SubstituiÃÃo homofÃnica: aspectos teÃricos e prÃticos / Homophonic substitution: theoretical and practical aspects

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

This thesis has as main purposes: a) to review the information-theoretic treatment given to the GÃntherâs type of homophonic substitution, b) to propose improvements of this approach, c) to investigate the practical implementation of homophonic substitution systems, considering that the plaintext symbol probabilities are rational numbers. The concept of strongly ideal cryptosystems introduced by Shannon is focused since it provides the motivation for any type of homophonic substitution. The definition of variable-length homophonic substitution is revisited together with the necessary and sufficient condition for such substitution to be perfect, i.e., to create a completely random sequence. Some standard homophonic substitution schemes as well as some constrained homophonic substitution schemes are analyzed. Two new standard homophonic substitution schemes are introduced. A constrained homophonic substitution scheme is proposed as well as an alternative solution to the classical problem of generating a discrete uniform probability distribution using two or more biased coins using this type of scheme. The techniques presented in this thesis contribute not only to obtain cryptosystems more resistant to cryptanalysis but also to random number generation which is used to perform tests and simulation of communication systems as well as other computational applications

ASSUNTO(S)

homophonic substitution teoria da informaÃÃo random numbers generation criptografia cryptography engenharia eletrica substituiÃÃo homofÃnica information theory geraÃÃo de nÃmeros aleatÃrios

ACESSO AO ARTIGO

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