What is "achterbahn"

In cryptography, Achterbahn is the name of a synchronous stream cipher algorithm submitted to the eSTREAM Project of the eCRYPT network. In the final specification the cipher is called ACHTERBAHN-128/80, because it supports the key lengths of 80 bits and 128 bits, respectively. Achterbahn was developed by Berndt Gammel, Rainer Göttfert and Oliver Kniffler. Achterbahn means rollercoaster (in German), though a literal translation of the term would be eight-track, which indicates that the cipher can encrypt eight bit streams in parallel.

The parameters of the cipher are given in the following table:

ACHTERBAHN-80

ACHTERBAHN-128

Max. key length

80 bit

128 bit

Max. IV length

80 bit

128 bit

Max. frame length

2

2

Internal state

297 bit

351 bit

ACHTERBAHN-128 is downward compatible and can produce the same keystream as ACHTERBAHN-80 if so desired. The keystream generator of ACHTERBAHN-128/80 is based on the design principle of the nonlinear combination generator, however it deploys primitive nonlinear feedback shift registers ( NLFSR) instead of linear ones ( LFSR).