• Paul Crowley, cryptolabs Amsterdam
• Stefan Lucks, Univ. Mannheim

Final proceedings version of paper presented at FSE 2001.

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.

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Related resources

• zip file including paper presenting Leviathan
• The NESSIE project

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.