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Paper: Generic Attacks on Unbalanced Feistel Schemes with Expanding Functions

Authors:
Valérie Nachef
Jacques Patarin
C?me Berbain
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URL: http://eprint.iacr.org/2007/449
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Abstract: \begin{abstract} Unbalanced Feistel schemes with expanding functions are used to construct pseudo-random permutations from $kn$ bits to $kn$ bits by using random functions from $n$ bits to $(k-1)n$ bits. At each round, all the bits except $n$ bits are changed by using a function that depends only on these $n$ bits. C.S.Jutla \cite{Jut} investigated such schemes, which he denotes by $F^d_k$, where $d$ is the number of rounds. In this paper, we describe novel Known Plaintext Attacks (KPA) and Non Adaptive Chosen Plaintext Attacks (CPA-1) against these schemes. With these attacks we will often be able to improve the result of C.S.Jutla. We also give precise formulas for the complexity of our attacks in $d$, $k$ and $n$. \end{abstract}
BibTeX
@misc{eprint-2007-13729,
  title={Generic Attacks on Unbalanced Feistel Schemes with Expanding Functions},
  booktitle={IACR Eprint archive},
  keywords={block ciphers},
  url={http://eprint.iacr.org/2007/449},
  note={extended version of a paper published at Asiacrypt 2007 valerie.nachef@u-cergy.fr 13850 received 1 Dec 2007, last revised 3 Dec 2007},
  author={Valérie Nachef and Jacques Patarin and C?me Berbain},
  year=2007
}