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Published in:
2007 | OriginalPaper | Chapter
Perfect Block Ciphers with Small Blocks
Authors : Louis Granboulan, Thomas Pornin
Published in: Fast Software Encryption
Publisher: Springer Berlin Heidelberg
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Existing symmetric encryption algorithms target messages consisting of elementary binary blocks of at least 64 bits. Some applications need a block cipher which operates over smaller and possibly non-binary blocks, which can be viewed as a pseudo-random permutation of
n
elements. We present an algorithm for selecting such a random permutation of
n
elements and evaluating efficiently the permutation and its inverse over arbitrary inputs. We use an underlying deterministic RNG (random number generator). Each evaluation of the permutation uses
O
(log
n
) space and
O
((log
n
)
3
) RNG invocations. The selection process is “perfect”: the permutation is uniformly selected among the
n
! possibilities.