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Paper 2007/449

Generic Attacks on Unbalanced Feistel Schemes with Expanding Functions

Jacques Patarin and Valérie Nachef and Côme Berbain

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}

Note: There are new attacks in Section 6.

Metadata
Available format(s)
PDF
Publication info
Published elsewhere. extended version of a paper published at Asiacrypt 2007
Keywords
block ciphers
Contact author(s)
valerie nachef @ u-cergy fr
History
2009-04-05: last of 2 revisions
2007-12-05: received
See all versions
Short URL
https://ia.cr/2007/449
License
Creative Commons Attribution
CC BY
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