Libelle is a German

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 cipher

Cipher

In cryptography, a cipher is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...

 system, developed by the Federal Office for Information Security

Federal Office for Information Security

The Bundesamt für Sicherheit in der Informationstechnik is the German government agency in charge of managing computer and communication security for the German government...

. The algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

 is not publicised, in an attempt to make cryptanalysis

Cryptanalysis

Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...

 more difficult. In order to keep the algorithm secret, it is only distributed as a microchip named Pluto and not as a piece of software.

It is possible to have a secret cipher algorithm while still reaping the benefits of public cryptography research: one way is to make a non-weakening change to a public algorithm, like changing the Nothing up my sleeve number

Nothing up my sleeve number

In cryptography, nothing up my sleeve numbers are any numbers which, by their construction, are above suspicion of hidden properties. They are used in creating cryptographic functions such as hashes and ciphers. These algorithms often need randomized constants for mixing or initialization purposes...

s, or chaining the public cipher with an unrelated secret cipher.

A BSI specification document about Pluto gives these numbers: 64 bit block size, 160 bit key size. Supported modes: ECB, CBC, CFB/OFB with 1,8,16,32 or 64 bits.

See also

• Skipjack
  Skipjack (cipher)
  In cryptography, Skipjack is a block cipher—an algorithm for encryption—developed by the U.S. National Security Agency . Initially classified, it was originally intended for use in the controversial Clipper chip...
  
  
• Pluto data sheet from the BSI