoma, kad duomenų sauga priklauso ne tik nuo šifravimo algoritmo, bet ir nuo kitų informacijos saugos aspektų: raktų apsaugos, jų paskirstymo, atsitiktinių skaičių generavimo būdų. / This work presents cryptography, its history, main principles of cryptography, types of ciphers, their application range, advantages and disadvantages. Key concepts and term are also defined. Complexity of attacks and requirement to cryptographic systems are listed and described. A question of the existence of the absolutely safe ciphers is considered. The main encryption modes and cryptanalysis methods are described. Research of the most prominent block ciphers and their importance to many cryptographic systems is presented in this work. The structure of block ciphers, their resistance to cryptanalysis are given in details and expositive strength of block ciphers. Their advantages and disadvantages are discovered and stated. Ciphers application range, their potential and restrictions are researched. Criteria of the resistance of ciphers to cryptanalysis, their importance and the reasons of cipher reliability are analyzed. After analyzing the block ciphers such us: DES, GOST, LOKI 91, SAFER K-64, FEAL–8, Blowfish, AES (Rijndael), their inter comparison was performed. It was noted that the reliability of ciphers depends on their resistance to cryptanalysis methods, key length and their architecture. The following major advantages of ciphers as flexibility of realization, changeable key length and facilitating cipher durability are discovered. The following conclusion has been drawn, that data safety depends not only on ciphers, but also on other aspects of information safety... [to full text]

The purpose of this thesis work was to conduct a general research on existing security techniques and come up with a considerable algorithm for data security in cloud storage. Cloud storage is an infrastructure or is a model of computer data storage in which the digital data is stored in logical pools. It unifies object storage for both developers and enterprises, from live applications data to cloud archival. It help to save valuable space on PC computers or mobile devices and provides the easy storage and access of data anywhere in the world. However, just as the benefits of cloud computing abounds, so also are the risks involved. If data are not well secured or encrypted before deployment for storage in the cloud, in case of negligence on the side of the developers, then hackers can gain unauthorized access to the data. The behavior of existing security algorithms on data were studied, the encryption and decryption process of the each algorithm on data was studied and also their weaknesses against attacks. Apart from data encryption, security policies also plays an important roll in cloud storage which was also covered in this report. The research work was conducted through the use of online publications, literature review, books, academic publications and reputable research materials. The study showed that regardless of the challenges in cloud storage, there is still a suitable algorithm for protecting data against attack in the cloud.

This master's thesis is about making draft and implementing land-line phone call encryption using FITkit. The ultimate goal is to find suitable compression and encryption methods, implement or adapt them for FITkit board and create functional solution.

In this project you can find a study about different encryption algorithms, which are use to safeguard the information on messages over the network. We have developed a client-server application which will send information through the network which has to be secured. There are two kinds of encryption algorithms, the symmetric and the asymmetric key algorithms. Both were used to establish the communication, the asymmetric algorithm (RSA) is used to set up a symmetric key and then, all the communication process is done only with the symmetric algorithm (Blowfish). / En este proyecto encontraras un estudio sobre diferentes algoritmos de encriptación, que son usados para salvaguardar la información en mensajes por la red. Además hemos desarrollado una aplicación cliente-servidor que enviara información a través de la red de forma segura. Hay dos tipos de algoritmos de encriptación, los simétricos y los asimétricos. Ambos tipos de algoritmos son utilizados para establecer la comunicación, el asimétrico (RSA) es utilizado para establecer la clave del simétrico y a partir de entonces se utilizara exclusivamente el algoritmo simétrico (Blowfish).