[Resource Topic] 2016/398: Algebraic Insights into the Secret Feistel Network (Full version)

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Title:
Algebraic Insights into the Secret Feistel Network (Full version)

Authors: Léo Perrin, Aleksei Udovenko

Abstract:

We introduce the high-degree indicator matrix (HDIM), an object closely related with both the linear approximation table and the algebraic normal form (ANF) of a permutation. We show that the HDIM of a Feistel Network contains very specific patterns depending on the degree of the Feistel functions, the number of rounds and whether the Feistel functions are 1-to-1 or not. We exploit these patterns to distinguish Feistel Networks, even if the Feistel Network is whitened using unknown affine layers. We also present a new type of structural attack exploiting monomials that cannot be present at round r-1 to recover the ANF of the last Feistel function of a r-round Feistel Network. Finally, we discuss the relations between our findings, integral attacks, cube attacks, Todo’s division property and the congruence modulo 4 of the Linear Approximation Table.

ePrint: https://eprint.iacr.org/2016/398

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