LEVIATHAN is a stream cipher

Stream cipher

In cryptography, a stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream . In a stream cipher the plaintext digits are encrypted one at a time, and the transformation of successive digits varies during the encryption...

 submitted to NESSIE

NESSIE

NESSIE was a European research project funded from 2000–2003 to identify secure cryptographic primitives. The project was comparable to the NIST AES process and the Japanese Government-sponsored CRYPTREC project, but with notable differences from both...

 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

Keystream

In cryptography, a keystream is a stream of random or pseudorandom characters that are combined with a plaintext message to produce an encrypted message ....

, much like CTR mode

Block cipher modes of operation

In cryptography, modes of operation is the procedure of enabling the repeated and secure use of a block cipher under a single key.A block cipher by itself allows encryption only of a single data block of the cipher's block length. When targeting a variable-length message, the data must first be...

 or Salsa20

Salsa20

Salsa20 is a stream cipher submitted to eSTREAM by Daniel Bernstein. It is built on a pseudorandom function based on 32-bit addition, bitwise addition and rotation operations, which maps a 256-bit key, a 64-bit nonce , and a 64-bit stream position to a 512-bit output...

, 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

Cycles per byte

Cycles per byte is a unit of measurement which indicates the number of clock cycles a microprocessor will perform per byte of data processed in an algorithm. It is commonly used as a partial indicator of real-world performance in cryptographic functions....

 on a Pentium II

Pentium II

The Pentium II brand refers to Intel's sixth-generation microarchitecture and x86-compatible microprocessors introduced on May 7, 1997. Containing 7.5 million transistors, the Pentium II featured an improved version of the first P6-generation core of the Pentium Pro, which contained 5.5 million...

 processor.

LEVIATHAN is considered broken due to distinguishing attacks which require 2³⁶ bytes of output and comparable effort.

External links

• LEVIATHAN specification (ZIP
  ZIP (file format)
  Zip is a file format used for data compression and archiving. A zip file contains one or more files that have been compressed, to reduce file size, or stored as is...
  
  file) — link dead. Available from the Internet Archive