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Published in:
2010 | OriginalPaper | Chapter
On Generalized Feistel Networks
Authors : Viet Tung Hoang, Phillip Rogaway
Published in: Advances in Cryptology – CRYPTO 2010
Publisher: Springer Berlin Heidelberg
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We prove beyond-birthday-bound security for most of the well-known types of generalized Feistel networks: (1) unbalanced Feistel networks, where the
n
-bit to
m
-bit round functions may have
$n\ne m$
; (2) alternating Feistel networks, where the round functions alternate between contracting and expanding; (3) type-1, type-2, and type-3 Feistel networks, where
n
-bit to
n
-bit round functions are used to encipher
kn
-bit strings for some
k
≥ 2; and (4) numeric variants of any of the above, where one enciphers numbers in some given range rather than strings of some given size. Using a unified analytic framework, we show that, in any of these settings, for any
ε
> 0, with enough rounds, the subject scheme can tolerate CCA attacks of up to
q
~
N
1 −
ε
adversarial queries, where
N
is the size of the round functions’ domain (the larger domain for alternating Feistel). Prior analyses for most generalized Feistel networks established security to only
q
~
N
0.5
queries.