In 1976, Diffie and Hellman proposed the concept of public key cryptosystem (PKC). The application and research of public key cryptography are arisen in the modern cryptography. In 2005, Sun, Hsieh, and Hwang (S.H.H.) proposed an electronic mail protocol based on classic public key cryptography. The technique of the Certificate of Encrypted Message Being a Signature (CEMBS) that Bao proposed in 1998 is applied on session key sharing of their e-mail system. In the same year, Dent pointed out that the first one of S.H.H.¡¦s e-mail protocols cannot suffice the property of forward secrecy. Thus, Kim, Koo, and Lee (K.K.L.) proposed two e-mail protocols based on signcryption concept which is proposed by Zheng in 1997 to overcome the flaw of S.H.H.¡¦s e-mail protocol in 2006. Lin, Lin, and Wang (L.L.W.) pointed out that the second one of S.H.H.¡¦s protocols cannot achieve forward secrecy and then they improved the protocol. In 2007, Yoon and Yoo claimed that the second one of K.K.L.¡¦s protocols is still vulnerable to two possible forgery attacks. In this thesis, we will make deep discussions about secure e-mail protocols based on PKC with providing the property of forward secrecy and then build a novel e-mail protocol to withstand the above attacks. Our proposed e-mail protocol can achieve the properties of authentication, confidentiality, integrity, non-repudiation and forward secrecy.

Submitted by Daniele Amaral (daniee_ni@hotmail.com) on 2016-09-15T16:05:03Z No. of bitstreams: 1 DissWCCJ.pdf: 1969639 bytes, checksum: cbe6746c0279668ba7ff3b8de72d8caf (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:51:53Z (GMT) No. of bitstreams: 1 DissWCCJ.pdf: 1969639 bytes, checksum: cbe6746c0279668ba7ff3b8de72d8caf (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:51:57Z (GMT) No. of bitstreams: 1 DissWCCJ.pdf: 1969639 bytes, checksum: cbe6746c0279668ba7ff3b8de72d8caf (MD5) / Made available in DSpace on 2016-09-16T19:52:02Z (GMT). No. of bitstreams: 1 DissWCCJ.pdf: 1969639 bytes, checksum: cbe6746c0279668ba7ff3b8de72d8caf (MD5) Previous issue date: 2015-08-21 / Não recebi financiamento / Cryptography is a fascinating topic, concerning the practical point of view, and it is useful to access bank accounts, e-mails and social networks. According to this perspective, this study aimed to show how simple it may be to make use of cryptography. It was proved, through the work performed, that it is possible for students from elementary and high school to encrypt and decrypt messages using R.S.A. Cryptography, which involves the concept of creating public keys and private keys for the encryption of messages. A simple but powerful activity on the utility view was assigned to show students from the 9th grade of elementary school and from the 1st and 2nd years of high school from a private school in São Paulo State how interesting and pleasurable the use of Mathematics can be. Such activities are not usually present in the traditional didactic materials. The theoretical tools, containing theorem and corollaries, as well as their demonstrations, which mathematically justify the validity of techniques and the algorithm used on R.S.A. Cryptography will be presented. The activities do not assume sophisticated prerequisites and can be applied in the classroom, in real situations, so that the students can appreciate the beauty of Mathematics. / A criptografia é um assunto fascinante do ponto de vista prático; é útil para acessar contas bancárias, e-mails e redes sociais. Segundo esta perspectiva, esta dissertação baseou-se em mostrar o quão simples pode ser a utilização da criptografia. No trabalho realizado foi mostrado que é possível, para alunos do Ensino Fundamental e Médio, codificar e decifrar mensagens utilizando a criptografia - RSA, a qual envolve o conceito da criação de chaves públicas e chaves privadas para a codificação de mensagens. Uma atividade simples, porém importante do ponto de vista utilitário, foi aplicada para mostrar aos alunos do 9º ano do Ensino Fundamental, da 1ª e 2ª séries do Ensino Médio de uma escola particular do interior paulista para mostrar o quão interessante e prazerosa pode ser a utilização da Matemática. Tais atividades não constam usualmente nos materiais didáticos tradicionais. Nesta dissertação será apresentado o ferramental teórico, contendo teoremas e corolários, assim como suas demonstrações, os quais justificam, matematicamente, a validade das técnicas e do algoritmo utilizados na criptografia – RSA. As atividades não pressupõem pré-requisitos sofisticados, podendo ser aplicadas em sala de aula, em situações reais, para que os alunos apreciem a beleza da Matemática.