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LEVIATHAN
Bias in the LEVIATHAN stream cipher
Paul Crowley
and Stefan
Lucks
In Mitsuru Matsui, editor, Fast Software
Encryption: 8th International Workshop, Lecture Notes in
Computer Science, Yokohama, Japan, April 2001.
Springer-Verlag. To appear.
Abstract. We show two methods
of distinguishing the LEVIATHAN stream cipher from a random stream
using 
bytes of output and
proportional effort; both arise from compression within the
cipher. The first models the cipher as two random functions in
sequence, and shows that the probability of a collision in 64-bit
output blocks is doubled as a result; the second shows artifacts
where the same inputs are presented to the key-dependent S-boxes
in the final stage of the cipher for two successive outputs. Both
distinguishers are demonstrated with experiments on a reduced
variant of the cipher.
Related resources
LEVIATHAN is a new stream cipher developed by David McGrew and
Scott Fluhrer of Cisco for the NESSIE
project, which uses an innovative structure based on a forest
of binary trees to map a key onto a stream of 2^48 32-bit word
outputs, in such a way that it is efficient to seek in the stream,
or to produce many consecutive outputs. This makes it especially
well suited to IPSec encryption.
The NESSIE submission states "Cisco has a patent pending
related to LEVIATHAN."
Amusingly, Scott Fluhrer presented the first cryptanalysis
of my block cipher, Mercy, at the same
conference that this paper was presented.
ciphergoth.org >
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LEVIATHAN