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Introdução De Mecanismos De Segurança Em Sistemas De Correio Eletrônico

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Introdução De Mecanismos De Segurança Em Sistemas De Correio Eletrônico Introdução de Mecanismos de Segurança em Sistemas de Correio Eletrônico Paulo Sergio Pagliusi Dissertação de Mestrado Instituto de Computação Universidade Estadual de Campinas Introdução de Mecanismos de Segurança em Sistemas de Correio Eletrônico Paulo Sergio Pagliusi fevereiro, 98 Banca Examinadora: • Prof. Dr. Cláudio Leonardo Lucchesi (Orientador) Instituto de Computação — UNICAMP • Prof. Dr. Routo Terada Instituto de Matemática e Estatística - USP • Prof. Dr. Paulo Lício de Geus Instituto de Computação — UNICAMP • Prof. Dr. Ricardo Dahab (Suplente) Instituto de Computação — UNICAMP Co-orientador: • Prof. Dr. Luiz Eduardo Buzato Instituto de Computação — UNICAMP Introdução de Mecanismos de Segurança em Sistemas de Correio Eletrônico ii Este exemplar corresponde à redação final da Dis- sertação devidamente corrigida e defendida por Paulo Sergio Pagliusi e aprovada pela Banca Exa- minadora. Campinas, 27 de Fevereiro de 1998. Prof. Dr. Cláudio Leonardo Lucchesi (Orientador) Dissertação apresentada ao Instituto de Computa- ção, UNICAMP, como requisito parcial para a ob- tenção do título de mestre em Ciência da Compu- tação. iii iv © Paulo Sergio Pagliusi, 1998. Todos os direitos reservados. v À memória de meu avô, Godofredo Pagliusi. vi Resumo Este trabalho tem por objetivo apresentar e avaliar um sistema criado para prover segurança ao ambiente de correio eletrônico do editor Emacs: o programa ProtegeMail. Construído na linguagem Emacs LISP, o ProtegeMail consiste em uma extensão dos subsistemas de correio eletrônico do Emacs (VM, RMAIL, MH-E e GNUS). Ele funciona como uma interface modular para chamar funções criptográficas existentes nos programas de segurança de e-mail PGP e RIPEM. Inicialmente, este trabalho apresenta e discute a funcionalidade, a segurança e os protocolos, padrões e programas relacionados com o conceito de correio eletrônico. Em seguida, apresenta os aspectos específicos da utilização de criptografia em correio eletrônico. Depois, descreve e compara os pacotes PGP e PEM. Também apresenta e analisa a escolha do Emacs como ambiente alvo. Por fim, descreve e avalia o sistema ProtegeMail, através de suas principais funções e da segurança que proporciona ao usuário. vii Abstract The major goal of this work is to present and to evaluate a system created to provide security for the Emacs editor electronic mail environment: the ProtegeMail program. Developed with Emacs Lisp language, ProtegeMail consists of an Emacs e-mail subsystems (VM, RMAIL, MH-E and GNUS) extension. It operates like a modular interface, calling cryptographic functions existing in PGP and RIPEM e-mail security programs. First, this work presents and discusses the functionality, security, and the protocols, standards and programs related with electronic mail concept. It then presents specific aspects of criptography applied to electronic mail. After this, it describes and compares PGP and PEM packets. It also presents and analyzes the choice of Emacs as a target environment. Finally, it describes and evaluates the ProtegeMail system, through its main functions and the security that it provides to the user. viii Agradecimentos Desejo expressar meus sinceros agradecimentos aos Professores Cláudio Leonardo Lucchesi (Orientador) e Luiz Eduardo Buzato (Co-orientador) pela assistência fornecida na preparação deste trabalho. Além disso, agradeço ao pessoal do Grupo Cripto do Instituto de Computação da UNICAMP, em especial aos colegas Monteiro, Jerônimo, Oliva, Lucas, Keesje e Luiz Eduardo cuja disposição em conhecer e se familiarizar com as necessidades do ProtegeMail foram bastante úteis durante a fase de implementação e testes deste Projeto. Agradeço também aos membros do “staff” do Instituto de Computação, aos colegas da Marinha e companheiros de curso Núccio, Marques, Lúcio, Silva Roberto, Augusto e Francisco. E ao pessoal da Diretoria de Telecomunicações da Marinha e do Centro de Análises de Sistemas Navais por suas valiosas contribuições. É importante ressaltar o apoio de meus pais, Adauto e Nilza, a paciência e a dedicação de minha querida mulher, Márcia, e o carinho dos meus filhos, Daniel e Rodrigo, para a consecução deste projeto. ix ÍNDICE ANALÍTICO Resumo........................................................................................................................................................................... vii Abstract ........................................................................................................................................................................ viii Agradecimentos ............................................................................................................................................................. ix Lista de Figuras ........................................................................................................................................................... xiii Lista de Tabelas ........................................................................................................................................................... xiv Glossário de Siglas........................................................................................................................................................ xv Prefácio: A Importância do Correio Eletrônico Seguro ......................................................................................... xix 0. Introdução ................................................................................................................................................................... 1 0.1. OBJETIVO .............................................................................................................................................................. 3 0.2. IMPORTÂNCIA DO TRABALHO ............................................................................................................................... 3 0.3. ORGANIZAÇÃO ...................................................................................................................................................... 4 PARTE I: CORREIO ELETRÔNICO................................................................................................................................... 6 1. Funcionalidade............................................................................................................................................................ 6 1.1. CONCEITOS BÁSICOS............................................................................................................................................. 7 1.2. ATRIBUIÇÃO DE NOMES ........................................................................................................................................ 8 1.3. FORMATO DA MENSAGEM..................................................................................................................................... 8 1.3.1. O Formato RFC 822..................................................................................................................................... 9 1.3.2. Cabeçalho e Corpo da Mensagem.............................................................................................................. 10 1.4. SINTAXE DE ENDEREÇOS..................................................................................................................................... 13 1.4.1. Nome da Mailbox....................................................................................................................................... 14 1.4.2. Domínio ...................................................................................................................................................... 16 1.5. ARQUITETURA DO CORREIO ELETRÔNICO .......................................................................................................... 19 1.5.1. Componentes Básicos................................................................................................................................. 20 1.5.2. Procedimentos do SMTP............................................................................................................................ 21 1.5.3. A Transferência de Mensagens pelo SMTP............................................................................................... 24 1.5.4. A Expansão de Apelidos ............................................................................................................................ 29 1.6. ATRIBUTOS TECNOLÓGICOS DO CORREIO ELETRÔNICO ..................................................................................... 31 2. Segurança .................................................................................................................................................................. 34 2.1. O PROBLEMA DA SEGURANÇA DOS SISTEMAS DE E-MAIL ................................................................................. 35 2.1.1. O Problema da Coleta e As Ameaças à Segurança.................................................................................... 37 2.1.2. O Gerenciamento das Chaves..................................................................................................................... 40 2.1.3. Métodos de Ataque..................................................................................................................................... 45 2.1.4. Serviços de Segurança................................................................................................................................ 49 2.1.5. Padrões e
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