LEVIATHAN (cipher)
[Image:Leviathan-cipher.png|right|300px|thumb|LEVIATHAN's tree-based keystream generation] LEVIATHAN is a stream cipher submitted to NESSIE by Scott Fluhrer and David McGrew. It is a seekable stream cipher, which means that the user may efficiently skip forward to any part of the keystream, much like Block [cipher modes of operation|CTR mode] or Salsa20, but unlike those ciphers generating contiguous blocks of the keystream is made especially efficient by LEVIATHAN's unique tree structure based stream generation. LEVIATHAN achieves around 11 cycles per byte on a Pentium II processor.
LEVIATHAN is considered broken due to distinguishing attacks which require 236 bytes of output and comparable effort.