Generalised S - Box Nonlinearity NES / DOC / UIB / WP 5 / 020 / A Matthew
نویسنده
چکیده
In this paper the (effective) bias of certain generalised linear approximations to the S-box are considered. Whereas, in the literature, the cryptanalyst typically restricts this search to linear approximations over Z2, we here consider linear approximations over Z4 and, more generally still, consider approximations which are linear in the sense that they can be completely factorised into the tensor product of length-two vectors. Consequently, significantly higher biases can be found in comparison to Z2-linear approximations.
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