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Erschienen in:
2006 | OriginalPaper | Buchkapitel
Generic Attacks on Unbalanced Feistel Schemes with Contracting Functions
verfasst von : Jacques Patarin, Valérie Nachef, Côme Berbain
Erschienen in: Advances in Cryptology – ASIACRYPT 2006
Verlag: Springer Berlin Heidelberg
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In this paper, we describe generic attacks on unbalanced Feistel schemes with contracting functions. These schemes are used to construct pseudo-random permutations from
kn
bits to
kn
bits by using
d
pseudo-random functions from (
k
–1)
n
bits to
n
bits. We describe known plaintext attacks (KPA) and non-adaptive chosen plaintext attacks (CPA-1) against these schemes with less than 2
kn
plaintext/ciphertext pairs and complexity strictly less than
O
(2
kn
) for a number of rounds
d
≤2
k
–1. Consequently at least 2
k
rounds are necessary to avoid generic attacks. For
k
=3, we found attacks up to 6 rounds, so 7 rounds are required. When
d
≥2
k
, we also describe some attacks on schemes with generators, (i.e. schemes where the
d
pseudo-random functions are generated) and where more than one permutation is required.