Critères de sécurité des algorithmes de chiffrement à clé secrète

Marion Videau 1
1 CODES - Coding and cryptography
Inria Paris-Rocquencourt
Abstract : The work done during my thesis concerns two different aspects of the
security of secret key ciphers. The first part is devoted to the study
of the security of iterated block ciphers against last round attacks
based on distinguishers. The results especially concern a
generalisation of a higher order differential attack that was lead
against MISTY1 algorithm. The origin of this attack and of its
generalisation has been explained thanks to the properties of the
Walsh spectra of the highly nonlinear functions used in the
cipher. Hence, it has been possible to mount a generic attack against
all Feistel ciphers using confusion functions whose Walsh spectra are
divisible by a high power of 2. Indeed, this property leads to an
upper bound for the degree of the composition of such functions which
can be noticeably smaller than the trivial bound. Thus the attack we
have mounted leads to a new security criterion for iterated block
ciphers which lies on the divisibility of the Walsh spectra of the
round functions. The second part of my work is a study of
cryptographic properties of symmetric Boolean functions. Starting from
a structural property of one representation of symmetric Boolean
functions, we improve existing results concerning algebraic degree,
balance, resiliency, propagation criterion and nonlinearity of such
functions. Besides, we compute explicitly the Walsh spectra of all
symmetric Boolean functions of degree 2 and 3. We also determine all
the balance symmetric Boolean functions of degree less than or equal
to 7, for all number of variables.
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https://tel.archives-ouvertes.fr/tel-00011927
Contributor : Marion Videau <>
Submitted on : Sunday, March 12, 2006 - 5:28:40 PM
Last modification on : Thursday, February 7, 2019 - 1:33:11 AM
Long-term archiving on : Monday, September 17, 2012 - 12:30:41 PM

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  • HAL Id : tel-00011927, version 1

Citation

Marion Videau. Critères de sécurité des algorithmes de chiffrement à clé secrète. Autre [cs.OH]. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00011927⟩

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